Download Deforming the Earth`s Crust

Change Over Time
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CO: SWBAT describe the forces that deform
Earth’s crust.
LO: SWBAT create a “cootie catcher” to review
plate boundaries, motion, and features.
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Describe two types of stress that deform
rocks
Describe three major types of folds
Explain the differences between the three
major types of faults
Identify the most common types of
mountains
Explain the difference between uplift and
subsidence
Explain how weathering changes the Earth’s
surface
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Have you ever tried to bend something only
to have it break?
How can a material bend at one time and
break at another?
It has to do with stress.
◦ Stress is the amount of force per unit area on a
given material.
◦ Stress can deform the Earth’s crust.
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The process by which the shape of a rock
changes because of stress
Two types of stress
◦ Compression
 the type of stress that occurs when an object is
squeezed
 occurs at convergent plate boundaries
◦ Tension
 The type of stress that occurs when forces act to
stretch an object
 Occurs at divergent plate boundaries
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The bending of rock layers because of stress
in the Earth’s crust
Common types of fold
◦ Anticline – upward-arching fold
◦ Syncline – downward, troughlike folds
◦ Monocline – rock layers are folded so that both
ends of the fold are horizontal
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The surface along which rocks break and
slide past each other
◦ The blocks of crust on each side of the fault are
called fault blocks
 Hanging wall
 Footwall
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Three main types
◦ Normal faults
◦ Reverse faults
◦ Strike-slip faults
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When rocks are pulled apart because of
tension
Causes the hanging wall to move down
relative to the foot wall
Usually occur when tectonic forces cause
tension that pulls rocks apart
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When rocks are pushed together by
compression
Hanging wall moves up relative to the
footwall
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When rocks are moved horizontally by
opposing forces
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Mountains exist because tectonic plates are
continually moving around and colliding with
one another
Three common types
◦ Folded mountains
◦ Fault-block mountains
◦ Volcanic mountains
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Make up the highest mountain ranges
Form when rock layers are squeezed together
and pushed upward
Appalachian Mountains – formed when North
America and Africa collided
Alps in central Europe, the Ural Mountains in
Russia, and the Himalayas in Asia
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Form when tension causes large blocks of the
Earth’s crust to drop down relative to other
blocks
Sharp jagged peaks
Tetons in Wyoming
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Most located at convergent boundaries where
oceanic crust sinks into the asthenosphere at
subduction zones
The rock that is melted in subduction zones
forms magma, which rises to the Earth’s
surface and erupts
Can also form under sea
◦ Can rise about the ocean surface to become islands
◦ Ring of Fire
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Vertical movements in the crust
◦ Uplift
 Rising of regions of Earth’s crust to higher elevations
 Rocks may or may not be highly deformed
◦ Subsidence
 Sinking of regions of Earth’s crust to lower elevations
 Rocks do not undergo much deformation
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Types of uplift
◦ Formation of mountains
◦ Rebound
 When large areas of land rise without deforming
 Slowly springs back to its previous elevation
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Rocks that are hot take up more space than
cooler rocks
◦ As the lithosphere cools, it becomes denser and
takes up less volume causing the crust to sink
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Can also occur when the lithosphere becomes
stretched in rift zones
◦ A rift zone is a set of deep cracks that forms
between two tectonic plates that are pulling away
from each other
◦ As tectonic plates pull apart, stress between the
plates causes a series of faults to form along the
rift zone
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Major events such as earthquakes and
volcanoes are not the only processes that
shape Earth’s surface.
Earth’s surface is gradually changed through
weathering.
◦ Weathering is a process in which rocks are broken
down into smaller pieces through the action of
wind, water, roots, and animals.
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Mechanical weathering
◦ Breaks rock apart without changing their chemical
composition
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Water seeps into cracks in a rock and freezes
Plant roots
Burrowing animals
Rock, sand, and soil particles carried by wind or water
Chemical weathering
◦ Changes the chemical composition of the rocks
 Air, water, salts, and acids may react with the minerals
in the rocks to form new substances
 Weakens the rock