Weathering, Erosion & Soil

External Forces that Shape Earth: Weathering

• Weathering: processes that change the characteristics of rock

• Creates sediment, or small pieces of rock (mud, sand, silt)

Sandstone hills on the Utah-Arizona border

Types of Weathering

Mechanical• Changes SIZE or SHAPE• Ex. Rocks splitting due to

ice or tree roots

Chemical• Changes COMPOSITION• Ex. Iron rusting, damage

caused by acid rain

External Forces: Erosion• Material is moved by wind, water, ice or

gravity• Reshapes landforms, coastal regions and rivers

Water Erosion

• Can be vertical or horizontal- streams can become deeper & wider

• Creates V-shaped valleys• When a river empties

into an ocean, it deposits sediment in a fan-like landform called a delta

• Examples: waves changing the coastline, Grand Canyon

Nile River Delta

Wind Erosion• Dust storms can carry

6,000 tons of sediment per cubic mile of air

• May produce new landforms

• Loess- wind blown silt & clay sediment that becomes fertile soil

Arizona

Glacier: large, long-lasting mass of ice that moves due to gravity

Glacial Erosion

• Glaciation is the changing of landforms due to glaciers

• Creates U-shaped valleys

Rocks left behind by a glacier may form a ridge or hill called a moraine

Building Soil

• Weathering & erosion help form soil

• Soil: mixture of weathered rock, organic matter (humus), air and water

• Soils and climate determine what types of vegetation can grow in a location