Erosion and Deposition Changing the Earth’s Surface

Erosion and Deposition Erosion is the process of moving weathered rock and soil from one place to another Deposition is the process of dropping sediments in new locations, thus building new land forms

Changing the Earth’s Surface Weathering, erosion, and deposition form a cycle of forces that wear down and build up the Earth’s surface

Agents of Erosion The 5 main agents of erosion include Gravity Wind Running Water Glaciers Waves

Gravity Erosion When gravity alone causes materials to move downhill, it is called Mass Movement or mass wasting

4 Types of Mass Movement Creep and Slump are types of slow mass movements Landslides and mudflows are examples of rapid mass movements

Slump Loose material or rock layers slide down a slope as one large mass

Creep Sediments move downhill very slowly due to continual freezing and thawing - cause leaning fence posts and curved tree trunks

Rockslides and Landslides Talus - broken rock at the bottom of a cliff Frost action causes large blocks of rock to break loose from a steep slope and tumble quickly downhill

Mudflows A thick mixture of sediment and water break loose and flow down a slope Logan Mudflow Story

Mass Movement Slump, creep, rockslides, and mudflows all more likely to happen on steep slopes. They all depend on gravity! They usually occur after a heavy rain or in the spring because water adds weight and makes the sediment slick.

Glacial Erosion A slow moving mass of ice and snow is a glacier. Glaciers move because pressure from the layers above cause the bottom layer to partially melt. Gravity pulls the glacier downhill on this layer of water. (Ice skating!)

Types of Glaciers The two types of glaciers are continental and valley Greenland and Antarctica are the only continental glaciers left Valley glaciers are found in mountain regions all over the world. They begin at the top of the mountain where temperatures are always cold and it snows all year round. The ice gets so heavy that it begins to slowly move down the mountain.

How Glaciers Erode As glaciers move they push loose sediment out of their path. It is pushed in front, carried underneath, or piled up along the sides Plucking - picking up rock underneath and on the sides of the glacier Striations - Scratch marks that occur when glaciers move past rock.

Glacial Deposits Some glacial deposits include cirques, horns, till, outwash, moraines, drumlins, glacial lakes, and U-Shaped Valleys

Wind causes erosion by deflation and abrasion Wind Erosion Wind causes erosion by deflation and abrasion Deflation is when wind blows across loose sediments picking up light material and leaving the heavy stuff behind Abrasion is wind sandblasting

Wind deposition Wind deposits its sediment in a very fine powder called loess. Sometimes the loess builds up against an obstacle creating sand dunes

Have you heard of the Great Dust Bowl? In the 1930’s catastrophe hit the Farmers of the Great Plains. In 1932, crops withered and died in fields because of droughts. Then in the following years, drought , combined with severe dust storms passed over the Plains, turning them into a vast dust bowl.

Dust Bowl Dust from Texas coated the inside of houses in Chicago. Dust clouds from the Great Plains traveled as far east as the Atlantic coast. Farmers were ruined, and many lost their farms.

Water Erosion Water erosion occurs more frequently in places with lots of rain, steep slopes, and little vegetation. Water erodes more sediment than any other agent of erosion! Places with little plant growth have greater erosion because there are no plants to absorb the water and hold the soil in place

Types of Water Erosion The main types of water erosion are sheet erosion, rill erosion, gulley erosion, and river erosion

Sheet Erosion When a heavy rain is deposited on a flat area, the water builds up faster than it can seep into the ground. The sheet of water will move down a gentle slope. Removes thin layers of soil. Can go unnoticed for long periods of time, gradually removing the nutrients and organic matter from the soil.

Rill and Gulley Erosion A rill is a tiny stream formed from a heavy rain. If water continues to travel down the same rill, it can form a gulley

River Erosion Gullies widen to form streams which widen to form rivers Young rivers move quickly through a steep valley and often have rapids and waterfalls These rivers create V-Shaped valleys

River Erosion When a river matures, it begins to slow down and create bends called meanders

River Erosion

River Deposition Some river deposits include Alluvial fans, deltas, flood plains, levees, and oxbow lakes

Waves The powerful force of waves constantly erodes and shapes the shoreline

Wave Erosion Waves erode the shoreline by abrasion Water can dissolve the natural cement that holds rock together Wave erosion causes cliffs, sea stacks and sea caves

Wave Deposits Wave deposits sediments creating beaches, sand bars, and sand pits

How can Gravity drive the whole process of Erosion?

How can Human Activity be an agent of Erosion?

What can Humans do to decrease erosion? Plant vegetation Build terraces Don’t build on steep slopes Be careful