Internal Forces that Shape the Earth (Plate Actions)

Plate Tectonics

• Continental Drift – plates move slowly across upper mantle

• “Pangaea” – supercontinent existed 250 million years ago

Divergent Boundary• Plates separate / spread apart

A. Mid ocean ridge• Two ocean plates separate

B. Rift Valley

• Two land plates separate

Convergent Boundaries• Plates collide

A. Mountains• Two land plates collide

B. Island Chains

• Two ocean plates collide

C. Ocean Trench and Mountains

• Land and ocean plates collide

Transform Boundary

• Two plates slide against each other

A. Fault

V. Earthquakes and volcanoes form along plate boundaries

External Forces that Shape the Earth

Weathering• The breaking down of rock into sediment

Physical Weathering

Chemical Weathering

Erosion

• The carrying away

of sediment

A. Water is the greatest agent of erosion

B. Wind

C. Glaciers / Ice

Landforms

1. Created by tectonic processes1. Mountains, valleys

2. Created by erosion1. Plateau, plains

3. Created by sediment deposition1. Sand dune, floodplain

Most regions have a combination of all three types

Example:

Mountain range formed by tectonic activity.

Erosion forms deep valleys between the mountains.

Sediment eroded from the mountains is deposited at the mountains’ bases.

Creates an alluvial fan.

Alluvial fan: fan-shaped deposit of mud and gravel often found at the base of mountains.

Stream erodes the sediment in the alluvial fan and carries them to a river mouth.

Sediment moves into the ocean and sinks, or it may accumulate and build a delta.