Chapter 10 The Movement of the Earth’s Crust

Chapter 10 The Movement of the Earth’s

Crust

THE FORCES WITHIN THE

EARTH PUSH AND PULL ON THE

EARTH’S CRUST.

Think back to Section 9.3The Earth’s

Crust

The Earth’s Crust:

Continental Crust

Oceanic Crust.

Continental Crust av. 32 km

Oceanic Crust av. 8 km

The Earth’s crust moves as a result of the stress or forces within the Earth.

Which brings us toChapter 10

The Movement of the Earth’s Crust

Stressare forces that push and pull on the Earth’s crust causing it to undergo deformation.

As rocks under go

stress

They slowly change

shape and volume

Also, they move up

and down

The movement causes the

rocks to break, tilt, and fold.

Deformation is the

breaking, tilting, and folding of

rock.

StressCauses rocks to slowly

change shape and volume.

3 Types of Stress

Compression Tension Shearing

Compression

Tension

Shearing

Compression, tension, and shearing of rocks

can cause the rocks to

Fracture or crack.

Fault

Break or crack along which rocks move

Large faults within the Earth’s crust result from the movement of tectonic plates

A Normal Fault occurs when tension or pulling apart acts on a fault. The hanging wall will move down

relative to the foot wall.

Tension

A Reverse Fault occurs when compression or pulling apart acts on a fault causing the hanging wall to

move up relative to the foot wall.

Compression

Thrust Fault is a special type of reverse fault that is formed when compression causes the hanging wall to

slide over the foot wall.

A lateral fault occurs when shearing acts on a fault which causes blocks of rock to slide horizontally past each other left or right.

Shearing

Fault-block mountains are formed by blocks of rock uplifted by 2 normal faults.

Example: Cordilleran Mountains in Western USA

Fault Block Mountain

Rift Valleys

are formed by 2 normal faults sliding down

Example: Death Valley, California USA

Nearly five and a half million years ago, what we today call Baja California used to be part of the Mexican mainland, and then it began pulling away as tectonic forces underneath split the land apart. Now, Baja California is slowly moving northwest. Some geology experts say that the northernmost extension of this rift, or tear, is the area we call Death Valley, while others claim it to be in the Salton Sea. There is even some plausible scientific evidence to support the idea that this tearing of the land could extend as far north as southern Oregon. There are those who refer to this phenomenon as the Baja Rift.

A fold is a bend in rock.

Anticline is an upward fold.

Syncline is a downward fold.

Factors that will determine whether rocks will fault or

fold

Temperature•Hotter: Folds

Pressure•Greater: Fold

Rock type•Brittle: Fault•Ductile: Fold

How Stress Applied•Gradually: Fold•Suddenly: Fault

Plateau may be formed by:

Slow flat topped fold

Appalachian Plateau

Vertical faulting

Colorado Plateau

Molten lava flows on surface of Earth

layer by layer

Rivers often carve a large plateau into

smaller plateaus

Grand Canyon in Colorado

Plateau

Vertical Fault

Plateau

Plateau: Top of Volcano

Grand Canyon in Colorado Plateau

Magma – molten rock beneath the Earth’s Surface

Lava - molten rock beneath the Earth’s Surface

Dome – oval or circular uplift by rising magma, fluid collects beneath the surface and pushes up like a blister

Dome Mountains – domes that have been worn away in some places leaving separate peaks