Desert Systems

: Deserts are open systems- generally in dynamic equilibrium

• Inputs:
  • Water enters the system through infrequent rainstorms.
  • Sediment can be carried into a desert system by wind or water.
  • Energy: Insolation = the solar radiation that reaches the Earth
    Insolation is strong in Deserts as:
    • There aren’t usually any clouds to block it
    • Mid to low latitudes deserts, the Sun’s rays hits the Earth at high angles
    • High levels of insolation > high daytime temperature and cloudless skies > nights are cold; rapid temperature changes > steep pressure gradients that drive strong winds.
    • High insolation > water evaporates quickly > ground dry > sediments more mobile.
  • Runoff:
    • Precipitation = infrequent + unpredictable in deserts. When it does rain = form of intense storms > causes high inputs of energy into localised areas.
    • Only few plants intercepts rainfall > a lot of surface runoff.
    • Ground surface = baked hard by the Sun + exposed to rock because soil is eroded > decreases infiltration + increases runoff.
  • Wind: created by air moving form high pressure areas to low pressure areas. Where pressure gradients are high (big diff between high & low pressure), winds very strong
    • Some areas; wind blows the same direction consistently (prevailing wind) > causes more sediment erosion + transports than winds change direction frequently
    • Lack of vegetation > wind can blow long distances without obstruction
  • Flows: Sediment is moved by:
    • Weathering
    • Erosion
    • Transportation
    • Deposition
  • Stores: Sediment stored in Landforms and water is ground of river
  • Outputs:
    • Water evaporates rapidly or may leave the system as runoff.
    • Sediment may be carried out of the system by wind or water.

Feedback loops:

• – Feedback: High temp=Evaporation=Ground drier=Easily eroded=dust clouds=block radiation
• + Feedback: Wind hits obstacle, slows down, drops load, forms young dune which acts as obstacle

Sediment Sources:

1. A lot of the sediment in deserts come from ancient processes:
   1. Before they were deserts, areas were wet enough for rivers/lakes
   2. Sediment was transported into the system in rivers and deposited on the beds of lakes. When they dried up, the sediment became available for building dunes and other depositional landforms.
   3. Other areas were underwater, so they still have marine deposits from millions of years ago.
2. Sediment is still being brought into desert system today:
   1. Some comes from underlying parent that’s been weathered.
   2. Rivers also bring sediment into deserts – many only flow occasionally, so when they dry up, the sediment they were carrying is left behind on the riverbed or, if they flood, on the surrounding desert surface.
   3. Wind also transports sediments into deserts and deposits it there.
3. Deserts are both recipients of sediment and sources. Dust clouds form when strong winds blow fine particles out of the desert – these are sometimes transported thousands of miles.

Sediment Budget: The difference between inputs and outputs

• If sediment inputs are higher than outputs, the sediment budget is positive
• If sediment inputs are lower than outputs, the sediment budget is negative.
  Where the sediment budget is positive (more deposition), landscapes are dominated by depositional landforms, e.g. sand dunes.
• Where the sediment budget is negative (more erosion), landscapes are dominated by erosional landforms, e.g. inselbergs.