Erosional Forces

1. Erosional Forces

2. Erosion • Wearing away of surface materials by gravity, water, wind, or glaciers. • Deposition- process where sediments are dropped by erosion agents as they lose energy.

3. Mass movement occurs as gravity moves materials down a slope as one large mass. • Examples: Slumping, Creeping, Rock Falls/Slides, & Mudflows • Steep slopes can be made safer with vegetation, drainage pipes, and walls of concrete or railroad ties.

4. Glaciers • Large masses of ice and snow that slowly move on land causing erosion. • Plucking- erosion process caused by moving glaciers picking up boulders, gravel, & sand. • Scour & scrape the soil and bedrock. • Grooves & striations indicate the direction a glacier moved.

5. Glaciers deposit a mixture of different sized sediments (till) when they retreat. • Moraine- a ridge, or pile, of deposit left at the end of a glacier. • Outwash- material deposited in layers by the meltwater of a glacier, with largest pieces closer to the glacier.. • Eskers – outwash deposit formed as meltwater rivers within the ice deposit sand & gravel within their channels.

6. Zone of Accumulation Snowline Crevasses Zone of Wastage

7. Types of Glaciers • Continental Glaciers-huge masses of ice and snow that cover large areas of land. • Covers 10% of Earth near the poles. (Antarctica & Greenland) • Ice Ages - periods of widespread glaciation over the last 2 to 3 million yrs. • Thicker than some mountain ranges.

9. Valley Glaciers- exist in mountain ranges. • Cirques- bowl-shaped basins in the sides of mountains. • Arête- a long ridge that forms when two valley glaciers erode a mountain side-by-side. • Peaks- form when valley glaciers erode a mountain from several directions. • Valleys formed by glaciers are “U” shaped

11. Wind • Scatters dust or volcanic ash over thousands of kilometers. • Deflation- wind removes small particles of loose sediment, leaving behind heavier materials. • Abrasion- wind behaves like a sandblaster blowing sand grains against rocks wearing them down. The

12. Windbreaks – rows of trees planted to slow down wind in order to reduce erosion. • Dunes – mounds of sediment drifted by wind.

13. Water Erosion

14. Surface Water Runoff • Rainwater that doesn’t soak in to the ground or evaporate. • Affected by: • Amount of rainfall • Length of time it falls • Steepness, or slope, of the land • Amount of vegetation

15. Rivers & Streams • River system –network of groundwater & streams that come together to form a system. • Drainage Basin- area of land from which a stream or river collects runoff. • The Mississippi River drainage basin is the largest in the United States

16. Young River • Flows swiftly through a narrow valley. • May have rapids & waterfalls. • Erodes the bottom faster than the sides. • “V” shaped valleys

17. Mature Stream • Flows smoothly through the valley. • Erodes more on the sides. • Forms meanders & oxbow lakes. • Carves a flat, broad valley floor called a floodplain.

18. Old Stream • Flows smoothly through a floodplain it has carved.

19. flood plain meanders oxbow lake valley wall

20. Delta – fan shaped area formed by sediments that are deposited as water empties into an ocean or lake. • Alluvial Fan – fan shaped area formed by sediments that are deposited as water empties from a mountain valley onto a flat open plain.

21. Groundwater • Groundwater is water that soaks into the ground and collects in the pores of the underlying soil. • Soil and rock are permeable if water can pass through the pore spaces. (Sandstone) • Soil and rock are impermeable if water can not pass through the pore spaces. (Granite) • Aquifer – a layer of permeable rock that lets water move freely. • Zone of Saturation : area where all the pores are filled with water. • Water Table : upper surface of the zone of saturation.

22. Aquifer Zone of Saturation Zone of Aeration Water Table

23. Wells are used to pump groundwater from an aquifer to the surface. • Artesian wells – wells that don’t require a pump because the water is under pressure. • Spring – free flowing water because the water table is so close to the surface. • Geyser – hot spring that erupts peroidically, shooting water & steam into the air. The the

24. Caverns are formed by Carbonic acid dissolving limestone rock, thereby enlarging cracks to form chambers. • Stalactites– Calcium carbonate deposits that hang from a cave’s ceiling. • Stalagmites – Calcium carbonate deposits that form on a cave’s floor.

25. Other Features: Soda Straws Columns Cave Popcorn Draperies Cave Pearls

26. Ocean Shoreline • Shoreline Forces • Waves pound against pound against shores. • Currents move sediments along the shoreline. • Tides carry sediment out to sea & bring in new sediment.

27. Rocky Shorelines • Rocks & cliffs • C. Sandy Beaches • Beaches –deposits of sediments parallel to the shore. • Barrier Islands – fragile sand deposits that parallel the shore but are separated from the mainland.