2. Erosion Or... How to make molehills out of mountains.

3. What is Erosion? Weathered rock particles (sediments) are transported through the process of erosion. Any process that moves sediments from one place to another is called erosion. Over time, erosion shapes and lowers Earth’s surface.

4. Transporting Systems of Erosion Several components: An agent of erosion such as: moving water, wind, ice, or human activity. The sediments being moved. A driving force.

5. THE DRIVING FORCE GRAVITY –Usually works together with water, wind or ice to move sediments. –Can work on its own.

6. Mass Movements (Wasting) Slow mass wasting Soil creep

8. Rapid mass wasting Rockfalls

10. Landslides

11. Mudflow

12. Slump

13. Running Water Most common agent of erosion –Runoff Temporary – can carve out rills or gullies –Streams and rivers Permanent – confined to a channel

14. Streams and Rivers Carry sediments in different ways –Solution – dissolved minerals –Suspension – silts and clays –Bedload – largest sediments slide, roll, or bounce along bottom

15. Deposition and Sorting A stream looses velocity when entering quiet waters so its ability to transport sediment decreases. Particles drop to the bottom. This is deposition. Large particles settle first. Other particles settle according to size. Smallest particles (clay) drift the farthest and settle last. This is sorting. Boulders Cobbles Pebbles Sand Silt Clay

16. Rounded Sediments from Abrasion

17. Landforms YOUNG rivers create V-shaped valleys –Most energy expended in downcutting –Valley slope quite steep –River gradient can also be quite steep

18. MATURE rivers broaden their valleys. –More energy expended sideways –Valley slopes less steep –River gradient not as steep

19. Rivers in OLD AGE have very broad valleys –Most energy expended sideways –Has many meanders –River gradient almost flat

20. Erosion can create spectacular scenery. Crustal uplift and river erosion created the Grand Canyon over millions of years.

21. Watershed or Drainage Area Often, rivers are fed by many tributaries over a large area. This is called a watershed.

22. The largest in the U.S. is the Mississippi River watershed. It drains 42% of the lower 48 states.

23. The lower Mississippi River has a very broad valley with many meanders. Here, it is a river in old age.

24. Imagine trying to pilot a river boat through all of the meanders.

25. Oxbow Lakes Meanders are often cut off when a river floods. When this happens an oxbow lake is created.

26. Where Erosion and Deposition Occur

27. Flood Plain Rivers with broad valleys are prone to flooding. During flooding a river overflows its banks into the wider valley and deposits sediments forming a flood plain. Farmers often locate on flood plains because they have fertile soil for growing crops.

28. During times of severe flooding there is much property damage. Sometimes at a cost of many billions of dollars.

29. Delta Where a river enters a quiet body of water its transported sediments deposit at the mouth. This is called a delta.

30. River areas are diverse ecosystems that are inhabited by many species of wildlife.