# Deforming the Earth’s Crust

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Deforming the Earth’s Crust

Stress is the amount of force per unit area on a given material
Deformation Stress is the amount of force per unit area on a given material The process by which the shape of a rock changes because of stress is called deformation

Deformation Two types of deformation can occur to rocks under stress
Layers can bend when stress is applied to them When too much stress is applied, they can reach their elastic limit and break

Compression & Tension Compression is the type of stress that occurs when an object is squeezed Tension is stress that occurs when forces act to stretch an object such

Folding Folding is the bending of rock layers because of stress in the Earth’s crust Scientists assume that all rock layers start off horizontal So when scientists see a fold, they know deformation has occurred

Types of Folds There are two main types of folds
Anticlines, upward, arching fold Synclines, downward, trough-like folds

Some rock layers break when too much stress is applied to them.
Faulting Some rock layers break when too much stress is applied to them. The surface along which a rocks break and slide past each other is called a fault

Faulting The two sides of a fault are known as the hanging wall and the footwall The type of fault that forms is dependent on where the hanging and footwall are located

There are three types of faults that occur Normal Faults
Types of Faulting There are three types of faults that occur Normal Faults Reverse Faults Strike-Slip Faults

Normal Faults When rocks are pulled apart because of tension, normal faults often form When a normal fault moves, it causes the hanging wall to move down relative to the footwall

Reverse Fault When rocks are pushed together by compression, reverse faults often form When a reverse fault moves, it causes the hanging wall to move up relative to the footwall Special type of reverse fault occurs when the hanging walls continues to be pushed over top of footwall called a “thrust fault”

Strike-Slip Fault Forms when opposing forces cause rock to break and move horizontally If you were standing on one side of the fault when it moved, the ground on the other side would appear to move to your left or right

Thrust Fault

Plate Tectonics & Mountain Building
When tectonic plates collide, land features that start as folds and faults, can eventually become large mountain ranges When tectonic plates undergo compression and tension, they can form mountains in several ways

Folded Mountains Form when rock layers are squeezed together and pushed upward These mountains form at convergent plate boundaries Appalachian Mountains 390 million years ago

Fault-Block Mountains
When tectonic forces put enough tension on the Earth’s crust, a large number of normal faults can occur Fault-Block mountains form when tension causes large blocks of the Earth’s crust to drop down relative to other blocks Often leaves sharp, jagged peaks

Volcanic Mountains Located at convergent plate boundaries where oceanic crust sinks into the asthenosphere at subduction zones The rock that is melted at subduction zones forms magma which rises to the surface and erupts

Volcanic Mountains Sometimes these mountains can rise above the sea and become islands A majority of the tectonically active volcanic mountains have formed around the Pacific Plate which is known as the Ring of Fire

Uplift is the rising of regions of Earth’s crust to higher elevations
Uplift and Subsidence Uplift is the rising of regions of Earth’s crust to higher elevations Subsidence is known as the sinking of Earth’s crust to lower regions

Uplifting of Depressed Rock
One way areas rise without deforming is a process known as rebound Rebound occurs when the crust slowly springs back to its previous elevation Rebound happens when a weight is removed from a region ( glacial melting)

Tectonic Letdown Subsidence can occur when the lithosphere becomes stretched A rift zone is a set of deep cracks that forms at a divergent plate boundary As the plates move apart, the rift zone begins to subside between the plates

Question 1 What are two types of deformation?

Answer Layers of rock can bend when stress is applied to them and if too much pressure is applied then the layers can break

Question 2 What type of fold has an upward, arching fold that looks like the letter ‘A’? Syncline Monocline Anticline

Answer The answer is C. An anticline has an upward, arching fold

Question 3 What type of fault forms when opposing forces cause rock to break and move horizontally? Normal Fault Reverse Fault Strike-Slip Fault

Answer The answer is C. A strike-slip fault is formed when opposing forces cause the rock to break and move horizontally.