Lithospheric Processes, Hazards and Management
Structure of the Earth
1. The Core
 Inner and outer core, outer liquid about 3500km radius, inner solid about 1255km
 The core is heavy and dense, and nickel-iron alloy called Nife
2. The Gutenberg Discontinuity
 Separates core from mantle, zone of discontinuity
 Slowing of seismic waves in region
3. The Mantle
3.1 Lithosphere, Asthenosphere and Mesosphere
 Deepest solid layer is mesosphere, the semi-molten layer is the asthenosphere, the
solid layer above, including crust, is lithosphere
 The rigid lithosphere is broken into plates which can move over the molten
asthenosphere
4. The Mohorovicic Discontinuity
 Between crust and lithosphere
5. The Crust
 Outermost layer of Earth. Continental crusts thicker than oceanic crusts, and often older
because of the impermanence and subduction of oceanic crust
5.1 Oceanic Crust (Sima)
 Made of basalt, or sima (silica and magnesium), so it is dense at 3gm/cm3
5.2 Continental Crust (Sial)
 Granitic, or sial (silica and aluminium), less dense at 2.7g/cm3
Theory of Continental Drift
1. Essence of Theory
 All continents were joined 225 million years ago as Pangaea, which split into Laurasia
and Gondwanaland, and further drifting resulted in their present locations today
2. Supporting Evidence
2.1 Continental Refits
 Observation that the shorelines and continental shelves of several continents fit
each other, such as S America and Africa
2.2 Structural and Lithological Evidence
2.2.1 Structural Evidence
 Belts of structures such as fold mountains and shields should be traceable
from one edge of a continent to a previously joined one
 Caledonian Mountains in Scotland and Scandinavia can be linked to the
Appalachians in the United States
2.2.2 Lithological Evidence
 Sequence of rock types, or stratigraphy, there is a high correlation of rock
types during the time when continents were supposedly joined
2.3 Palaeomagnetic Evidence
2.3.1 Magnetic Field and Rock Magnetism
 A rock gains its magnetism when it is iron rich and cools beyond Curie
temperature (400-600C), aligning with the prevailing magnetic field
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 If age of rock is known, rock magnetism can determine the position of
magnetic poles at time of formation of rock
2.3.2 Polar Wandering Curve
 Collection of rock samples of varying ages, can determine location of poles
at different times. If positions for North pole are plotted through time for a
continent, a polar wandering curve is derived
 These show that the poles appear to have moved greatly over time, but it is
known to be rather improbable.
 Furthermore, each continent has its own curve
 Either each continent has its own poles, or the continents have moved
relative to each other
 On a refit map, the poles all fall within the range of the actual poles
2.4 Palaeoclimatic Evidence
2.4.1 Glaciation of the Southern Continents
 Tillites and striae are present on Southern continents, which are now close
to the equator, thus the climate would not be suitable for the formation of
such features
 Also, glaciers moved inland from the ocean in Africa, S America and
Australia, which is impossible since glaciers move towards the ocean, unless
there was land there previously
2.4.2 Glaciation in Africa and South America
 Extensive glacier erosion in Africa and tillite deposition in South America
can be explained if they were connected previously
2.5 Palaeontological Evidence
 Fossil evidence – fossils of certain ancient animals and plants are widespread and
found on many continents, which would indicate that they used to be joined
3. Limitation of Theory
 The mechanism for movement was unknown, but is now proposed to be the theory of
Plate Tectonics
Theory of Plate Tectonics
1. Seafloor Spreading
1.1 The Sea-floor Spreading Hypothesis
 Discovery of mid-ocean ridges and rift valleys and splitting due to tension. Also,
ocean basins were found to be relatively young
 Mid-ocean ridges were the locations for generation of new crust due to cooling
magma forming new crust where it diverged
1.2 Supporting Evidence
1.2.1 Rock Magnetism
 The earth’s magnetic field frequently reverses its polarity, so Vine and
Matthews suggested that fossil magnetism at such rift valleys will have
alternating bands of normal and reversed polarity symmetrical on both
sides of the rift
 Confirmed by magnetic survey of Reykjanes Ridge and other mid-ocean
ridges
1.2.2 Geothermal Heat Flow
 Generated by Earth’s interior, measured by thermistor probe
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1.2.3
1.2.4
1.2.5
 Over mid-ocean ridges, temperature may be several times higher than
normal, which may be from mantle injection
Seismic Activity Distribution
 Mid-ocean ridges are centres of activity, key areas of volcanoes and
earthquakes
Dating of Volcanic Activity
 In Iceland, most recent volcanic activity occurs in a band down the centre,
with older volcanoes moving east and west
 North Atlantic, farther from ridge are older islands, which can be explained
by sea-floor spreading
Pattern of Sedimentation
 Moving away from ridge, one should find older sediment on older crust
 Deep Sea Drilling project produced evidence regarding sedimentation
pattern
2. Subduction
2.1 The Subduction Hypothesis
 If sea-floor spreading is accepted, subduction accounts for the Earth’s volume
staying constant, since crust has to be remelted somewhere
2.2 Supporting Evidence
2.2.1 Seismic Activity Distribution
 Most intense seismic activities coincide with ocean trenches
2.2.2 Distribution Pattern of Earthquake Foci
 Benioff’s examination of the Kurile Trench shows that earthquake foci get
deeper further from the trench and towards the cordillera of island arcs
 Termed the Benioff Zone, about 45 degree inclination. Line of disturbance
caused by passage of oceanic plate as it was subducted
2.2.3 Geothermal Heat Flow
 Geothermal heat is cooler over ocean trenches, indicating cold crust
descending and cooling the mantle
3. Mantle Convection Currents
 The earth’s plates move around the surface of the earth via convection. New crust
generated by upwelling magma at mid-ocean ridges, plates move away, carrying
continents, and at ocean trenches they are re-absorbed into the mantle
 Decoupling of the lithosphere and asthenosphere
 Source of tectonic movement is the heat generated by residual cooling off of planet,
and the decay of radioactive materials in the core, releasing heat
 Rocks nearer to source are heated and become less dense and more buoyant than
surrounding rock, rising to base of lithosphere, moving laterally and releasing heat, and
then sinking to remix. This cycle maintains the convective motion
4. Limitations of the Theory
 Paradoxes: the possibility of an expanding Earth
Global Structural Landforms
1. Divergent/Constructive Plate Boundaries
 Zones of tension where plates split and are pulled apart, and new crust is formed
 Either 2 convective flows are dragging plates apart, or mantle plumes or hot spots cause
tensional stress, where doming and three-armed rifting occurs
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1.1 Rift Valleys
 Hot rising plume causes crustal stretching and formation of tensional cracks. Plates
move away from upwelling, broken slabs are displaced down, creating downfaulted
valleys called rifts or rift valleys
1.1.1 Features of Rift Valleys
 Large tracts of land may be broken up, and vertical displacement can
produce horsts and graben
 Horsts are slabs of crust left upstanding, and graben are crust
downthrown by rifting
1.1.2 The East African Rift Valley
 Extends from Jordan to Mozambique, 5500km. In central part, divides into
two branches, Albertine and Gregory rifts
 The Kenyan rift valley exemplifies main features of rift faulting
 Simplest faulting results when two parallel faults allow valley floor to sink
between inward-facing scarps, producing bold and high fault scarps at 600m
or more
 More commonly, a number a faults result in step faulting, and smaller faults
result in grid faulting
 Volcanoes also occur in rift valley due to crustal weaknesses, such as
Longonot, Kilimanjaro
 Lakes also occur where rifting goes below the water table, such as Naivasha
and Malawi. Soda lakes as a result of sodium carbonate from magma and
volcanoes also occur, like Magadi and Natron
1.1.3 Merits of the Concept of Three Armed Rifting
 Tension caused by mantle plume explains plan of rift, which is three armed,
like the Rhine Rift Valley and the Red Sea Rift system, who both have failed
arms in the Hess arm and the Abyssinian Rift.
 Also, the uplift and tilt of horsts and graben is explained by mantle plumes
but not simple tension
1.2 Mid Ocean Ridges
1.2.1 Features of Mid-ocean Ridges
 Further spreading will cause rift valleys to lengthen and deepen into ocean
 Thousands of km long, hundreds of km wide, about 0.6-3km above seafloor
 Hot mantle decreases density due to thermal expansion, causing rocks near
ridge to elevate. As they move away, the cool and subside due to density
 Central rift runs down middle of most ridges like in Red Sea, where
temperature is higher and pillow like appearance of lava due to rapid
cooling underwater
 Great transform faults, resulting is staggered path
1.2.2 The Mid-Atlantic Ridge
 Great submarine mountain chain
1.2.3 Volcanic Islands
 Atlantic islands located close to mid ocean ridges where is reaches surface
of the sea, like the Azores, Ascension Island and St Helena
 Majorly, Iceland, a tholeiitic basalt plateau. A rift valley, the Central
Icelandic Depression, lies down centre of island, coinciding with recent
volcanic activity
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 Iceland grows outward from centre, so rocks get older further from fissure
2. Convergent/ Destructive Plate Boundaries
 Main stresses which occur are compressional. Depends on the type of crust involved
 Oceanic-oceanic results in the denser plate being subducted
 Continental-oceanic results in the oceanic plate being subducted
 Continental-continental results in folding since neither is dense enough to subduct much
2.1 Ocean Trenches
 Long narrow troughs in the ocean bed marking zones of subduction, Mariana Trench
is deepest at 11022m deep
 Found where trench fringes a continent due to continental-oceanic collision, or in
the ocean floor as a result of oceanic-oceanic collision. The former has high
incidence of active volcanoes, and the latter has volcanic island arcs
2.2 Continental Volcanic Arcs
 Orogenesis occurs when sediments along coasts are compressed by folding and
faulting to form mountain chains such as Andes, Alps and Himalayas
 Continental-oceanic, continental volcanic arcs may be formed
 Oceanic crust is bent and subducted, leading to partial melting of the water-rich
oceanic crust, magma formed less dense and slowly rises, which is usually andesitic
or granitic in nature, cooling and crystallizing greatly underground to give batholiths
 Magma may migrate to surface, causing volcanic eruptions. When volcanoes have
been eroded, the batholiths are exposed and observable
 Faults occur in shallow zone of mountain, and deeper underground intense
metamorphism of rocks occur
2.3 Island Arcs
 May be produced by an oceanic-oceanic collision
 Formed by partial melting of plate and lithosphere along the Benioff Zone
 Lava ascends to form arc of volcanic islands, such as Japanese islands and Aleutians
 Lavas are dominantly andesitic, which have 15% more silica and 3 times potassium
oxide by weight than ordinary basalt
 Composition of andesites vary in proportion to depth of Benioff Zone, with more
andesite the deeper it is
 Heat produced for melting is caused by friction between the two plates
2.4 Fold Mountains
 Continental-continental collision causes crust to be fused together because neither
is dense enough to sink and subduct
 They are pushed up to form mountain ranges such as the Alps and Appalachians
 Intense folding, faulting and buckling up of material. Deeper buried rocks maybe
more plastic due to higher temperatures, and thus only fold, not fracture
3. Transform Plate Boundaries
 Zones of shearing where plates slide past each other at transform or strike-slip faults
 Limited construction and destruction
 Zones of intensely shattered rock, forming narrow valleys on land and ridges on the sea
floor
3.1 The San Andreas Fault
 Major branches include Hayward and Calaveras faults
 Great length and complexity, thus named a fault system
 Offset stream channels and elongated ponds mark the fault and its movement
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 Responsible for earthquakes along the fault, as segments either slip regularly or
store energy for years where rocks are more elastic, generating earthquakes of
varying intensities
4. Hot Spots
 Intraplate activity and large scale landforms are explained by mantle plumes instead of
plate tectonics
 Regions where flow of geothermal heat is higher than average, commonly sites of
volcanism and the lava is rich in alkali (Group I) metals
 They remain relatively stationary
4.1 The Hawaiian Chain of Islands
 A stationary hot spot and a moving seafloor, a volcano can only remain in contact
with the hot spot for about a million years, after that the volcano will become
inactive
 The Hawaiian islands provide evidence – volcanoes increase with age away from
Hawaii
4.2 Other Hot Spot Activities
 Possibly in other areas like the Mid-Atlantic Ridge or Yellowstone National Park
 Exact role in plate tectonics is unclear
Seismic Activities
1. Causes and Characteristics of Earthquakes
 95% of earthquakes are interplate at plate boundaries. Intraplate earthquakes are less
common
1.1 Deformation and Fracture of Rocks
 At the outermost layer of crust, rocks are strong but brittle. When plates move,
compression, tension or shear of rocks build up pressure, resulting in concentrated
releases of energy, forming faults.
 May come in a single shock or series of shocks
 Friction at plate boundaries build stresses and strain, bending and deforming rocks.
When limits of deformation are exceeded, the rocks rebound, releasing energy,
producing earthquakes
1.2 Earthquakes and Faulting
 Fracture in a rock along which movement occurs is a fault. Movement along a fault
can be vertical or horizontal
 Rocks above a fault is the hanging wall, rocks below is the foot wall
 Dip-slip faults – in a normal fault, hanging wall moves down. In a reverse fault, the
hanging wall moves up. The break in slope is a fault scarp. Normal is often divergent,
reverse often convergent
 Strike-slip faults – left-slip and right-slip, depending on direction.
 Most fault systems appear as a combination of fault movements
1.3 Focus and Epicentre
 Focus is the point where an earthquake releases the elastic strain by fracturing
 Can be shallow (70km), intermediate (70-300km) or deep (300-700km)
 At divergent and transform, normally shallow focus, but at convergent normally at
the Benioff Zone
 Epicentre is the point on crust directly above focus
1.4 Seismic Waves
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 Seismic waves spread out from focus in all directions
 Body waves radiate in all directions, surface waves are vibrations trapped near the
surface of the earth
 Primary pressure waves are longitudinal body waves travelling by compression and
expansion, while secondary shear waves cause ground to vibrate perpendicular up
and down. Primary waves are faster and thus felt first, but secondary waves are
more destructive because buildings can withstand little horizontal stress.
 Love waves are surface waves that cause horizontal shearing, and Rayleigh waves,
or ground roll, travel like ripples. Love waves are generally faster, but Rayleigh more
destructive
 Surface waves are slower but more destructive than body waves because they
induce resonance in buildings
1.5 Global Patterns of Earth’s Seismicity
1.5.1 Divergent Boundaries
 Narrow belts of shallow-focus earthquakes coinciding with crests of oceanic
ridges at divergent boundaries – less than 70km deep, small magnitude
 Crests of oceanic ridges – normal faulting, basaltic magma intrusions. Also,
vertical faulting, associated with ridge topography
 Shallow focus at transform faults – no volcanic activity
1.5.2 Convergent Boundaries
 Widespread and intense – subduction zones, inclined at moderate to steep
angles, focuses as deep as 700km – can be brittle at that depth
1.5.3 Intraplate Seismicity
 Not associated with known faults or historical activity – result from crustal
stresses e.g. uplifting of mountains like Himalayas
 Built up stress by plate moving vertically while moving over asthenosphere
2. Earthquake Magnitude and Intensity
2.1 Intensity and the Mercalli Scale
 Intensity is the strength of shaking by an earthquake at a location, determined by
effects on people, structures and the environment
 The Modified Mercalli Scale measures damage and human perception of an
earthquake by using descriptors
 It is not a measure of an earthquake’s size or energy, but rather its perceptible
effects and damages, thus useful for comparing effects
 Dependent on variations in population density, building materials and methods and
distance from epicenter
 Useful in ranking earthquakes before technology was available to measure them, as
well as creating isoseismal graphs
2.2 Magnitude and the Richter Scale
 Magnitude refers to the absolute size of and amount of energy released by the
earthquake, using amplitudes of the seismic waves
 The Richter Scale is used to measure magnitude
3. Effects of Earthquakes
3.1 Ground Motion
 Passage of seismic wave through surface rock layers and regolith – damage and
destroy buildings
3.2 Tsunamis
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 Series of large waves created by abrupt displacement of water. Long period, crests
are very high and troughs very low. Troughs arrive at shore first, causing sea level to
fall and exposing the seabed
 Generated when sea floor abruptly deforms and displaces the overlying water,
especially submarine earthquakes at subduction boundaries
 Boxing Day Indian Ocean Tsunami in 2004 – 230000 in 14 countries died
3.3 Landslides and Liquefaction
 At convergent plate boundaries, steep slopes are prone to landslides when shaken.
 Also, soil layers may liquefy, causing mudflows. Liquefaction is particularly
dangerous as soil in a suspended state cannot bear any load, causing structures built
on it to collapse
 Landslides in Gansu Province, December 16, 1920, killed 180000
 1964 Niigata, El Salvador’s land is tephra, consolidated pyroclasts
3.4 Fires
 Fires caused due to fracturing of gas pipes, ruins of wooden and other flammable
materials. Exacerbated due to blocked streets and damage water supplies
 Tokyo 1923, lunchtime. Wooden fuel, typhoon created fire storms, water main were
broken
 San Francisco, 1906 – 700 deaths and $400 million in property damage due to fires
3.5 Factors Affecting Damage
 Natural phenomena only become natural hazards when humans are affected
 Several factors: population density, prediction abilities, geology and topography,
magnitude, preparation, governance and economic ability, building design, time of
earthquake
4. Managing Earthquakes
4.1 Earthquake Forecasting and Prediction
4.1.1 Earthquake Forecasting
 Identifies areas prone to earthquakes and man-made structures vulnerable
to damage from earthquake shaking. Can be used to develop building codes
and response plans
 Less precise, long term, based on seismic gaps
4.1.2 Earthquake Prediction
 Calculating likelihood of an earthquake of a certain magnitude in a given
timeframe. Scientists monitor earthquake precursors.
 Animal behaviour: Suspicious animal behaviour before onset of earthquakes
– 1975 EQ in Haicheng. Animals 7.5 times more likely to go missing a week
before an earthquake – 75% accuracy
 Tiltmeters: earthquakes are accompanied by tiny tilts of the earth’s surface,
so these are used to measure variations and changes in slope
 Seismic monitoring: use of seismographs e.g. Global Seismic Network.
Singapore’s Meteorological Services Division has 7 seismic stations
 Recurrence Intervals: Average times between ruptures are recurrence
intervals, used to calculate probability. Seismic gaps are areas which are
likely to break badly in future e.g. 1975 research in Los Angeles – eight
major earthquakes since 565, spaced at intervals of 55 and 275 years
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 Foreshocks: many large earthquakes are preceded by foreshocks. Past data
allows calculations whether small foreshocks will result in a large mainshock
later, such as the San Andreas fault
4.1.3 Problems Associated with Earthquake Prediction
 There is currently no foolproof method
 Animal behaviour failed to predict the 1976 Tangshan earthquake, no
foreshocks nor precursors
 Recurrence intervals and foreshocks are only averages, not precise e.g.
Parkfield California, predicted in 1993 but only struck in 2004
4.2 Mitigating Earthquake Hazards
4.2.1 Building Design
 Isolated-base technology – flexible support placed between structure and
foundation, counteracting movement of seismic waves and preventing
resonance
 Work well in new buildings, but most structures in earthquake prone zones
were built before such techniques were developed
4.2.2 Hazard Mapping
 Show hazards from earthquakes that experts agree could occur
 Useful in identifying areas prone to liquefaction, landslides and ground
shaking, in order to set insurance, develop safety codes and identify safe
locations
4.2.3 Controlled Earthquakes
 Pumping water into ground under high pressure to release pressure and act
as lubricant – old oil wells in Colorado and South Africa
 However, the magnitude might not be able to be controlled, and can result
in more damage
4.2.4 Evacuation Measures
 Earthquake drills educate population, properly designed warning system, so
evacuation is possible.
 Haicheng 1975, buildings evacuated several hours before earthquake.
Successful because a variety of signals were monitored
4.3 Earthquake Response
 Response efforts occur in stages: search and rescue, immediate relief such as
medical attention, shelter and food, reconstruction, recovery and long term
development
 Immediate relief: food and water, hygiene and disease, shelter, medical care,
communication, crime (looting) and psychological support
Extrusive Volcanism
1. Components of Volcanic Eruptions
1.1 Lava Flows
 Magma is molten rock beneath earth’s surface. Magma is less dense than
surrounding rock, moving towards surface, upon reaching is called lava
1.1.1 Types of Magma
 Three distinct types, depending on their silica content: basaltic (50%),
andesitic (60%) and rhyolitic (70%)
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
Finer grained rocks have lesser time available to crystallize because they
cool at the surface (basalt, andesite and rhyolite)
 Coarser grained rocks cool underground and thus produce larger crystals
(gabbro, diorite and granite)
 Basalt, being fluid, limited time for crystallization. Rhyolitic magma is more
viscous, flows less readily and has more time to crystallize. Thus basalt and
granite are more common than gabbro or rhyolite
1.1.2 Types of Lava
 Less fluid magma usually solidifies underground, intrusive volcanism
 Fluid magma more likely to make way to surface to form lava flows, such as
basaltic magma forming pahoehoe and aa flows
 Underwater, most are pillow lavas
1.1.3 Pasty Lava – High Viscosity
 Restricted to continental edges and strings of islands – Carribean, Japan
 Piles up around vent as lava dome, made of rhyolite
1.2 Pyroclasts
 Pulverised rock and lava, deposit of pyroclasts is tephra
1.2.1 Types of Pyroclasts
 Ash (<2mm), lapillis (2-64mm), bombs and blocks (>64mm)
 Ash falls occur when ash ejected into atmosphere settles over wide area.
Ash flow are clouds of ash and gas flowing along land surface
 Bombs are twisted, globular shapes which cooled while being ejected,
blocks are angular pieces of rock ripped from volcano during eruption
 Sorting of material – heavier material falls closer to volcano
1.2.2 The Generation of Lahars/Mudflows
 Large composite volcanoes can form mudflows or lahars
 When ash and debris become saturated with water, such as snow or ice
melt due to eruption (Mount St. Helens in May 1980, 30km/h), lahars can
form destroying homes and infrastructure – up to 100km/h
1.3 Gases
1.3.1 Composition of Volcanic Gases
 Largely water vapour, then carbon dioxide, sulphur and nitrogen
1.3.2 The Generation of Nuee Ardente/Pyroclastic Flows
 Formed when hot, incandescent gases combine with rocks and ash
 Due to the hot gases, they travel extremely fast due to being almost
frictionless, up to 200km/h, found 100km from source
2. Types of Volcanic Eruptions
 Can be mild or violent, depending on the nature of the magma
2.1 Magma and Viscosity
 Viscosity depends on silica content of magma. Rhyolitic magma is thus viscous and
forms short, thick flows but basalt is more fluid and travels longer – up to 150km
 Higher temperature = lower viscosity and longer flows
 The greater the gas content, the more fluid magma is
2.2 Magma and Nature of Eruption
 Depends on viscosity and gas content of magma
 At higher pressure, more gas can be dissolved in magma. As magma rises up,
pressure is largely reduced, allowing gases to be released
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 These gases form bubbles. Fluid magma allows gas to escape readily, but viscous
magma impedes the escape of gas. Thus, fluid magma eruptions are less violent, but
viscous magma collect gases as bubbles which increase in pressure, resulting in
more explosive ejections
 Furthermore, viscous magma is likely to clog up vents, such as in lava domes,
building up even more pressure
2.3 Types of Eruption
 Basaltic lava tends to form shield volcanoes and runny lava. Eruptions such as
Icelandic (basalt plateau), Hawaiian (shield, runny flows) and Strombolian (explosive,
frequent gas explosions of runny lava) are attributed to basaltic lava.
 Rhyolitic magma tends to form composite volcanoes with viscous lava. Eruptions
include Vulcanian (violent, viscous lava with many pyroclasts), Vesuvian (more
violent, powerful blasts of gas) and Plinian (most explosive, greating great clouds of
gas and debris and pyroclastic flows).
3. Features of Extrusive Volcanism
3.1 Shield Volcanoes
 Basaltic lava form broad, domed structures called shield volcanoes
 Average surface slope of a few degrees, normally less than 10, but wide base over
100km in diameter
 Small percentage of pyroclastic material, largely successive layers of basaltic lava,
which form thin sheets over large distances, such as Mauna Loa and Mauna Kea
 Convex slope, since it flows readily at summit but as it cools, becomes more viscous
and so slope angle increases near the base
3.2 Composite Volcanoes
 Stratovolcanoes are formed by relatively viscous andesitic or rhyolitic magmas
 Large and symmetrical, concave slope formed by alternate layers of lava and tephra
 Sorting of pyroclastic material with more bombs and blocks near summit, gradually
sorting to ashes
 Steep summits and flatter bases due to this sorting, concave profile
 May form lava domes, plugging the central vent
 Mount Mayon and Fujiyama, Vesuvius, Pompeii
3.3 Cinder Cones
 Volcanic peaks consisting of pyroclastic cinders
 Pyroclasts accumulate around vents after being ejected by eruptions
 Form small, steep-sided cones of about 33 degrees depending on angle of repose of
materials
 Parasitic cones on or near larger volcanoes, often in groups. Many form within
calderas of larger volcanoes, final stage of activity
 Wizard Island in Crater Lake, Oregon, formed after Mount Mazama’s summit
collapse to form caldera
3.4 Basalt Plateau
 Largest amount of volcanic material is exuded from fissures in the earth
 Very fluid basaltic lava, successive flows building lava plains (Deccan Plateau). Can
flow up to 150km from source
 Basalts are resistant to erosion while surrounding rock may not, and thus can form
plateau basalts
3.5 Calderas
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 Circular depressions in volcano summit, normally composite
 Formed when summit collapses into empty magma chamber below after an
eruption (Crater Lake, Oregon)
4. Volcanic Hazards
 Lava flows are a hazard to property, confined to the slopes only. At frequently active
volcanoes, lava flows are generally well understood by residents
 Ash fall, extending 1000km away, can bringing total darkness, suffocating animals,
smothering plant life and preventing machinery use
 Pyroclastic flows and mudflows, greatest hazard, developing rapidly, up to 200km/h
5. Volcanic Hazard Management
5.1 Prediction of Volcanic Eruptions
 First outburst of activity can be predicted, mostly fluid eruptions impossible to
predict subsequent direction or intensity – Kilauea, Hawaii, Nov 1959 forecasted
 Viscous magma still cannot be predicted – Nevado del Ruiz, Columbia, Nov 1985,
killed 20000 in heated mudflows
5.1.1 Land Deformation Measurement
 Ground deformations around volcanoes due to underground movements of
magma. Mt St Helens – tiltmeters 0,5-1.5m a day preceding eruption
 Tiltmeters successfully predicted Kilauea
5.1.2 Seismic Activity Monitoring
 Magmas can apply stress to rocks, fracturing them. Such earthquakes occur
at depths of less than 10km, low magnitude
 Volcanic tremors – long period vibrations indicating resonance (predicted
Mt Redoubt in Alaska on 2 Jan 1990), and regular vibrations indicating
origin and nature of magma
 Not all activity associated with volcanism – can indicate cessation of activity
5.1.3 Geomagnetic and Geoelectric Effects
 Volcanoes contain ferromagnetic materials, changing local magnetic field.
Magnetism reduces with temp, decreasing field may indicate rising magma.
Field may increase due to piezomagnetism as pressure and stress exerted
 Resistivity of subsurface layers of volcano. Telluric currents may indicate
natural conduits for magma movement
5.1.4 Gases Analysis
 Analysing gaseous constituents – restricted by need to analyse instantly
5.2 Volcanic Hazard Mitigation
 Look at measurement of slopes to indicate buildup of magma, seismometers and
seismographs (long period event, resonance, compression, Bernard Chouet),
analysis of gas activity and content (Williams, fumaroles, but may not be accurate
due to clogging of vents)
 Hazard Management: Evacuation (Mount Pinatubo), planning beforehand, diversion
of lava flows and mudflows (Sakurajima’s drainage channels to divert lahars but cost
a lot of money, Iceland’s cooling of lava flow to solidify, requires a lot of water)
5.3 Response to Volcanic Eruptions
 Lava flows are likely to follow existing valleys, can be diverted or cooled
 Eruptions cannot be contained or directed – evacuation considered. Need adequate
morgue facilities, local emergency facilities for burns or lungs damaged by hot ash,
apparatus for emergency workers and civilians like face masks
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 Local guidelines for heavy ash fall following Mount St Helens in 1980. Sweep ash
from roofs, authorities equipped to measure levels of toxic gases, analyse particle
size. Alternative sources of drinking water located. Transport may not work due to
ash fall – can also interfere with radio and TV transmissions.
Classification of Rock Types
Rock cycle – movement of material through space and time as it is transferred and transformed from one
type of rock in one location to other rock types and places.
1. Igneous Rocks
 Solidification of molten magma or lava. Most common rock type.
 Crystal of minerals, often silicates. Crystallisation of these materials causing rock to
solidify
 Nature of rock dependent on mineral content and rate of crystallisation
1.1 Intrusive vs. Extrusive Igneous Rocks
 Intrusive rocks were formed under the surface, and mostly have large crystals
(phaneritic) due to slow cooling and crystallization underground (thousands to
millions of years). Granite. Coarse texture.
 Extrusive were formed above surface from cooled lava. Microscopic crystals
(aphanitic) due to quick cooling. Basalt. Fine texture.
2. Sedimentary Rocks
 Distinguished by strata present in rocks, separated by bedding planes.
2.1 Types of Sedimentary Rocks
2.1.1 Sedimentary Rocks of Mechanical Origin
 Rocks where the constituent material has been derived from elsewhere and
transported as solid particles to the ultimate site of deposition
 Detrital/clastic rocks
 Loose clasts or organic material undergo diagenesis, causing clasts to bind
together, and in the process of lithification turn into rocks
 Diagenetic processes occur by compaction (buried under great pressure)
and cementation (minerals crystallizing in pore spaces, cementing clasts
together)
 Transporting agents of wind and water tend to sort particles by size, so size
is a subdivision for clastic rocks
 Small (<0.062mm, clays), medium (0.062-2mm, sandstones), large (>2mm,
conglomerates, breccias)
2.1.2 Sedimentary Rocks of Chemical Origin
 Precipitation from a solution of dissolved salts, of chemical origin
 Formed close to site of deposition and mixed with detrital sediments
 E.g. evaporates – formed by evaporation of salts in shallow seas (anhydrite,
gypsum, halite) and lithified
2.1.3 Sedimentary Rocks of Organic Origin
 Formed by accumulation of organic matter remains, such as fossils
 Limestone – from remains of sea creatures subjected to diagenetic
processes, calcium carbonate and calcareous rocks
3. Metamorphic Rocks
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 Changing mineralogical composition or physical structure of rock via high pressure and
temperature
 Uses tectonic forces, such as plate movement, to compress and heat rocks. Happens in
the solid state
3.1 Contact vs. Regional Metamorphism
 Contact metamorphism only involves extreme heat, not pressure. Grade of
metamorphism depends on distance from heat source.
 Chemical content does not change, but can be altered, such as water composition or
recrystallisation e.g. limestone to marble
 Regional metamorphism involves both temperature and pressure, and often occur
at convergent plate boundaries
 Gradual increases in heat and pressure can lead to metamorphic gradation
 Recrystallisation perpendicular to compressional force can lead to layered
appearance, or foliated texture
Weathering
The in situ breakdown of rock by natural agents. Response by rocks at surface to low temperatures,
pressures, and the presence of air and water. Denudation of the landscape.
1. Geometry of Rock Breakup
1.1 Block Disintegration
 Breaking down of rocks into large blocks, common in rocks with well developed
bedding planes or joints intersecting at right angles
 Concentrated weathering at secondary joints leads to large, angular boulders, such
as limestone
 Commonly the first stage, followed by other modes of weathering
1.2 Granular Disintegration
 Rock is broken down into numerous smaller fragments into grains, common in
crystalline rocks like granite and sedimentary rocks like sandstone
 Grains separated along the original crystal or grain boundaries
1.3 Exfoliation
 Detachment of concentric slabs from the rock mass, leaving behind smaller
spheroidal bodies. Also known as spalling.
 Thickness depends on process – insolation weathering leads to smaller layers,
pressure release leads to thicker layers
1.4 Frost Shattering
 Disintegration of rock along new surfaces of breakage to produce highly angular
fragments with sharp edges. Irregular because they do not break along defined
planes of weaknesses
1.5 Spheroidal Weathering
 Rock rounded from an initial block shape, as a result of uneven weathering on the
rock surface, with edges and corners being eroded more rapidly
2. The Processes of Weathering
2.1 Physical Weathering
 Uses mechanical force to break up the rock, often depending on temperature
fluctuations to produce stresses, thus superficial and occurs only near surface
2.1.1 Pressure Release / Dilatation
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
2.1.2
2.1.3
2.1.4
Breaks down rock through exerting physical stress. Can lead to sheet joints
or exfoliation
 Regolith above rock removed by erosion, resulting in lesser pressure and
expansion of rock, potentially fracturing it
 Can result in sheet joints, aiding the weathering process
 In extreme situations, exfoliation occurs forming exfoliation domes,
followed by block disintegration into smaller rocks
 Rocks formed at great depths are particularly susceptible
 Can occur on a micro scale – granular disintegration
Freeze-Thaw Weathering / Frost Shattering
 Water from precipitation enters joints and beddings in rocks. Upon freezing,
expands about 9%, exerting pressure
 Closed system generates pressure which can easily exceed rock tensile
strength
 Repeated stress with each cycle of thawing and freezing can lead to
cryofracturing over time
 Can occur on a smaller, granular scale when water penetrates pore spaces
and freezes into ice crystals, such as in chalk
 Requires oscillation about freezing point, such as a wide diurnal
temperature range in Alpine environments
 Moisture content of rock is important – if not saturated, freeze-thaw has
lesser effect since the pores can absorb water
Insolation Weathering
 Disintegration of rocks due to expansion and contraction through heating
and cooling, effective in large diurnal temperature range (deserts)
 Rock is poor conductor of heat, so heating is confined to surface. Sharp
thermal gradient develops, with surface expanding more than within,
causing stresses to develop
 If stresses exceed strength, sheet joints form leading to exfoliation of thin
layers (since limited to surface)
 Can result in granular levels – if grains are made of different colours, darker
colours expand more, such as darker mica than sandstone within granite
 Efficacy – may not be very significant since exfoliation is on a very small
scale. Also, Blackwelder and Griggs’ experiment showed that water is more
significant (no change even with 100C of changes for 244 years)
 However, laboratory results do not reflect real conditions, such as stress
from rocks surrounding, or not really 244 years of weathering experienced
Salt Weathering
 Physical weathering, although chemical reaction is involved
 When water within rock is saturated with salt, salt will crystallize and exert
pressure on rock
 This process, repeated over time with salt crystals growing, can split rocks
 Often cause honeycombing patterns
 Important in arid environments, as groundwater is brought to surface by
capillary action, evaporating and leaving salt behind
 Salt inflicts thermal expansion or by wetting and crystallizing
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 Coastal deserts are susceptible due to availability of salt water and high
temperatures
2.2 Chemical Weathering
 Breakdown of rocks by altering chemical composition of minerals by water, oxygen,
acids. Can occur at great depths due to infiltration and percolation of water
 Thus dependent on availability of water. Produces fine grained regolith
2.2.1 Solution
 By soil moisture and groundwater. Quartz can dissolve in water to give silica
in solution
2.2.2 Carbonation
 Weakened by carbon dioxide dissolved in rainwater. Calcite (limestone)
reacts with carbonic acid to form calcium and calcium bicarbonate, which
can dissolve in solution with water
2.2.3 Hydration
 Affects rocks which can take up water, absorbing water into minerals. Can
cause expansion of a mineral. Iron oxide is hydrated by water to give
hydrated iron oxide
2.2.4 Hydrolysis
 Reaction with pure water. Feldspar reacts with water to give kaolinite as an
eventual end product
2.2.5 Oxidation
 Reaction with oxygen from soil or atmosphere. Rusting of iron with oxygen
to give iron oxide
2.3 Biological Weathering
 Any weathering carried out by living organisms or their by-products
 Biomechanical weathering: carried out by plant roots prising and breaking rocks
apart, common in urban areas. Opens passageways to allow for water and other
forms of weathering
 Biochemical weathering: by plants, organic matter creating organic acids to carry
out chemical weathering and chelation
2.4 Classification of Weathering
 Most rock disintegration is affected by complex interplay of all three processes,
difficult to truly distinguish them
 Operate in conjunction to assist each other
3. Climate and Weathering
 Determinants of the rate and type of weathering: rock characteristics, climate,
geological structure, vegetation and soil cover, level of water table, topography of local
areas, man’s activities. Climate is one of the most important.
3.1 Weathering in Different Climatic Zones
 Much weathering depends on water and temperature
 Differences in precipitation and temperature thus has effects on weathering in the
different morphoclimatic regions
3.1.1 Weathering in the Humid Tropical Regions
 High temperature results in faster chemical weathering (van’t Hoff: speed
of reaction increases 2.5 times with rise of 10C)
 High precipitation also results in more chemical weathering (solution,
hydration, hydrolysis etc.)
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 Dense vegetation and organic matter helps chemical weathering, almost 4
times as rapid in humid tropics than temperate regions
 Physical weathering limited due to masking effect of thick regolith covering
surface
 Uniformly high temperature does not support it either
 Results in thick layer of regolith due to deep chemical reaction. Regolith
removal is slow due to vegetation, so there is a build-up of regolith
3.1.2 Weathering in the Seasonally Humid Tropical Regions
 Due to heavy seasonal rainfall, chemical weathering is also rapid, but not as
much as the tropics
 Less dense vegetation also means easier removal of regolith and thus
thinner layer, which can expose the basal surface of weathering
3.1.3 Weathering in the Hot Arid Environment
 Physical weathering dominant due to high range of diurnal temperature,
especially insolation and salt weathering
 Only some chemical weathering, due to sources of moisture such as
infrequent rains, dew and fog
 In general, low rates of weathering and largely superficial, so regolith is very
shallow. Furthermore, no cover or organic material means it is removed
without time to accumulate
3.1.4 Weathering in the Temperate Regions
 Chemical weathering is only moderately active due to moderate
temperatures and rainfall
 Physical weathering can play an important role through freeze-thaw
weathering in winter, but it rarely goes to any great depth
3.1.5 Weathering in the Glacial Regions
 Abundant snowfall and low temperatures oscillating around 0C means
freeze-thaw weathering is dominant in glacial regions
 In summer, rain falling can dissolve carbon dioxide and oxygen to form
weak acids
3.2 Peltier’s Diagrams
 Shows relationship between climate and both types of weathering
3.3 Strakhov’s Diagram
 Precipitation and average temperature’s correlation with basal surface of
weathering (divides weathered from unweathered rock)
4. Rock Characteristics and Weathering
 While on macro scale, climate differences affect weathering, on a local scale,
weathering is more influenced by rock type
4.1 Rock Strength and Hardness
 Harder rocks are more resistant to physical weathering, depending on minerals
making up the rock and strength of cementation between minerals
 Older rocks are normally harder since they undergo more cementation and
compression
4.2 Chemical Composition
 Affects resistance to chemical weathering, determines if minerals are susceptible or
not
 Limestone prone to carbonation due to being mainly calcium carbonate
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 Sedimentary rocks may have resistant clasts, but not resistant cement
 May affect physical weathering, such as different coloured minerals affecting
expansion and contraction, leading to granular disintegration
4.3 Rock Texture
 Coarse or fine grained. Coarse grained rocks allow for chemical weathering to
reduce coherence, and large pore spaces allow for high primary permeability,
trapping water for chemical and frost weathering
 Numerous boundaries between fine grains increases surface area for chemical
agents, speeding up chemical process
4.4 Rock Structure – Joints and Beddings
 Selective weathering along lines of weaknesses in rocks, high secondary
permeability allowing water to easily penetrate, increasing surface area for both
chemical and physical weathering
5. Other Factors Affecting Weathering
 Topography affects weathering, as steep slopes aid to remove regolith
 Altitude affects weathering – above the tree line, temperature is suitable for freezethaw, but too high is not because of lack of oscillation around 0
 Aspect affects weathering, like whether it is on north-facing or south-facing sides
6. Landforms Associated with Weathering
6.1 Scree/Talus Slopes and Block Fields
 Commonly associated with freeze thaw weathering. Screes or talus are made of
angular fragments of rock accumulated at the bottom of steep slopes
 Can form blockfields on gentler slopes
6.2 Exfoliation Domes
 Formed by exfoliation of massive rock, like granite, due to pressure release and
unloading, sheeting
6.3 Limestone Pavements
 Formation by chemical weathering along joints. Limestone surface exposed to reveal
joints, which are enlarged via carbonation, forming clints and grykes
Mass Movement
1. Initiation of Mass Movements
 Mass movement is downslope movement of weathered materials in response to
gravity
 Dependent on shear strength and shear stress of slope
1.1 Shear Strength vs. Shear Stress
 Depends on instability on hill slope when equilibrium has been disturbed
 Safety factor is measured by ratio of resistance against movement to force trying to
enact movement (shear strength against shear stress)
 Speed of movement depends on how much stress exceeds strength
1.2 Factors Affecting Mass Movement
1.2.1 Gravity, Slope Angle and Shear Stress
 Gravity induces movement downslope, depending on angle of slope and
weight of regolith
 Angle of repose is when stress = strength, when friction balances gravity
 Regolith is pulled down faster on steeper slopes
1.2.2 Nature of Slope and Shear Strength
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 Sand and gravel slopes generate friction between particles
 Silt and clay slopes depend on cohesion and water
 Rock slopes depend on internal strength of solidification and crystallization
 Bedding planes or joints of weakness might focus failure on these areas
1.2.3 Role of Water
 Water increases stress while decreasing strength
 Rainfall can saturate soil, reducing cohesion due to pore pressure between
pore spaces. It also lubricates, reducing friction. Also increases weight
 A bit of water is still necessary for maintaining cohesion in clays
1.2.4 Role of Triggering Mechanisms
 Earthquakes can trigger mass movements by vibrating and shaking regolith
materials loose, reducing friction
 Undercutting of slopes can also trigger
2. Classification and Types of Mass Movement
2.1 Carson and Kirby’s Classification of Mass Movement
 Plots mass movements along a continuum, flexible classification according to speed
and moisture content
2.2 Mass Movement Processes
2.2.1 Soil Creep
 Slow but widespread and highly effective. More material is moved by creep
than any other means. Creep is faster in dryer, colder areas (10mm/year)
 Gravity creep and soil heave. Gravity creep occurs when soil particles are
disturbed by flora and fauna, which then move downslope because of
gravity. Chain movement of particles continues until initial movement is
absorbed
 Soil heave happens because of expansion and contraction, due to heating
and cooling, wetting and drying or frost action.
 Expansion heaves at right angles to surface, but contraction is affected by
gravity to give a net downslope migration
2.2.2 Solifluction
 Common in periglacial areas. Waterlogged soil slides slowly over the
impermeable permafrost, resulting in solifluction lobe
2.2.3 Fall
 Occur on steep slopes where angle of friction is greatly exceeded. Slope
made of hard rocks which are able to maintain high angles
 Weathering allows detaching of rock to fall due to gravity. Falls until it
reaches its angle of repose
2.2.4 Slide
 Sudden and rapid, occur at high relief and unstable slopes. Triggering action
is usually needed
 Mass slides down a shear plane until it shatters at the bottom. Slide planes
can be lubricated or selectively weathered
 Landslides occur in sands or clays, due to buildup of groundwater,
increasing stress while decreasing friction strength
 Common when weak layers support heavier ones above
2.2.5 Slump
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 Occur in weaker rocks than slides, have a rotational movement along a
curved slip plane, resulting in terraces and a flow at the bottom
 Occur where moisture is concentrated at base of water soaked clay rich soil
 When the lower toe becomes mobile due to water, after heavy rain, it flows
away, resulting in material slumping away from the top
2.2.6 Flow
 Soil moisture content is high, rapid form of movement. Flow is greatest at
surface and decreases to zero at the bottom
 Internal deformation under its own weight, dependent on saturation of
water, like clay, so fine particles are prone to flows
 Earthflows are linear movements of moist clay rich regolith. Slower than
landslides, a few feet/hour, day, or even month
 Mudflows are more rapid and less viscous, occur in areas with sparse
vegetation, and is thus quickly saturated
2.2.7 Others
 Debris and snow avalanches are also possible
3. Human Activities and Mass Movement
3.1 Human Induced Mass Movements
3.1.1 Undercutting and Mass Movement
 Undercutting a previously stable slope, such as building roadways on
mountainous terrain
 As a result, landslides are more common, and slopes are more saturated
 12 September 1995, Kulu, Himachal Pradesh, India, landslide killed 65
people due to undercutting of slope
3.1.2 Construction and Mass Movement
 Clifftop buildings increases the stress on slopes, increasing instability
 Holbeck Hall Hotel in Scarborough, 5 June 1993, rainfall plus hotel caused
the ground to slump
3.1.3 Deforestation Due to Population Pressure
 Cities like Hong Kong and Rio de Janeiro expanding onto marginal land to
accommodate population pressure. New roads and buildings built on
deforested steep slopes, which reduces stability
4. Managing Hazards Associated with Slope Failure
 Worldwide, landslides have caused average of 7500 deaths/year and US$20billion per
year from 1980-2000. Landslides increase as more people settle in less suitable areas –
most deaths occur in LDCs.
4.1 Predicting/Preventing Slope Failures
4.1.1 Landslide Hazard Maps
 Avoid building in places prone to landslides – GIS can used to make debris
flow and landslide hazard maps, prescribing restrictions in land use like road
building, timber harvesting, housing subdivisions
4.1.2 Controlled Development
 Pre-construction assessment: Study of area before construction, geologic
feasibility report. Modify landscape as little as possible
 Controlled development: Controls on hillside development through zoning
laws (affluent countries: hillside properties for scenery, congested cities:
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slums on hillside like favelas) Should not be any construction steeper than
27 degrees
4.1.3 Slope Monitoring
 Monitoring: extensometers and tiltmeters to detect micromovement on
slopes
 Modelling: Computer modeling to simulate scenario of mass movement,
useful in land use planning, hazard planning and evacuation plans
4.2 Mitigating Slope Failures
4.2.1 Improving Drainage
 Drainage: Proper drainage required to prevent saturation of soil and reduce
water pressure, such as outlets and culverts
4.2.2 Improving Vegetation Cover
 Vegetation: Should be left in natural state to enhance drainage and increase
stability by removing water through evapotranspiration. Can also stabilize
slopes.
4.2.3 Construction of Retaining Structures
 Retaining structure: Holds back earth and stabilizes soil and rock from
downslope movement, such as gabions and walls
 Debris catch or dam: Structures used to catch falling material and trap flow
debris, such as wire netting, dams and barriers
4.2.4 The Use of Weights
 For slopes overloaded at the top, add load to the lower part of the slide to
resist movement – pile heavy boulders on toe to increase stability. Angle
can be changed by removing slope top, adding weight to base, remaking
entire slope with lower angle.
4.3 Responding to Slope Failures
 Search and rescue, provision of medical care, food, shelter, water, long term
recovery. Like earthquakes and volcanoes.
Limestone and the Karst Landscape
1. Limestone
1.1 Formation of Limestone
 Calcite deposition in deep-sea conditions, calcareous remains of plant and animals
 Skeletons filled with mud and precipitates, diagenetic processes form limestone
1.2 Types of Limestone
 Importantly, carboniferous limestone forms landforms, but not oolite
1.3 Characteristics of Limestone
 Carboniferous limestone and dolomite
1.3.1 Chemical Composition
 Limestone at least half the rock contains more than 50% carbonate
minerals, with calcite as most common, pure limestone is at least 90%
calcite
 Physically resistant to weathering, but chemically unstable, carbonation
 Landform associated with limestone is probably solutional and found in
humid or temperate regions
1.3.2 Structural Control
 Low primary permeability and high secondary permeability
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 Selective weathering at joints, not uniform weathering, will occur.
Carboniferous limestone’s secondary permeability is much higher than
oolite, explaining landform formation in carboniferous and not oolite
 Older the rock, lower primary and higher secondary, due to increased
lithification with age
1.3.3 Weathered End Product
 Leaves behind little impurities after weathering because most is removed in
solution, but still leaves behind insoluble calcite which will blanket the
surface, preventing further erosion
 Leaves behind little regolith, in contrast with granite
2. Karst Landforms
2.1 Enclosed Depressions
 Common in karst areas, enclosed basins where precipitation is drained internally by
subterranean conduits. Extent of depression depends on rainfall, thus determining
types of landforms in temperate and humid
2.1.1 Dolines
 Medium sized closed depressions
 Percolating rainwater causes selective weathering at fissures and bedding
planes, especially where groups of fissures are
 Rate of solution becomes greater due to increased surface area, void
created and subsides, producing depression
 Throughflow directed towards base of hollow, enhancing solution and
continuing cycle
2.1.2 Uvalas
 A combination of dolines into areas with sub-basins and uneven floors,
increasing size but decreasing number of depressions
2.1.3 Cenotes / Collapse Dolines
 Depressions with circular, smooth-walled vertical shaft, develop where
water filled cave just below ground
 Fractured rock weakened by percolating rainwater and upward solution of
cave water, collapsing and producing a shaft
2.1.4 Cockpit Karsts
 Same as dolines, but torrential nature of rainfall in humid tropics causes
surface flow and weathering via surface gullying along joints, causing
elongated depressions along joints which eventually interconnect, forming
deep irregular cockpits separated by cones
2.1.5 Tower Karsts
 Further weathering of cockpits until base level of erosion is reached,
clogging up the floor with impermeable calcite. Weathering then forms the
cones into tower karsts
2.2 Karren Features
 Microsolutional features which form on exposed limestone surfaces
 Clints and grykes, limestone pavements, exposed plain of limestone caused by
glacial erosion. Blocks and grooves created by joints are accentuated by chemical
weathering
 Karren forms, such as spitzkarren in tropical and Mediterranean areas where
processes have operated for a long time in high rainfall
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 Grykes bounding clints are widened and deepened by erosion
2.3 Drainage Features
2.3.1 Karst Gorges
 Karst landscapes may contain major rivers, due to being in early stages of
karstification when fissures are not yet developed enough to absorb rivers
 Valleys eroded by streams are gorges, with vertical cliffs and scree slopes
 Well-jointed limestone maintains verticality by falling when weakened, no
other mass movement results in no gentle sloping
2.3.2 Swallow Holes, Dry Valleys and Blind Valleys
 Rivers flowing on limestone will eventually create openings in rock bed due
to selective weathering, creating a swallow hole which leads into
subterranean drainage
 Downcutting of valley will stop downstream, forming a dry valley and may
create a cliff due to reversal of gradient
 Upstream, vertical erosion continues, downcutting the blind valley
 Successive sinks cause headward migration of stream and developing new
blind valleys
 Streams may eventually reemerge as resurgent streams
2.4 Caves
 Limestone caves are subterranean stream networks, carved out by the water it
channeled
 Groundwater dissolves rock along joints and bedding planes, forming large cavities
 Cave conduits are formed due to low primary and high secondary
 Migration of water table can cause caves to form at different levels
 Speleotherms – depositions of calcite. Water supersaturated with carbon dioxide
will cause crystallization of calcite, forming stalactite on ceilings, and water dripping
onto ground forms stalagmites, eventually joining to form columns
Granite and Associated Landforms
1. The Formation and Characteristics of Granite
1.1 Formation of Granite
 Intrusive igneous rock formed from solidification of rhyolitic magma underground
 Solidifies to form batholiths, plutonic features
 Exposed after denudation of landscape
 Especially prone to pressure release as a result
1.2 Characteristics and Weathering of Granite
1.2.1 Chemical Composition
 Quartz, feldspar and other minor minerals
 Prone to chemical weathering of hydrolysis: Feldspar -> kaolinite clay
 Forms gruss, residual debris, within which are embedded corestones due to
block and spheroidal weathering
1.2.2 Rock Texture
 Phaneritic, large crystals
1.2.3 Rock Structure
 High secondary permeability due to shrinkage joints and sheet joints as a
result of cooling and pressure release
 Selective weathering along joints, block disintegration and spheroidal
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2. Granite Landforms
2.1 Landform Development in the Humid Tropics
 High temperatures and rainfall cause rapid chemical weathering, resulting in deep
regolith of saprolite
2.1.1 Model of Deep Weathered Layer
 Ruxton and Berry’s time dependent model of weathering
 Mature stage: Zone 1 is residual debris, Zone 2 is residual debris with
corestones, Zone 3 is corestones with residual debris, Zone 4 is partially
weathered rock
2.2 Landform Development in the Seasonally Humid Tropics
 Thinner regolith than humid trops, due to lesser chemical weathering during
drought period, as well as lesser vegetation to prevent surface runoff from removing
the regolith layer, may expose basal surface of weathering
2.2.1 Tors
 Small hills or heaps of boulders rising abruptly from surface
 Exposed by stripping to basal weathering surface e.g. Zimbabwe, Dartmoor
2.2.2 Inselbergs
 Steep sided isolated hills
 Ruwares are incipient inselbergs, with smooth convex surfaces. In
etchplains (land surfaces with more than one phases of deep weathering
followed by removal of regolith), pluvial periods cause dominant selectvie
weathering where joints are numerous. Interpluvial periods cause surface
wash to strip regolith due to degenerating vegetation. Undulating basal
surface of weathering exposed the ruware. With repeated cycles of pluvial
periods, ruware becomes higher
 Bornhardts are the next stage, where heights can exceed 300m with a
convex summit with rock slabs due to sheet joints because of pressure
release, but the rock dome is otherwise very durable
 Blocky inselbergs resemble tors, where rectangular jointing is prominent,
with selective weathering giving is similar appearance to tors
 Castle koppies are degraded, old inselbergs subjected to weathering. Low,
irregular hills
2.3 Landform Development in the Temperate Regions
2.3.1 Temperate Tors
 Dartmoor. Probably due to previous climates, when warmer, more tropical
climates were experienced by current temperate areas
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