Engineering Geology - Chapter 13 - Deserts

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Engineering Geology - Chapter 13 - Deserts
2012-12-20 17:50:24
Engineering Geology Civil Geotechnical Minnesota Deserts

Chapter 13 - Deserts
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  1. List at least 3 of the 4 common types of dunes
    • Possible Answers:
    • barchan dunes;
    • transverse dunes;
    • parabolic dunes;
    • longitudinal dunes.
  2. Describe Barchan Dunes:
    • -Barchan dunes generally develops where the sand supply is limited.
    • -Crescent shaped dune with a steep face on the inward or concave side. The horns of the crescent point downwind. 
    • -They are typically seperate from one another and move across a baren surface.
  3. Describe Transverse Dunes:
    • -Transverse dune form when more sand is available
    • -Long and relatively straight dunes oriented perpendicular to the wind direction.
  4. Describe Parabolic Dunes:
    • Parabolic Dunes are similar in shape to barchan dunes, but require a lot more sand and very strong winds.
    • They are more deeply curved and the horns point upwind instead. Vegetation commonly anchors the horns
    • Commonly found inland from an ocean beach. 
  5. Describe Longitudinal Dunes:
    • Longitudianl Dunes are the largest dunes.
    • Very tall/large symmetrical ridges that are exceptionally straight and evenly spaced. 
    • Scientists aren't sure how they are formed, but some theories suggest that it has something to do with crosswinds.
  6. Which are the two distinct desert landscapes in southwestern US?
    the Colorado Plateau; and the Basin and Range province.
  7. What is the name given to the soil consisting of silt and clay particles deposited by wind?
  8. What is a Playa? 
    Playa: A very flat surface underlain by a dry lake bed of hard, mud-cracked clay
  9. What is Loess?
    soil consisting of silt and clay particles deposited by wind
  10. he major difference between a mesa and a butte is one of
    A. shape
    B. rock type
    C. size
    D. elevation
    C. size
    (this multiple choice question has been scrambled)
  11. The Basin and Range province covers almost all of
    A. Utah
    B. Nevada
    C. Texas
    D. Colorado
    B. Nevada
    (this multiple choice question has been scrambled)
  12. What is a Ventifact?
    Rocks with flat, wind-abraded surfaces
  13. Which is not a type of dune?
    A. longitudinal
    B. parabolic
    C. barchan
    D. all of the preceding are dunes
    E. transverse
    D. all of the preceding are dunes
    (this multiple choice question has been scrambled)
  14. what is a plateau?
    a broad flat-topped area elevated above the surrounding land and a steep cliff face.
  15. what is the difference and/or relationship between a mesa and a butte?
    Both are remnants left over when a plateau erodes away. They are like flat-topped hills with steep, cliff sides and capped by a resistant rock layer. A mesa is large and broad, while a butte is narrow and small. Most buttes form from the continued erosion of mesas. 
  16. what is a bajada?
    A broad ramp of sediment formed at the base of mountains when alluvial fans merge.
  17. what are pediments?
    a gently sloping erosional surface cut into the solid rock of a mountain range in a dry region. It is usually covered by a thin veneer of gravel. Usually develops uphill from bajadas as the mountain retreats.
  18. The removal of clay, silt, and sand particles from the land surface by wind is called
    A. abrasion
    B. deflation
    C. depletion
    D. deposition
    B. deflation
    (this multiple choice question has been scrambled)
  19. Which is NOT a reason that much of the southwestern United States is desert?
    A. it is near 30° North
    B. the western mountains create a rain shadow
    C. it is a great distance from the ocean
    D. cold ocean currents in the Pacific cause high evaporation rates in the land
    C. it is a great distance from the ocean
    (this multiple choice question has been scrambled)
  20. A surface layer of closely packed pebbles is called
    A. deflation
    B. a blowout
    C. desert pavement
    D. desert varnish
    C. desert pavement
    (this multiple choice question has been scrambled)
  21. Which is characteristic of deserts?
    A. limited rainfall
    B. slow chemical weathering
    C. all of the preceding
    D. internal drainage
    E. flash floods
    C. all of the preceding
    (this multiple choice question has been scrambled)
  22. The defining characteristic of a desert is
    A. shifting sand dunes
    B. high temperatures
    C. all of the preceding
    D. none of the preceding
    E. low rainfall
    E. low rainfall
    (this multiple choice question has been scrambled)
  23. True or False: A desert has to be hot and sandy
    False - The defining characteristic of a desert is low rainfall. It can be any temperature. Antarctica, which is cold and snowy, is a large desert because it recieves very little precipitation during the year. 
  24. How does a flash flood in a dry region differ from most floods in a humid region?
    A flash flood has high runoff creating sudden local floods of high discharge over a short duration of time; normally dry beds become raging rivers after a thunderstorm. With average floods, they are more predictable and over a longer period of time, whereas with flash floods, they are fairly unpredictable, and over a short period of time.
  25. Give two reasons why wind is a more effective agent of erosion in a desert than in a humid region.
    • Humid regions have less change in air temperature while desert regions have a high variation in extreme temperatures, therefore the wind tends to be stronger in desert regions.
    • Also, the sediment itself is easier to blow around because the lack of moisture means that it is less heavy and there is nothing concreting sediments together.
  26. Define Desert
    A desert is any arid region that receives less than 25 cm of precipitation per year.
  27. Where are most of the world's deserts located? Why?
    • Most of the world's deserts are located in two bands around the world, one near latitude 30 degrees North and one near latitude 30 degrees South.
    • In the global air circulation, air rises near the equator and cools creating a lot of preciptation and the tropical environments found there. This air then sinks again around 30 degrees north and south. As it sinks, it compresses and heats up, creating the dry, arid environments that create deserts.
  28. What are Desert washes? 
    Desert washes, or arroyos, are commonly steep-sided, with flat floors covered by loose sediments (a result of rare but highly erosive flash flood events).
  29. What are the characteristic landforms of the Colorado Plateu? 
    flat-lying sedimentary rocks that are heavily eroded into plateaus, mesas and buttes.
  30. What is a sand dune?
    Sand dunes are mounds of loose sand grains piled up by the wind. There are four common shapes for sand dunes, but many dunes cannot be classified and are very irregular.