Chapter 7.1

1. Chapter 7.1 Erosion and Deposition Changing Earth’s Surface

2. Erosion • The process by which natural forces move weathered rock and soil from one place to another.

3. Sediment • This is the material moved by erosion. • Sediment may consist of pieces of rock or soil or the remains of plants and animals. • Both weathering and erosion produce sediment.

4. Deposition • Deposition occurs where the agents of erosion deposit (or lay down) the sediment. • Deposition changes the shape of the land.

5. Weathering, erosion, and deposition act together in a cycle to wear down and build up Earth’s surface. • Erosion and deposition are at work everywhere on Earth.

6. Gravity • Gravity is the force that moves rocks and other materials downhill. • Gravity causes Mass Movement. • Types of mass movement include: • Landslides • Mudflows • Slumps • Creep

7. Landslides • This is the most destructive of mass movement. • Landslides occur when rock and soil slide quickly down a steep slope.

8. Mudflows • This 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%. • Mudflows often occur after heavy rains in a normally dry area. • They can be very dangerous.

9. Slump • In a slump, a mass of rock and soil suddenly slips down a slope. • The material in a slump moves down in one large mass. • It often occurs when water soaks the bottom of soil that is rich in clay.

10. Creep • Creep is the very slow movement downhill of rock and soil. • Creep is so slow that you can barely notice it.

11. Section 7.2 • Water Erosion

12. Moving water is the major agent of the erosion that has shaped Earth’s land surface.

13. Runoff • As water moves over the land, it carries particles with it. • The moving water is called runoff. • Runoff is the water that moves over Earth’s surface.

14. Rills and Gullies • As runoff travels, it forms tiny grooves in the soil called rills. • As a rill moves into another, they grow larger, forming gullies. • As water flows through gullies, it moves rocks and soil with it. This enlarges the gullies through erosion. • Gullies contain water only after it rains.

15. Streams and Rivers • Gullies join together to form a larger channel called a stream. • A stream is a channel along which water is continually flowing down a slope. • Small streams are also called creeks or brooks. • As streams flow together, they form larger and larger bodies of flowing water. • A large stream is often called a river.

16. Erosion by Rivers • As a river flows from the mountains to the sea it can form a variety of features: • Valleys • Waterfalls • Flood plains • Meanders • Oxbow lakes

17. Waterfalls • As a river moves over harder rock, the softer rock moves away. The hard rock erodes slowly. • The area where the softer rock has moved away creates a waterfall. • Areas of rough water called rapids occurs where a river tumbles over hard rock.

18. Flood Plain • Lower down on its course, a river usually flows over more gently sloping land. • The river spreads out and erodes the land, forming a wide river valley. • A flat, wide area along a river is called a flood plain. It can often overflow its banks during a flood.

19. Meanders • A river often develops meanders where it flows through easily eroded rock or sediment. • A meander is a loop-like bend in the course of a river.

20. Oxbow Lake • Sometimes a meandering river sometimes forms a feature called an oxbow lake. • An oxbow lake is a meander that has been cut off from the river…often due to floods.

21. Deposits by Rivers • As water moves it carries sediment with it. • It will then drop (or deposit) some of the sediment. • As the water slows down, fine particles fall to the river bed. Larger stones quit rolling and sliding. This can create: • Alluvial fans • Deltas

22. Alluvial Fans • An alluvial fan is a wide, sloping deposit of sediment formed where a stream leaves a mountain range. • This deposit of sediment is shaped like a fan.

23. Deltas • Sediment that deposits where a river flows into an ocean or lake builds up a landform called a Delta

24. Groundwater Erosion • Sometimes water will soak through the ground. • It fills the openings in the soil and trickles into cracks and spaces in layers of rock. • Groundwater is the term that geologists use for this underground water.

25. Cave Formations • Inside limestone caves, deposits called stalactites and stalagmites often form. • A deposit that hangs like and icicle from the roof of a cave is know as a stalactite. • Slow dripping builds up a cone-shaped stalagmite from the cave floor.

26. Karst Topography • If the roof of a cave collapses because of the erosion of underlying limestone, the result is a depression called a sinkhole. This type of landscape is called karst topography after a region in Eastern Europe.