earth science

why are normal faults common along divergent boundaries?

a lot of tension is produced at divergent boundaries.

rift zone

a set of deep cracks that forms at a divergent boundary.

monocline

a type of fold. in a monocline, rock layers are folded so that both ends of the fold are horizontal.

syncline

a type of fold. in a syncline, the oldest rocks are found on the outside of the fold. most synclines are u-shaped

anticline

a type of fold. in an anticline, the youngest rocks are found on the outside of the fold. most anticlines are n-shaped

why does ocean crust far from a mid-ocean ridge subside?

as it cools, it becomes denser and sinks.

how do mountains form?

as tectonic plates move over earth's surface, the edges of the plates grind against each other. this produces a lot of stress in the earth's lithosphere. over very long periods of time, the movements of the plates can form mountains.

deform

change shape

(fact)

changes in the weight on the crust can also cause uplift or subsidence.

what kind of convergent boundary have the Andes mountains formed on?

continent-ocean

what are causes of subsidence and uplift?

temperature changes can cause uplift and subsidence. hot rocks are less dense than cold rocks with the same composition. therefore, as hot rocks cool, they may sink.

what kind of stress forms at fault-block mountains?

tension

stress

the amount of force per unit area that is placed on an object

fault

the crack that forms when rocks break and move past each other. the blocks of rock that are on either side of the fault are called fault blocks.

how is the hanging wall different from the footwall?

the hanging wall is above the fault and the footwall is below the fault.

what are the two types of vertical movements in the crust?

uplift and subsidence.

uplift

uplift happens when parts of earth's crust rise to higher elevations. rocks that are uplifted may or may not be deformed.

(fact)

volcanic mountains can form on land or on the ocean floor. volcanoes on the ocean floor can grow so tall that they rise above the surface of the ocean. these volcanoes form islands.

volcanic mountains

volcanic mountains form when melted rock erupts onto earth's surface. most major volcanic mountains are found at convergent boundaries.

footwall

when a fault forms at an angle, one fault block is called the footwall. the footwall is the fault block that is below the fault.

hanging wall

when a fault forms at an angle, one fault block is called the hanging wall. the hanging wall is the fault block that is above the fault.

(fact)

when crust is under tension, rocks are stretched.

rebound

when crust slowly rises back to its original elevation.

folding

when rock layers bend under stress

when do normal faults form?

when rocks are pulled apart.

when are reverse faults formed?

when rocks are pushed together.

when do strike-slip faults form?

when rocks slide past each other horizontally.

why does it take a very long time for most mountains to form?

most mountains are resolved off plate movements, since plates move very slowly, mountains form very slowly.

how do folds indicate that deformation has happened?

most rocks are horizontal when formed. they can show folded shapes only when deformed.

how can mountains form?

mountains can form in three ways: through folding, faulting, or volcanism.

(fact)

old, cold crust far away from a ridge has a lower elevation than young, hot crust at the ridge.

how can you figure out what kind of fault it is?

one way is to look at the rock layers around the fault.

tension

stress that pulls rock apart. therefore, normal faults are common along divergent boundaries, where earth's crust stretches.

shear stress

stress that pushes different parts of the rock in different directions. therefore, strike-slip faults are common along transform boundaries, where tectonic plates slide past each other.

compression

stress that pushes rock together. therefore, reverse faults are common at convergent boundaries, where plates collide.

subsidence

subsidence happens when parts of the crust sink to lower elevations. unlike some uplifted rocks, rocks that subside do not deform.

fault-block mountains

fault-block mountains form when tension makes the lithosphere break into many normal faults. along these faults, pieces of the lithosphere drop down compared with other pieces which produces fault-block mountains.

folded mountains

folded mountains form when rock layers are pushed upward. folded mountains usually form at convergent boundaries, where continents collide.

(fact)

if cold rocks are heated, they may rise.

normal fault

in a normal fault, the hanging wall moves down, or the footwall moves up, or both. normal faults form when rock is under tension.

reverse fault

in a reverse fault, the hanging wall moves up, or the footwall moves down, or both. reverse faults form when rock is under compression.

strike-slip fault

in a strike-slip fault, the fault blocks move past each other horizontally. strike-slip faults form when rock is under shear stress.