Deserts

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Deserts
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Deserts

• Dry places that have a dry climate-the yearly
  precipitation is less than the evaporation loss
• Dry regions cover 30 of the Earths surface
• Concentrated in sub-tropics, mid-latitudes, and
  polar regions

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Meteorology Principles

• Warm, less dense air rises
• Rising air cools
• Moisture carrying capacity of air decreases
• Precipitation occurs
• Cold, dense air sinks (moisture depleted)
• Sinking air warms
• Moisture carrying capacity increases
• Warm air can hold more moisture than cold air

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Low-Latitude Deserts
Types of Deserts

• Along the equator is a Low pressure system, air
  rises
• Along 30o N and S - High Pressure systems exist
  (Subtropical high-pressure belt, air sinks and
  warms
• As air mass warms it can hold more moisture any
  available water evaporates

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Cold-Water Coasts

• Cold dry air from ocean moves over warm dry land
• Land warms air mass
• As air mass warms it can hold more moisture any
  available water evaporates

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Rain Shadows Orographic Uplift

• Warm, humid air masses move off of ocean
• As the mass approaches a mountain it begins to
  rise
• Rising air cools
• Moisture carrying capacity decreases
  precipitation occurs on the windward side
• Cold, dry air mass moves over mountains and
  descends on the leeward side
• Descending air warms and picks up moisture
• Dry region is a Rain Shadow the process is
  orographic uplift

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Desert Locations
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Weathering in Arid Climates

• Mechanical Weathering is dominant
• Lack of moisture and organic acids limit chemical
  weathering
• Chemical weathering does occur, but the it takes
  longer

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Water and Deserts

• Ephemeral streams are present in desert areas
• Deserts lack vegetation
• Rainfall is infrequent, but intense when it
  occurs
• Runoff is high get flash floods
• One storm can do an enormous amount of erosion
  (triggering mass wasting and transporting
  sediment)
• Water does the majority of erosional work in the
  deserts

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Wind Transport of Sediment

• Similar to stream transport both air and water
  are fluids
• Wind systems have both a bed load and suspended
  load
• Bed Load
• Primarily sands, can be gravels and
• larger particles
• Particles move by saltation (sands) or
  creep (rolling or sliding particles larger than
  sand)
• Causes abrasion mechanical weathering
• Suspended Load
• Primarily silt with some clay
• Wind has a capacity and competence

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Wind Erosion

• Insignificant in erosional processes
• Two mechanisms
• Deflation
• Loose particles of sand and dust are lifted from
  the surface
• Abrasion
• Sandblasting of particles

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Desert Pavement

• Deflation occurs leaving behind coarse particles
  to large to carry

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Daily Questions

• Identify and appropriately place 10
  characteristics in the Venn Diagram.

• Transport sediment in direction of movement
• Can transport large boulders
• Form dunes
• Occur most frequently at high latitudes
• Few associated plants and animals
• Occur on at least five continents
• Features formed have generally diminished in size
  over the last few decades
• Commonly found at low elevations
• More likely to occur at high elevations
• Preserve a record of past climates
• Characterized by the presence of snow and ice
• Associated with erosion and deposition
• Material is not sorted
• Material is sorted
• Evaporation exceeds precipitation
• Cross beds form in deposits
• Faster moving
• Controlled by climate patterns
• Involves water

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3 8 14 16
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1 6 10 12 21
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2 13 19
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