Chapter 7 - Erosional Forces

Earth’s Erosional ProcessCh 7

7.1 GravityErosion and Deposition

Erosion - the movement of material from one location to another Agents of erosion are: gravity, glaciers, wind and water.

Deposition – the dropping of sediments or depositing of them.

7.1 GravityI. The 4 agents that cause erosion:

1. Gravity

2. Glaciers

3. Wind

4. Running Water

II. 3 things these agents of erosion have in common:1. All wear away materials and carry them off.2. They erode only when they have energy of motion. (Kinetic)3. They drop their load of sediments when energy decreases.

• Mass Movement – movement of material down slope• Slump – loose material of rock layers slip down a

slope.

Major cause:heavy rains or earthquakes loosen weak materials.

Creep – sediments slowly inch their way down slope, notice telephone poles

Landslides

La Conchita, California.

What started as a crack – Ended?

Rockslides – large blocks of rock break away, tumbling down the slope.

Major cause: freezing/thawing.

Major cause: ice wedging, heavy rains, earthquakes.

Mudflows – thick mixture of sediments and water flowing down slope.

Major cause: heavy rains.

4. Four characteristics all mass movements have in common:1. More likely to happen on steep slopes.2. All depend on gravity.3. Often occur after heavy rain.4. Make slopes less steep.

7.3 Glaciers

Continental glaciers are huge masses of ice & snow that cover entire continents.

Greenland Antarctica

Valley glaciers are ‘rivers’ of ice that occur high in the mountains. They are found in Canada, the Alps, & the Himalayas.

Ice ages – periods when glaciers cover much of the land. The last one began 2-3mya- ended about 20,000ya.

Only about 10 % of earth is covered by glaciers today.

Glaciers erode by abrading (scraping), and plucking: carrying off rock fragments frozen in the bottom of the glacier.

Glaciers create and by dragging large rock fragments that gouge the bedrock.

indicate the direction the glacier moved.

Cirque – bowl-shaped basins in the sides of mountains.

cirque

Arête – a ridge carved by 2 glaciers.

Arête

Horn – a sharpened peak carved by 3 or more glaciers.

Horn

U-shaped valley – erosion from sides and bottom.

U-shaped valley

Till – mixture of different sized sediments.

Till

Moraine – a ridge of till.

Moraine

Moraine

Outwash – sediments deposited by glacial meltwater.

Outwash

– large chunks of ice that break loose from continental glaciers.

Each year in the North Atlantic about 16,000 icebergs break loose from glaciers.

More than of Earth’s fresh water is locked up in glacial ice.

Wind 7.4

1. Deflation-wind removes fine sediments, leaves heavy ones behind.

Desert Pavement

Abrasion-windblown sand strikes rocks breaking off fragments. This is similar to sandblasting.

2. Sand storms-wind blows sand with great force. Sand grains bounce along and collide with other sand grains, causing more to rise into the air. They seldom bounce higher than ½ meter from the ground. This occurs most often in deserts, beaches, and dry riverbeds.

Dust storms-fine soil particles weigh less than sand, wind can pick them up and blow them high into the atmosphere. The storms blow topsoil from open fields, overgrazed areas.

3. Windbreaks-farmers plant trees as windbreaks to prevent soil erosion. As the wind hits the trees, its energy of motion is reduced and it cannot lift particles.

4. Grasses are the best vegetation to plant to stop wind erosion because they have a fibrous root system that holds soil in place.

5. Loess-large deposits of fine windblown sediments (like talcum powder). Many farmlands in the mid-western U.S. are on fertile soils that have evolved from loess deposits.

6. Sand dunes are mounds of sand drifted by the wind