Deforming the Earth’s Deforming the Earth’s CrustCrust

Faults and FoldsFaults and FoldsChapter 7 Section 4Chapter 7 Section 4

Deformation• The process by which the shape of a

rock changes because of stress.• There are two types of stress that

occur in rocks:• Compression• Tension

Compression • Compression occurs when rock

is squeezed.

• Compression happens when two plates collide at a convergent boundary.

• Compression occurs and forms large mountain ranges.

Compression/ Mountain BuildingCompression/ Mountain BuildingThe Himalayas, for example, were raised by the compression that accompanied collision of the Indian plate with the Eurasian plate. Another example is Europe's Alps and Jura mountains which were also formed by horizontal compression, generated in their case by collision with the African plate and the Eurasian plate.

TensionTension• Tension occurs when an Tension occurs when an object is stretchedobject is stretched..• Tension Tension occurs when plates move away fromoccurs when plates move away from

each othereach other at plate boundaries. at plate boundaries.• At the Mid-Atlantic ridge the seafloor is At the Mid-Atlantic ridge the seafloor is

spreading at a rate of about 3cm per year. spreading at a rate of about 3cm per year. The frequency of earthquakes at a mid-The frequency of earthquakes at a mid-ocean ridge will depend on how much ocean ridge will depend on how much tension is happening at that point. The more tension is happening at that point. The more tension means the more seafloor spreading, tension means the more seafloor spreading, resulting in a higher frequency of resulting in a higher frequency of earthquakes at a particular mid-ocean ridge. earthquakes at a particular mid-ocean ridge.

FoldingFolding Folding is the Folding is the bending of rock layers bending of rock layers

due todue to stressstress in the Earth’s crust. in the Earth’s crust. Depending on how rock layers Depending on how rock layers

deform, different deform, different types of foldstypes of folds occur:occur:

AnticlineAnticline SynclineSyncline MonoclineMonocline

Anticline

• An anticline is an upward-arching fold.• An anticline is formed when there is

horizontal stress on rock layers.

Horizontal stress

Syncline

• Synclines are downward folds.• They are also caused by horizontal stress.

Horizontal Stress

Monocline

• Monoclines are rock layers that are folded so that both ends of the fold are horizontal.

Faults• Some rock layers break when stress is

applied to them.• The surface along which rocks break

is called a fault.• The blocks of crust on each side of the

fault are called fault blocks.• A fault has a foot wall and a hanging

wall.

FootwallFootwall

Footwall

You could walk up this face of the fault, on foot, hence the name footwall.

Hanging WallHanging Wall You could hang from this wall.You could hang from this wall.

Hanging Wall

This is a normal fault. Notice how the rock layers are the same at the red lines.

Hanging wall and FootwallHanging wall and Footwall

3 Types of Faults• Normal Fault• Reverse Fault• Slip-Strike Fault

Normal Fault

• Rocks are pulled apart because of tension.

In a normal Fault, the hanging wall slides down the footwall.

FootwallHanging wall

Reverse Fault

In a reverse fault the hanging wall is pushed upward due to compression.

Strike-Slip Fault

Opposing forces cause rocks to move horizontally. Earthquakes occur along these faults.

San Andreas Fault, CaliforniaStrike-Slip Fault

3 Most Common Types of Mountains

• Mountains exist because tectonic plates are continually moving around and colliding with each other.

• There are 3 types of mountains, named for how they form:

• Folded Mountains• Fault-Block Mountain• Volcanic Mountain

Folded Mountains• Folding is a process in which the Earth's plates are pushed

together in a roller coaster like series of high points and low points. Folding bends many layers of rocks without breaking them. The Appalachian Mountains and Rocky Mountains of the United States, and the Alps of Europe are examples of mountain ranges that were formed by folding. Folded Strata (Layers)

Fault- Block Mountains• Mountains sometimes form when many layers of the Earth's crust are

moved vertically upward at fault lines by pressures caused by plates colliding. Fault lines are great cracks in the crust. The mountains that are formed in this way are called fault-block mountains. The Sierra Nevada mountains in California and Nevada, and the Grand Teton range of Wyoming are examples of fault-block mountains.

Fault block mountains form when tension causes large blocks of crust to drop down relative to other blocks.

Volcanic Mountains

• Volcanic mountains are forms when magma erupts from a divergent boundary and hardens.

• Many volcanic mountains exist under the sea.

• Some volcanic mountains rise above the surface of the ocean to from islands, Hawaii for example.

Hawaiian Islands