Chp 8.2 Erosion and Deposition

1. Chp 8.2 Erosion and Deposition

2. The Geologic Cycle • Erosion is the process by which natural forces move weathered rock and soil from one place to another. • The material moved by erosion is sediment. • When the agents of erosion lay down sediment, deposition occurs. 5 Agents of Erosion Gravity Running water Waves Rain Glaciers Wind

3. Agent # 1: Gravity- Mass Wasting • Mass wasting: • Is a form of erosion caused mainly by gravity. • Commonly occurs when the ground becomes soaked with rainwater. • When the weight becomes too great, the mass of soil will begin to slide. • Can occur from vibration from earthquakes, heavy machinery, blasting

4. Landslides • mass wasting that occurs when rock and soil slide rapidly down a steep slope. Mudslides / Mudflows • A mudflow is the rapid downhill movement of a mixture of water, rock, and soil. The amount of water in a mudflow can be as high as 60 percent. Slump & Soil Creep • A slump is a type of mass movement in which a mass of rock and soil rapidly slips down a slope. It looks as if someone pulled the bottom out from under part of the slope. • Creep is the very slow downhill movement of rock and soil. It occurs most often on gentle slopes.

5. Agent #2: Running Water • Precipitation can do any of 3 things: • Evaporate or Soak-in or RUN OFF ! • Water running downhill is the major agent of erosion that has shaped Earth's land surface. • Amount of runoff affected by: • Amount of Rainfall, Plant Population, Shape of the land, Soil saturation

6. Climate & Erosion • Areas that receive large amounts of precipitations, are more likely to experience mass wasting. • Also there is more vegetation • Prevent landslides because the roots of plants help to hold sediments in place.

7. Water & Erosion • Stages of Stream Development • Rivers change as water moves from the mountains down to lakes or oceans. • Steep slopes allow the water to flow downhill rapidly. • Development of Meanders • Meanders are curves in the stream. • The curves tends to become wider and wider. • Deposition occurs inside the meander. • Erosion occurs outside of the meander.

8. Stream Development

9. Flooding • Occurs when the water level in a river rises above the usual height and overflows the sides of its banks. • Floodplain • Is a wide, flat valley that is located along the sides of some rivers and streams.

10. Agent #3: Waves • Waves shape the coast through erosion by breaking down rock and transporting sand and other sediment. • Beach: is a landform consisting of loose sand and gravel. • Cliff: formed by the cutting action of waves at the base of rocks that are exposed along the coasts. • When large waves hit the shore, their energy can break apart rocks.

11. The LongshoreCurren • Waves come in at an angle. • The waves bend until they are approximately parallel to the coast. • They retreat from the beach perpendicular to the shore. • Most great amount of sediment along coasts.

12. Agent #4: Wind Erosion • Wind is the weakest agent of erosion. • Sand dunes: when heavier sediments that blows along the ground surface and it is pushed into piles. • Loess: windblown silt that was carried in the air.

13. Agent #5: Glaciers • Glaciers: large masses of ice and snow, moving 2.5 cm per day. • There are two kinds of glaciers continental glaciers and valley glaciers. • Plucking - As a glacier flows over the land, it picks up & pushes rocks along w/ it. • The rocks trapped under the glacier create scratches. • Till: builds along the sides and fronts of glaciers called moraines. • Outwash: consists mostly of sand and gravel. • Continental Glaciers • Today, found only on Antarctica & Greenland • Covered most of North America & Europe during past Ice Ages • Able to flow in all directions. Valley Glaciers When a glacier melts, it deposits the sediment it eroded from the land, creating various landforms. The mixture of sediments that a glacier deposits directly on the surface is called till.