Movement of the Earth’s Crust

Dynamic Earth

Chapter 1

Mr. McKay

Earth’s Changing Surface

Stress in the Earth’s crust is caused by forces pushing and pulling on it

Crust: the surface or outermost layer of the Earth Continental crust makes up the

land masses Between 32 to up to 70 km thick

Oceanic crust lies beneath the oceans

Around 8 km thick

How do we know about the interior of the Earth?

Convection Currents in the Mantle

Types of Stress The forces of stress change the shape and volume of

the crust and can cause it to move Deformation: The Breaking, Tilting, and Folding of rocks Prefix de = undo Form = shape or configuration

Compression Compression

occurs when the rocks are pushed together Causes the rocks

to become denser and smaller in volume

Rocks are pushed higher up and deeper down

Tension Tension pulls on

the rocks causing them to stretch out This causes the

rocks to be thinner so they increase in volume but decreases in density

Shearing

Shearing pushes the rocks in opposite directions Causes the rocks to twist or

break apart Examples of deformation

San Andreas Fault

Earth's Landmass Formation

Fracture: the cracking or rocks from stress Where rocks fracture along

flat surfaces without moving they are called joints

Blocks form where the different sets of joints cross one another

Faulting Fault: a break or

crack along which rocks move

Hanging wall: the block of rock above the fault plane

Foot wall: the block of rock below the fault plane

Faulting Lecture Faulting Demonstrati

on

Normal Fault Normal Fault: when tension causes the hanging

wall to move down to the foot wall Vertical fault

Reverse Faults Reverse fault: when compression causes the the hanging wall to move up relative to the foot wall Vertical fault

This fault has the same setup as a normal fault, but reversed, which explains it’s nameJust like the normal fault, one side of the reverse fault is at an angle of the otherThis fault produced part of the Appalachian Mountains in the eastern United States

Thrust Faults Thrust fault: when

compression causes the hanging wall to slide over the foot wall Horizontal fault Mixes up the layers

of rock and carries them miles away from their original home

Lateral (Strike-Slip) Fault One block moves to the right or left in relation to

the other block Horizontal movement Shearing

Faulted Mountains Fault-Block Mountains:

mountains formed by blocks of rock uplifted by normal faults Several normal faults in one

area can cause mountain ranges

Found along the west coast from Mexico into Oregon

How Do Mountains Form?

The forces of plate movement can build up Earth's surface, so over millions of years, movement of faults can change a perfectly flat plain into a gigantic mountain rangeSometimes, a normal fault uplifts a block of rock, so a fault-block mountain formsWhen a piece of rock between two normal faults slips down, a valley is createdMountain FormationMountain Animation

Mountains Formed by Folding

Sometimes, under current conditions, plate movement causes the crust to foldFolds are bends in rock that form when compression shortens and thickens part of Earth's crust

Folds can be microscopic or huge The Appalachian Mountains

are formed from folds Some folds are hidden

underneath other layers of rocks, hills, etc.

These plate collisions can produce earthquakes because rock folding can fracture and lead to faults

Anticlines and Synclines   Geologists use the terms syncline and anticline to describe downward and upward folds in rock An anticline is a fold in a rock that arcs upward A syncline is a fold in a rock that arcs downwardThese folds in rocks are found on many parts of the earths surface where compression forces have folded the crust

What determines faulting or folding? Temperature: higher temps during compression

result in folding rather than faulting Pressure: the higher the pressure the more likely

they are to fold Rock Type: brittle versus ductile (able to be

stretched or bend) How the Stress is Applied: the more gradually

stress is applied the more likely the rocks will fold

Faulted Valleys Rift Valleys: valleys

formed when the block of land between two normal faults slides downward. Death Valley, CA

PlateausThe forces that elevate mountains can also raise plateaus, a large area of flat land elevated high above sea level Some form when a vertical fault pushes up a large flat piece of rockLike a lasagna, a plateau consists of many layers, so it is wider than it is tall

May be formed by: a flat-topped fold vertical faulting a series of molten

rock flows Magma reaches the

surface through cracks in the ground

Domes Dome: uplifted area

created by rising magma The magma underneath

doesn’t rise to the surface but pushes the layers of rock above up

Black Hills, SD

The Floating Crust

Mantle: layer of the Earth beneath the crust 2900 km thick Made up very dense

flowing rock The less dense crust floats

on top Isostasy: The balance

between the downward force of the crust and the upward force of the mantle

If material is lost or added to the crust it will float higher or lower in the mantle allowing the crust to rise or sink in areas In northern areas where massive

amounts of ice have thawed the crust has risen due to a loss in material

Think about Antarctica The Mississippi river basin has

dumped millions of tons of mud into the Gulf of Mexico but instead of piling up the weight has caused the crust to sink so the depth of the water has not changed