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Deserts. Deserts. Dry places that have a dry climate-the yearly precipitation is less than the evaporation loss Dry regions cover 30% of the Earth’s surface Concentrated in sub-tropics, mid-latitudes, and polar regions. Meteorology Principles. Warm, less dense air rises Rising air cools

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Deserts1
Deserts

  • Dry places that have a dry climate-the yearly precipitation is less than the evaporation loss

  • Dry regions cover 30% of the Earth’s surface

  • Concentrated in sub-tropics, mid-latitudes, and polar regions


Meteorology principles
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


Low latitude deserts

Types of Deserts

Low-Latitude 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


Cold water coasts
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


Rain shadows orographic uplift
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



Weathering in arid climates
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


Water and deserts
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


Wind transport of sediment
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


Wind erosion
Wind Erosion

  • Insignificant in erosional processes

  • Two mechanisms

    • Deflation

      • Loose particles of sand and dust are lifted from the surface

    • Abrasion

      • Sandblasting of particles


Desert pavement
Desert Pavement

  • Deflation occurs leaving behind coarse particles to large to carry


Daily questions
Daily Questions

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

Has a dissolved load

Have a competence and capacity

5 15

Identify and appropriately place 10 characteristics in the Venn Diagram.

3 8 14 16

18

1 6 10

12 21

4 7 9 11

2 13 19

17 20


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