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 Sutty 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• Is 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.