Geology Unit 8

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truleo
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210084
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Geology Unit 8
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2013-03-31 20:14:27
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geology mass wasting earth
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Geology Unit 8
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  1. What would define a ground slope?
    Slope created as the result of erosional processes, igneous activity or tectonic activity.
  2. What is mass movement or slope failure?
    Movement of the regolith and masses of rock downhill. Mass movement is a major geologic process operating on all slopes. The associated movement speeds can vary from millimeters per year to more than 200 mph.
  3. What is the difference between a talus and a talus slope?
    Talus is when rock ans soil fragments that accumulated in a pile at the base of a ridge or cliff. Talus slope is an inclined surface (hillside or mountain side) of talus.
  4. Draw and describe an angle of repose that is associated with loose sediments.
    • The steepest angle at which loose grains will remain stable without sliding downslope, generally 30° for dry sand. Everything that is stacked hasan angle of repose.
  5. What is cohesive force?
    The resistance of an object to move downhill.
  6. Which factor is probably most important that strengthens cohesive forces?
    Friction.
  7. How much "relative amounts" of water is needed to increase cohesion?
    Stickiness of particles can hold the soil grains together. "Moist" is the most sticky phase that can hold sediments together.
  8. How does removal of vegetation reduce cohesive forces?
    Can no longer help bind sediments together reduces cohesion.
  9. How does excess water content weaken cohesion? (how does water content play a role?)
    High water content can weaken cohesion because abundant water both lubricates (overcoming fiction)and adds weight to a mass.
  10. Draw a picture and describe expansion/contraction or wetting/drying cycles. (always on exams).
    on page 2
  11. Compare a slope equlibrium.
    A slope in equilibrium generally has flat lying bedrock, such as hard limestone that will form gentile cliffs and softer shales that form gentle slopes.
  12. Why is a slope gradient important in regards to mass movement?
    Because the steeper the gradient, the faster that mass movement can take place.
  13. Describe how one type of mass movement can change to another type of mass movement.
    One type of mass movement can change over to another type of mass movement, such as creep movement becoming a debris flow.
  14. Define mass movement creep, including freeze/thaw that we drew in class.
    page 3.
  15. What physical objects on Earth's surface are associated with creep (how do you recognize that creep is occurring)?
    • Tilted posts and curved fence lines.
    • Curved tree trunks.
    • Deformed roadways and power-line poles.
    • Bulges or wavelike swells in soil. 
    • "Bending" of steep-dipping rocks.
  16. Discuss the effects of expansive clays in South Texas, especially on foundations during droughts and periods of heavy rainfall.
    Can shrink during dry periods.
  17. Describe a typical "mixture" that can form a debris flow.
    A mixture of mud, water and rock fragments (regolith) of all sizes that flow down slope as viscous, almost solid liquid.
  18. What can be the common "lubricant" for debris flows?
    Water ( and sometimes air trapped beneath the flow" can lubricate the debris flow.
  19. Describe the Blackhawk Slide.
    Had the largest debris flow in the U.S. at speed of 270 mph.
  20. How do we distinguish lahars from other type of debris flows?
    Lahars are volcanic debris flow made up of volcanic ash and lava flows. Water source for lubricating lahars include melting glaciers, lakes, rains on volcanoes.
  21. Along which tectonic zone are lahars most common?
    Lahars are more common with volcanoes that are found along tectonic convergent zones.
  22. What is the relationship between Tacoma, WA and Mt. Ranier in regard to lahars?
    Mt. Rainier of Washington State is famous for its lahars. Communities near Mt. Rainier often practice "lahar drills" for safety. Keep in mind that Mr. Rainier could send lahars upon Tacoma, WA. After all, Tacoma is built on top of many ancient lahars.
  23. What happens to consistency or hardness of the mud when a mudflow stops flowing?
    When a mudflow stops, the consistency of the mudrapidly becomes hard (because of it's low water content).
  24. Describe a boulder field.
    Long,relatively narrow masses of angular rock debris that moves very slowly.
  25. Describe the general configuration of a rock glacier.
    Long, tongue-like masses of angular rock debris that resemble glacier in outline and moves at rates of inches to feet per year.
  26. True landslides involve movement along ___ ___ ___.
    ...defined slippage planes.
  27. Define the differences between rockfall and rockslide.
    • Rockfall is a freefall of fragment ranging from a single grain to a huge block. Rockfalls make up most of the talus slopes. 
    • Rockslide is rapid movement of a large block of rock along a bedding plane, joint or plane of structural weakness.
  28. What caused the disaster at the Vaiont Dam in Italy?
    Rockslides.
  29. Describe slumps and how you might recognize one.
    A mass-movment "block" that leaves a distinct curved (spoon-shaped) incision.
  30. What is the most common cause of subaqueous slumps?
    By wave erosion.
  31. Where will be found some of the largest oceanic slumps in the Pacific?
    Largest slumps usually occur in alongside oceanic, volcanic islands.
  32. Where will be found some for the largest oceanic slumps in the Atlantic?
    Hawaii
  33. How do we define an avalanche?
    A large flowing mass of ice, snow and sometimes rock, that can reach speeds of 350 mph.
  34. What happens to the snow within an avalanche when it stops?
    When the movement stops, the ice instantly freezes into a rock-hard, solid mass.
  35. Why are drain pipes used with mass movement control methods?
    To prevent water-pressure buildup.
  36. Why are woven rock baskets useful for mass movement control methods?
    To prevent mass movement.
  37. Explain use of roof bolts and netting for mass movement control.
    Roof bolts with "wire netting" over an exposure of loose rocks (long bolts drilled into the rocks that holds the wire fending).

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