Chapter 1

Movement of the Earth’s Crust

Earth’s Changing Surfaces

• Crust- is the surface, or outermost, layer of the Earth.

• Two types

– Continental crust

• Makes up earths landmasses

• About 32 kilometers thick in most places

• Under mountains can be up to 72 kilometers thick

Two types continue

• Oceanic crust

– Found under the ocean floor

– Usually about 8 kilometers thick

Stress on Crust

• As the rocks of the crust undergo stress, they slowly change shape and volume.

• Rocks will move up, down, or sideways

– Movement causes the rocks to break, tilt, and fold

Deformation

• Deformation- the breaking, tilting, and folding of rocks.

• Three basic types

– Compression- squeezes the rocks of the crust

• This causes the rocks to move closer together

• Makes the rocks denser and smaller in volume

• Pushes the rock higher up and deeper down

• Examples- trash compactor, squeezing clay in your hands

Basic types

• Tension- pulls on the rocks of the crust, causing them to stretch out over time.

– Rock under tension becomes thinner in the middle than at the ends.

– Volume of the rock increases, its density decreases.

– Examples- taffy being pulled, silly putty being pulled between your fingers.

Basic types

• Shearing- pushes rocks of the crust in two opposite directions.

– Causes rocks to twist or tear apart

– They bend or break apart

– Examples- rubbing two pieces of limestone together

Faulting

• Fault- a break or crack along which rocks move

– Movements along a fault can be up, down, or sideways

– Earthquakes often occur along faults

– Hanging wall- the block of rock above the fault

– Foot wall- the block of rock below the fault

Two types of Faults

• Normal fault- if tension is acting on a fault, the hanging wall will move down relative to the footwall.

• Reverse fault- if compression is acting on a fault, the hanging wall will move up relative to the footwall.

– Thrust fault- is formed when compression causes the hanging wall to slide over the foot wall.

• usually mixes up the order of the layers in rock

Faulted Mountains and Valleys

• Fault-block mountains- mountains formed by blocks of rocks uplifted by normal faults.

• Rift valleys- valleys are formed when the block of land between two normal faults slides downward.

Folding

• Fold- a bend in a rock ( like a rug sliding across the floor).

• Two types of folds

Anticlines

• Anticlines- the upward fold in a rock

• This is how the Appalachian Mountains are formed

• Is not always higher than the surrounding area

• Anticlines can be under hills, valleys, or flat areas.

Syncline

• Syncline- a downward fold in a rock

Difference between Fault or Fold

• Four factors that determine if a rock will fold or fault.

– Temperature

– Pressure

– Rock type

– Stress

Plateaus

• Plateaus- is a large area of flat land that is raised high above sea level

Domes

• Domes- uplifted area created by rising magma

• Formed when fluid collects beneath the surface and pushes up on overlaying layers, forming a raised spot in the immediate area but leaving the surrounding regions flat and undisturbed.

Floating Crust

• In the mantle the rock flows slowly (like molasses). Because the mantle is much denser than the crust, the solid, rocky crust floats on the mantle.

• The floating crust exerts a downward force on the mantle, and the mantle exerts an upward force on the crust.

– Isostasy- the balancing of the downward force of the crust and the upward force of the mantle.

• Rising of landmasses

– Examples- Norway, Sweden, and Finland have increased in elevation over a period of time.

• Sinking of landmasses

– Mississippi river has deposited millions of tons of mud and sand in the Gulf of Mexico and the water level has remained the same.