Movement of the Earth’s Movement of the Earth’s CrustCrust

Essential QuestionsEssential Questions

Describe how the Earth’s crust is deformed.Describe how the Earth’s crust is deformed.–How does the formation of mountains, valleys, plateaus, and domes relate to stress?–How do faulting and folding change the appearance of the Earth’s surface?

Define isostasy and explain its effect on the Define isostasy and explain its effect on the movement of the Earth’s crust.movement of the Earth’s crust.

How Does Earth’s Surface How Does Earth’s Surface Change?Change?

• Stress pushes and pulls on the Earth’s crust.

• The rocks slowly change shape and volume

• They move up or down or sideways• The breaking, folding or tilting of rocks is

called deformation.• 3 types of stress – compression, tension

and shearing.

What is Compression?What is Compression?

• Squeezes the rocks of the crust. Moves particles closer making rocks more dense.

• Rocks are pushed both higher up and deeper down.

What is Tension?What is Tension?

• Pulls on rocks of crust causing them to stretch out over a larger area.

• Becomes thinner in the middle

• Volume increases while density decreases

What is ShearingWhat is Shearing

• Pushes rocks of crust in 2 opposite directions.• Causes rocks to twist or tear.• Not compressed or stretched, just bent or

broken apart

What are the results of What are the results of compression, tension and compression, tension and

shearing?shearing?

• Change a rock’s volume, shape or both

• Can cause rocks to fracture, or crack

• Fractures along numerous flat surfaces which show no displacement are called joints. They are generally parallel to each other.

• If rocks have joints that form in more than one direction they may break into blocks.

What is FaultingWhat is Faulting

• A break or crack along which rocks move is called a fault.

• Rocks on one side of a fault slide past the rocks on the other side.

• Movement can be up, down or sideways.

• Earthquakes often occur along faults

What are the two blocks of rocks What are the two blocks of rocks that make up a fault?that make up a fault?

• Hanging wall – block of rock above the fault• Foot wall – block of rock below the fault

What are the types of faults?What are the types of faults?

• Normal fault – tension acts on a fault and the hanging wall moves down relative to the foot wall

Reverse FaultsReverse Faults

• Reverse fault – compression acts on a fault and the hanging wall moves up relative to the foot wall.

Thrust FaultsThrust Faults• Thrust fault – special type

of reverse fault where the hanging wall slides over the foot wall. The movements are almost horizontal where normal and regular reverse faults are mostly vertical. Thrust faults often cause older rocks to be above younger rocks.

• Lateral fault – shearing causes blocks of rock to slide horizontally past each other

What are faulted Mountains and What are faulted Mountains and Valleys?Valleys?

• Fault-block mountains – caused by blocks of rock uplifted by normal faults– Ex. Cordilleran mountain

region of North America. Extends from central Mexico to Oregon, and Idaho. Includes western Utah, Nevada and eastern California

• Rift valleys – formed when the block of land between 2 normal faults slides downward. – Ex. Death Valley in California

What is folding?What is folding?

• Fold – a bend in a rock.• Anticline – upward fold in

a rock• Syncline – downward fold

in a rock• Folds vary in sizes• Ex. Of folded mountains –

Appalachian mountains extend from Alabama to Canada

Why do some rocks fold and some Why do some rocks fold and some fault?fault?

• Temperature is one factor – hotter more likely to fold

• Pressure – greater pressure, more likely to fold• Rock type

– brittle – break when stress is applied – ductile – bend under stress

• Application of stress – if applied gradually the rocks will usually fold– if applied suddenly the rock will usually fault

What are plateaus?What are plateaus?

• Large area of flat land raised high above sea level, wider than it is tall, surrounded by steep cliffs

• Rock layers in a plateau remain flat• Formed by:

– a slow flat-topped fold, Ex. The Appalachian plateau which lies west of the Appalachian mountain.

– Vertical faulting, Ex. Colorado Plateau which lies west of the Rocky Mountains

– Series of molten rock flows, Ex. Columbia Plateau, in Oregon, Washington and Idaho

• Rivers often carve a plateau into many smaller plateaus. Ex. Colorado river carving the Colorado Plateau forms the Grand Canyon

What are Domes?What are Domes?

• Uplifted area created by rising magma. Magma pushed upward but does not reach the Earth’s surface. Stress causes the rock layers to fold upward. Eventually magma cools and forms hardened rock.

• When domes wear away they form many separate peaks called dome mountains. Ex. Black Hills of South Dakota and Wyoming

What is Isostasy?What is Isostasy?

• The balance of the downward force of the crust and the upward force of the mantle

• The more material that is added to an area of crust, the lower the crust floats on the mantle. The less material on the crust, the higher the crust will float on the mantle

• Examples of changes – melting glaciers removing weight from the crust – end

up floating higher– added mud and sand from river discharge causes

crust to float lower.

IsostasyIsostasy

http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/tectonics_landforms/folding.html

http://www2.nature.nps.gov/geology/usgsnps/deform/ghangft.html

http://library.thinkquest.org/17457/volcanoes/features.plateaus.php

http://www.lpi.usra.edu/science/treiman/greatdesert/workshop/volcanos2/index.html

http://www.collection.erdw.ethz.ch/index_en.cfm?content=english/ausstellung/geologie_palaeontologie/gesteinsdeformationen.htm&m=223

http://www.eos.ubc.ca/~ehearn/research2.html

CreditsCredits

http://wapi.isu.edu/envgeo/EG5_earthqks/eg_mod5.htm

http://www.consrv.ca.gov/CGS/information/publications/teacher_features/faults.htm

http://www.geo.cornell.edu/geology/classes/RWA/GS_326/326_Gallery.html

http://www.geol.lsu.edu/henry/Geology3041/lectures/21MetamorphicIntro/MetamorphicIntro.htm