Movement Of The Earth’S Crust

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 San Andreas Fault in California

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 Demonstration

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 name Just like the normal fault, one side of the reverse fault is at an angle of the other This 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 range Sometimes, a normal fault uplifts a block of rock, so a fault-block mountain forms When a piece of rock between two normal faults slips down, a valley is created Mountain Formation Mountain Animation

Mountains Formed by Folding Sometimes, under current conditions, plate movement causes the crust to fold Folds 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 downward These 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

Plateaus The 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 rock Like 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

Movement Of The Earth’S Crust

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