EARTH’S INTERNAL PROCESSES
Chapter 25
I. THE PLATE TECTONICS THEORY – 25.1
A. Continental Drift
1. Please Define Continental Drift:
Two hundred million years ago the
supercontinent, called Pangaea, separated into
pieces that drifted over the surface of the Earth
like rafts on water.
2. Who first proposed Continental Drift?
Alfred Wegener first proposed Continental
Drift.
3. When was Continental Drift first proposed?
In 1915, about 100 years ago.
4. What was the first and large supercontinent
called? Pangaea
5. Evidence for continental drift
a. Coastlines
1. Alfred Wegener observed that the
eastern coastline of South America
fit together with the western coastline
of Africa.
b. Fossils
1. What large land animal and plant
supported Continental Drift?
a.) Cynognathus
b.) Lystrosaurus
c.) Mesosaurus
d.) Glossopteris
c. Rocks and mountains
1. Examples are:
a.) Cape Fold Belt
b.) Appalachians mountains
6. The controversy
Wegener, however, could not explain how
the continents drifted. He suggested that
Earth’s rotation, the gravitational pull of the
Sun and the Moon, and the centrifugal
force moved the continents. Physicists
quickly concluded that these forces were
unable to explain continental drift.
B. Seafloor Spreading Hypothesis
1. Please Define Mid-Ocean Ridge:
A system of mountain ranges with a rift valley between them that
extends around Earth on the seafloor; formed where
oceanic plates spread apart due to magma rising from Earth’s
mantle.
2. Please Define Rift Valley:
Long narrow depression formed in between
the peaks along the mid-oceanic ridge.
3. Rocks and sediments on the seafloor
a. Where are the oldest rocks found on Planet
Earth?
The oldest rocks are on the Continents and the
youngest rocks on the Seafloor. The difference in age
can only be explained if rocks on the Seafloor
are continually being created at a mid-ocean ridge.
b. Where are the youngest rocks found on
Planet Earth?
The youngest rocks are found on the ocean
seafloor which are being created at a midocean ridge.
4. Magnetic polarity of rocks
a. Rocks equal distances from either side of
the Mid Oceanic Ridge have the same
magnetic polarity.
C. The Plate Tectonics Theory
1. Please Define Continental Plate:
The Earth’s surface is made of separate
slabs of rigid rock called plates that move
slowly over Earth’s upper mantle.
2. Convergent plate boundaries
a. Please Define Convergent Plate Boundary:
Boundary where two plates collide, and
produces either subduction zones or
continental collisions.
b. Subduction zones
1.) Please Define Subduction:
The movement of a dense oceanic plate under a
buoyant continental plate.
2.) Example of a Continental-Oceanic
Convergent Plate Boundary.
The Andes Mountains in South America are an example
of a continental- oceanic convergent plate boundary.
3.) Example of an Oceanic-Oceanic Convergent
Plate Boundary.
Japan is an example of an oceanic-oceanic
convergent plate boundary.
c. Continental collision
1.) Example of Continental-Continental
Convergent Plate Boundary.
Along some convergent plate boundaries, two
continental plates of equal density collide and do not
subduct. Because no subduction occurs, the plates
collide and buckle upward to form a high range of
folded mountains. Volcanic activity is absent and there
is no deep-sea trench. The Himalaya Mountains in
Asia are an example of a continental-continental
convergent plate boundary.
c. Continental collision
1). Example of Continental-Continental
Convergent Plate Boundary.
c. Continental collision
Indian plate collides with the Asian plate
to make the Himalaya Mountains in Asia.
3. Divergent plate boundaries
a. Please Define Divergent Plate Boundary:
The boundary between two plates that
are moving apart. The magma rises
between the plates, erupts from a rift
valley as lava, and then cools to form new
crust.
3. Divergent plate boundaries
A mid-ocean ridge is one example of a divergent plate boundary. In some
places, such as the East African Rift, divergent plate boundaries create
intraplate rift valleys that form in the middle of a continent.
4. Transform plate boundaries
a. Please Define Transform Plate Boundary:
Tectonic plate boundary in which plates
slide horizontally past each other in
opposite directions.
4. Example of Transform plate Boundary:
The San Andreas Fault in California is an
example of a transform plate boundary.
Earthquakes are common along transform
plate boundaries.
D. Plates in Motion
1. Convection
a. Please Define Convection:
Transfer of thermal energy in a fluid by the movement of
warmer and cooler fluid from one place to another.
2. Slab pull, ridge push, and friction
a. Please Define Slab Pull:
When subduction occurs along a
convergent plate boundary, a force called
slab pull helps to move the plates.
b. Please Define Ridge Push:
In contrast to slab pull, ridge push moves
plates along a mid-ocean ridge.
c. Please Define Friction as it pertains to Plate
Motion:
Friction between a plate and the mantle also has an affect
on plate motion. For example, plates that drag continental
material along with them are slower than those that drag
oceanic material.
II. EARTHQUAKES – 25.2
A. Earthquake Distribution
1. Please Define Earthquake:
Sudden movement or vibration of ground that
occurs when rocks slip and slide along enormous
cracks in Earth’s crust.
2. Where do Earthquakes occur?
Earthquakes occur at tectonic plate
boundaries.
3. Earthquakes depth
a. Where are Earthquakes shallow?
Earthquakes that occur along divergent and transform
plate boundaries tend to be shallow, typically less than
70 km depth.
b. Where are Earthquakes deep?
However, earthquakes that occur along convergent plate
boundaries commonly occur at depths greater than 70 km.
B. Causes of Earthquakes
1. Deformation
a. Please Define Deformation:
A force applied to an object can cause the object to
change its shape, or be deformed.
b. What are the four main types of stress that
causes Earthquakes?
1.) Compression stress, in which an object is squeezed or
shortened.
2.) Tension stress, in which an object is
stretched or lengthened.
3.)
Shear stress, in which different parts of an object are
moved in opposite directions along a plane.
4.) Torsion stress, in which an object is twisted.
c. Types of deformation
1. What are the different types of
Deformation?
a.) Elastic deformation occurs when a material, such
as rock, deforms as stress is applied but snaps
back into its original shape when the stress is
removed.
b.)
Plastic deformation occurs when a material changes shape
as a stress is applied and remains in the new shape when the
stress is removed.
2. Energy release
a. Please Define Fault:
Crack in Earth’s crust along which rock has moved.
b. Please Define Elastic Rebound:
The sudden release of strain energy from rock as it moves
along a fault.
C. Seismic Waves
1. Please Define Focus:
Point of origin for an earthquake, the point from which
seismic waves originate.
2. Please Define Epicenter:
The point of Earth’s surface directly above the focus of an
earthquake.
3. Primary waves
a. Please Define Primary wave:
Primary waves are also called P-waves are
similar to waves that travel along a coiled
spring. Primary waves cause particles inside the
Earth to move back and forth in the same
direction that the wave is traveling. P-waves
are faster seismic waves and can travel through
Earth’s interior with speeds between 5 km/s
and 7 km/s. P-waves travel through both solids
and liquids.
3. Primary Wave
4. Secondary waves
a. Please Define Secondary waves:
Secondary waves, or S-waves, are another type of body
wave. Secondary waves are like Transverse waves in
which the wave moves right angles to the direction of
the wave. S-waves travel more slowly than P-waves.
Unlike P-waves, S-waves can travel only through solids.
4. Secondary waves
5. Surface waves
a. Please Define Surface waves:
Surface waves only travel on Earth’s surface. They move in
a more complex manner, rolling like ocean waves. Buildings,
roads, and power lines are often damaged by the side-toside rocking motion that results from surface waves.
5. Surface waves
D. Earthquake Measurement
1. Logarithmic scale
a. Please Define the Richter Scale:
The Richter Scale measures the energy released
during the earthquake. It is a logarithmic scale that
represents a 10-fold increase in wave amplitude from
one magnitude to another.
a. Richter Scale
b. Please Define the Mercalli Scale:
This scale ranges from 1 to 12. A rank of 1 on
the scale represents an earthquake that is
rarely felt by anyone. A rank of 12 reflects
earthquakes that cause the most severe
damage.
b. Mercalli Scale:
E. Earthquake Damage
1. Earthquake Damage causes:
a.) Collapsed buildings
b.) Landslides
c.) Fires
d.) Tsunamis
E. Earthquake Damage
2. Earthquake-safe structures
a. How are buildings made safe during
Earthquakes?
1.) Design a system that allows the whole structure to
move as a unit. Base isolated systems use bearings
that separate the building from the ground.
2.) By using building materials that bend rather
than break during an earthquake.
III. EARTH’S INTERIOR – 25.3
A. Earth From the Inside-Out
1. Refraction
a. How does Refraction show the
interior of our Planet?
Refraction occurs when a change in speed causes a wave
to bend and change direction. The refraction and change
of speed of seismic waves as they pass through Earth
provides evidence of Earth’s layered structure.
b. Speed and direction
1.) Please Define Discontinuity:
Boundary between two layers of
material that have different densities.
2.) What is the Mohorovicic Discontinuity?
This discontinuity separates Earth’s crust and mantle.
Seismic waves can change both speed and direction when
they encounter this discontinuity.
2. Shadow zones
a. Please Define Shadow Zones:
Area on Earth’s surface where no seismic waves from a
given Earthquake are recorded.
b. The inner and outer cores
1.) What is the composition of the solid
Inner Core?
Iron, nickel, oxygen, and sulfur.
2.) What is the composition of the liquid Outer
Core?
Silicates, aluminum, and calcium.
B. Composition of Earth’s Layers
1. Please Define Lithosphere:
The layer of Earth made of rocky material broken up into
tectonic plates, consists of Earth’s crust and uppermost
mantle.
2. Please Define Asthenosphere:
The plastic-like layer of Earth made of partially-molten rock
material directly beneath the tectonic plates.
IV. VOLCANOES – 25.4
A. Volcano Formation
1. Why is Magma forced upward from
the Earth’s Asthenosphere or Upper Mantle?
Because magma is a liquid, it is less dense than the
surrounding solid rock.
B. Plate Boundaries and Hot Spots
1. Convergent plate boundaries
a. Why are Volcanoes found along
Convergent Plate Boundaries?
They form where tectonic plates collide along
subduction zones.
3. Divergent plate boundaries
a. Why are Volcanoes found along Divergent Plate
Boundaries?
Most of this activity goes unnoticed because
it occurs under water at mid-ocean ridges. However,
there are places where volcanic activity due to divergent
plates occurs on land. An example of this the East
African Rift Valley.
East African Rift Valley- Divergent plate boundary
3. Hot spots
a. Why are Volcanoes found at Hot Spots?
Hot spots are areas of volcanic activity where
magma moves toward Earth’s surface in large,
ballon-like plumes. Hot spots are stationary and
the Hawaiian Islands are volcanic islands
formed when the oceanic pacific plate moved
over a hot spot.
Hawaiian Islands are formed under a Hot Spot.
Yellowstone National Park Volcanoes where
formed under a Hotspot.
C. Eruptive Products
1. Lava
a. Please Define Lava:
Underground magma that erupts to the
Earth’s surface.
b. Please Define Viscosity:
A fluid’s resistance to flowing.
c. Please Define Silica:
Chemical compound, silica dioxide (SiO2),
a common ingredient in most magma and
much of Earth’s crust.
2. Pyroclastic material
a. Please Define Pyroclastic Material:
Any solid material that erupts from
a volcano.
b. Pyroclastic Material described in terms of
size.
1. Ash
2. Globules
3. Volcanic cinders
4. Volcanic blocks
3. Gases
a. What kind of Gases erupt from a Volcano?
1.) Water vapor- most abundant gas.
2.) Carbon dioxide-next most abundant gas.
3.) Sulfur dioxide-can combine with oxygen and water
in the atmosphere to form droplets of sulfuric acid.
D. Eruptive Styles
1. What are Felsic Magmas?
Thick, cool, and sticky felsic magmas have high
viscosities and resist eruption, causing the pressure
inside a volcano to increase. Consequently an explosive
eruption occurs for this type of magma.
2. What are Mafic Magmas?
In contrast, running Mafic magmas have low
viscosities and they erupt quietly. These eruptions are
characterized by fluid lava flows having a high temperature
along divergent plate boundaries and hot spots.
E. Types of Volcanoes
1. Cinder cone volcanoes
a. Please Define Cinder Cone Volcano:
Small steep-sloped volcano with a short eruption cycle,
composed of cinder, formed at vents in Earth’s crusts,
often around the central vent of a larger volcano.
2. Shield volcanoes
a. Please Define Shield Volcano:
Large, broad, flat volcano composed of layer upon layer
of basaltic lava flows made up of thin mafic lava.
3. Composite volcanoes
a. Please Define Composite Volcano:
Large and steep-sided volcano composed of layers of
thick flowing felsic lava and ash.
4.Comparison of the three types of Volcanoes.
V. CHAPTER 25 REVIEW
A. Please do Check Concepts 34-40 on page
802 in your Text.
B. Please do Standardized Test Practice 1-6
on page 804 in your Text.