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Weathering, Erosion, and Soil

What type of rock is this, how can you tell?. Weathering, Erosion, and Soil. Yosemite Valley, California. Mountains Carved by Glaciers. Grand Canyon, Arizona. Carved out by the Colorado River. Bryce Canyon, Utah. Acidic Rainfall has worn away these rocks.

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Weathering, Erosion, and Soil

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  1. What type of rock is this, how can you tell? Weathering, Erosion, and Soil

  2. Yosemite Valley, California Mountains Carved by Glaciers

  3. Grand Canyon, Arizona Carved out by the Colorado River

  4. Bryce Canyon, Utah Acidic Rainfall has worn away these rocks. The harder rocks remain standing… but for how long?

  5. Weathering • Process by which rocks are broken down due to exposure to processes occurring at the Earth’s surface • Caused by • Water • Waves • Wind • Gravity • Glaciers The 2 G’s and the 3 W’s

  6. 2 Types of Weathering • A. Mechanical Weathering also called Physical weathering • Rock is broken down into smaller pieces of the same material • (no change in composition) • B. Chemical Weathering • The breakdown or decomposition of rock that occurs when minerals arechanged into different substances • (change in composition)

  7. Mechanical/Physical Weathering • Frost (Ice) Wedging • Process in which water freezes in the cracks of rock and wedges (pushes) it apart because water expands when it freezes. • Occurs where there are frequent freezes and thaws.

  8. Explain what is happening.

  9. Frost/Ice Wedging can cause Potholesto form in pavement

  10. Mechanical/Physical Weathering 2. Abrasion • The wearing awayof rock material by grindingaction • Usually caused by sediment in Wind, Water, and Glaciers

  11. Windabrasion-sandblasting effect on stationary rocks as seen here in Arches National Park

  12. Hydraulic abrasion-water & sediments flowing over boulders as seen here in Ohiopyle State Park, Pennsylvania Notice the rounded river rocks

  13. Mechanical/Physical Weathering 3. Plants and Animals • Plant rootscan split rock • Also known as: “Root pry”or “Root action” • Animals digholes ,breaks up rocks

  14. Tree growing out of rock, Shenandoah National Park Tree roots also break up sidewalks

  15. Exfoliation- gradual peelingof layersdue toupliftand frost action, typical of granite domes like those in Yosemite N.P. Mechanical/Physical Weathering

  16. Exfoliation of Igneous rock

  17. Chemical Weathering • Chemical Weathering • The breakdown or decompositionof rock that occurs when minerals are changedinto different substances • (change in composition) • Involves Water,water vapor, Acids,and/or Oxygen O2

  18. Chemical Weathering • Hydrolysis • Carbonic Acidin water dissolvesCalcite. This chemical weathering can hollow out underground Caverns Limestone and Dolomite both dissolve because they contain Calcite

  19. Acid rain (carbonic acid) weathering the details of statues and tombstones Ex: Marble and Limestone

  20. Chemical Weathering • Oxidation • Oxidation of minerals with iron (magnetite, pyrite) results in the formation of rust or iron oxide. • This is why Mars is the red planet • Copper turns rocks green

  21. Rate of Weathering • How fast a rock weathers depends on 3 factors: • Surface area • Rock composition • Climate

  22. Rate of Weathering • Surface area • The greater the surface area, the faster the weathering rate • There are more surfaces to be weathered

  23. Rate of Weathering • Rock composition • Some minerals are more resistant than others • For example, quartz is more resistant (harder) than calcite Quartz Calcite

  24. Rate of Weathering • Climate (long term pattern of moisture and temperature) • Weathering rates are faster in warm, wetclimates Desert vs. Rainforest

  25. Erosion • Erosion • The removaland transportof weathered materials by natural agents such as • Caused by • Glaciers • Running water • Gravity • Wind • Waves

  26. Glaciers • Mass of compacted ice and snow that moves under its own weight

  27. Glaciers • Friction at the base of the glacier is reduced by a thin film of melt water. • Glaciers account for about 75%of the fresh water on Earth

  28. Glaciers can leave behind large boulders that are known as an erratic

  29. Glaciers • Glaciers can move lots of sediment that can carve striations (grooves) into rocks These Striations show how glaciers moved

  30. Glacial Deposits • Drift or Till- all sediment that is deposited by glacial activity • Loess: fine powder, pulverized rock, that blankets much of the northern mid-west • Moraine: ridge or pile of boulders, gravel, sand, and silt left at the end of a glacier • Esker: type of outwash that accumulates in the channels and tunnels of a glacier

  31. Glacial Landforms • Horne: a pyramid shaped peak where 3 or more cirques meet • Cirque • Steep-walled bowl-shaped depression

  32. Glacial Landforms • Trough • U-shaped valley, Glaciers carve U shaped valleys

  33. Arete • Narrow flat-topped ridge that forms between two parallel troughs or cirques Glacial Landforms • Hanging valley • Straight drop-off at the end of a trough

  34. Glacial Landforms • Moraine: Pile of mixed sediments that have been carried and dropped by the glacier

  35. Glacial Landforms • Eskers -Mounds of rock from melt tunnels

  36. Streams and Rivers • Velocity - How fast the water moves • Gradient - The steepness, the slopethat a river or stream travels • Discharge - The amount of water that moves past a certain point in a river in a given amount of time • If there is a steep gradient, high velocity, and a large discharge, then Erosion will be severe! • Rivers have energy to move lots of sediment, and even large boulders.

  37. River stages affect:Velocity,Gradient,& dischargewhich cause Erosion

  38. Seven Bends of the Shenandoah Is the Shenandoah and old river or a young river? • River meanders • Bends in the river, shows how mature a river is.

  39. Erosion-Mass Movement • The downward transportation of weathered materials by gravity Massive Landslide

  40. Erosion-Mass Movement • Creep • Slump • Mudflow/Earthflow • Landslide/Rockslide

  41. Erosion-Mass Movement:A large mass of sediment drops down!

  42. Erosion-Mass Movement • Creep • Very slow movement of earth material. • Caused by repeated freezing and thawing. • Sediments are loosened by expanding frost and contracting thaw. • Leaning fence posts and telephone poles are a sign of Creep.

  43. Fence posts leaning due to creep

  44. Erosion-Mass Movement • Slump • Slow downward movement of a large mass of soil • Occurs when underlying sediments are weakened by heavy rains • Characterized by a curved scar in the land surface.

  45. Slump can cause road hazards

  46. Erosion-Mass Movement • Mudflow/Earthflow • Thick pastes of sediments that travel downhill at great speeds • Usually occur in dry areas that get a large quantity of rain all at once • Leaves a cone shaped deposit

  47. Mudflow in the Blue RidgeMooreman’s Gap near Charlottesville

  48. Erosion-Mass Movement • Landslide/Rockslide • Fast movement of large blocks of rock • Occurs in very steep vertical cliffs • Accelerated by ice wedging

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