External Forces That Shape the Earth

Weathering

Weathering refers to physical or chemical processes that change the characteristics of rocks.

Sediment is produced by weathering and

is identified as mud, sand or silt.

Mechanical Weathering

• Mechanical Weathering only changes the size of the rock.

Chemical Weathering

• Chemical Weathering occurs when a rock is changed into a new substance as a result of an interaction between elements in the air or water and minerals in the rock.

Erosion

• Erosion occurs when weathered material is moved by action of the wind, water, ice or gravity.

• These actions work by grinding rock into smaller pieces.

Water Erosion

• Water erosion occurs as stream and rivers flow carrying loose material downstream.

• Abrasion can be caused by transported particles.

• The water can dissolve chemical elements in the rock causing the composition of the rock to change.

Water Erosion

Deltas

• Deltas are created as sediment from rivers are deposited in a fan shaped pattern at the ocean.

Wind Erosion

• Wind Erosion is similar to water erosion except the wind carries and deposits the sediment.

Loess Deposits

• Loess (LOH uhs) is wind blown silt and clay sediment. In China deposits are several hundred feet deep.

Glacial Erosion

• A glacier is a long-lasting mass of ice that moves because of gravity.

• Glaciation is the changing of landforms by glaciers.

• Massive glaciers also cut U-shaped valleys in the land.

Moraine

• Glaciers carry rocks and when the glacier melts these rocks are left behind. Often these rocks create hills or ridges called a moraine.

Building Soil

• Weathering and erosion are a part of the process of building soil.

• Soil is a mix of weathered rock, organic matter (humus), air and water that supports plant growth.

• Organic matter supports the growth of plants by supplying food.

• Water and air share pores in the soil.

Soil Factors

• Geographers study soil by looking at 5 factors.

• Parent material is the composition of the original rock.

• Relief-steeper slopes erode more easily but does not produce soil quickly.

• Climate- Hot climate produce a different soil than cold, wet different than dry.

• Organisms include plants, small animals like worms, ants and bacteria that decompose material. Help to loosen soil.

• Time- The amount varies but a rough average would be 2.5 cubic centimeters per century.