PHYSICAL GEOLOGY GEOE209
REVIEW
By: Mohanad Abotaleb
2023/ 2024
GEOE 209
Contents
About These Notes .................................................................................................................................................................. 5
How To Study Physical Geology? .......................................................................................................................................... 6
Lecture 1 “Introduction to Physical Geology” ........................................................................................................................ 7
“Origin of Galaxy and Solar System” ................................................................................................................................. 7
“Geology” ........................................................................................................................................................................... 7
“The Earth” ......................................................................................................................................................................... 8
“Plate Tectonics theory”.................................................................................................................................................... 10
“WILSON CYCLE (Plate Cycle)” ................................................................................................................................... 11
Lecture 2 “Minerals”............................................................................................................................................................. 12
“Introduction” ................................................................................................................................................................... 12
“Atoms” ............................................................................................................................................................................ 12
“Physical Properties of minerals” ..................................................................................................................................... 12
“Rock-forming Minerals” ................................................................................................................................................. 13
Lecture 3 “IGNEOUS ACTIVITY” ...................................................................................................................................... 15
“What’s a rock” ................................................................................................................................................................. 15
“The Rock Cycle”: ............................................................................................................................................................ 15
“Igneous Activity” ............................................................................................................................................................ 16
“Volcanoes”....................................................................................................................................................................... 20
“Origin of magma” ........................................................................................................................................................... 24
“Plate tectonics and igneous activity” ............................................................................................................................... 25
Lecture 4 “Weathering”......................................................................................................................................................... 27
“Earth's External Processes” ............................................................................................................................................. 27
“Weathering”..................................................................................................................................................................... 27
Lecture 5 “Soil” ................................................................................................................................................................... 31
“What’s soil” ..................................................................................................................................................................... 31
“Soil Texture and Structure” ............................................................................................................................................. 31
“Soil Profile”..................................................................................................................................................................... 32
“Soil Types” ...................................................................................................................................................................... 33
“Controls of Soil Formation” ............................................................................................................................................ 34
“Soil Degradation” ............................................................................................................................................................ 35
“Weathering creates ore deposits.” ................................................................................................................................... 36
Lecture 6 “SEDIMENT AND SEDIMENTARY ROCKS” .................................................................................................. 37
“Sedimentary Environment” ............................................................................................................................................. 37
“Sediment Transport and Deposition” .............................................................................................................................. 37
“Classification of sedimentary rocks”............................................................................................................................... 38
“Sediment to Sedimentary Rock” ..................................................................................................................................... 39
“Important Terminology” .................................................................................................................................................. 40
“Chemical Sedimentary Rocks”........................................................................................................................................ 42
“Sedimentary Facies and Depositional Environment” ...................................................................................................... 43
“Evaporation in a Lake”.................................................................................................................................................... 45
“Carbonaceous deposits (Mainly coal)”............................................................................................................................ 45
“Ferruginous deposits (Bog iron)” .................................................................................................................................... 45
“Transgression and Regression (Walther’s rule:)” ............................................................................................................ 45
“Sedimentary structures” .................................................................................................................................................. 46
Lecture 7 “Metamorphic Rocks” .......................................................................................................................................... 47
What's matamorphisim...................................................................................................................................................... 47
Agents of metamorphism: ................................................................................................................................................. 48
Types of Metamorphism ................................................................................................................................................... 49
Index mineral paragenesis ................................................................................................................................................. 50
Classification of Metamorphic Rocks ............................................................................................................................... 51
Metamorphic Zones and Facies ........................................................................................................................................ 52
Environment of Metamorphism ........................................................................................................................................ 53
Resources from Rocks and Minerals ................................................................................................................................ 54
Lecture 8 “Deformation, Mountain Building” ...................................................................................................................... 55
“Deformation”................................................................................................................................................................... 55
“Stress” ............................................................................................................................................................................. 55
“Strain” ............................................................................................................................................................................. 55
“Strike and Dip” ................................................................................................................................................................ 56
“Ductile Deformation: Folds” ........................................................................................................................................... 56
“Brittle Deformation: Fractures” ...................................................................................................................................... 59
Mountain Building (Orogenesis) ...................................................................................................................................... 62
Lecture 9 “Earthquakes” ....................................................................................................................................................... 66
What’s an Earthquake ....................................................................................................................................................... 66
Causes of Earthquakes ...................................................................................................................................................... 66
Earthquake Waves ............................................................................................................................................................. 66
Categories of earthquakes based on the depth. ................................................................................................................. 68
Aftershocks and Foreshocks ............................................................................................................................................. 68
Locating an Earthquake .................................................................................................................................................... 68
Earthquake Belts and Plate Tectonics ............................................................................................................................... 69
Determining the Size of Earthquakes................................................................................................................................ 70
Earthquake Destruction ..................................................................................................................................................... 72
Earthquake Prediction ....................................................................................................................................................... 73
Earth's layered structure .................................................................................................................................................... 74
Lecture 10 “Geologic Time” ................................................................................................................................................. 76
The Importance of Dating ................................................................................................................................................. 76
Relative Dating ................................................................................................................................................................. 77
Unconformities ................................................................................................................................................................. 79
Correlation ........................................................................................................................................................................ 81
Fossils ............................................................................................................................................................................... 82
Absolute Dating ................................................................................................................................................................ 82
Lecture 11 “MASS WASTING” ........................................................................................................................................... 89
What’s Mass Wasting ........................................................................................................................................................ 89
Effect of gravity/Shear Strength........................................................................................................................................ 89
Factors of mass movements .............................................................................................................................................. 90
Triggering Mechanisms of Mass Wasting ......................................................................................................................... 92
Classification of mass movements .................................................................................................................................... 93
Geology and Slope Stability ............................................................................................................................................. 97
Safety Measures ................................................................................................................................................................ 98
Reviewing Shapes ............................................................................................................................................................. 99
Lecture 12 “Runing Water” ................................................................................................................................................. 101
The Hydrologic Cycle ..................................................................................................................................................... 101
Runing Water .................................................................................................................................................................. 102
Streamflow ...................................................................................................................................................................... 105
The Work of Running Water ........................................................................................................................................... 105
Drainage Basin and Drainage Divide.............................................................................................................................. 107
Stream Channels ............................................................................................................................................................. 109
Stream Valley Development ............................................................................................................................................ 111
Stream Valleys on Mars .................................................................................................................................................. 114
Depositional Landforms.................................................................................................................................................. 115
Floods and flood control ................................................................................................................................................. 116
Lecture 13 “Groundwater” .................................................................................................................................................. 117
Importance of Groundwater ............................................................................................................................................ 117
Distribution and movement of groundwater ................................................................................................................... 118
How Groundwater Moves ............................................................................................................................................... 120
Factors Influencing the Storage and Movement of Groundwater ................................................................................... 121
Wells and artesian systems .............................................................................................................................................. 121
Springs, Hot Springs, and Geysers.................................................................................................................................. 122
Groundwater and Environmental Problems .................................................................................................................... 123
The Geologic Work of Groundwater ............................................................................................................................... 125
Lecture 14 “Glaciers”.......................................................................................................................................................... 127
Glaciers: a part of two basic cycles in the Earth system ................................................................................................. 127
Formation and Movement of Glacial Ice ........................................................................................................................ 128
Glaciers Erosion .............................................................................................................................................................. 130
Glacial Deposits .............................................................................................................................................................. 131
Important figures about glaciers deposits ....................................................................................................................... 134
Glaciations over Earth’s History ..................................................................................................................................... 135
Evidence for Older Glaciation ........................................................................................................................................ 138
Lecture 15 “Deserts and Wind” .......................................................................................................................................... 139
What’s a desert ................................................................................................................................................................ 139
Geologic processes in arid climates ................................................................................................................................ 141
Basin and Range ............................................................................................................................................................. 141
Transportation of sediments by Wind ............................................................................................................................. 143
Erosion by Wind ............................................................................................................................................................. 144
Wind deposits .................................................................................................................................................................. 146
Desertification ................................................................................................................................................................. 148
Lecture 16 “Coasts (Shorelines)” ........................................................................................................................................ 149
The anatomy of the coasts ............................................................................................................................................... 149
Waves formation ............................................................................................................................................................. 150
COASTAL PROCESS .................................................................................................................................................... 151
Major coastal landforms.................................................................................................................................................. 152
Important figures about costal landforms ....................................................................................................................... 154
Major coast types ............................................................................................................................................................ 157
Stabilizing the cost .......................................................................................................................................................... 157
Tides ................................................................................................................................................................................ 159
Sea-level change ............................................................................................................................................................. 161
Coral reefs ....................................................................................................................................................................... 161
Rocking Our Geology Exam: Cheers to Success!............................................................................................................... 162
Fair Use Disclaimer ............................................................................................................................................................ 163
About These notes
Hello there, fellow Engineers
!
I hope this message finds you in good spirits and ready to dive into the exciting world of
Physical Geology. As you embark on this academic journey, I want to warmly welcome my
study notes. Whether you are a seasoned scholar or just getting started, these notes are
designed with you in mind. This note is a friendly gift from your Egyptian friend and
colleague. Hopefully, it will help you with your path through this semester!
Studying can be challenging but remember that every small effort counts. Consistency is
the key to mastering any subject. So, take a deep breath, believe in yourself, and let's tackle
this together!
I have a big faith in the Ayah “ayet” that is saying “{‫سعَى‬
Which means
َ ‫ان إالَّ َما‬
َ ‫ْس ِلإلن‬
َ ‫”}وأَن لَّي‬.
ِ ‫س‬
َ
in English “And that the human being attains only what he strives for”, in Turkish “Ve
insan için, çalışmasından başka bir şey yoktur”. So, here is a friendly reminder to make
sure that you’re doing your best, to receive the best results “grades”.
These notes are based on "Earth an Introduction to Physical Geology 12 Edition c2017
Tarbuck & Lutgens" and the Lecture notes. In addition, these notes aren't made for any
commercial use; they are only for the benefit of the students and academic use. It can't be
sold or used in any way that violates the copyrights of its original owners.
Feel free to reach out if you have questions or want to share your insights. We're all in this
together, and your success is vital to the entire study community.
Happy studying!
Mohanad Abotaleb
How To Study Physical Geology?
❖ Physical Geology can be divided into two parts:
1) Lecture part
2) Field trips
❖ The focus of these notes is on the lecture part.
❖ So how do you study this subject?
❖ Know that this course is fundamental, so you need to take it with care and be willing to learn it by heart.
❖ You will need the terms you learn here for future courses and your career as a geological engineer.
❖ So, to study efficiently, you need to follow these steps (After saying "Bismillah"
):
1) Get ready before the lectures.
a) Reading the topics from your book before the lecture will give you general knowledge before the
lecture time.
b) The book we referred to has some helpful video links to help you.
c) The first read will make a base for receiving detailed information from your professor.
d) Organize the main topics as you read so you know what you expect to hear in the lecture.
e) Studying these notes can only be enough for you to get good grades, but learning from the book is
what will make you a reasonable, successful geologist.
2) Attend the lecture and pay attention to the professors.
a) We have high-class professors, so take the lectures; you will learn a lot of information and fill the
gaps left in your head after the first reading.
b) Relate the ideas you read before the lecture with the concepts you learned from the professors.
c) Take notes and record the hints you hear from in the lecture.
d) Feel free to ask the professor about points you need help understanding.
3) After the lecture, study these notes as a summary.
a) It would be best if you studied writing.
b) More than reading is required.
c) Train on memorizing important concepts, tables, and charts by writing them multiple times.
4) Evaluate yourself by solving the sample questions in the Q&A file.
a) Mark the questions you couldn't answer to review them again next week.
5) Sharing is caring.
a) Make sure to help your friends by solving or reviewing; this will fix the information in your head
and give you inner peace as you are a good person.
❖ Remember step 3 (a).
❖ Remember step 3 (b).
❖ Remember step 3 (c).
❖ So, to sum up:
1) Read the chapter book before the lecture.
2) Attend the lecture.
3) Study the notes.
4) Solve the sample questions.
5) Sharing is caring.
❖ Following these steps in this course and any other course will guarantee you an AA at the end of it.
❖ o, let us say Bismillah, and we begin to nail it!
Lecture 1 “Introduction to Physical Geology”
“Origin of Galaxy and Solar System”
❖ Theory vs Hypothesis vs Law:
Hypothesis
testing
Theory
Generalization
Law
❖ Hypothesis:
1) Definition: Specific, testable proposition to explain observed phenomena.
2) Characteristics: Testable, specific, predictive.
3) Example: If more sunlight, then increased photosynthesis.
❖ Theory:
1) Definition: Comprehensive, well-substantiated explanation of natural phenomena.
2) Characteristics: Broad, tested, dynamic, supported by evidence.
3) Example: Big Bang Theory.
❖ Law:
1) Definition: Descriptive statement summarizing consistent, universal relationships.
2) Characteristics: Descriptive, universal.
3) Example: Newton's Law of Universal Gravitation.
❖ The Milky Way and our solar system are thought to have originated instantaneously in what’s called The Big Bang.
❖ Our universe is 13.7 billion years old.
❖ Solar Nebula Hypothesis:
1) Our solar system originated as a nebula or turbulent rotating cloud of gas and dust that underwent
gravitational collapse, rotation, flattening, and development of eddies.
2) Local gas and solid particle condensation led to accretion into planets and loss of ‘lighter’ materials from
the inner solar system.
3) Substances in the solar system are divided into gases, ice, and rocks based on their melting temperature.
❖ Our Solar System can be divided into
1) Jovian planets: composed primarily of gases and ice (Jupiter, Saturn, Uranus, Neptune, and Pluto).
2) Terrestrial Planets: have a rocky composition (Mercury, Venus, Earth, and Mars).
❖ The Earth consists of various interactive subsystems. These subsystems include the atmosphere, hydrosphere, biosphere,
and solid earth. The size of the subsystem changes over time.
“Geology”
❖ Geo − A prefix meaning “Earth,” Logos “Science.” Together means “The study of Earth.”
❖ Geology − The study of the planet Earth, the materials of which it is made, the processes that act on these materials, the
products formed, and the history of the planet and its life forms since its origin.
❖ Geology considers the physical forces that act on the Earth.
❖ Clues on the origin of the planet are sought in a study of the Moon and other extra-terrestrial bodies.
❖ The knowledge thus obtained is placed in the service of man, to aid in discovery of minerals and fuels of value in the
Earth’s crust, to identify geologically stable sites of the dangers associated with the mobile forces of a dynamic Earth.
❖ Geology is generally divided into two broad areas:
1) Physical Geology: is the study of Earth materials, such as minerals and rocks, as well as the processes
operating within the Earth and upon its surface.
2) Historical Geology: examines the origin and evolution of the Earth, its continents, oceans, and life.
❖ Nearly every aspect of geology has some economic or environmental relevance.
❖ Many geologists are involved in exploration for mineral and energy resources, using their specialized knowledge to
locate the natural resources on which our industrialized society is based.
❖ As the world demand for these non-renewable resources increases, geologists are intensifying their search and applying
the basic principles of geology in increasingly sophisticated ways.
❖ The use of Geology:
1) Geology helps to solve many of our environmental problems.
2) Finding ground water.
3) Monitoring surface or underground water pollution.
4) Safe locations for dams.
5) Safe locations for waste disposal sites.
6) Safe locations for power plants.
7) Design earthquake-resistant buildings.
8) Making short-term and long-term range predictions about earthquakes & volcanic eruptions and potential
destruction that may result.
❖ Geological Sectors
1) Mineralogy: studies of minerals, their chemistry, atomic structure, and conditions of formation. Utilizes
principles of chemistry and physics.
2) Petrology: studies of rocks, their chemistry, atomic structure, and conditions of formation. Utilizes
principles of chemistry and physics.
3) Geochemistry: detailed studies of the chemical aspects of Earth materials (rocks, minerals, and water).
Utilizes principles of chemistry and physics
4) Volcanology: studies of volcanic processes and deposits. Utilizes principles of physics.
5) Stratigraphy: studies of the deposition and evolution of sequences of rock layers. Utilizes principles of
physics and biology.
6) Sedimentology: studies of weathering, mass wasting, transport, and deposition of sediments. Utilizes
principles of chemistry, physics, and biology.
7) Paleontology: studies of ancient plant and animal life forms (fossils). Utilizes principles of biology.
8) Geomorphology: studies of landforms, their development and impact on surficial geology. Utilizes
principles of physics.
9) Hydrogeology: studies of groundwater resources, subsurface flow behavior and potential migration of
pollutants. Utilizes principles of chemistry and physics.
10) Structural Geology: studies of rock mechanical characteristics and processes that deform rocks. Utilizes
principles of physics.
11) Tectonics: studies of the development of ocean basins and continents. Utilizes principles of physics.
12) Geochronology: studies and determination of the age of Earth materials. Utilizes principles of physics and
chemistry.
13) Solid-earth Geophysics: studies of the physics of the Earth (magnetism, gravity, and seismicity) and
geologic processes. Utilizes principles of physics.
“The Earth”
❖ The Earth is unique among the planets of our solar system in that:
1) It supports life.
2) has oceans of water.
3) has an atmosphere.
4) has a variety of climates.
❖ The Earth is a 4.6-billion-year-old dynamic planet.
❖ The Earth is not a simple, unchanging planet. Rather, it is a complex dynamic body.
❖ Earths processes are extremely slow on human time scale, and too large to duplicate in labs.
❖ The processes acting on earth are:
1) Internal: Volcanism, Earthquakes, Mountain building processes.
2) External: Weathering and erosion, Mass wasting, Running water, Groundwater, Glaciers, Work of wind and
deserts, Shorelines and Waves.
“The Interior of Earth”
❖ The Earth was initially homogeneous, but its interior has separated (differentiated) with cooling into distinct
concentric rock layers (as the crust, mantle, and core).
Crust
Core
Mantle
10-13 g/cm³
16%
3.3 - 5.7 g/cm³
83%
Phase
small, solid Inner
Core
larger, liquid Outer
Core
The Lower Mantle: Solid,
forms most of Earth’s
interior by volume.
The Asthenosphere:
behaves plastically and
slowly flows.
The Uppermost Mantle:
surrounds the
asthenosphere. It is solid.
Solid
Solid
Composition
Iron (Fe) and small
amount of Nickel
PERIDOTITE (igneous
rock containing abundant
Fe & Mg)
Si and Al
(igneous rock:
granite)
Si and Mg
(igneous rock:
Basalt)
Density
Volume
Continental
Crust
2.7 g/cm³
10 - 90 km
Oceanic Crust
3.0 g/cm³
5 - 10 km
❖ The Lithosphere (Plate) is a Cool, solid, rigid brittle and consisting of uppermost mantle and crust.
❖ The thickness of the Lithosphere is up to 100 km.
“Plate Tectonics theory”
❖ Plate Tectonics theory explained as:
1) The lithosphere is divided into plates that move over the asthenosphere.
2) Zones of volcanic activity, earthquake activity or both mark most plate boundaries.
3) It’s based on data from ocean basins.
4) It is a kinematic theory that deals with the “outer rigid layer” of the earth (Lithosphere).
5) plates cover all the surface of the earth without any gaps between them, so it’s well-closed system.
❖ Plate Boundary Types:
❖ Subduction Zone: When oceanic plate collides with a continental one, the denser oceanic plate sinks beneath the
continental plate.
❖ As the subducting plate descends into the Earth, it gets hotter, and its interaction with the mantle produces magma
(molten Earth material).
❖ As magma rises, it reaches to earth’s surface and erupts forming Volcanoes as chains.
“WILSON CYCLE (Plate Cycle)”
❖ Steps of Wilson Cycle/ Plate cycle:
1. RIFTING
2. OCEANIC SPREADING
3. MATURE OCEAN
4. SUBDUCTION
5. CLOSURE OF OCEAN
6. COLLISION
7. AMALGAMATION
❖ Isostasy: refers to the equilibrium or balance of the Earth's crust, particularly the lithosphere, as it floats on the semifluid asthenosphere beneath it. This concept helps explain the distribution of weight and the elevation of Earth's
features, including mountains, continents, and ocean basins.
Lecture 2 “Minerals”
“Introduction”
❖ A mineral is:
1) Natural.
2) Inorganic.
3) Solid.
4) Highly ordered structure of atoms.
5) Having a known chemical composition.
❖ Mineraloid: Looks like a mineral but lacks an orderly internal structure.
❖ Elements are the basic building blocks of minerals and there are over 100 known elements.
“Atoms”
❖ Atoms are the smallest particles of matter. It has all the characteristics of an element.
❖ Nucleus: central part of an atom that contains:
1) Protons: positive electrical charges.
2) Neutrons: neutral electrical charges.
❖ Energy levels, or shells: Surround nucleus, Contain electrons, negative electrical charges.
❖ Atomic numbers: The number of protons in an atom's nucleus.
❖ Bonding atoms: atoms that tend to form a compound with two or more elements.
❖ Ions: atoms that gain or lose electrons.
❖ Isotopes: elements that have varying number of neutrons. It has different mass numbers (the sum of the neutrons
plus protons). Many isotopes are radioactive and emit energy and particles.
“Physical Properties of minerals”
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Planar surfaces of the mineral are called crystal faces.
Angles between crystal faces are constant for any particular mineral.
Color is the most obvious, but often misleading physical property of minerals.
Different colors may result from impurities.
Streak is the color of a mineral in powdered form.
Luster: is how mineral’s surface reflects light. It has two types: Metallic luster, Non-metallic luster.
Hardness: is how easy it is to scratch a mineral. It’s scaled by Mohs Scale of Hardness.
Mohs Scale of Hardness is a relative scale. It consists of 10 minerals, ranked 1 to 10.
Cleavage: tendency of a mineral to break along planes of weakness.
Minerals that do not exhibit cleavage are said to fracture.
Minerals break in a glass-like manner: conchoidal fracture.
Do not confuse cleavage planes with crystal faces! Crystal faces are just on the surface and may not repeat when
the mineral is broken.
“Rock-forming Minerals”
❖ A few dozen minerals are called rock-forming minerals.
❖ The elements that compose most rock-forming minerals are oxygen (O), silicon (Si), aluminum (Al), iron (Fe),
calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg). (O, Si, Al, Fe, K, Na, K, Mg).
❖ Most abundant atoms in Earth’s Crust are oxygen (46.6% by weight) and silicon (27.7% by weight).
❖ Minerals may be subdivided into two major groups:
1) SILICATES (most abundant)
2) NON-SILICATES (~8% of Earth’s crust).
❖ Silica Tetrahedra: The building block of most common rock forming minerals.
“Rock-forming Silicate”
❖ Rock-forming Silicate Minerals are divided upon two ways:
1) Groups based upon composition: Ferromagnesian (Fe, Mg), Non-ferromagnesian (K, Na, Ca, Al) .
2) Groups based upon tetrahedral arrangement: independent tetrahedra (Olivine), tetrahedra are arranged in
chains (Pyroxene group), tetrahedra are arranged in double chains (Amphibole group).
❖ Pyroxenes (Mineral Group) is a Single Chain Silicate. Found in Oceanic Crust, Silica poor (<20%).
❖ Amphiboles (Group of minerals) is a Double Chain Silicate structure. Found in Continental Crust. It contains more
silica and less iron than pyroxene.
❖ Micas (Muscovite and Biotite) is a Sheet Silicate structure. Found in Continental Crust. It contains More silica and
less iron than Amphiboles.
❖ Clays (Mineral Group) are Hydrated, sheet silicates from weathering of other silicates.
❖ Feldspars (Orthoclase and Plagioclase) and Quartz are Framework/ 3D structure. Found in Continental Crust. It
contains More silica than micas, no iron.
❖ Carbonates are a major non-silicate rock-forming group. It’s found in the rocks “limestone and marble”.
❖ Halite and gypsum are found in sedimentary rocks.
Lecture 3 “IGNEOUS ACTIVITY”
“What’s a rock”
❖ Rock: is a solid aggregate of minerals of one or more kinds. It’s a consolidated aggregate of particles of other rocks.
Exceptions: coal and natural glass aren’t rocks.
“The Rock Cycle”:
❖ Rock cycle Shows the interrelationships among the three rock types.
❖ A full rock cycle does not always take place due to "shortcuts" or interruptions.
1) e.g., Sedimentary rock melts.
2) e.g., Igneous rock is metamorphosed.
3) e.g., Sedimentary rock is weathered.
4) e.g., Metamorphic rock weather.
“Igneous Activity”
❖ Rocks resulting from volcanic eruption are widespread but present only a small portion of the total rocks formed.
❖ Plutons: magma cools below the Earth’s surface and forms bodies.
❖ Plutons typically underlie areas of extensive volcanism and are the sources of overlying lava and fragmental
materials ejected during explosive eruptions.
❖ Volcanism and plutonism occurs at or near plate boundaries.
“Magma and Lava”
❖
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Magma: molten rock material below the Earth’s surface.
Lava: Magma at the Earth’s surface.
Magma tends to move upward towards the surface since it is less dense than the solid rock that it was derived from.
Magma erupts on to the surface as lava flows. Can be forcefully ejected into the atmosphere as particles called
pyroclastic materials.
❖ When crustal rocks melt and form magma, the magma is typically SILICA-RICH and contains considerable amount
of Al, Ca, Na, Fe, Mg and K.
❖ Not all magma originates by melting of crustal rocks, however some are derived from UPPER MANTLE rocks that
are composed of ferromagnesian minerals/silicates: thus, magma will be less in silica but rich in Fe and Mg.
“Magma composition”
❖ Depending on the silica content, magma is distinguished into five types:
Magma type
Silica content
Felsic
(> 65% SiO2)
Intermediate
(53-65% SiO2)
Mafic (basaltic)
(45-53% SiO2)
Ultramafic
(< 45% SiO2)
Composition
considerable amount of Na, K &
Al but little Mg, Fe & Ca
something in between felsic and
Mafic
silica poor, more Ca, Mg & Fe
but less Na, K & Al
high concentrations of
magnesium (Mg) and iron (Fe)
“Viscosity”
❖ Viscosity: is the resistance to flow.
❖ Temperature and Composition (mainly silica content) are controlling factors of viscosity. Hot lava flows more
readily than cooler lava (stiff). High silica content magma is more viscose than poor silica magma.
“Igneous Rocks”
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Igneous Rocks form as magma cools and crystallizes.
Rocks formed inside Earth are called plutonic or intrusive rocks.
Rocks formed on the surface are formed from lava and are called volcanic or extrusive rocks.
Crystallization of magma happens when ions are arranged into orderly patterns.
Crystal size is determined by the rate of cooling:
1) Slow rate forms large crystals. coarse-grained texture (Phaneritic texture)
2) Fast rate forms microscopic crystals. fine-grained texture (Aphanitic texture)
3) Very fast rate forms glass. Forming Volcanic glass
The process of Crystallization involves the formation of Crystal Nuclei and their subsequent growth.
Atoms in magma are in constant motion. When cooling begins some atoms bond to form SMALL GROUPS (or
Nuclei) whose arrangement of atoms correspond to the arrangement in mineral crystal. As other atoms in the liquid
chemically bond to these nuclei; they do so in an order geometric arrangement.
Vesicular texture is when the rock has vesicles. (Vesicles: small holes or cavities formed by the trapping of water
vapor or other gases during the cooling of magma).
Amygdaloidal if vesicles are filled with secondary minerals.
“Bowen's reaction series”
❖ Bowen's reaction series which shows the order of mineral crystallization (the sequence in which minerals
crystallize) Influenced by crystal settling in the magma, Assimilation and Magma mixing.
“Classification of igneous rocks”
❖ Granitic rocks
1) Composed almost entirely of light-colored silicates - quartz and feldspar.
2) Also referred to as felsic feldspar and silica (quartz).
3) High silica content (about 70 percent).
4) Common rock is granite.
❖ Basaltic rocks
1) Contain substantial dark silicate minerals and calcium-rich plagioclase feldspar.
2) Also referred to as mafic: magnesium and ferrum (iron) 
3) Common rock is basalt.
❖ Ultramafic Rocks
1) Dunite – Olivine
2) Peridotite – olivine + pyroxene + plagioclase
3) Pyroxenite – Pyroxene
❖ Mafic to Felsic Rocks
1) Basalt – Gabbro [Mafic]
2) Andesite – Diorite [Intermediate]
3) Rhyolite – Granite [Felsic]
❖ Pegmatite:
1) Coarsely crystalline intrusive rocks, containing Minerals measuring at least 1 cm across or even larger
2) It refers to a texture: most of them are essentially composed of qtz, K-felds, Na-plg that usually
corresponds to composition of a granite.
“Intrusive igneous activity”
❖ Most magma is emplaced at depth.
❖ Plutons are classified according to its Orientation with respect to the host (surrounding) rock:
1) Discordant – cuts across existing structures.
2) Concordant – parallel to features such as sedimentary strata (layer).
❖ Types of igneous intrusive features
1) Dike: a tabular, discordant pluton
2) Sill: a tabular, concordant pluton. Buried lava flows and may exhibit columnar joints.
3) Laccolith: Like a sill but much bigger. Lens shaped mass. Arches overlying strata upward.
4) Batholith: Largest intrusive body. Often occur in groups Surface exposure +100 𝑘𝑚2 (smaller bodies are
termed stocks). Frequently form the cores of mountains.
“Volcanism”
❖ Volcanism: Process whereby magma and its associated gases rise through the Earth’s crust and extrude onto the
surface or into the atmosphere.
❖ Volcano Classification in terms of activity:
1) Active: erupted during historic times (Etna in Sicily, Fujiyama in Japan).
2) Dormant: not erupted recently but may do so again (Vesuvius).
3) Extinct (inactive): not erupted during recorded history and show no evidence of doing so.
❖ One of the factors affecting viscosity of magma is dissolved gases (volatiles). It provides the force to extrude lava.
Violence of an eruption is related to how easily gases escape from magma. Viscous magma produces a more
violent eruption.
“Materials associated with volcanic eruptions.”
❖ There are three materials associated with volcanic eruptions:
1) Gases
2) Lava flows
3) Pyroclastic materials
❖ Gases are 1 to 5 percent of magma by weight. It’s mainly water vapor (50-80%) and Carbon Dioxide. It can also
contain Nitrogen, Sulfur gases, CO, Hydrogen, and Chlorine.
❖ When magma rises towards the surface, the pressure is reduced, and the contained gases begin to expand.
❖ Felsic Magma: expansion is INHIBITED and gas pressure increases. Thus, pressure may become great enough to
cause an EXPLOSION and produce pyroclastic material (Ash).
❖ Mafic Magma: allow gas to expand and escape easily which is being a quite eruption (Effusive).
❖ Lava flows: Fiery streams of incandescent rock material: their geometry differs considerably, depending on their
viscosity and Pre-existing topography. Basaltic lavas are more fluid.
❖ Types of lava:
1) Pahoehoe lava (resembles braids in ropes; lava that solidifies into ropy or corded shapes with a smooth
surface; Hawaiian word meaning satin-like).
2) Aa lava (rough, jagged surface when it cools).
❖ Pyroclastic materials: means "Fire fragments”.
❖ Types of pyroclastic material:
1) Ash and dust: fine, glassy fragments (< 2 mm)
2) Pumice: from "frothy" lava
3) Lapilli: "walnut" size (2-64 mm)
4) Cinders: "pea-sized"
5) Particles larger than lapilli (>64 mm):
a) Blocks – hardened lava
b) Bombs – ejected as hot lava.
“Volcanoes”
“General features of a Volcano”
❖ Main parts of the volcano:
1) Conduit (pipe): carries gas-rich magma to the surface.
2) Vent: the opening through which volcanic materials are ejected
3) Crater: Steep-walled depression at the summit. often resulting from the collapse or explosive activity
associated with the vent.
❖ Caldera: a summit depression greater than 1 km in diameter.
❖ Parasitic cones: smaller volcanic cones that form on the sides of a larger, main volcano. They are connected to the
main volcano and share the same source of magma.
“Types of volcanoes”
❖ Types of volcanoes varies according to its (size, shape, and type of lava)
Volcano’s Type
Shape
Size
Shield volcano
Broad and slightly domed
Largest – H>9km –
R>50km
Cinder cone
Steep slope angle
Stratovolcano
Composite cone
Small- H>0.3km- R>0.5km
Large- H>3km- R>6km
Composition
Basaltic lava
Ejected lava fragments
More info
The largest type of volcano
Frequently occur in groups
Examples
Mauna Loa in Hawaii
Mekegölü, Karapınar
(Konya)
Interbedded lavas and
pyroclastic
Most violent type of
activity
Most are adjacent to the
Pacific Ocean. Mt. Rainier
❖ Composite cone (or stratovolcano) Often produces Nuée Ardente and Lahar.
❖ Nuée Ardente: Fiery pyroclastic cloud made of hot gases infused with ash. It flows down the sides of a volcano at
speeds up to 200 km (125 miles) per hour.
❖ Lahar: volcanic mudflow.
Nuée Ardente
Lahar
“Other volcanic landforms”
❖ Calderas:
1) Steep walled depression at the summit.
2) Formed by collapse.
3) Nearly circular.
4) Size exceeds one kilometer in diameter.
5) Results a carter lake and a Wizard Island.
❖ Fissure eruptions and lava plateaus:
1) Fluid basaltic lava extruded from crustal fractures called fissures.
❖ Volcanic Necks:
1) Volcanic Necks: are resistant vents left standing after erosion has removed the volcanic cone.
2) e.g., Columbia Plateau
❖ Pillow lavas:
1) Pillow shaped lavas formed during underwater eruptions.
❖ Columnar Joints:
1) Parallel, prismatic columns common in basaltic lavas and formed due to volume reduction (shrinkage)
during cooling.
“Pyroclastic Rocks”
1. Ash: volcanic rock fragments of less than 2 mm.
2. Tuff: volcanic ash and larger particles ejected from a vent during a volcanic eruption.
3. welded tuff: Welded tuff is a pyroclastic rock that was sufficiently hot at the time of deposition so that the
particles weld together.
4. Bomb: A volcanic bomb is a mass of molten rock larger than 64 mm in diameter, formed when a volcano ejects
viscous fragments of lava during an eruption (they were airborne lava).
5. Volcanic blocks: A fragment of rock lager than 64 mm in diameter and is erupted in a solid condition.
6. Volcanic Breccia: volcanic breccia is pyroclastic rock composed of angular volcanic fragments larger than32 mm
which were solidified before aerial flight and deposition.
“Origin of magma”
❖ Magma originates when essentially solid rock melts. (The rocks of the crust and upper mantle).
❖ Factors that influence the generation of magma from solid rock:
1) Role of heat: Earth’s natural temperature increases with depth (geothermal gradient) is not sufficient to
melt rock at the lower crust and upper mantle.
▪ Additional heat is generated by:
a) Crustal rocks heated during subduction.
b) Rising of the hot mantle rocks.
c) Friction along faults (very limited).
2) Role of pressure: Increase in confining pressure causes an increase in melting temperature. A drop in
confining pressure can cause decompression melting. Lowers the melting temperature. Occurs when rock
ascends.
3) Role of volatiles: Primarily water (CO2,NO2, H2S etc.). Cause rock to melt at a lower temperature. Play
an important role in subducting ocean plates.
❖ Partial melting: Igneous rocks are mixtures of minerals. Melting occurs over a range of temperatures Produces a
magma with a higher silica content than the original rock.
“Plate tectonics and igneous activity”
❖ Global distribution of igneous activity is not random, it can be put in three groups:
1) First group: located on the margins of the ocean basins (intermediate, andesitic composition).
2) Second group: confined to the deep ocean basins (basaltic lavas).
3) Third group: includes those found in the interiors of continents.
❖ Most volcanoes are in the first group located on the margins of the ocean basins.
❖ Plate motions provide the mechanism by which mantle rocks melt to form magma.
1) Convergent plate boundaries: deep-ocean trenches are generated. The descending plate partially melts,
and magma slowly rises upward.
2) Divergent plate boundaries: The greatest volume of volcanic rock is produced along the oceanic ridge
system. The lithosphere pulls apart, less pressure on underlying rocks, Partial melting occurs, and large
quantities of fluid basaltic magma are produced.
3) Intraplate igneous activity: Activity within a rigid plate. Plumes of hot mantle material rise, Form
localized volcanic regions called hot spots. Examples include the Hawaiian Islands and the Columbia
River Plateau in the northwestern United States.
❖ Rising magma can form:
a) Volcanic island arcs in an ocean (Aleutian Islands)
b) Continental volcanic arcs (Andes Mountains)
Lecture 4 “Weathering”
“Earth's External Processes”
❖ Weathering: the disintegration and decomposition of material at or near the surface.
❖ Mass wasting: the transfer of rock material downslope under the influence of gravity.
❖ Erosion: the incorporation and transportation of material by a mobile agent, usually water, wind, or ice.
“Weathering”
❖ Weathering is being classified into two types:
1) Physical breakdown (Disintegration)
2) Chemical alteration (Decomposition)
❖ Weathering is affected by the following Environmental Conditions according to its location:
1) At depth:
a) There is no O₂ nor H₂O.
b) There is High pressure and temperature.
2) At or near surface:
a) There is O₂ and H₂O.
b) There is low pressure and temperature.
c) There are atmospheric gases, acids, and organisms.
❖ Parent Material: the original rock being weathered, broken down into smaller pieces or dissolved.
❖ Erosion: The removal of the weathered material.
❖ Transportation is done by agents such as running water, wind, glaciers.
❖ Deposition: creating sediments.
❖ Weathering provides raw materials for sedimentary rocks and soils.
❖ Differential weathering is caused by variations in:
1) The composition of the parent rock.
2) The structure of the parent rock.
❖ Differential weathering Creates unusual and spectacular rock formations and landforms.
❖ Weathering occurs in varying amounts in different environments even within the same area which results in
differential weathering.
A. “Physical (Mechanical) Weathering”
❖ Physical (Mechanical) Weathering happens when the physical process breaks rock material into smaller pieces
that retain the chemical composition of the rock.
❖ Types of the Physical weathering:
1) Frost action
2) Pressure release
3) Thermal expansion and contraction
4) Salt crystal growth
5) Activities of organisms
1. Frost wedging (Frost action)
❖ Frost action is the result of freezing and thawing of water in cracks and cavities as the following repeating steps:
1) Freezing: expanses the water (by about 90%) and exerts pressure/force on the walls of cracks widening
and extending it by frost wedging.
2) Thawing: is the opposite of the freezing prosses where ice melts releasing the pressure from the rock
❖ Repeated freezing and thawing causing rocks to get detached.
❖ Frost wedging is common in the areas where temperature is swinging above and below the freezing point.
2. Pressure Release
❖ Pressure Release is common in rocks that are formed at depth.
❖ Buried intrusive bodies (batholiths) are stable under high pressure. When uplifting occurs (due to erosion)
pressure releases, rocks contain energy releases it by expansion.
❖ The expansion results in the formation of two topographic elements:
1) Sheet joints: large fractures parallel to the topographic surface.
2) Exfoliation: slabs bound by sheet joints may slip, slide or spall (break) off the host rock forming an
exfoliation dome.
3. Thermal Expansion and Contraction
❖ Thermal Expansion and Contraction is the change in the volume of solids and rocks in response to heating and
cooling (the change of temperature).
❖ Deserts (during day 30°C or more; during night gets below zero). Heating results in expansion while Cooling
results in contraction.
❖ Expansion and contraction are not uniform throughout the rock according to:
1) Rocks that are poor conductors of heat, their outer part are more heated up than its inner parts.
2) Darker minerals absorb heat faster than the light-colored minerals.
❖ Consequently, surface expands more than interior or differential expansion between minerals is creating the
stresses that cause fracturing.
4. Salt Crystal Growth
❖ Salt Crystal Growth is the expansion and crystallization of dissolved salts within porous rocks, minerals, or
structures, due to the evaporation of water carrying these salts. This is resulting in the physical breakdown and
deterioration of the material.
❖ Growing crystals Exerts enough force to widen cracks expelling particles in porous rocks.
5. Activities of Organisms
❖ Animals, Plants and Bacteria are playing an important rule in the weathering process.
❖ Animals like worms, reptiles, rodents burrow material from depth to surface. The roots of plants large bushes and
trees wedge themselves into cracks in rocks widening and breaking it.
B. “Chemical Weathering”
❖ Chemical Weathering is a process whereby rock materials are decomposed by chemical alteration of the parent
material.
❖ Chemical Weathering alters the internal structures of minerals by removing or adding elements.
❖ Clay minerals are the chemical alteration of feldspars.
❖ Some minerals are completely dissolved or decomposed but others are more resistant, simply liberated from the
parent material.
❖ Chemical weathering agents are:
1) water (The most important agent).
2) Acids.
3) Organisms: lichens at the surface.
4) Plants: remove ions from soil.
❖ The stability of common minerals is just the opposite of their order of crystallization in Bowen’s Reaction series.
❖ Types of Chemical Weathering:
1) Solution
2) Oxidation
3) Hydrolysis
1.
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Solution
Dissolution occurs when the ions of a substance become disassociated from one another in a liquid .
Water is a remarkable solvent.
Most minerals are not very soluble in pure water because the attractive forces of water molecules are not
sufficient to overcome the forces between particles in minerals.
2.
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Oxidation
Oxidation is the reactions of oxygen to form oxides or (if water is present) Hydroxides.
The rusting of iron is when iron combines with oxygen to form iron oxide called Hematite.
Atmospheric oxygen works for alteration, but mostly the oxygen dissolved in water is more.
3. Hydrolysis
❖ Hydrolysis is a chemical reaction between the Hydrogen (H+) ions and Hydroxyl (OH‐) ions of water and mineral
ions. Hydrogen ions replace positive ions of minerals.
❖ Hydrogen ions attack the ions in the orthoclase structure, and some liberated ions are incorporated in a developing
clay mineral, while others simply go into solution.
“Spheroidal Weathering”
❖ The rectangular shape forms a spheroidal shape because that is the most stable shape to assume.
❖ The characteristics of Spheroidal Weathering are:
1) Corners are attacked by weathering from three sides.
2) Edges are attacked from two sides.
3) Flat surfaces are weathered uniformly.
❖ Consequently, corners are edges are worn out more rapidly.
❖ Spheroidal Weathering is common in granitic rocks cut by joints.
“Factors Controlling the Rate of Chemical Weathering”
❖ Advanced mechanical weathering aids chemical weathering by increasing the surface area since chemical
processes operate on the surface of particles.
❖ Factors Controlling the Rate of Chemical Weathering:
1) Particle size
2) Climate
3) Parent material
1.
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Particle Size
The greater the size, the more effective the weathering.
Small particles have larger surface areas compared to their volume than do large particles.
Surface increases but the volume remains constant.
Mechanical weathering reduces particle size, thus contributing to chemical weathering by exposing more surface
area.
2. Climate
❖ Temperature and humidity are the most crucial factors for chemical weathering.
❖ Chemical weathering is most effective in areas of warm temperatures and abundant humidity. It’s rapid at high
temperatures and in the presence of water. More effective in the tropics than in arid or arctic regions.
❖ Effects of weathering extend to depths of several tens of meters in tropics while it’s being a few meters in arid or
arctic regions.
3.
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Parent Material
Some rocks are chemically more stable than others and are not altered as rapidly by chemical processes.
Quartzite is stable and alters very slowly.
Granite is decomposing rapidly because feldspars and ferromagnesian minerals are unstable.
Clay + Fe results in oxides and quartz.
Lecture 5 “Soil”
“What’s soil”
❖ Soil is:
1) An interface in the Earth system.
2) A combination of minerals, water, and air.
3) Layers of weathered, unconsolidated material that contains organic matter and is capable of supporting
plant growth.
❖ Regolith is a layer of unconsolidated rock and mineral fragments.
❖ Regolith consists of:
1) volcanic ash.
2) sediment deposited by wind and stream.
3) weathered rock material in place.
❖ Humus is dark in color and is derived by bacterial decay of organic matter.
❖ Humus contains:
1) Carbons
2) Nitrogen (lesser than original material)
❖ Humus is resistant to further bacterial decay.
❖ The Typical components in a soil that yields good plant growth are:
1) 25% Air
2) 25% Water
3) 45% Mineral matter
4) 5% Organic matter
“Soil Texture and Structure”
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Texture refers to the proportions of different particle sizes like Sand (large size), Silt, Clay (small size).
Loam is the mixture of all three sizes, and it is the best suited for plant life.
Soil particles clump together to give the soil its structure.
There are four basic soil structures:
1) Platy
2) Prismatic
3) Blocky
4) Spheroidal
“Soil Profile”
❖ Soil forming processes operate from the surface downward.
❖ Horizons: the zones or layers of soil.
1. Horizon “O”
❖ Then layer of organic matter.
❖ The characteristics of Horizon “O”:
1) Few cm’s thick.
2) Rich in organic matter.
3) Plant remains are observable in it.
4) Its lower part is Humus.
2. Horizon “A” (Topsoil)
❖ Zone of leaching.
❖ The characteristics of Horizon “A”:
1) Intense biological activity (plant roots, bacteria, fungi, and warms)
2) The upper part is darker because of organic matter.
3) Contains clay and chemically stable minerals such as quartz.
4) Fe‐oxides, Clays, and Carbon are leached downward.
5) Pale and sandy.
6) Water percolating downward through it (LEACHING)
7) Water dissolves soluble minerals and carries them away or downward to lower layers.
3. Horizon “B” (Subsoil)
❖ Zone of accumulation.
❖ The characteristics of Horizon “A”:
1) Material leached downward accumulates at this horizon.
2) Calcium carbonate may built‐up (concretions)
3) Accumulation occurs in irregular masses.
4) Fewer organisms and less organic matter
5) Clayey and stained in red or brown by hematite and limonite.
6) Gets hard when dry.
7) Sticker when wet.
4. Horizon “C”
❖ Partly altered parent material.
❖ The characteristics of Horizon “A”:
1) Composed of incompletely weathered material
2) Parent material is the underlying bed rock being subjected to weathering.
3) Transitional zone between the weathered (rock or soil) and nonweathered bedrock.
4) Contains rock fragments, Mineral fragments, and very little organic matter.
“Soil Types”
❖ There are Hundreds of soil types worldwide.
❖ We have three very generic types.
1) Pedalfer (Al+Fe)
2) Pedocal (Al+Ca)
3) Laterite (Al+Fe+other elements)
1. Pedalfers
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Pedon means soil. Pedalfers are rich in Al and Fe.
Pedalfers soil is found in Humid regions.
It is best developed under forest vegetation.
It has Abundant moisture.
It’s Dark due to organic matter.
Soluble matters are leached from zone A
Horizon “A”: dark grey and rich in organic matter
Horizon “B”: Accumulating iron oxides, Al‐rich clays, and Fe‐oxide
2. Pedocals
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It’s rich in calcite.
Pedocal soil is found in the arid and semi‐arid regions. So, it is less chemical weathered.
Pedocal soil is less organic.
Horizon “A”: is light in color and contains more insoluble matter.
Horizon “B”: soil evaporates, CaCO₃ leached and precipitated where it forms irregular masses can form Caliche.
Na‐salts precipitates in deserts where water evaporates creating alkali soils.
3. Laterite
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Common in the Tropic areas.
Have intense chemical weathering and leaching is complete.
Red color extends to depths of tens of meters.
Contains Al‐hydroxides, Fe‐oxides, clay minerals and quartz.
If parent material is rich in AL, Al‐hydroxides forms horizon “B” forming “Bauxite”.
It Supports plant life.
Hardpan is a hard layer of earth material. It’s difficult to dig or drill.
❖ Caliche is the cementation of soil by CaCO₃.
“Controls of Soil Formation”
1. Climate
❖ Climate is a very important factor.
❖ At the Tropic area there is an intense chemical weathering. So, deep soils are being made up of soluble mineral
matter.
❖ At the Arctic and Deserts areas there is a weak chemical weathering so thing solis are being made up of soluble
minerals and material derived from mechanical weathering.
❖ Climate influence:
1) The type and rate of weathering,
2) Amount of water moving through and over the soil
3) The type of vegetation (strengthen the soil that roots increase cohesion).
2. Parent material
❖ Residual soil is the soil which its parent material is bedrock. Which means it develops from weathering of the
rock directly below.
❖ Transported soil is the soil which its parent material has been carried from elsewhere and deposited.
❖ Parent material influences:
1) The rate of soil development (rate of weathering)
2) Oil composition. For example, shales produce a lot of clay and sandstone produces sandy soil.
3) Physical properties of soil. For example, permeability or drainage, shrink‐swell potential (amount of
expansive clay), cohesive strength (clayey soils are "sticky", this aids cohesion).
3. Relief & Slope: climate changes with elevation
❖ Slope Angle:
1) Steep slopes often have poorly developed soil.
2) Flat to undulating upland surface is Optimum.
❖ Direction the slope faces:
1) The Northern hemisphere, slopes facing North receive less sunlight than South‐facing slopes. If the slope
is steep, then no sunlight reaches the N‐facing slope.
❖ The direction the slope is facing influences.
1) Soil temperature
2) Moisture
❖ Steeper slopes accelerate erosion.
❖ If the rate of erosion is faster than the rate of soil development, we get thin soil or no soil even.
❖ Soils on steeper slopes also have lower water contents (lower infiltration) which means less weathering and less
vegetation.
❖ Soils in low‐lying areas have higher water content, hence, more weathering. This results in thicker soils and more
vegetation.
4. Time
❖ Time is important in all geologic processes •
❖ The amount of time to evolve varies for different soils is (2.5cm/ century). Longer times gives a better fully
developed soil.
5. Organic Activity: fertility
❖ It refers to the activities done by plants and animals.
❖ Organisms influence the soil's physical and chemical properties.
❖ Organisms furnish organic matter to soil.
“Soil Degradation”
❖ Soil Degradation is any decrease in soil productivity or loss of soil to erosion.
❖ Types of Soil Degradation:
1) Erosion
2) Chemical deterioration
3) Physical deterioration
1. Erosion
❖ Erosion is the removal of soil by wind and water when natural vegetation is removed.
❖ Types of erosion:
1) Sheet Erosion: is the erosion distributed over the surface and removes thin layers of soil.
2) Rill Erosion: is the erosion when running water scours small channels.
❖ If Rill Erosion’s channels can be eliminated by plowing, then it’s “rill.”
❖ If Rill Erosion’s channels are too deep (30 cm or more) to be plowed, then it’s “gullies.”
❖ The Consequences of erosion:
1) Thes soil gets contaminated by pesticides and fertilizers.
2) Reservoirs get filled with sediment.
❖ The benefit of Soil erosion is that it’s Recycling Earth’s materials.
❖ Natural rates of erosion depend on:
1) Soil characteristics
2) Climate
3) Slope
4) Type of vegetation
2. Chemical Deterioration
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Chemical Deterioration results from the over usage of the soil to maintain agricultural productivity.
Insufficient by chemical fertilizers
Clearing of soil by their natural vegetation results in more productivity.
Pollution results from the disposal of domestic wastes, industrial wastes, oil, and chemicals.
Salinization is an increase in concentration of salts results in unfitness to agriculture.
3. Physical Deterioration
❖ Physical Deterioration is compaction due to overlying material.
“Weathering creates ore deposits.”
❖ Weathering creates ore deposits by a process called secondary enrichment.
❖ In the process it concentrates metals into economical deposits
❖ It takes place in one of two ways:
1) Removing undesired material from the decomposing rock, leaving the desired elements behind.
2) Desired elements are carried to lower zones and deposited.
❖ Examples ore deposits by weathering:
1) Bauxite, the principal ore of aluminum
2) Many copper and silver deposits
Lecture 6 “SEDIMENT AND SEDIMENTARY ROCKS”
“Sedimentary Environment”
❖ Any geographical area in which sediment is deposited is a Sedimentary Environment.
“Sediment Transport and Deposition”
❖ Classification of Sedimentary Rocks:
1) Detrital (Clastic) Sedimentary Rocks.
2) Chemical and Biochemical Sedimentary Rocks.
❖ Agents of Transportation:
1) Running water transports sand and gravel.
2) Wind or air transports sand sized and smaller materials.
3) Glaciers transports particles of any size.
❖ All particles are transported away by transporting agents and deposited in a Sedimentary Basin. In any basin
sediments are deposited generally as horizontal layers or beds.
1. “Sediment Transport in Water”
❖ Types of Sediment Load in water:
1) Dissolved Load
2) Suspended Load
3) Bed Load
❖ Bed Load is divided into two types which are rolling or traction bed load and saltation Load.
❖ Suspended and dissolved loads are carried as the water flow. Suspended load may be deposited when water stop
moving in a basin and form mud or claystone. Dissolved load will be deposited as chemical sedimentary rocks.
2. “Wind Transport”
3. “Glacial Transport”
❖ Glaciers are large scale convey belts that picks up, transport, and deposit sediment.
“Classification of sedimentary rocks”
“Sediment to Sedimentary Rock”
❖ Compaction is the reduction in volume due to the overburden weight.
❖ Cementation occurs between grains sticking them together.
❖ Common cements are:
1) Calcite CaCO₃
2) Quartz SiO₂
3) Hematite Fe₂O₃
4) Gypsum CaSO₄. H₂O
5) Clay minerals
❖ Steps of creating sediment rocks:
“Important Terminology”
❖ Important terms for sedimentary rocks:
1) Roundness and Sorting
2) Porosity and Permeability
3) Diagenesis
1. Roundness and sorting
a. “Roundness”
❖ Roundness is the angularity of the grains, or the fragments of the sedimentary rocks formed by mechanical
wearing of particles.
b. “sorting”
❖ Sorting is the size distribution of grains or fragments. It indicates the energy of transportation.
2. Porosity and Permeability
a. Porosity”
❖ Porosity is the amount of pore space in a rock or other earth material (like a sand deposit). In other words, it´s
how much fluid a material can hold.
❖ Effective or connected porosity is indicted the ratio of the connected pore volume to total volume of the rock.
“Types of Porosity”
1. Primary Porosity (before and during lithification)
❖ Primary Porosity is controlled by grain size, grain packing, particle shape, and the distribution of grain sizes.
2. Secondary Porosity (after lithification)
❖ Secondary Porosity can be a mechanical process created by stress compaction, plastic deformation, brittle
deformation, and fracture evolution.
❖ Secondary Porosity can be a chemical process created by dissolution, reprecipitation, and mineralogical changes.
b. “Permeability”
❖ Permeability describes how easily fluid can move through rock.
❖ Permeability is related to the how well connected the pore spaces are and to the grain size or pore volume of the
rock.
3. Diagenesis
❖ Diagenesis is the change of sediments or pre-existing sedimentary rocks into a different sedimentary rock during
and or after lithification, at temperatures less than 200°C and pressures less than that required for the formation of
metamorphic rocks.
❖ Recrystallization occurs under low temperature and low pressure. If any of them becomes higher, the rock turns
into a metamorphic rock.
“Chemical Sedimentary Rocks”
❖ Chemical sedimentary rocks are the direct precipitation of dissolved material (dissolved load).
❖ Chemical sedimentary rocks form by inorganic processes or organic processes done by the activities of the
organisms.
❖ Examples of Chemical Sedimentary Rocks:
1) Evaporites (various salts, NaCl, CaSO4, NaHCO3 etc.)
2) Limestone and Dolostone (CaCO3, (Ca, Mg)Co3)
3) Chert (Amorphous Silica, Agate, Opal, Chalcedony etc.)
4) Travertine (CaCO3 from thermal springs)
5) Coal (Carbon)
❖ Fossiliferous Limestone: A sedimentary rock rich in calcium carbonate that contains a multitude of well-preserved
fossils, typically from marine organisms.
❖ Coquina: A sedimentary rock composed of loosely cemented shell fragments and other marine debris, known for
its coarse and granular texture.
❖ Oolitic Limestone: A sedimentary rock made up of small, spherical grains called ooids, often forming in shallow
marine environments, with a granular and sandy texture.
“Sedimentary Facies and Depositional Environment”
❖ Can be classified into three categories on terms of area of deposition:
1) Terrestrial (Continental): Fluvial (alluvial fan, river), Lacustrine, Glacial, Desert
2) Transitional: Delta, Beach, Tidal
3) Marine: Shallow Marine (continental shelf), Bathyal (continental Slope), Abyssal (Deep Sea).
❖ The Transition from Continental to Oceanic Crust is consisting of three levels:
1) Continental Shelf
2) Continental Slope
3) Continental Rise
“Continental Margin Types”
❖ Continental Margin Types are two:
1) Active Margin
2) Passive Margin
❖ Limestone solubility depends on the concentration of CO2 in the ocean water.
❖ Colder ocean water dissolves more CO2, this makes the calcite compensation depth (called CCD) shallower.
Therefore, CCD changes with the temperature and pressure, since pressure is the function of depth, temperature of
the ocean water is the main variable.
❖ Cold water dissolves more CO2 while warmer waters dissolve less CO2. So warm ocean water means deeper
CCD while colder water means shallower CCD.
“Evaporation in a Lake”
“Carbonaceous deposits (Mainly coal)”
❖ When logs and branches of trees are covered by sediments, they are cut off from oxygen and turn into coal.
“Ferruginous deposits (Bog iron)”
❖ In very shallow lakes, swamps and marshes bacteria causes deposition of various iron compounds.
“Transgression and Regression (Walther’s rule:)”
❖ Walther’s rule: Facies we see side by side today, appear on by on in geological time due to sea level fluctuations.
“Sedimentary structures”
❖ Sedimentary structures are formed during sedimentation processes and are preserved after diagenesis.
1) Bedding: A package of sediment deposited in a single depositional episode. a bed is a layer that’s bigger
than 1cm thick. It’s called Lamina if the thickness is less than 1cm.
2) Cross bedding: inclined layers of sediment within a larger rock unit, formed by the migration of
sediments in response to wind or water currents.
3) Graded bedding: a sedimentary structure characterized by a vertical arrangement of sediment particles in
which the coarsest particles are at the bottom, and the finest particles are at the top, resulting from a
settling process after a turbulent event like a storm or underwater landslide.
4) Ripple mark: small-scale sedimentary structures that appear as wave-like patterns on the surface of sand
or silt beds, created by the action of wind or water currents.
5) Sole mark: sedimentary structures found on the undersides of sedimentary layers. They often include
features like Flute mark, Groove mark.
6) Fossils and Fossil traces: biogenic sedimentary structures
7) Concretion: A concretion is a rounded, often spherical mass of mineral matter that has precipitated from
fluids within the pores of sedimentary rocks.
8) Nodule: A nodule is a rounded, irregularly shaped solid mass of mineral or rock material found within a
sedimentary rock or sediment
9) Geode: A geode is a hollow, typically spherical, or ovoid rock cavity lined with crystals or mineral
deposits. Geodes are formed when mineral-rich fluids fill cavities within rocks.
10) Rain pits: small depressions or markings on the surface of sedimentary rocks or soft sediments, resulting
from the impact of raindrops on loose materials.
11) Mud cracks: polygonal patterns of cracks that form in drying mud or clay-rich sediments when they
shrink and split as they lose moisture.
12) Sediment body shape:
a) Shoestring: A shoestring sediment body is a long and narrow deposit that often appears as a
ribbon or elongated belt of sediment within a rock sequence.,
b) Wedge: A wedge-shaped sediment body is wider at one end and tapers to a narrower point at the
other.
c) Sheet (Blanket): A sheet or blanket sediment body has a relatively uniform thickness and
extensive lateral extent, covering a wide area with a consistent sedimentary layer.
❖ Beds are separated from other beds by bedding planes and are distinguished from other beds by color,
composition, gain size etc.
Flute marks
Lecture 7 “Metamorphic Rocks”
What's matamorphisim
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Metamorphic Rocks means "Changed form" rocks. (Meta = Change, Morpho = Shape).
Produced from preexisting Igneous rocks, Sedimentary rocks and Other metamorphic rocks.
Metamorphic process usually occurs beneath the Earth’s surface.
Metamorphism: is the solid state transformation of pre‐existing rock (original rock or parent rock) into texturally
and/or mineralogically distinct new rock.
Metamorphisem is a result of any pre‐existing rock subjected to high temperature, high pressure or both.
Degrees of metamorphism: (Exhibited by rock texture and mineralogy)
1) Low‐grade: (low temperatures and pressures)
▪ e.g., shale becomes slate.
2) High‐grade: (high temperatures and pressures)
▪ obliteration of original features.
The metamorphic and igneous rocks forms the crytalline basement rocks that underlie the sedimentary rocks of
continent’s surface.
The basement rocks are widely exposed in regions of the continents known as shields, which have been stable
during the past 600 Ma.
They also occur at the core of the mountain ranges. Some of the oldest dated rock is 3.96 Ba from the Canadian
Shield are metamorphic. This indicates that they were fromed from even older rock.
The importance of metamorphic rocks:
1) Provide information about the geological processes operating within Earth and about the way these
processes varied in time.
2) From the occurrence of certain minerals, geologists determine aproximate temperature and pressure
conditions that parent rock was subjected.
3) Provides information about the physical and chemical conditions at different depths withim the crust.
4) Some metamorphic rocks are economically important.
▪ Marble and slate are used in construction.
▪ Garnet and emery are used as gemstones and abrasives.
▪ Talc is used in cosmetics, in the manufacturing of paint and lubricants.
▪ Aspestos is used for insulators and fireproofing.
▪ Kyanite is used for fire‐resistant materials for spark plugs.
The processes that forms metamorphisem:
1) Recrystallization: Minerals change size and shape.
2) Phase Change: new minerals form with same chemical formula but different crystal structure.
3) Neocrystalization: completely new minerals form from unstable old ones.
▪ E.g. a shale is converted into garnet‐mica‐schist.
4) Pressure solution: Mineral grains partially dissolve under pressure
5) Plastic deformation: mineral grains soften and deform under heat and pressure.
Characteristics and Changes Due to Metamorphism:
1) Texture.
2) Mineral content.
3) Presence or absence of Foliation.
Agents of metamorphism:
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Heat.
Confining Pressure.
Differential Stress.
Chemically Active Fluids.
1. Heat
❖ Heat increases the rate of chemical reactions which may produce new minerals.
❖ Heat source:
1) Come from intrusive magmas.
2) Result from deep burial in the Earth’s crust, during subduction.
❖ Geothermal gradient:
1) During subduction: 25°C/km.
2) Normal geothermal gradient: 35°C/km.
❖ Minerals tend to become in equilibrium with the newly increased temperature conditions due to intrusion or deep
burial that gave way to metamorphism.
2. Confining Pressure
❖ When rocks are buried, they are subjected to increasingly greater Lithostatic Pressure due to weight of the
overlying rocks equally applied in all directions.
❖ As a result of pressure:
1) minerals may become more closely packed.
2) minerals recrystallize to form smaller and denser minerals.
3. Differential Pressure
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Differential pressure: is pressure which is not equally applied to all sides and consequently the rock is distorted.
Differential pressure results in a deformation during mountain building processes
Differential pressure produces distinctive metamorphic textures and features.
Vertical Pressure: Pv= q*g*z (q: average density of overburden rocks, g: acceleration due to gravity, z: depth)
Most of the rocks comprising the crust of the earth have density between 2.6 and 2.7g/cc.
4. Chemically Active Fluids
❖ In almost every region where metamorphism occurs, water and carbon dioxide are present in varying amounts
along mineral grain boundaries or pore‐spaces of rocks.
❖ These fluids, which may contain ions in solution enhance metamorphism by increasing the rate of chemical
reactions.
❖ Olivine + water → Serpentine + carried away in solution (a result of sea water moving through hot basaltic rocks)
❖ Source of Fluids:
1) Water trapped in pore‐spaces of sedimentary rocks
2) Volatile fluid within magma
3) Dehydration of water‐bearing minerals such as gypsum, CaSO4.2H2O
Types of Metamorphism
1) Contact Metamorphism: heating by intrusives.
2) Dynamic Metamorphism: associated with fault zones .
3) Regional Metamorphism: Pressure and tempreture change due to subduction and mountain building
processes.
1. Contact Metamorphism
❖ Contact metamorphism takes place when a body of magma alters the surrounding country rock.
❖ At shallow depths, an intruding magma:
1) Raises the temperature of surrounding rock, causing thermal alteration.
2) Release of hot fluids into the country rock by cooling intrusion. This aids the formation of new minerals.
❖ Important factors in contact metamorphism:
1) Initial temperature (mafic magmas are hotter than felsic magmas)
2) Size of intrusion
3) Fluid content of the magma and or country rock (hot and wet magmas are rich in active fluids)
❖ Temperature reaches 900⁰C adjacent to intrusion, but gradually decreases with distance.
❖ The zone affected by these changes is called the aureole.
❖ The rocks closer to the intrusion experience higher temperatures, while those farther away may undergo lowergrade metamorphism.
❖ Aureole: is the altered zone of rock surrounding an intrusive igneous body. It results from contact metamorphism,
where the heat and pressure from the intrusion transform the surrounding rocks.
❖ The metamorphic aureole varies in width depending on:
1) Size of intrusion
2) Temperature of intrusion
3) Composition of intrusion and the country rock
❖ Sills and dikes have aureoles of a few cm wide whereas large intrusive bodies (like batholiths), several km’s wide.
❖ During final stages of cooling of magma, large amounts of hot, watery solutions are often released which may
react with the country rock to produce new minerals (Hydrothermal Alteration). They may form valuable mineral
deposits.
2. Dynamic Metamorphism
❖ It is associated with fault zones (a fracture along which movement has occurred) where rocks are subjected to
high differential pressures.
❖ As a result of the Dynamic Metamorphism mylonite form.
❖ Mylonite is a hard, dense, fine‐grained rock characterized by foliation and lineation restricted to narrow zones
adjacent to faults.
❖ High shearing pressure completely pulverizes the country rock and essentially “smears” the fine particles together,
producing a characteristic mylonitic texture.
3. Regional Metamorphism
❖ Regional metamorphism is due to tremendous temperature, pressure and deformation within the deeper portions
of the Earth’s crust.
❖ Regional metamorphism is obvious along convergent plate boundaries where rocks are intensely deformed and
recrystallized during convergence and subduction.
Index mineral paragenesis
❖ Rocks exhibit a gradation of metamorphic intensity from areas that were subjected to the most intense pressures
and/or highest temperatures to areas of low pressures and temperatures which is recognized by metamorphic
minerals.
❖ There is gradation of metamorphic intensity according to depth and temperature. This can be recognized by the
type of metamorphic minerals that are present.
❖ Index Minerals: certain metamorphic minerals are known to form only within specific temperature and pressure
ranges.
❖ Index Minerals are used to recognize low‐grade, intermediate‐grade, and high‐grade metamorphic rocks.
❖ E.g., clay‐rich rock (Shale):
1) low‐grade (~200°C) → chlorite forms
2) high‐grade (~500°C) → sillimanite forms
Classification of Metamorphic Rocks
❖ Classification of Metamorphic rocks is being according to textures:
1) Foliated texture:
▪ Minerals are in a parallel alignment.
▪ Minerals are perpendicular to the compressional force.
2) Nonfloated texture:
▪ Contain equidimensional crystals.
▪ Resembles a coarse-grained igneous rock.
❖ Slate → Phyllite → Schist → Gneiss → Amphibolite → Migmatite
❖ Rocks subjected to heat and differential pressure during metamorphism typically have minerals arranged in a
parallel fashion, known as foliation.
❖ Based on the size and shape of minerals, foliation is:
1) Coarse: granular minerals such as quartz and feldspar are segregated into roughly parallel zones that
differ in composition and color. It is also known as compositional foliation.
2) Fine: individual grains cannot be recognized with unaided eye (e.g., Slate).
❖ Common foliated metamorphic rocks:
1) Slate: Fine‐grained, Splits easily.
2) Schist: Strongly foliated "Platy", Types based on composition (e.g., mica schist).
3) Gneiss: Strong segregation of silicate minerals. "Banded" texture.
❖ In some metamorphic rocks, mineral grains do not show an observable preferred orientation, but consist of mosaic
of roughly inter‐equidimensional minerals are said to be non-foliated.
❖ Non-foliated result from either:
1) Contact metamorphism.
2) Regional metamorphism of rocks in which no platy or elongate minerals are present.
❖ Non-foliated metamorphic rocks are mainly of two types:
1) Those composed mainly of one mineral (marble or quartzite)
2) Those in which the different mineral grains are too small to be seen by naked eye (greenstone and
hornfels)
❖ Common non‐foliated metamorphic rocks:
1) Marble: Parent rock is limestone, Large, calcite crystals, Used as a building stone, Variety of colors.
2) Quartzite: Parent rock – quartz sandstone, grains are fused.
Metamorphic Zones and Facies
❖ Metamorphic zones: Areas of equal metamorphic grade and are determined by occurrence of certain index
minerals.
❖ Metamorphic facies: A group of metamorphic rocks characterized by particular mineral assemblages occurring
under the same broad metamorphic ranges (temperature and pressure).
❖ There are several commonly recognized metamorphic facies, and they are often depicted on a pressuretemperature (P-T) diagram. Some of the well-known metamorphic facies include:
1) Low-Grade Metamorphic Facies:
▪ Zeolite Facies: Characterized by the presence of zeolite minerals. It occurs at low temperatures
and low pressures.
2) Medium-Grade Metamorphic Facies:
▪ Greenschist Facies: It forms under higher temperatures and pressures than zeolite facies.
▪ Amphibolite Facies: Characterized by the presence of minerals like amphibole and plagioclase
feldspar. It indicates higher temperatures and pressures than greenschist facies.
3) High-Grade Metamorphic Facies:
▪ Granulite Facies: This facies is associated with high temperatures and pressures.
4) Ultra-High-Pressure (UHP) Metamorphic Facies:
▪ Blueschist and Eclogite Facies: These facies represent rocks that have experienced extremely
high pressures, often associated with subduction zones.
Environment of Metamorphism
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Contact or thermal metamorphism
Hydrothermal metamorphism
Burial and subduction zone metamorphism
Regional metamorphism
Metamorphism Along Fault Zones
Impact Metamorphism
Shock Metamorphism
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Shock Metamorphism is rare when earth is struck by a comet or an asteroid.
Impact generates compressional shock wave that yields extremely high pressures.
Heat vaporizes or melts large masses of rock.
These conditions generate high‐pressure minerals.
Resources from Rocks and Minerals
❖ Metallic mineral resources (Gold, silver, copper, mercury, lead, etc.)
❖ Concentrations of desirable materials are produced by.
1) Igneous processes
2) Metamorphic processes
❖ Most important ore deposits are generated from hydrothermal solutions (hot water).
❖ Hydrothermal solutions (hot water) are:
1) Hot and contains metal‐rich fluids.
2) Associated with cooling magma bodies.
3) Types of deposits include ‐ Vein deposits in fractures or bedding planes.
4) Disseminated deposits which are distributed throughout the rock.
❖ Nonmetallic mineral resources:
❖ Two broad groups
1) Building materials (e.g., limestone, gypsum)
2) Industrial minerals (e.g., fluorite, corundum, sylvite)
Lecture 8 “Deformation, Mountain Building”
“Deformation”
❖ Deformation is a general term that refers to all changes in the original form and, or the size of a rock body.
❖ Most crustal deformation occurs along plate margins.
❖ Factors that influence the strength of a rock:
1) Temperature.
2) Confining pressure.
3) Rock type (Rheology).
4) Time.
❖ Deformed rocks are showing the dynamic nature of the Earth.
❖ Many ancient rocks are fractured or highly contorted, clearly indicating that the forces within the Earth caused
deformation during the past.
❖ This deformation is not restricted to the past, however, seismic activity and continuing deformation at plate
boundaries indicate that deforming forces remain active.
❖ Most of the preserved deformation occurs during Mountain building processes.
❖ Stress is the force acting on the rock.
❖ Stress = Force/Area
❖ Strain is the deformation caused by stress.
❖ If the intensity of stress is greater than the internal strength of the rocks, it will be strained.
“Stress”
❖ Types of stress:
1) Compression:
a) When rocks are squeezed or compressed by external forces directed to one another.
b) Shortening and thickening by folding and faulting
2) Tension:
a) Forces acting in opposite direction along the same line.
b) Lengthening and thinning; rocks are pulled apart.
3) Shear:
a) Forces act parallel to one another but in opposite directions.
b) Displacement of adjacent layers along closely spaced planes.
“Strain”
❖ Strain types:
1) Elastic Strain: Deformed object returns to its original position when the stresses are released.
2) Plastic Strain: Deformed object cannot recover its original shape.
❖ When stress is applied to rocks, they respond first by elastic strain, but when strained beyond their elastic limit
they cannot recover their original shape anymore.
❖ Plastic Strain results in a permanent deformation.
❖ The amount of plastic deformation rocks exhibit before fracturing depends on their ductility.
❖ Rocks at or near the surface are brittle.
❖ Rocks at depth with high pressure and temperature are ductile.
❖ Ductile rocks are having a considerable plastic deformation.
❖ Brittle rocks have little or no plastic deformation before fracturing.
❖ The amount of strain depends on:
1) Kind of stress applied.
2) Amount of pressure.
3) Temperature.
4) The rock types.
5) Length of time the rock is subjected to stress.
6) Hydrothermal fluids.
“Strike and Dip”
❖ Strike and Dip are used to describe the orientation of deformed rock layers.
❖ Strike: Is the direction of line formed by the intersection of a horizontal plane with an inclined plane.
❖ Dip: Is the measure of maximum angular deviation of an inclined plane from horizontal, perpendicular to strike.
“Ductile Deformation: Folds”
❖ Folds: Rocks bent into a series of waves (up- and down arched features).
❖ Most folds result from compressional forces which shorten and thicken the crust.
❖ Parts of the fold:
1) An Axile plane
2) A Hinge
3) Two Limbs
❖ Types of Folds:
1) Anticline (A-Shaped):
a) Upfolded or arched rock layers.
b) Each limb dipped away from each other.
c) oldest rock is exposed at the core.
2) Syncline:
a) Downfolded rock layers.
b) Each limb dips toward each other.
c) The youngest rock is exposed at the core.
3) Monocline:
a) simple bend or flexure in otherwise horizontal, or uniformly dipping rock layer.
❖ Types of Anticlines:
1) Symmetrical:
a) Limbs are mirroring images; axial plane is vertical.
b) Each limbs dip at the same angle.
2) Asymmetrical:
a) limbs are not mirror images; axial plane is inclined.
b) Limbs dip at different angles
3) Overturned:
a) One limb is tilted beyond the vertical: so, both limbs dip in the same direction.
b) One limb has been rotated 90 degrees from its original position so that it is now upside down.
4) Recumbent:
a) An overturned fold That lies on its side.
b) Axial plane is horizontal.
❖ Plunging Folds: Folds that are tilted by tectonic forces that cause their hinge lines to slope rather than have a
horizontal orientation. The hinge lines of the plunging fold dip downward (plunge) and penetrate Earth’s surface.
❖ Other types of folds:
1) Dome:
a) Circular, or slightly elongated.
b) Up warped displacement of rocks.
c) Oldest rocks in core.
2) Basin:
a) Circular, or slightly elongated.
b) Down warped displacement of rocks.
c) Youngest rocks in core.
❖ Classification of folds on terms of its thickness:
1) Open
2) Tight
3) Isoclinal
“Brittle Deformation: Fractures”
❖ Fractures are surfaces along which rocks has lost cohesion.
❖ Types of fractures:
1) Joints
2) Faults
1. Joints
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Joints are fractures along which no movement has occurred, or movement is perpendicular to the fracture walls.
Fractures may open-up, but the rocks on opposite side of fracture show no movement parallel to the fracture.
Joints are the commonest structures in rocks.
Brittle deformation by fracturing on all near-surface rocks.
Joints form in response to compression, tension, or shear stresses.
They are related to large-scale structures like folds and faults.
Types of joints:
1) Columnar joints: Cooling of magma in dykes, sills, and thick lava flows.
2) Sheet joints: Pressure release mechanism.
2. Faults
❖ Faults are fractures (breaks) in rocks along which appreciable displacement has taken place:
❖ In faults blocks on opposite sides of fracture move parallel to the fracture surface (fault plane).
❖ Parts of the fault:
1) Hanging wall
2) Foot wall
3) Fault plane
❖ Types of faults
1) Dip-slip fault
2) Strike-slip fault
3) Oblique-slip fault
Dip-Slipp faults:
❖ Faults in which movement is primarily parallel to the dip (inclination) of the fault surface are called dip-slip
faults.
❖ Types of dip-slip faults:
1) Normal fault:
a) Hanging wall block moves down.
b) Associated with fault-block mountains.
c) Prevalent at spreading centers.
d) Caused by vertical stress (tension).
2) Reverse and thrust faults:
a) Hanging wall block moves up.
b) Caused by strong compressional stresses.
c) Thrust fault is a type of reverse fault having a dip less than 45 degrees.
A. Normal Fault
Strike-slip Faults
❖ A Strike-slip fault is a fault in which the dominant displacement is horizontal and parallel to the strike of the fault
surface.
❖ Large strike-slip fault that cuts through the lithosphere.
❖ Strike-slip faults are often associated with plate boundaries.
❖ Strike-slip fault types:
1) Sinistral/ left lateral: causes the crustal block on the opposite side of the fault to move to the left as you
face the fault.
2) Dextral/ right lateral: causes the crustal block on the opposite side of the fault to move to the right as you
face the fault.
Oblique-Slip Faults
❖ Oblique-Slip Faults Fare faults that exhibit both dip-slip and strike-slip movement.
❖ Oblique-Slip Faults are caused by a combination of shearing and tensional or compressional stress.
Mountain Building (Orogenesis)
❖ Orogenesis refers to processes that collectively produce a mountain belt.
❖ Most mountain building occurs at convergent plate boundaries.
❖ Types of mountain building systems:
1) Convergent plate boundaries systems.
2) Divergent plate boundaries systems.
Convergent plate boundaries mountain buildings systems
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Aleutian Type: island arcs
Andean Type: continental magmatic arcs
Continental collisions type (Alpine type): continental crust converges.
Continental accretion (Cordilleran type): Terranes collide with the continent.
Aleutian-type Mountain building system (island arcs)
Aleutian-type Mountain building creates island arcs.
It happens where two oceanic plates converge, and one is subducted beneath the other.
Volcanic island arcs because of the raising magma.
This type of mountain building system is found in shrinking ocean basins, such as the Pacific.
Examples: Mariana, Tonga, Aleutian, and Japan arcs
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Andean Type Mountain building system (continental magmatic arcs)
This type happens at Oceanic-continental crust convergence zone.
Example: Andes Mountains.
Phases of development of Andean type mountain belt:
1) Starting with a passive margin prior to the formation of a subduction zone.
2) Subduction zone forms between the oceanic crust and the continental crust.
3) Deformation process begins.
4) Continental volcanic arc forms.
❖ An Example of inactive Andean-type orogenic belt: Sierra Nevada Range and California's Coast Ranges.
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Continental collisions type (Alpine type)
This type of mountain formation happens where two plates with continental crust converge.
In this type of mountain formation, No subduction and very little production of magma.
Example: India and Eurasian plate collision creating the Himalayan Mountains and Tibetan Plateau.
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Continental accretion (Cordilleran type)
At this type of mountain building small crustal fragments collide with and accrete to continental margins.
Accreted crustal blocks are called terranes.
Types of terranes:
1) Island arcs:
a) Appalachian Piedmont terranes (western margin of North America).
b) Japan.
2) Sheared off continental fragments:
a) Madagascar.
b) Most of southwestern California.
Divergent plate boundaries mountain buildings systems
❖ The type that’s building mountains from a divergent plate boundary is called fault-block mountains.
❖ Fault-block mountains characterized by normal faults.
❖ It happens as:
1) Crustal extension results in high heat flow.
2) High heat flow causes a crystal uplift, allowing volcanism.
3) normal faulting breaks the landscape into chunks, some of which slide down relative to their neighbors.
Principle of isostasy
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Floating crust in gravitational balance as a function of thickness and density
Thickness and density both contribute to the presence of ocean basins and continental masses.
Thickening crust at convergent margins contributes to uplift shown by wave-cut platforms high above sea level.
When weight is removed from the crust by erosion or removal of thick ice sheets, crustal uplift occurs.
This process is called isostatic adjustment.
Lecture 9 “Earthquakes”
What’s an Earthquake
❖ An earthquake is the sudden vibration of Earth produced by the rapid release of energy.
❖ The vibration of Earth caused by sudden release of energy, usually because of faulting which involves
displacement of rocks along fractures.
❖ Rock slippage originates in the ground at the focus or hypocenter.
❖ Stored up energy is released as seismic waves that radiate in all directions from the focus.
❖ The epicenter is the point on the ground surface directly above the focus.
Causes of Earthquakes
❖ Causes of weak Earthquakes can be:
1) Massive landslide
2) Meteorites
3) Volcanic eruptions
❖ Over tens to hundreds of years, stress builds up from plate movement.
❖ Eventually, stress along the fault overcomes the frictional resistance, and slip initiates as the rocks break.
❖ The deformed rocks “snap back” to their original position in a process called elastic rebound.
Elastic Rebound Theory
❖ Elastic Rebound Theory Explains how earthquakes occur.
❖ Elastic Rebound is having 3 stages:
1) When rocks are strained or deformed, they store energy and bend.
2) When the inherent strength of the rocks is exceeded, they rupture, releasing energy in the form of
earthquake waves that radiate outward in all directions.
3) Upon rupture, the rocks rebound to their former undeformed shape.
Earthquake Waves
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Seismology is the study of earthquake waves.
Earthquake recording instrument is called seismograph.
The resulting record of the waves is called a seismogram.
Earliest studies of earthquake waves date back almost 2000 years to the Chinese.
❖ Types of earthquake waves:
1) Body Waves
a) Primary (P) waves
b) Secondary (S) Waves
2) Surface waves
1. Body waves
❖ Body waves are having two types:
1) Primary (P) waves
2) Secondary (S) Waves
a. Primary (P) waves
❖ Characteristics of P waves:
1) Push-pull (compressional) motion.
2) Travels through solids, liquids, and gases.
3) Greatest velocity of all earthquake waves.
4) It’s changing the volume of the rock
❖ Sometimes animals can hear the P waves of an earthquake, but usually humans only feel the “bump” of these
waves.
b. Secondary (S) Waves
❖ Characteristics of P waves:
1) "Shake" motion
2) Travel only through solids
3) Slower velocity than P waves
4) changing the rock’s shape but not its volume.
2. Surface waves
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Complex motion
Slowest velocity of all waves.
surface waves tend to have the greatest amplitude.
Large-amplitude waves produce the most shaking, so surface waves usually account for most damage during
earthquakes.
Categories of earthquakes based on the depth.
❖ The categories of earthquakes based on the depth of their focus are:
1) Shallow focus: focal depth of < 70 km
2) Intermediated focus: focal depth of 70 –300 km
3) Deep focus: focal depth of > 300 km
Aftershocks and Foreshocks
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Numerous small earthquakes, called aftershocks, usually follow a major earthquake.
Aftershocks diminish in number, magnitude, frequency, and intensity in the months following.
Although aftershocks are weaker than the main event it can cause severe damage to already weaken structures.
May be hundreds of thousands of aftershocks.
Foreshocks are minor earthquakes that sometimes precede a major earthquake by days, weeks, or months.
Foreshocks
Major
Earthquake
Aftershocks
Locating an Earthquake
❖ Seismic waves travel at different speeds and therefore arrive at a seismograph at different times.
❖ The first wave to arrive is P-waves which travel at nearly twice the velocity of S-waves that follow, and then the
surface waves.
❖ P-S time interval: the difference between the arrival times of the P- and the S-waves, which is a function of the
distance of the seismograph station from the epicenter.
❖ Time-travel graphs are used to find the distance to the epicenter of the earthquake.
❖ The average travel times of P- and S-waves for any specific distance have been determined and published.
❖ Time distance graph illustrates the difference between the arrival times of P- and S-waves as a function of the
distance of the seismograph from focus.
❖ The further the waves travel, the greater the time between the arrivals of P- and S-waves.
❖ Steps of locating the Epicenter:
1) Three station recordings are needed to locate the epicenter.
2) A circle equal to the epicenter distance is drawn around each station.
3) The point where three circles intersect is the epicenter.
Earthquake Belts and Plate Tectonics
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Earthquake zones are closely correlated with plate boundaries.
95% of energy released from earthquakes originates along the circum-Pacific belt.
Most earthquakes occur along megathrust faults (Benioff Zone) of convergent plate boundaries.
The Alpine-Himalayan belt is another region of strong earthquakes.
Tectonic activity is attributed to the collision of the African and Indian Plates with the Eurasian Plate.
Divergent plate boundaries are associated with frequent but weak seismic activity.
Determining the Size of Earthquakes
❖ Two measurements are used to describe the size of an earthquake:
1) Intensity
2) Magnitude
1. Intensity:
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A measure of the degree of earthquake shaking at a given locale based on the amount of damage.
We measure it with the “Modified Mercalli Intensity Scale”.
Maps are drawn with isoseismal lines to divide the affected areas into various intensity zones.
Intensity may be used to approximate the epicenter.
Intensity factors:
1) The amount of energy released by earthquakes (magnitude)
2) Distance forms an earthquake epicenter.
3) Focal depth of the earthquake
4) Population density.
5) Local geology (Nature of the material upon which the structure rests)
6) Type of building construction employed.
7) Duration of the shaking
8) The design of the structure
2. Magnitude:
❖ An estimate of the amount of energy released at the source of the earthquake.
❖ We measure it with the “Richter Scale.”
Earthquake scales:
a.
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Modified Mercalli Intensity Scale
The Modified Mercalli Intensity scale was developed using California buildings as its standard.
It’s based on property destruction in a region.
Values of the earthquake change based on the distance from the epicenter.
The drawback of intensity scales is that destruction may not be a true measure of the earthquake’s actual severity.
b.
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Richter Magnitude Scale
Concept introduced by Charles Richter in 1935.
The Richter scale is calculated by measuring the amplitude of the largest seismic wave recorded on a seismogram.
It’s a logarithmic scale that accounts for the decrease in wave amplitude with increased distance.
Base-10 logarithmic: an increase in magnitude represents a 10-fold increase in a wavelength.
Each unit of Richter magnitude equates to roughly a 32-fold energy increase.
6 vs 5: 10 & 32 / 6 vs 4: 100 & 1024 / 6 vs 3: 1000 & 32768.
c. Moment Magnitude
❖ Moment Magnitude measures the total energy released during an earthquake.
❖ Moment Magnitude is calculated by:
1) The average amount of slip on the fault.
2) The area of the fault surface slipped.
3) The strength of the faulted rock.
❖ Moment Magnitude can also be calculated by modeling data from seismograms.
Earthquake Destruction
❖ Destruction results from:
1) Ground shaking
2) Liquefaction of the ground
3) Ground failure
4) Fires
5) Tsunami
1. Destruction From Ground Shaking
❖ Destruction from Seismic Vibrations is a result of the amplification of seismic waves.
❖ Soft sediments amplify seismic waves more than solid bedrock.
2. Destruction From Liquefaction
❖ Liquefaction is the process where loosely packed, waterlogged sediments behave as a fluid during the intense
shaking of an earthquake.
❖ Liquefaction causes foundation failures.
3. Destruction From Ground failure (Landslides and Ground Subsidence)
❖ Ground shaking causes loose sediments on a slope to slump.
4. Destruction From Fire
❖ Fire can start when gas and electrical lines are destroyed by an earthquake.
❖ Broken water lines make fire control problematic.
5. Tsunami
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A tsunami is a series of large ocean waves.
Most tsunamis are generated by displacement from a megathrust fault.
In open water, the wave amplitude is less than 1 meter, and the wavelength can be larger than 700 meters.
Close to shore, the water “piles up” and some tsunamis can exceed 30 meters in height.
Earthquake Prediction
❖ Earthquake Prediction for:
1) Short-range forecasts.
2) Long-range forecasts.
Can Earthquakes Be Predicted?
❖ The goal is to provide a warning of the location and magnitude of a large earthquake within a narrow time frame.
❖ Seismic Risk Maps: using analysis of historical records and the distribution of known faults, A MAP is produced
to show ‘likelihood and potential severity of future earthquakes’.
a. Short-range forecasts
❖ There is no reliable method yet devised for short-range prediction.
❖ Possible precursors of major earthquakes for short terms:
1) Monitor changes in ground elevation
2) Measure strain in the rocks
3) Measure changes in groundwater level
4) Frequency of foreshocks
b. Long-range forecasts
❖ It’s about giving the probability of earthquakes of a certain magnitude occurring on a time scale of 30 to 100 years
(or more).
❖ These forecasts are useful guides for building codes.
❖ Possible precursors of major earthquakes for long terms:
1) Seismic gaps:
a) Seismic gaps are tectonically quiet zones along a fault where strain is currently building up.
b) The stored strain will be released in a future earthquake.
2) Paleo-seismology:
a) Paleo-seismology is the study of prehistoric earthquakes.
b) By digging a trench across a fault zone, scientists look for evidence of ancient faults (mud
volcanoes and offset sedimentary strata).
Earth's layered structure
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Most of our knowledge of Earth’s interior comes from the study of P and S earthquake waves.
Traveling times of P and S waves through Earth vary depending on the properties of the materials.
Notice that S waves travel only through solids.
Mohorovičić discontinuity:
1) Velocity of seismic waves increases abruptly below 50 km of depth.
2) Mohorovičić discontinuity separates crust from underlying mantle.
❖ Earthquake Shadow zone:
1) Absence of P waves from about 105 degrees to 140 degrees around the globe from an earthquake.
2) Explained if Earth contained a core composed of materials unlike the overlying mantle.
❖ Inner core:
1) Discovered in 1936 by noting a new region of seismic reflection within the core.
2) Size was calculated in the 1960s using echoes from seismic waves generated during underground nuclear
tests.
Discovering Earth’s composition
❖ Oceanic crust:
1) Prior to the 1960s scientists had only seismic evidence from which to determine the composition of
oceanic crust.
2) Development of deep-sea drilling technology made the recovery of ocean floor samples possible.
❖ Mantle:
1) Composition is more speculative.
2) Lava from the asthenosphere has a composition similar to that which results from the partial melting of a
rock called peridotite.
❖ Core:
1) Evidence comes from meteorites.
2) Composition ranges from metallic meteorites made of iron and nickel to stony varieties composed of
dense rock like peridotite.
3) Earth’s magnetic field supports the concept of a molten outer core.
4) Earth’s overall density is also best explained by an iron core.
Lecture 10 “Geologic Time”
The Importance of Dating
❖ Rocks record geologic and evolutionary changes throughout Earth’s history.
❖ Without a time, perspective, these events have very little meaning.
❖ The Snowball Earth hypothesis proposes that during one or more of Earth's icehouse climates, Earth's surface
became entirely or nearly entirely frozen, sometime earlier than 650 million years ago during the Cryogenian
period.
❖ A hominid is any member of the biological family Hominidae. These are the "great apes", living and extinct.
❖ At present there are humans, chimpanzees, gorillas, and orangutans. The word "hominid" has been used in various
ways.
❖ Geologic time is fundamental to understanding both the physical and biologic
❖ history of our planet.
❖ Geologists use two different frames of reference when speaking of geologic time:
1) Relative Dating: placing geologic events in sequential order as determined from their position in
geologic record but do not tell us how long ago a particular event occurred.
2) Absolute Dating: results in specific dates for rock units or events expressed in years before the present.
❖ Today geologic time scale is really a dual scale: a relative scale based on rock sequences with radiometric dates
expressed as years before the present added to it.
Relative Dating
❖ Relative Dating is placing rocks and events in a sequence.
❖ Before the development of radiometric dating techniques, geologists had no reliable means of absolute age dating
and depended solely on the relative dating methods which allow events to be placed in sequential order.
❖ The principle of Uniformitarianism assumes that present-day processes have operated through out geologic time.
❖ Relative dating relies on some principles that help us to know which rocks are older than the others in a certain
sequence.
❖ There are six fundamental geologic principles used in relative dating.
❖ Relative dating principles:
1) Principle of Superposition
2) Principle of Original Horizontality
3) Principle of Lateral Continuity
4) Principle of Cross-cutting Relationships
5) Principles of inclusions
6) Principles of Fossil Succession
1. Principle of Superposition
❖ The Principle of Superposition states that “oldest rocks are on the bottom”.
❖ In an undisturbed successions of sedimentary rock layers, the oldest layer is at the bottom and the youngest layer
is at the top.
❖ The Principle of Superposition is the basis for relative age determination of strata and their contained fossils.
2. Principle of Original Horizontality
❖ The Principle of Original Horizontality states that sediments are originally deposited horizontally.
❖ Sedimentary particles settle from water under the influence of gravity, sediment is deposited in essentially
horizontal layers.
❖ Therefore, a sequence of sedimentary rock layers that is inclined from horizontal suggests tilting after deposition
and lithification.
3. Principle of Lateral Continuity
❖ The principle of Lateral Continuity states that sediments extend laterally (Horizontally) in all directions until they
thins and pinches out or terminates against the edge of the depositional basin.
4. Principle of Cross-cutting Relationships
❖ The Principle of Cross-cutting Relationships states that “younger feature cuts through an older feature”.
❖ According to the Principle of Cross-cutting, an igneous intrusion or fault must be younger than the rock it intrudes
or cuts.
❖ Notice that buried lava flows and sills look very similar in a sequence of strata.
❖ A buried lava flow is older than the rocks above but younger than the rocks below (principle of superposition).
❖ On the other hand, the sill is younger than all the beds below it and younger than the bed immediately above it.
5. Principles of inclusions
❖ The principles of inclusions states that if one rock contained within another, then the rock containing the
inclusions is younger than the included one.
❖ Inclusions or fragments of one rock contained within a layer of another are older than the rock layer itself.
6. Principles of Fossil Succession
❖ The Principles of Fossil Succession states that fossils at the bottom of a sequence are older than those at the top of
the sequence.
❖ This principle is also known as the principle of faunal and floral succession.
Unconformities
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Unconformity is a surface of non-deposition or erosion that separates younger strata from older ones.
Unconformity represents a break in geologic record or time.
Any interval of geologic time that is not represented by strata is called “Hiatus”.
Types of Unconformities:
1) Para-conformity.
2) Dis-conformity.
3) Angular unconformity.
4) Non-conformity.
1. Para-conformity
❖ Para-conformity is a surface of erosion and non-deposition between younger and older beds that are parallel with
one another.
❖ Para-conformity is a type of unconformity where there is a break in sedimentation, but no apparent erosion or
deformation of the existing rock layers.
❖ The layers above and below the para-conformity appear parallel, suggesting a period of non-deposition or very
slow deposition.
❖ It can be challenging to identify para-conformities because there may not be obvious physical evidence of a gap in
the rock record.
2. Dis-Conformity
❖ Disconformity is a well well-defined erosional surface separates the older from the younger parallel beds.
❖ In a disconformity, the contact between the older and younger rock layers is typically marked by erosional
features, such as channels or surfaces of erosion.
❖ There may be evidence of weathering and erosion during the hiatus in sedimentation.
3. Angular unconformity
❖ Angular unconformity is an erosional surface on tilted or folded strata over which younger strata have been
deposited.
❖ There are some cases where both the older and the younger strata may dip, there unconformity can be defined if
angles are different (generally older strata dips more steeply).
4. Non-conformity
❖ Nonconformity is observed if the erosional surface cut into metamorphic or igneous rocks, is covered by
sedimentary rocks.
Correlation
❖ Correlation refers to the process of matching and establishing relationships between rock units or strata in
different locations based on their lithology, fossils, or other characteristics.
❖ The goal of correlation is to determine the equivalence of rocks in terms of age and deposition, helping geologists
create a consistent and accurate geological history for a region or even on a larger scale.
Fossils
❖ Fossils are the remains or traces of prehistoric life.
Types of fossils
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3.
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1) Petrified
2) Mold and Cast
3) Trace fossils
Petrified
Petrified refers to the process of turning organic material into stone through the replacement of the original
organic components with minerals.
The term is commonly associated with the petrification of wood or other plant materials, but it can also apply to
the preservation of animal remains.
In Petrified cavities and pores are filled with precipitated mineral matter.
Mold and Cast
Mold is created when a shell or other structure is buried in sediment and then dissolved by underground water.
The mold faithfully reflects only the shape and surface marking of the organism; it does not reveal any
information concerning its internal structure.
Casts are created if these hollow spaces are subsequently filled with mineral matter.
Trace fossils
Trace fossils are Examples of indirect evidence.
There are various types of trace fossils like:
1) Tracks
a) Tracks are animal footprints made in soft sediment that later turned into sedimentary rock.
2) Burrows
a) Burrows are tubes in sediment, wood, or rock made by an animal.
b) These holes may later become filled with mineral matter and preserved.
c) Some of the oldest-known fossils are believed to be worm burrows.
3) Coprolites
a) Coprolites are fossil dung and stomach contents.
4) Gastroliths
a) Gastroliths are highly polished stomach stones that were used in the grinding of food by some
extinct reptiles.
Fossils and correlation
❖ Index fossils are:
1) Widespread geographically.
2) Existed for a short range of geologic time.
Absolute Dating
Atomic structure reviewed.
❖ Mater is made of chemical elements.
❖ Each element is composed of nucleus (proton + neutron) and electron encircling the nucleus.
❖ The number of protons is the atomic number.
❖ The number of protons and neutrons is atomic mass numbers.
❖ An isotope is a mineral with the same atomic number but different atomic mass number.
❖ There are 92 naturally occurring isotopes on the earth.
❖ Most of the isotopes are stable.
❖ Some isotopes are radioactive and spontaneously decay to other more stable isotopes of elements.
❖ This process of creating stable isotopes releases energy.
❖ It is the decay rate of unstable isotopes which is used to determine the absolute age of rocks.
Absolute Dating Methods
❖ Absolute Dating can be done by various methods like:
1) Radioactivity and Radiometric Dating
2) Fission-track Dating
3) C14 Dating
4) Tree-ring Dating
5) Dating Sedimentary Strata Using Radiometric Dating
6) Magnetostratigraphy dating.
1. Radioactivity and Radiometric Dating
❖ Radioactivity is the Spontaneous breaking apart (decay) of atomic nuclei.
❖ Parts of the Radioactive decay are:
1) Parent: is an unstable isotope.
2) Daughter products: is an isotope formed from the decay of a parent.
❖ Half lifetime is the time it takes for one-half of the atoms of the original unstable parent element to decay to atoms
of new, more stable daughter element.
❖ Half lifetime is always constant and can be precisely measured in the laboratory.
❖ This process is a complex procedure, but it yields numerical dates.
❖ Most accurate radiometric ages are obtained from igneous rocks.
❖ Because certain elements are preferred by certain minerals and accepted into crystal structure, but most daughter
elements are not.
❖ After decay of those elements daughter products directly originated from the preferred elements and so they give
accurate ages.
❖ By measuring the parent-daughter element ratio and knowing the half-life of the parent element, the age of a
sample containing the radioactive element can be calculated.
❖ In sedimentary rocks, no dating can be done.
❖ The only mineral that can be measured in sedimentary rocks is “glauconite”.
❖ To use this method, we need a closed system.
❖ It is essential that neither parent nor daughter atoms have been added or removed from the system.
❖ Cross-checks are used for accuracy.
❖ If there is a leakage of daughter elements ages would be too young.
❖ If parent atoms are removed ages would be too old.
❖ Therefore, for accurate dating, samples must be fresh and un-weathered or subjected to high temperature or
intense pressure after crystallization.
2. Fission-track Dating
❖ The emission of atomic particles resulting from the spontaneous decay of Uranium within a mineral damage its
crystal structure.
❖ The damage appears as microscopic “linear tracks” that are visible only after the mineral is etched with
hydrofluoric acid.
❖ The age of sample is determined by the number of fissions tracks present and the amount of U the sample
contains.
❖ The older the sample, the greater the number of tracks.
❖ This method is useful to samples with ages between 40 Ma to 1.5 Ma years.
❖ The samples must not to be metamorphose, because during metamorphism the damaged crystal structures can be
repaired by annealing and consequently tracks disappear.
3.
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C14 Dating
To date relatively recent events, carbon-14 is used.
Carbon-14 is a radioactive isotope of carbon.
Because the half-life of carbon-14 is only 5730 years, radiocarbon dating can be used to date events from the
historic past as well as those from very recent geologic history.
4. Tree-ring Dating
❖ Tree-ring Dating is a method of dating by analyzing the growth rings in the cross-section of a tree trunk.
❖ This method is particularly useful for dating wooden artifacts, structures, and environmental changes.
5. Dating Sedimentary Strata Using Radiometric Dating
❖ Radiometric dating is a method used to determine the age of rocks and minerals by measuring the abundance of
certain radioactive isotopes and their decay products.
❖ While radiometric dating is commonly associated with igneous rocks, it can also be used for dating certain types
of sedimentary strata indirectly.
6. Magnetostratigraphiy
❖ Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences.
❖ The method works by:
1) collecting oriented samples at measured intervals throughout the section.
2) The samples are analyzed to determine their characteristic remanent magnetization (ChRM), that is, the
polarity of Earth's magnetic field at the time a stratum was deposited.
❖ This is possible because volcanic flows acquire a thermoremanent magnetization and sediments acquire a
depositional remanent magnetization, both of which reflect the direction of the Earth's field at the time of
formation.
❖ When measurable magnetic properties of rocks vary stratigraphically, they may be the basis for related but
different kinds of stratigraphic units known collectively as magnetostratigraphic units (magnetozones).
❖ The magnetic property most useful in stratigraphic work is the change in the direction of the remanent
magnetization of the rocks, caused by reversals in the polarity of the Earth's magnetic field.
❖ The direction of the remnant magnetic polarity recorded in the stratigraphic sequence can be used as the basis for
the subdivision of the sequence into units characterized by their magnetic polarity.
❖ Such units are called "magnetostratigraphic polarity units" or chrons.
❖ If the ancient magnetic field was oriented similar to today's field (North Magnetic Pole near the Geographic North
Pole) the strata retain a normal polarity.
❖ If the data indicates that the North Magnetic Pole was near the Geographic South Pole, the strata exhibit reversed
polarity.
Establishment of Geologic Time Scale
❖ Look at the next figure:
❖ Geologic time scale divides geologic history into units.
❖ The geologic time scale was originally created using relative dates.
❖ Subdivisions of the geologic time scale:
1) Eon (largest time span)
2) Era
3) Periods
4) Epochs (smallest time span)
❖ Difficulties in dating the time scale:
1) Not all rocks are datable.
2) Materials are often used to bracket events and arrive at ages.
Formalization of Anthropocene Epoch in Quaternary Period
❖ The Anthropocene Working Group recommended that the year 1950 serve as the starting point of the interval.
❖ This recommendation was based upon the idea that by this point in Earth’s history, plutonium isotopes caused by
nuclear weapons testing fallout would be concentrated enough to serve as an observable signal in rock strata.
❖ The world’s human population from about 1.6 billion–1.7 billion in 1900 to 7.8 billion by 2020.
❖ Because of this rapid increase:
1) Energy demand increased Which led to:
a) Energy derivation from wood and easily obtained fossil fuels (i.e., petroleum, natural gas, and
coal) expanded.
b) More Carbon dioxide (CO2) released.
2) Concrete production increased.
3) CO2 concentration in the atmosphere increased.
4) The problem of Global Warming and Climate Change increased.
a) Loss of ice in Antarctic Peninsula increased.
b) reduction in the size of mountain glaciers
c) More-frequent occurrence of extreme weather events in different parts of the world
d) Oceans absorb CO2 process of ocean acidification which affected the marine food chains.
5) changes to the hydrosphere include:
a) Increasing damming and diversion of rivers and streams.
b) The rapid extraction of groundwater from freshwater aquifers.
c) The creation of large oxygen-depleted areas near the mouths of rivers.
❖ The effects of some of the changes mentioned above will create unique signatures in layers of rock.
❖ The increased rate of soil erosion from intensive agriculture and land-use conversion.
❖ Rising air temperatures at the surface by the global warming.
❖ Glaciers and polar ice melting into seawater will expand a measurable rise in global sea level.
❖ Rising waters change the stratigraphy in some places by submerging low-lying areas and allowing the ocean to
deliver sediments farther inland than they do at present.
❖ Seawater pH declines, the depth at which carbonate minerals (e.g., limestone and chalk) form in the ocean will be
shallower than it was during preindustrial times.
❖ Many pre-existing carbonate formations will dissolve in response to increases in ocean acidity, leaving a signature
of striking dark layers of carbonate depleted rock.
❖ By far the most significant evidence of the Anthropocene in rock strata will be caused by a dramatic increase in
extinctions occurring during this period.
❖ Several ecologists have noted that the rate of species extinction occurring since the middle of the 20th century has
been more than 1,000 times that of the preindustrial period, comparable to the pace of other mass extinctions
occurring over the course of Earth’s history.
❖ The rapid extinction rate stems from the ongoing conversion of forests and other natural areas to agriculture and
urban land and accelerated climate change resulting from alterations to the carbon cycle.
❖ As a result, it is expected that there will be stark differences in the fossils found in layers of rock deposited
worldwide during preindustrial times and those that follow.
Lecture 11 “MASS WASTING”
What’s Mass Wasting
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Mass Wasting (Mass Movement): Downslope movement of material under the direct influence of gravity.
Most types of mass waste are aided by weathering and usually involve surficial material.
Movement occurs from imperceptible (extremely slow) to extremely high fast speeds as in the case of rock fall.
Landslide: All kinds of mass movements that cause loss of life, property damage, or a general disruption of human
activities.
In all processes the pull of gravity is the main force behind the mass wasting.
In mass wasting sediment is ultimately transported to the sea.
The combined effects of mass wasting and running water produce stream valleys.
Mass movements are important natural geomorphic agents that shape mountain landforms and redistribute sediment
and debris to gentler terrain and water bodies.
The earth mass may move in several ways:
1) Falling
2) Toppling
3) Sliding
4) Spreading
5) Flowing
6) By their combinations.
Effect of gravity/Shear Strength
❖ When the gravitational force exceeds the resistance force of the subject, slope failure (mass wasting) occurs.
❖ The resisting forces helping to maintain slope stability include the slope materials strength and cohesion, the
magnitude of internal friction between the grains, and external support of the slope.
❖ These factors collectively define a slope’s shear strength:
1) Materials strength
2) Cohesion
3) The magnitude of internal friction between the grains
4) External support of the slope
Shear Strength
❖ The shear strength of a material is its ability to resist forces that cause the material's internal structure to slide against
itself.
❖ The critical angle of repose of a granular material is the steepest angle of descent or dip relative to the horizontal
plane to which a material can be piled without slumping.
Factors of mass movements
❖ There are various factors affecting mass wasting:
1) Topography
2) Climate and Weathering of materials
3) Water content
4) Vegetation
5) Overloading (Overburden thickness),
6) Geology and slope instability
7) Triggering mechanisms
8) Undercutting
9) Duration (time)
1. Topography and Slope
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The topography effect is shown as the slope angle of the area.
Slope angles are a key parameter in estimating susceptibility to developing earth flows.
Slope angle is probably the major cause of mass wasting.
The Steeper the slope, the less stable it is.
Steeper slopes are more likely to experience mass wasting than gentler ones.
Loose, granular particles assume a stable slope called the angle of repose (repose = to be at rest).
Angle of repose is the steepest angle at which material remains in place.
There are several processes which steepen a slope like Undercutting of a stream or wave action: This removes the
base of the slope, increasing the slope angle and so increasing the gravitational force acting parallel to the slope.
2. Climate and Weathering of materials (Undercutting by a river)
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Abrasion and hydraulic action erode to create a plunge pool below the waterfall.
Over time this gets bigger, the size of the overhang increases until the hard rock is no longer supported.
An unsupported overhanging rock collapses and falls into the plunge pool.
This process continues and the waterfall retreats upstream.
A steep-sided valley is left where the waterfall once was.
This is called a gorge: a steep-sided valley left behind a retreating waterfall.
It forms when there are horizontal bands of hard rock positioned over exposed, less resistant (soft) rock.
The river flows over bands of softer and harder rocks.
Softer rock is eroded more quickly than the hard rock and this creates a step.
As erosion continues, the river undercuts the harder rock leaving an overhang.
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Undercuts (rocks and banks) usually are well-known hazards on a river and often are the site of fatalities.
Riverbanks, especially outside bends, are constantly eroded by moving water.
The bank becomes undercut, creating an entrapment.
Trees also can topple into the water from the undermining and create strainers.
❖ Wave action, especially during storms, often results in mass movements along the shores of oceans or lakes.
3. The Role of Water
❖ Although water is not always directly involved as a transporting medium, it plays an important role in mass
wasting.
❖ The addition of water from rainfall or snowfall or the melting of snow makes the material on the slope heavier.
❖ Water can reduce friction along a sliding surface.
❖ When sediment pores fill with water, cohesion among particles is destroyed.
❖ Water can lubricate materials.
❖ Water adds weight to a mass of material.
❖ Ϭe = Ϭn - Ϭw (Ϭe: Effective stress (grain to grain), Ϭn Normal stress, Ϭw Stress carried by pore water pressure).
❖ As the water increases, effective stress decreases and failure is most likely to occur.
4. Human effect (anthropogenic)
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Anthropogenic means a “Man-Made Disaster”.
Undercutting by man can be a reason for mass wasting.
Excavations for roads and hillside buildings or for engineering structures are other major causes of slope failure.
Grading the slope too steeply, or cutting it into its side, increasing the slope angle results in a failure.
5. Overloading
❖ Overloading is almost always the result of human activity.
❖ It results from dumping, filling, or piling up of material.
❖ Under natural conditions the slope material is carried by grain-to-grain friction along the contacts of the slope
material.
Triggering Mechanisms of Mass Wasting
❖ There are triggering actions for mass wasting:
1) Vibrations from earthquakes
2) Explosions
3) Excessive snow melt
4) Rain fall
5) Undermining
6) Loading
7) Laud of thunderstorm (e.g. Avalanches)
Classification of mass movements
❖ Characteristics of mass movements are:
1) Type of material involved (rock, regolith, snow)
2) Velocity of movement (fast, slow)
3) Character of moving material (chaotic cloud, slurry, coherent body)
4) Environment in which the movement takes place (subaerial, submarine).
Classification depending on the type of movement.
1. General types of movement
❖ Mass wasting can be divided into 4 types:
1) Falls
2) Slides
3) Flows
4) Complex Movements
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Falls
Rockfalls are a common type of extremely rapid mass movement.
In rockfalls, rocks of any size fall through the air as a free fall.
They occur in steep canyons, cliffs, and road cuts and build up accumulations of loose rocks and rock fragments,
called talus, at their base.
❖ Talus: An accumulation of broken rock at the base of a cliff.
❖ Rockfalls result from failure along the joint planes or bedding planes in the bedrock and are triggered by natural
or human undercutting of slopes, or by earthquakes.
❖ In cold climates many rockfall occur due to frost wedging.
❖ In other climates, water percolating through fractures results in chemical weathering (e.g. Limestone) and fall out
of large blocks.
❖ Rockfalls range in size from small rocks to massive falls of millions of cubic meters that block roads, bury towns,
and destroy buildings.
❖ They are very common in mountainous areas where roads are constructed by blasting and grading through steep
slopes.
2.
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Slides
Slides: downslope movement of material along one or more surfaces of failure.
The type of material may be rock or soil or a combination of both.
The rate of movement may be extremely slow to very rapid.
Most of the slides occur because the bedding and/or joint planes are parallel to the slope.
There are two types of slides:
a) Slump/rotational slide
b) Rock or block slide
a. Slumps
❖ In the Slump or rotational slide, movement is along a curved surface. Therefore, the material rotates backwards as
they move downslope.
❖ Slumps occur, in general, unconsolidated, or weakly consolidated material.
b. Rockslides
❖ In the rock or block slide, the rock moves along a planar surface as no rotation involved.
3.
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Flows
Flows are mass movements in which material flows as viscous fluid or displays plastic movement.
Flows rate ranges from extremely slow to extremely rapid.
In many cases movement begins as falls, slumps, or slides and changes into flows.
There are 5 subdivides of flows:
a) Mud Flows
b) Debris flows
c) Earth Flows
d) Quick clays
e) Solifluction
f) Creep
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Mud Flows
Mudflows are the most major mass movements.
They move very rapidly (~80km/h).
Mud flows consist of 50% silt and clay sized material combined with water <30%.
b. Debris flows
❖ Debris flows are composed of larger particles than mud flows and do not contain as much water.
❖ Debris are more viscous, slower yet as dangerous as mudflows because they can carry larger objects.
c. Earth Flows
❖ They move slower than either mudflows or debris flows.
❖ An earthflow develops as a slump at the upslope leaving a scarp, and flows slowly down slope as a thick, viscous
tongue shaped mass of wet regolith.
❖ Avalanche: is snow flow.
d. Quick clays
❖ Quick clay refers to a specific type of clayey material that experiences a significant loss of strength when it is
disturbed.
❖ Some clays spontaneously liquify and flow like water when they are disturbed and cause serious damage.
❖ They are composed of silt and clay particles made by grinding action of glaciers.
❖ Quick clays are glaciomarine formations that
❖ Quick clays can be found mostly in the Northern Hemisphere in several regions, such as parts of Norway, Canada,
Russia and the United States.
❖ They also occur during an earthquake (liquefaction).
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Solifluction
Solifluction is a flow of water-saturated soil over impermeable material.
Solifluction Indicates a non-frozen ground is present in the moving layer.
Occur in any climate when ground becomes water saturated but common in areas of permafrost.
Permafrost: In cold areas ground is frozen, during warmer periods upper part of the ground thaws, water and
sediment moves downwards.
❖ Solifluction reaches its maximum potential in the late spring and summer months when thaw saturates soil.
f. Creep
❖ Creep: Slowest type of movement and very widespread and significant mass wasting process in terms of total
amount of material moves down slope.
❖ Creep is extremely slow and occurs in all climates.
❖ Slow downslope movement of particles that occurs on every slope covered with loose, weathered material.
❖ One factor that contributes to creep is the alternating expansion and contraction of surface material caused by
freezing and thawing or wetting and drying.
❖ Each cycle therefore moves the material a tiny distance downslope.
4. Complex movements
❖ In general, one or more types of mass wasting processes occur together, the classification is named according to
dominant process.
❖ In cases when there is no dominant process (slump, slide, or flow) the process is a complex one.
Geology and Slope Stability
❖ For beds dipping parallel to the slope:
1) The water percolating within the material will decrease the cohesion and the friction between the grains.
2) This enhanced if the beds are clay bearing.
❖ Joints dipping parallel to the slope:
1) Like in bedding water percolating between joints will weather the rock and expand their opening until
load of the overlying material causes failure.
Safety Measures
❖ To Recognize and minimizing the effect of mass wasting we need to:
1) Study the slope
2) Identification of risky regions (landslide potential map),
3) Preventing undercutting,
4) Reduce the slope (cut-n-fill, benching)
5) Reducing subsurface water, apply drainpipes.
6) Constructing safety structures (retaining walls, rock bolts, iron bolts etc),
7) Re-vegetation: Planting vegetation
8) Controlled blasting of unstable slopes.
Drainpipes
Cut and Fill
Benching
Reviewing Shapes
Lecture 12 “Runing Water”
The Hydrologic Cycle
❖ Earth is unique in the solar system because:
1) It has the right size and distance from the Sun to have liquid water.
2) The Mantle convection brings water to Earth’s surface.
❖ The hydrologic cycle describes the movement of water through Earth’s four spheres.
❖ Earth’s four spheres are the (Geosphere, Hydrosphere, Atmosphere, Biosphere)
❖ The Hydrologic Cycle is consisting of five operations:
1) Precipitation
2) Evaporation
3) Infiltration
4) Runoff
5) Transpiration
❖ Distribution of Earth’s Water:
❖ Movement Through the Hydrologic Cycle:
1) Water evaporates from the oceans, plants, and soil and moves through the atmosphere.
2) Water leaves the atmosphere via precipitation.
3) Precipitation either soaks into the ground (infiltration), runs over the surface (runoff), or evaporates.
4) Transpiration involves water absorbed by plants and later transferred to the atmosphere.
5) As evaporation and transpiration both move water from the surface to the atmosphere, they are often
considered a combined process called evapotranspiration.
Runing Water
❖ The difference between runoff and infiltration depends on
1) Intensity and duration of rainfall
2) The amount of water already in the soil
3) The type of soil
4) Slope of the land
5) Nature of the vegetative cover
❖ Runoff Will Start as Sheet Flow
❖ Sheet flow develops into tiny channels called rills.
❖ Rills meet to form gullies.
❖ Gullies join to form brooks, creeks, or streams.
Brooks
Sheet Flow
Develops into
Rills
Meets to form
Gullies
Joins to form
Creeks
Streams
❖ Stream: a body of running water, confined to a channel, that runs downhill under the influence of gravity.
❖ A stream is any water the flows in a channel, regardless of size.
❖ A river carries a substantial amount of water and has many tributaries.
River Systems
❖ Except for extremely arid or polar regions, rivers drain much of the land area.
❖ Climate differences and human intervention influence the character of a river.
❖ River systems can be divided into three zones:
1) Sediment production
2) Sediment transportation
3) Sediment deposition
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Headwaters: upper part of stream near its source in the mountains.
Mouth: place where a stream enters sea, lake, or larger stream
Channel: a long, narrow depression eroded by a stream into rock or sediment.
Stream banks: sides of channel.
Streambed: bottom of the channel.
Floodplain: flat valley floor composed of sediment deposited by the stream.
Base level: Lowest point that a stream can erode to.
Discharge: volume of water flowing in the stream (the water passing through a point in seconds, expresses as
cubic meter per second)
❖ Capacity of a river: total amount of sediment load (other than dissolved load) it can carry.
❖ Competence of river: the largest particle size it can carry.
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Sediment is transported in trunk streams.
In balance, the amount of sediment being eroded equals the amount of sediment being deposited.
When a river reaches a large body of water, the energy decreases, and the river deposits sediments.
Typically, only fine sediments are deposited in oceans.
Discharge, Competence, and capacity are controlled by the stream velocity.
Longitudinal profile of a stream
❖ Longitudinal profiles are essentially irregular but have a general tendency towards the idealized form.
❖ Factors are changing with varying speeds, so adjustment of profiles to the controls is never complete and an
equilibrium between channel processes and channel slopes is never fully established!
❖ Only dynamic equilibrium is reached (partial adjustment).
❖ The Adjustment of base level to changing conditions is having two general types:
1) Ultimate change: if the sea level changed around the globe.
2) Temporary change: if the change is local, like a change in the level of the lake in which the river ends at.
❖ Changing causes readjustment of the stream deposition or erosion.
Streamflow
❖ Laminar flow is when water slowly flowing in a straight path.
❖ Turbulent flow is when water moving quickly in an erratic fashion (both horizontal and vertical movement).
❖ Factors Affecting Flow Velocity:
1) channel slope, or gradient
2) channel cross-sectional shape
3) channel size and roughness
4) discharge (the amount of water flowing in the channel).
❖ An increase in channel size will increase the cross-sectional area to wetted perimeter ratio, thus increasing
channel efficiency.
❖ Rough channels with boulder. etc., create turbulence and decreased velocity.
The Work of Running Water
❖ The Work of Running Water is represented in three operations:
1) Erosion
2) Transportation
3) Deposition
1. Erosion
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Erosion is related to slope, discharge, and bed and bank sediments.
Sand-sized particles are easily eroded.
Silt and clay-sized particles and gravels are harder to erode.
Channels with cohesive silty bottoms are typically narrower than sandy channels.
Streams cut channels into bedrock through three main processes:
1) quarrying
2) abrasion
3) corrosion
Quarrying: the removing of large blocks from the channel bed.
Abrasion: the process by which the bed and banks of a bedrock channel are ceaselessly bombarded by particles
carried into the flow.
Corrosion (rocks gradually dissolving in flowing water) can occur in limestone bedrock channels.
By scraping, bumping, and rubbing, abrasion both erodes sediments and polishes them.
❖ Potholes form when fast moving, swirling sediment in eddies abrades a hole.
2. Transportation
❖ Transported material is called the stream's load.
❖ There are three types of stream’s load:
1) Dissolved load (as solution in water)
2) Suspended load (as suspended material)
3) Bed load (saltation and rolling)
❖ Load is related to a stream's:
1) Competence: maximum particle sizes the stream can carry.
2) Capacity: maximum load amount the stream can move.
3. Deposition
❖ Stream sediments are known as alluvium.
❖ The sediments are moderately sorted deposits with Sub-rounded to well-rounded pebbles.
Drainage Basin and Drainage Divide
❖ A drainage basin or catchment basin is an extent or an area of land where all surface water from rain, melting
snow, or ice converges to a single point at a lower elevation, usually the exit of the basin, where the waters join
another body of water, such as a river, lake, reservoir, estuary, wetland, sea, or ocean.
❖ A drainage divide is an elevated boundary that separates neighboring drainage basins.
❖ In hilly areas, the drainage divide lies along peaks and ridges, while in flat lands the divide may be invisible.
❖ A topographic divide separates drainage basins.
❖ Drainage Basin or Catchment is the total area where a trunk river collects its water.
Drainage Patterns
❖ Drainage systems are patterns of the interconnected network of streams, rivers, and lakes in a particular area.
❖ Common drainage patterns are:
1) Dendritic
2) Radial
3) Rectangular
4) Trellis
Formation of a Water Gap
❖ A water gap is a notch where a river cuts through a ridge that lies in its path.
❖ Such gaps that no longer carry water currents are called wind gaps.
❖ There are two methods of formation of a Water Gap:
1) Antecedent Stream
2) Superposed Stream
1. Antecedent Stream
❖ In Antecedent Stream, the stream existed before the ridge was formed or mountain was uplifted.
❖ The stream maintains its original course and pattern despite the changes in underlying rock topography.
2.
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Superposed Stream
In Superposed Stream, the stream was eroded into a preexisting structure.
A stream that forms over horizontal beds that overlie folded and faulted rock with varying resistance.
Having cut down through the horizontal beds, the stream retains its course and pattern as it proceeds to erode the
underlying rocks despite their distinctive character.
Stream Channels
❖ We can divide stream channels into two basic types:
1) Bedrock Channels
2) Alluvial Channels
❖ Bedrock channels are channels in which the streams are actively cutting into solid rock.
❖ Alluvial channel is when the bed and banks are composed of unconsolidated sediment or alluvium, the channel.
Alluvial channel
❖ Two common types of alluvial channels are:
1) Meandering channels
2) Braided channels
1. Meandering Channels
❖ Streams transport suspended sediment in broad, sweeping bends called meanders.
❖ Meandering channels evolve over time:
1) The outside of a meander (cutbank) is a zone of active erosion.
2) The inside of a meander (point bar) is a zone of deposition.
3) Through time, the bends in a channel can also migrate and eventually join.
❖ A meander that has been cut off from joined bends is called a cutoff oxbow lake.
Formation of Cut Banks and Point Bars
❖ A point bar is a depositional feature made of alluvium that accumulates on the inside bend of streams and rivers
below the slip-off slope.
❖ Point bars are composed of sediment that is well sorted and typically reflects the overall capacity of the stream.
❖ Point bars are found in abundance in mature or meandering streams.
❖ They are crescent-shaped and located on the inside of a stream bend, being similar to but smaller than towheads,
or river islands.
Formation of an Oxbow Lake
❖ An oxbow lake is a U-shaped Lake that forms when a wide meander of a river is cut off, creating a free-standing
body of water.
❖ forms when a meandering river erodes through the neck of one of its meanders.
1) meanders tend to grow and become more curved over time.
2) The river then follows a shorter course that bypasses the meander.
3) The entrances to the abandoned meander eventually silt up, forming an oxbow lake.
❖ Because oxbow lakes are Stillwater lakes, with no current flowing through them, the entire lake gradually silts up,
becoming a bog or swamp and then evaporating completely.
2. Braided Channels
❖ A braided channel is a network of converging and diverging channels that thread among numerous islands or
gravel bars.
❖ A generous portion of the load is coarse material.
❖ Bank material is easily eroded and reworked.
❖ A braided stream has eyots (Islands) of deposited material within the channel.
Stream Valley Development
❖ Valley sides are shaped by:
1) Weathering
2) Overland flow
3) Mass Wasting
Valley Deepening
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Downcutting: the process of deepening a valley by erosion of the streambed.
V-shaped valleys typically form from downcutting combined with mass wasting and sheet erosion.
Streams cannot erode below their base level.
Basel level can be sea level, a lake, or the bottom of a closed basin.
The downcutting rate can be rapid if a stream is well above base level.
Valley Widening
❖ Lateral erosion widens stream valleys by undercutting stream banks and valley walls as stream swings from side
to side across the valley floor.
❖ Headward erosion is the slow uphill growth of a valley above its original source by gullying, mass wasting, and
sheet erosion.
Graded streams
❖ A graded stream has the necessary slope and other channel characteristics to maintain the minimum velocity
required to transport the material supplied to it.
❖ A graded system is neither eroding nor depositing material but simply transporting it.
❖ There is a delicate balance between available sediment load and transport capacity.
❖ Graded streams have characteristic concave-up longitudinal profile.
❖ Rapids and waterfalls have been smoothed out by extensive erosion over an extended period.
Narrow VS wide Valleys
❖ Characteristics of narrow valleys :
1) V-shaped
2) Rapids
3) Waterfalls
❖ Characteristics of wide valleys:
1) Pan/U-shaped
2) The stream is near base level.
3) Downward erosion is less dominant.
4) Stream Energy is directed from side to side.
The formation of waterfalls
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Waterfall: area where flowing river water drops abruptly and vertically.
Waterfalls represent major interruptions in river flow.
Waterfalls like rapids form in the upper course because of differentiated erosion.
If the river channel flows across different bands of geology with varying resistance, then the softer less resistant
rock will be eroded faster creating a step in the river.
❖ The hydraulic action of the water enlarges this step over time creating the waterfall.
❖ Due to the force of the water a deep plunge pool forms at the base of the waterfall.
❖ Faults may bring hard and soft rocks together and encourage the establishment of a waterfall.
Floodplain
❖ Development of floodplain:
❖ Floodplain features:
1) Naturel levees
2) Meanders
3) Cutoffs
4) Oxbow lakes
Stream terraces
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Stream terraces: Step-like landforms found above a stream and its floodplain.
Occurs when river rapidly cuts downward into its own floodplain.
Represents sudden change in rate of erosion.
Can be caused by rapid uplift, drops in base level, changes in underlying lithology or climate changes.
Incised meanders
❖ Incised meanders form as river meanders are cut vertically downward following uplift or lateral erosion and
downcutting proceed simultaneously.
❖ May be produced by profound base level changes, as when rapid tectonic uplift occurs.
Stream Valleys on Mars
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Stream Valleys on Mars are evidence of different climate in past.
Liquid water is not stable on surface of Mars with mars being too cold and the atmospheric pressure too low.
Stream channels and terraces suggest long-term erosion by flowing water.
Lack of smaller tributaries is puzzling, but these do exist for channels networks in more ancient terrains on Mars.
Depositional Landforms
❖ The depositional landforms formed by streams are:
1) Deltas
2) Natural levees
3) Alluvial fans
1. Deltas
❖ Deltas form where sediment-charged streams reach a temporary or ultimate base level and enter the still waters of
a lake, an inland sea, or the ocean.
❖ Delta can be also described as a fan shape deposition at the mouth of a stream (Into water).
2. Natural levees
❖ Levee formation:
3. Alluvial fans
❖ Alluvial fans are fan-shaped deposits that accumulate along steep mountain fronts.
Floods and flood control
❖ Floods are the most common geologic hazard.
❖ Causes of floods:
1) Weather
2) Human interference with the stream system
❖ Engineering efforts
1) Artificial levees
2) Flood-control dams
3) Channelization
4) Nonstructural approach through sound floodplain management
Lecture 13 “Groundwater”
❖ Groundwater is the water present beneath Earth's surface in narrow fractures in the bedrock and in open spaces
(pores) of soil, sand, sediment, and rock.
❖ Groundwater is stored in and moves slowly through geologic formations of soil, sand and rocks called aquifers.
❖ Aquifers is a layer of porous substrate that contains and transmits groundwater.
Importance of Groundwater
Groundwater and the Hydrosphere
❖ 6/10 of 1 percent of the hydrosphere is groundwater.
❖ Groundwater is the largest reservoir of freshwater that is readily available to humans.
❖ Groundwater is used for drinking water by more than 50% of global population and around 99% (almost
everyone) of the rural population in the world.
❖ The largest use for groundwater (about 65%) is to irrigate crops.
❖ Groundwater is a vital component in many industrial processes.
❖ Groundwater also works as an erosional agent dissolving rocks produces Sinkholes and Caverns.
Distribution and movement of groundwater
What’s groundwater
❖ Rain falling steadily and gently on gradual slopes composed of materials that are easily penetrated by the water
means that a percentage of water soaks into the ground.
❖ Some of the water that soaks in does not travel far because it is held by molecular attraction as a surface film on
soil particles.
❖ This near-surface zone is called the zone of soil moisture.
❖ Water that is not held as soil moisture percolates downward until it reaches a zone where all the open spaces in
sediment and rock are completely filled with water which is the zone of saturation.
❖ Water in the zone of saturation is called groundwater.
❖ The area between the zone of soil moisture and the zone of saturation is called capillary fringe.
❖ Zone of aeration (Unsaturated zone): zone of soil moisture in addition to capillary fringe area.
❖ Unsaturated zone spaces are filled with air.
❖ In the zone of saturation all pore spaces in the material are filled with water.
Water table
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Water table: the upper limit of the zone of saturation.
The groundwater found below the water table comes from precipitation that has seeped through surface soil.
The water table level can vary in different areas and even within the same area.
The shape and height of the water table is influenced by the land surface that lies above it; it curves up under hills
and drops under valleys.
❖ Springs are formed where the water table naturally meets the land surface, causing groundwater to flow from the
surface and eventually into a stream, river, or lake.
Variation in the water level
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The depth of water table is highly variable, it varies seasonally and from year to year.
Changes in precipitation between seasons and years are affecting the depth of the water table.
During late winter and spring, when snow melts and precipitation is high, the water table rises.
During the summer months, the water table tends to fall, due in part to plants taking up water from the soil surface
before it can reach the water table.
There is a lag (Time Gap) between when precipitation infiltrates the saturated zone and when the water table rises.
This lag is because it takes time for water to trickle through spaces between sediments to reach the saturated zone,
although the process is helped by gravity.
The water table level is also influenced by human extraction of groundwater using wells.
Irrigation of crops can also cause the water table to rise as excess water seeps into the ground.
Groundwater Flow Pattern
❖ There is an interaction between groundwater and streams in three ways:
1) Gaining streams
2) Losing streams
3) Combination of gaining and losing streams
1. Gaining streams
❖ Gaining streams gain water from the inflow of groundwater through the streambed.
❖ The water table is higher than the stream surface.
2. Losing streams
❖ Losing streams lose water to the groundwater system by outflowing through the streambed.
❖ The water table is lower than the stream surface.
3. Combination of gaining and losing streams
❖ A stream can gain in some sections and lose in others.
How Groundwater Moves
❖ Groundwater moves very slowly.
❖ The average rate of movement for groundwater is 4 centimeters per day.
❖ A Simple Groundwater Flow System:
1) The force of gravity and pressure differences move groundwater.
2) Groundwater is replenished in areas of recharge.
3) Groundwater flows back to the surface in a discharge area.
Different Scales of Movement
❖ The area of groundwater flow systems varies from a few square kilometers to tens of thousands of square
kilometers.
❖ Regional groundwater systems interact with deeper, larger groundwater systems.
Factors Influencing the Storage and Movement of Groundwater
❖ The nature of subsurface materials strongly influences the rate of groundwater movement and the amount of
groundwater that can be stored.
❖ Two factors are especially important:
1) porosity
2) permeability.
1. Porosity
❖ Porosity: Percentage of pore spaces.
❖ Porosity determines how much groundwater can be stored.
2. Permeability
❖ Permeability is the ability to transmit water through connected pore spaces.
❖ Aquifer: a permeable and porous layer of material that allows water to move through.
❖ Aquitard: an impermeable layer of material that doesn’t allow water to move through.
Wells and artesian systems
❖ Wells are built for the pumping of water or oil.
❖ Pumping can cause a drawdown (lowering) of the water table.
❖ Pumping can form a cone of depression in the water table.
Artesian wells
❖ An Artesian system is a system in which water in the well naturally rises higher than the initial groundwater level.
❖ An artesian well resulting from an inclined aquifer that’s trapped in between two Aquitard layers.
Springs, Hot Springs, and Geysers
Springs
❖ A spring is a natural outlet from which groundwater flows up onto the ground surface.
❖ Springs can form under a four of conditions:
1) Where ground surface intersects water table
2) Where a perched water table intersects the surface
3) Where infiltrating water flows parallel to an impermeable layer
4) Along fractures and fault planes
Hot Springs
❖ Water in a hot spring is 6⁰C to 9⁰ C warmer than the mean annual air temperature of the locality.
❖ The water for most hot springs is heated by the cooling of igneous rock.
❖ Some hot spring water is warmed by the geothermal gradient.
Geysers
❖ Geysers are intermittent hot springs in which columns of water erupt with force.
❖ Occur where extensive underground chambers exist within hot igneous rock.
❖ How Geysers Work:
1) Groundwater heats
2) Because of the heat the water expands
3) The phase of water changes to steam
4) Because of the high pressure it erupts
Groundwater and Environmental Problems
❖ Environmental problems associated with groundwater:
1) Mining Groundwater
2) Land subsidence
3) Saltwater Intrusion
4) Contamination
1. Mining Groundwater
❖ In some regions groundwater is not a nonrenewable resource.
❖ In this case the water available to recharge the aquifer falls significantly short of the amount being withdrawn.
2. Land subsidence
❖ Subsidence: The ground sinks when water is pumped faster than natural recharging processes can replace it.
❖ Groundwater pumping is lowering of the groundwater table and compaction of the compressible aquifer resulting
in land subsidence.
3. Saltwater Intrusion
❖ Saltwater Intrusion: Along coastal areas, the main pollution may come from saltwater intrusion due to excessive
pumping of ground water.
4. Groundwater Contamination
❖ One common source for Groundwater Contamination is sewage and wastewater.
❖ Extremely permeable aquifers (coarse gravel) have such large openings that groundwater may travel long
distances without being cleaned.
❖ Sewage often becomes purified as it passes through a few dozen meters of an aquifer composed of sand or
permeable sandstone.
❖ Sinking a well can lead to groundwater pollution problems.
❖ Cone of depression will locally increase or reverse the slope of the water table.
❖ Groundwater contamination occurs when man made products goes into the underground water system.
❖ Products causing contamination such as:
1) gasoline
2) oil
3) road salts and
4) chemicals
❖ Groundwater contamination gets into the groundwater and cause it to become unsafe and unfit for human use.
The Geologic Work of Groundwater
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The Geologic Work of Groundwater is that basically groundwater dissolves rock.
Groundwater is a strong erosional force, as it works to dissolve away solid rock.
Most groundwater is often mildly acidic because it contains weak carbonic acid.
This situation forms when rainwater dissolves carbon dioxide from the air and from decaying plants.
Carbonic acid reacts with calcite in limestone to form calcium bicarbonate, a soluble material.
Groundwater is working slowly over many years and travels along small cracks.
Caverns
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The most spectacular results of groundwater’s erosional handiwork are limestone caverns.
Most caverns are created by acidic groundwater dissolving soluble rock.
About 30,000 – 35,000 caves have been discovered in Turkey.
Cavern development:
1) Acidic groundwater dissolves rock.
• The groundwater follows lines of weakness in the rock, such as joints and bedding
planes, and creates cavities over time.
2) Cavities enlarge into caverns.
• The dissolved material is carried away by the groundwater to streams and the ocean.
3) Cavern development occurs at different levels.
• The current cavern-forming activity occurs at the lowest elevation, reflecting the
relationship with the river valleys.
4) Cave passages are affected by surface streams.
• When surface streams cut their valleys deeper, the water table drops, and cave passages
are abandoned. When surface streams are stable, large cave passages can form.
Dripstone
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Calcium carbonate dissolved in the caves later deposited as dripping water evaporates.
This kind of rock is called Travertine.
Speleothem is the general name for all dripstone features or caves.
There are two types of Speleothems which are:
1) Stalactites: hanging from the ceiling
2) Stalagmites: growing form on the floor of a cavern
Karst Topography
❖ Karst topography is a landscape that has been shaped mainly by the dissolving power of groundwater.
❖ Some common features of Karst topography include:
1) Irregular terrain
2) Sinkholes or sinks
3) Striking lack of surface drainage
Development of a Karst Landscape
❖ During early stages, groundwater percolates through limestone along joints and bedding planes.
❖ Solution activity creates and enlarges caverns at and below the water table.
❖ With time, caverns grow larger, and the number and size of sinkholes increase.
❖ Surface drainage is frequently funneled below ground.
❖ Collapse of caverns and coalescence of sinkholes form larger, flat-floored depressions.
❖ Eventually solution activity may remove most of the limestone from the area, leaving isolated remnants.
Lecture 14 “Glaciers”
Glaciers: a part of two basic cycles in the Earth system
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Glacier: a thick mass of ice that forms over land from the compaction and recrystallization of snow.
Glaciers are also a flowing stream of ice.
Glaciers are a part of both the hydrologic cycle and rock cycle.
Types of glaciers
1) Valley (alpine) glaciers
2) Ice sheets (continental) glaciers
3) Other types (Ice caps and piedmont glaciers)
Glaciers are governed by a balance of snowfall, ice flow, and ablation.
Ablation: The loss of glacial ice or snow by melting, evaporation, or breaking off into icebergs.
Glaciers retreat by melting back, not by retracting.
Glaciers produce distinctive landforms and small-scale features.
1. Valley (Alpine) glaciers
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Alpine glaciers are found in mountainous areas.
Alpines are smaller than ice sheets, only covers a small region.
The Lengths of the alpine glaciers are greater than widths.
Alpines transform V-shaped valleys into U-shaped valleys and make the land more rugged.
2. Ice sheets (Continental) glacier
❖ Ice sheets are in a large scale and cover 10% of Earth’s land.
❖ It can be found in polar regions like:
1) Greenland – 1.7 million km2
2) Antarctica – 13.9 million km2
❖ The weight of the continental glaciers makes the land flatter.
Formation and Movement of Glacial Ice
❖ Glaciers have two zones:
1) Zone of accumulation: where snowfall exceeds losses by melting.
2) Zone of ablation (wastage): where losses exceed snowfall.
❖ Accumulation can be due to high altitude (mountain glaciers) or cold climate (continental glaciers).
Glacier formation
1) Snow Accumulation: Delicate hexagonal snowflakes accumulate.
2) Sublimation and Condensation: Air infiltrates, causing crystals to evaporate and condense.
3) Recrystallization: Snow becomes smaller, thicker, and more spherical, transforming into firn (granular
recrystallized snow).
4) Pressure and Compaction: Additional snow increases pressure, compacting lower layers.
5) Glacial Ice Formation: When the ice and snow thickness exceed 50 meters, firn fuses into a solid mass,
forming glacial ice.
❖ Transformation Rate: Varies based on snow accumulation; rapid in regions with abundant snow, slower in less
snowy areas.
Anatomy of a Glacier
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Terminus of the glacier: The lower edge of a glacier.
Crevasses: Open fissure in a glacier fracture zone.
Zone of fracture: Uppermost 50 meters of the glaciers.
Firn: A compacted mass of granular snow.
Equilibrium (firn) line / Snowline: the line between the zone of accumulation and the zone of ablation.
How Glaciers Move
❖ Weight (gravity) pulls ice down.
❖ Melting at bottom aids lubrication.
❖ These factors are causing two basic type of movements:
1) plastic flow
2) basal slip
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Plastic flow: A type of glacial movement that occurs within a glacier, below a depth of approximately 50 meters.
In plastic flow ice is not fractured.
Basal slip: A mechanism of glacial movement in which the ice mass slides over the surface below.
Glaciers move in a rate that varies from a few cm to 3000 cm /day.
The movement is faster in the middle.
Glaciers Erosion
❖ Glaciers erode by:
1) Plucking
2) Abrasion
❖ Plucking: A process by which pieces of bedrock are lifted out of place by a glacier.
❖ Abrasion: The grinding and scraping of a rock surface by the friction and impact of rock particles carried by ice.
❖ Rock flour: Ground-up rock produced by the grinding effect of a glacier which is forming pulverized rock.
❖ Striations: Scratches or grooves in a bedrock surface caused by the grinding action of a glacier and its load of
sediment.
Landforms created by Glacial Erosion
❖ Glaciers erosions are forming a lot of unique landforms like:
1) Glacial trough: A mountain valley that has been widened, deepened, and straightened by a glacier.
2) Hanging valley: A tributary valley that enters a glacial trough at a considerable height above the floor of
the trough.
3) Cirque: An amphitheater-shaped basin at the head of a glaciated valley produced by frost wedging and
plucking.
4) Arête: A narrow, knifelike ridge separating two adjacent glaciated valleys.
5) Horn: pyramid-like peak formed by glacial action.
6) Fiord: steep-sided inlet of the sea formed when a glacial trough was partially submerged.
Glacial Deposits
❖ Sediments of glacial origin are termed glacial drift, no matter how, where, or in what shape they were deposited.
❖ Types of glacial drift:
1) Till
2) Stratified drift
❖ Till is the unsorted sediment deposited directly by a glacier.
❖ Stratified drifts are the sediments laid down by glacial meltwater.
❖ Unlike glacial till, stratified drift shows some degree of sorting.
❖ The rock formed when glacial till is lithified is called Tillite.
1. Landforms Made of Till
❖ There are two types of landforms made of till:
a) Moraine
b) Drumlins
a. Moraines
❖ There are four main types of moraines:
1) Lateral moraine
2) Medial moraine
3) Ground moraine
4) End moraine
❖ Lateral moraine A ridge of till along the sides of a valley glacier composed primarily of debris that fell to the
glacier from the valley walls.
❖ Medial moraine is a ridge of till formed when two lateral moraines from two coalescing alpine glaciers join.
❖ Ground moraine is an undulating layer of till deposited as an ice front retreats.
❖ End moraine is a ridge of till marking a former position of the front of a glacier.
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:
1) Recessional moraine is an end moraine formed as the ice front stagnated during glacial retreat.
2) Terminal moraine is the end moraine that marks the farthest advance of a glacier.
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b. Drumlins
Drumlins: long smooth canoe-shaped hills made of till.
Drumlins are produced when advancing glaciers have run over earlier glacial moraines.
It forms in the areas that were once covered by continental ice sheets.
Drumlins are characterized by smooth, elongate, parallel hills.
2. Landforms Made of Stratified Drift
❖ There are two basic categories of features composed of stratified drift:
a) Ice-contact deposits
b) Outwash sediment
❖ Ice-contact deposit is an accumulation of stratified drift deposited in contact with a supporting mass of ice.
❖ Outwash sediments are materials deposited by melt-water streams in front of the margin of an ice sheet.
❖ Deltas forms when glacial stream s empty into lakes.
a. Ice-Contact Deposits
❖ There are two famous landforms made of Ice-Contact Deposits:
1) Eskers
2) Kames
❖ An Esker is a ridge composed largely of sand and gravel deposited by a stream flowing in a tunnel beneath a
glacier near its terminus.
❖ A Kame is a steep-sided hill composed of sand and gravel, originating when sediment collected in openings in
stagnant glacial ice.
b. Outwash sediment
❖ Outwash sediments are represented in a landform called Kettle holes.
❖ Kettle holes Depressions are created when blocks of ice become lodged in glacial deposits and subsequently melt.
Important figures about glaciers deposits
Glaciations over Earth’s History
Ice Age
❖ The last Ice Age began 2 to 3 million years ago.
❖ The geological time it appeared at is called the Pleistocene epoch.
❖ Ice covered 30% of Earth's land area.
❖ Indirect effects of Ice Age glaciers:
1) Migration of animals and plants
2) Rebounding upward of the crust (Isostasy)
3) Worldwide change in sea level
4) Climatic changes
Proposed possible causes of Ice ages
❖ There are two proposed possible causes for Ice ages:
1) Plate tectonics
2) Variations in Earth's orbit
1. Plate tectonics
❖ This theory states that:
1) Continents were arranged differently.
2) Some changes in oceanic circulation occurred.
3) Motions of tectonic plates brought land mass to high latitudes.
4) Volcanic activity produced dust that blocks solar radiation.
5) Changes in atmospheric composition led to a reduction in greenhouse gases.
2. Variations in Earth's orbit
❖ Changes in climate over the past several hundred thousand years are closely associated with variations in Earth's
orbit.
❖ There are two hypotheses depending on the variation in the earth’s orbit:
1) Milankovitch hypothesis
2) Astronomical hypothesis
1. Milankovitch hypothesis
❖ The shape (eccentricity) of Earth's orbit varies as:
1) The Angle of Earth's axis (obliquity) changes
2) The Axis wobbles (precession)
2. Astronomical hypothesis
❖ Astronomical explanation for glaciations and interglaciations based on cyclic variations in the solar energy
received at the Earth’s surface.
Proxy Data for ancient temperature
❖ There are three stable (non-radioactive) isotopes of oxygen. The most important are O16 and O18.
❖ When ocean water evaporates, molecules containing the lighter isotope of oxygen, O16, are more likely to "take
off" and enter the vapor phase.
❖ Normally, this wouldn't cause any permanent change in the oceans' isotopic chemistry because the molecules
would soon return to the ocean as rain.
❖ During an ice age, however, the water is locked up in glacial ice, so the oceans become isotopically heavy.
❖ Microscopic organisms constantly recording the oceans' oxygen by building it into their CaCO3 shells.
❖ When they die and fall to the bottom, they create a record of oceanic oxygen isotopes during their lives.
❖ We can reconstruct the ocean's isotopic history by looking at the ratio of oxygen isotopes present in their shells
deposited at different times.
❖ That ratio, in turn, tells us how much water was locked up as continental ice.
❖ Combining Oxygen Isotopes with atmospheric CO2, showed that climate over the last two million years has
alternated between glacial and interglacial states.
❖ We note the following:
❖ Glacial: Intervals of intense and extensive continental glaciations, characterized by dramatic climate fluctuations
and low average temperature.
❖ Interglacial: Interval of relatively constant warm climate with less continental glaciation. We have been in the
Holocene interglacial for the last 11,700 years.
❖ Ice-ages: Longer interval characterized by the prolonged alternation of glacial and interglacial. Earth has been in
an ice age for the last 2.5 million years, roughly.
❖ Note: The end of each glacial interval is marked by an abrupt warming.
❖ As the precision of measurements improves, this transition is found to be more and more abrupt, measurable in
the order of decades. On the contrary transitions to glacial conditions are less abrupt.
Antarctica in the Eocene period (65-35 million years ago)
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CO2 was about twice what it is today, Antarctica was connected to South America.
Then the Drake passage opened 35 million years ago, isolating Antarctica, and CO2 levels dropped.
Antarctica became glaciated in less than a million years and, Antarctic Circumpolar Current keeps it colder.
The Antarctic Circumpolar Current (ACC) provides fundamental control on the Antarctic ice system.
It isolates the Antarctic continent from directly receiving the overwhelming subtropical ocean surface heat.
This keeps Antarctic cooler.
Evidence for Older Glaciation
❖ Rocks called tillites (lithified glacial till) have distinctive textures that suggest emplacement of sediments by
glaciers.
❖ Unsorted rock particles including angular, faceted, and striated boulders.
❖ In some areas, old tillites directly overlie polished and striated crystalline rocks.
❖ Tillites formed during the late Paleozoic era in portions of the southern continents indicate that these landmasses
were once joined.
❖ These joined landmasses are also strong evidence supporting the theory of Plate Tectonics.
Lecture 15 “Deserts and Wind”
What’s a desert
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A desert is an area with less than 25 cm of annual precipitation.
It can be measured by the aridity index = potential evaporation/precipitation greater than 4.0.
Deserts may be cold, temperate, or hot.
All major continents have one type of desert or the other.
Desert Types
❖ There are five types of deserts:
1) Subtropical Desert
2) Leeward deserts
3) Interior Deserts
4) Coastal desert
5) Polar deserts
❖ Subtropical Desert are the deserts around the 30o Latitude (Tropics of Cancer and Capricorn).
❖ Deserts on the Leeward side are at the major Mountain ranges and called Rain-Shadow Desert.
❖ Coastal deserts are prevailing onshore wind cooled by cold ocean current.
❖ Interior Deserts are at the center of continents far from the oceans.
❖ Polar deserts are extremely cold and dry.
Geologic processes in arid climates
❖ Weathering in dry regions like deserts is not as effective as in humid regions.
❖ Mechanical weathering forms unaltered rock and mineral fragments.
❖ Some weak chemical weathering does occur forming clay and a thin soil.
The role of water in weathering
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Most erosional work in a desert is done by running water.
Water flows only during periods of rainfall and often occurs as heavy showers.
Heavy rains often cause flash floods.
Features of streams in the deserts:
1) Streams are dry most of the time.
2) Poorly integrated drainage.
3) Desert streams are said to be ephemeral (having short lifetime).
❖ Different names are used for desert streams including wash, arroyo, wadi, donga, and nullah.
Basin and Range
❖ In deserts region erosion mostly occurs without reference to the ocean (ultimate base level) because the interior
drainage never reaches the sea.
❖ During and following the uplift of the mountains, running water begins carving the elevated mass and depositing
large quantities of debris in the basin.
❖ Interior drainage into basins produces:
1) Alluvial fans and bajadas
2) Playas and playa lakes
❖ Alluvium is unconsolidated sediment deposited by a stream.
❖ An alluvial fan is a fan-shaped deposit of sediment formed when a stream’s slope is abruptly reduced.
❖ Over the years a fan enlarges, eventually coalescing with fans from adjacent canyons to produce an apron of
sediment called a bajada along the mountain front.
❖ Erosion of mountain mass causes local relief to continually diminish.
❖ Eventually mountains are reduced to a few large bedrock knobs called inselbergs projecting above a sediment
filled basin.
❖ On the rare occasions of abundant rainfall, streams may flow across the bajada to the center of the basin,
converting the basin floor into a shallow playa lake.
❖ Playa is the flat central area of an undrained desert basin.
❖ Playa lake is a temporary lake in a playa.
❖ Playas are composed of fine silts, clays and are occasionally encrusted with salts precipitated during evaporation.
Transportation of sediments by Wind
❖ Wind is having two types of loads that it transports:
1) Suspended Load
2) Bed Load
❖ Suspended Load is mostly consisting of dust (silt, clay, pollen, bacteria, salt crystals, etc.)
❖ Bed Loads are sediments moved along or near the ground.
❖ There are two ways in which bed loads are moving:
1) Rolling
2) Saltation
❖ Bed loads lifted off the ground momentarily due to force of collision with other grains.
❖ Wind doesn’t have dissolved load.
Erosion by Wind
❖ There are two types of erosions by wind:
1) Deflation
2) Abrasion
1. Deflation
❖ Deflation is when wind removes finer loose particles from the surface.
❖ Deflation Produces are:
1) Blowouts
2) Desert pavement
❖ Blowouts are depressions excavated by wind in easily eroded materials.
❖ Desert pavement is a layer of closely spaced coarse pebbles and gravel that forms after deflation.
2. Abrasion
❖ Abrasion is a mechanical scraping of a rock surface by friction between rocks and moving particles during their
transport by wind, glacier, waves, gravity, running water or erosion.
❖ There are two types of landforms formed because of abrasion:
1) Ventifacts
2) Yardangs
❖ Ventifact is a cobble or pebble polished and shaped by the sandblasting effect of wind.
❖ Ventifacts occurs as a wind-shaped stones with sharp-edge faces.
❖ Yardangs are streamlined wind-sculpted ridge that has the appearance of an inverted ship’s hull that is oriented
parallel to the prevailing wind.
❖ Because the sand-blasting effect of wind is greatest near the ground, these abraded bedrock remnants are usually
narrower at their base.
Wind deposits
❖ There are two types of wind deposits:
1) Sand Dunes
2) Sand Loess
1. Sand dunes
❖ Sand dunes are mounds and ridges of sand formed from the wind's bed load.
❖ Characteristic features of sand dunes:
1) Slip face
2) Cross beds
❖ Slip face is the leeward slope of the dune.
❖ Cross beds are sloping layers of sand in the dune.
❖ Dunes are hills of loose wind-born sand.
❖ Size, shape, and orientation of dune are determined by available sand, vegetation, and wind.
Formation and movement of sand dunes
Types of sand dunes
❖ There are five types of sand dunes:
1) Barchan dunes
2) Transverse dunes
3) Longitudinal dunes
4) Parabolic dunes
5) Star dunes
1. Barchans
❖ Barchans are crescent shaped with horns pointing downwind.
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Transverse
Transverse are ridges that are perpendicular to prevailing wind direction.
There is a dune form that is intermediate between isolated barchans and extensive waves of transverse dunes.
Such dunes, called Barchanoid dunes, form scalloped rows of sand oriented at right angles to the wind.
3. Longitudinal
❖ Longitudinal is a ridge that are parallel to prevailing wind direction.
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Parabolic
Parabolic dunes are also called Horseshoe.
Horseshoe (Parabolic) are crescent shaped with horns pointing upwind.
Parabolic dunes often form along coasts where there are strong onshore winds and abundant sand.
5. Star
❖ For star dunes winds are blowing from three or more directions.
2. Loess
❖ Loess is an extensive blanket of deposits of windblown silt.
❖ Primary sources of loess are deserts and glacial stratified drift.
Desertification
❖ Desertification is the invasion of desert conditions into formerly non-desert areas.
❖ Drought and overpopulation are the main causes of desertification.
❖ Signs of desertification:
1) Lowering of water table
2) Marked reduction of water supply
3) Increased salinity in water and soil
4) Progressive destruction of native vegetation
5) Accelerated soil erosion.
Lecture 16 “Coasts (Shorelines)”
The anatomy of the coasts
❖ The littoral zone is the region of a body of water, such as a lake, river, or ocean, that is near the shore.
❖ Littoral Zone is also described as the area where the water meets the land.
❖ The shoreline is the line that marks the contact between land and sea.
❖ Each day, as tides rise and fall, the position of the shoreline migrates.
❖ The shore is the area that extends between the lowest tide level and the highest elevation on land that is affected
by storm waves.
❖ The coast extends inland from the shore as far as ocean-related features can be found.
❖ The coastline marks the coast’s seaward edge, whereas the inland boundary is not always obvious or easy to
determine.
❖ The foreshore is the area that is exposed when the tide is out (low tide) and submerged when the tide is in (high
tide).
❖ The backshore is landward of the high-tide shoreline being usually dry, being affected by waves only during
storms.
❖ The nearshore zone lies between the low-tide shoreline and the line where waves break at low tide.
❖ The seaward of the nearshore zone is the offshore zone.
❖ A beach is an accumulation of sediment found along the landward margin of an ocean or a lake.
❖ Beaches consist of one or more berms.
❖ Berms are relatively flat platforms often composed of sand that are adjacent to coastal dunes or cliffs and marked
by a change in slope at the seaward edge.
❖ Beach face is the wet, sloping surface that extends from the berm to the shoreline.
Waves formation
Wave Characteristics
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Most ocean waves derive their energy and motion from the wind.
The tops of the waves are the crests.
Crests are separated by troughs.
Halfway between the crests and troughs is the still water level, which is the level the water would occupy if there
were no waves.
The vertical distance between trough and crest is called the wave height.
The horizontal distance between successive crests (or troughs) is the wavelength.
The time it takes one full wave (one wavelength) to pass a fixed position is the wave period.
The height, length, and period that are eventually achieved by a wave depend on three factors:
1) The wind speeds.
2) The length of time the wind has blown.
3) the fetch (distance that the wind has traveled across open water).
As the wave travels, the water passes the energy along by moving in a circle.
This movement of water is called circular orbital motion.
The turbulent water created by breaking waves is called surf.
COASTAL PROCESS
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Coastal processes are the set of erosion and deposition mechanisms operating along a coastline.
The land-water interaction is always highly dynamic, and they work towards an equilibrium condition.
The energy due to wind, waves and tides is constantly working in the coastal zone.
Dissipation of this energy (due to tide, wind, waves and current) gives way to various coastal landforms such as
beaches, mudflats, marshes, and mangroves etc.
Coastal processes are highly unpredictable.
Some of the coastal processes:
1) Sediment transport
2) Currents
3) Denudation
4) Deposition
5) Erosion
6) Flooding
7) Diffraction
8) Refraction
A longshore current is a moving mass of water that develops parallel to a shoreline.
Denudation is the process of wearing away or stripping down the shore.
Flooding is the overflow of water onto normally dry land.
The bending of waves, called wave refraction, plays an important part in shoreline processes.
erosion - the removal of sediment from a particular location by the action of wind or water.
❖ accretion - natural or artificial deposition of sediments along the coastline.
❖ beach nourishment - the restoration of a beach by the mechanical placement of sand on the beach for recreational
or shore protection purposes.
❖ Offshore transport - movement of sediment or water away from the shore.
❖ Onshore transport - movement of sediment or water toward the shore.
❖ Longshore transport (littoral/ Beach drift) - the displacement of sediment down the shore (parallel to the shore).
❖ cross shore transport - the displacement of sediment perpendicular to the shore.
❖ Rip current A strong, narrow surface or near-surface current of short duration and high speed that moves seaward
through the breaker zone at nearly a right angle to the shore.
Major coastal landforms
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You can see figures showing the mentioned landforms at the end of this section 🙌.
The same processes cause change along every coast, not all coasts respond in the same way.
Interactions among different processes and the relative importance of each process depend on local factors.
The factors include:
1) the proximity of a coast to sediment-laden rivers
2) the degree of tectonic activity
3) the topography and composition of the land
4) prevailing winds and weather patterns
5) the configuration of the coastline and nearshore areas.
❖ Features that originate primarily because of erosion are called erosional features.
❖ Features that originate primarily because of accumulations of sediment are depositional features.
Erosional Features
❖ The important erosional features are:
1) Wave-cut Cliffs
2) Wave-cut Platforms
3) Marine Terraces
4) Sea Arches
5) Sea Stacks
❖ wave-cut cliffs originate in the cutting action of the surf against the base of coastal land.
❖ A relatively flat, benchlike surface, called a wave-cut platform, is left behind by the receding cliff.
❖ If a wavecut platform is uplifted above sea level by tectonic forces, it becomes a marine terrace.
Depositional Features
❖ The important depositional features are:
1) Spits
2) Bars
3) Tombolo
4) Barrier Islands
5) Tidal flat
❖ A spit is a low tongue of land or a relatively long, narrow shoal extending from the land.
❖ The term Baymouth bar is applied to a sandbar that completely crosses a bay, sealing it off from the open ocean.
❖ A tombolo (tombolo = mound), a ridge of sand that connects an island to the mainland or to another island, forms
in much the same manner as a spit.
❖ Barrier island A low, elongate ridge of sand that parallels the coast.
❖ Tidal flat: Broad, horizontal plain between high and low tides
Other features
❖ There are some other features that’s not related to erosion or deposition like:
1) Rocky coast
2) Coastal wetland
3) Estuary
4) Coral reef
5) Tidal deltas
❖ Rocky coast: The coast where bedrock cliffs rise directly from the sea.
❖ Over time, irregular, rocky shorelines are modified by erosion and deposition to become smoother and straighter.
❖ Coastal wetland: Vegetated, flat-lying zone that floods with shallow water (swamps and marshes are common).
❖ Estuary: Flooded river valleys along the coast due to relative rise in sea level.
❖ Coral reef: Shallow water coral mounds
❖ Tidal delta A delta like feature created when a rapidly moving tidal current emerges from a narrow inlet and
slows, depositing its load of sediment.
❖ Gabions: Boulders and rocks are wired into mesh cages and usually placed in front of areas vulnerable to heavy to
moderate erosion.
The Evolving Shore
❖ A shoreline continually undergoes modification, regardless of its initial configuration.
❖ if a shoreline remains tectonically stable, marine erosion and deposition will eventually produce a straighter, more
regular coast.
Important figures about costal landforms
Major coast types
Stabilizing the cost
❖ Structures built to protect a coast from erosion or to prevent the movement of sand along a beach are collectively
known as hard stabilization.
❖ There are 3 ways to protect the cost:
1) Jetties
2) Groins
3) Breakwaters
❖ Jetties A pair of structures extending into the ocean at the entrance to a harbor or river that are built for the
purpose of protecting against storm waves and sediment deposition.
❖ Jetties are built in pairs perpendicular to the shore.
❖ Jetties are built to protect harbor entry.
❖ A groin (groin = ground) is a barrier built at a right angle to the beach to trap sand that is moving parallel to the
shore.
❖ Breakwater are Hard stabilization built parallel to the shoreline.
Tides
❖ Tides are regional changes in water level caused primarily by gravitational pull of the sun and moon on the water
layer surrounding the earth, in combination with earth rotation.
❖ High and low tides: the overall sea level rises and falls twice daily.
❖ Spring tides: sun, moon and earth in one line.
❖ Neap tides: when sun and moon at right angles.
❖ Effects of Tides on Beach profile (simplified):
❖ Effects of Tides in a Lagoon:
Sea-level change
❖ Sea-level change archaeologically important coastline modifications.
❖ Eustatic is the term referring to the Global Sea-level Change.
❖ Main reasons for sea-level change:
1) Sediment supply
2) Tectonic movements
3) Glacial activity (climatic changes)
❖ Drowned valleys are submerged river valleys or coastal plains formed by rising sea levels, creating estuaries with
a mix of freshwater and seawater.
Coral reefs
❖ A mass of limestone which has an upper surface controlled at the mean low-tide level.
❖ Builders of organic reefs:
1) corals
2) Calcareous algae
Rocking Our Geology Exam: Cheers to Success!
I extend my best wishes to all my friends and colleagues embarking on the upcoming physical
geology exam.
As we wrap up our collective efforts in mastering the intricacies of our planet's dynamic
processes, let us confidently approach the exam, knowing that our dedication and hard work
will undoubtedly bear fruit.
May your minds be sharp, and may you easily recall the knowledge we've acquired together.
Let me remind you of the Ayah “ayet” that is saying “{‫سعَى‬
Which means
َ ‫ان إالَّ َما‬
َ ‫ْس ِلإلن‬
َ ‫”}وأَن لَّي‬.
ِ ‫س‬
َ
in English “And that the human being attains only what he strives for”, in Turkish “Ve insan
için, çalışmasından başka bir şey yoktur”.
Trust in your capabilities and remember that this journey has enriched our understanding of the
Earth and forged lasting bonds among us.
Take a breath! … Do you know how geologists handle exam stress? They take a deep breath
and remind themselves that success takes time and pressure, much like the Earth's processes.
Keep calm and rock that test!
Here's to success in the exam and beyond.
May your knowledge flow like a well-sorted river, and may you avoid getting stuck in any
sedimentary layers of confusion!!
Mohanad Abotaleb
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