Desert 1

Geography 12

DESERT LANDFORMS
Deserts - def. - arid region characterized by little or no rainfall in which vegetation is scanty or absent unless specially adapted

region where evaporation exceeds precipitation

There are various causes of deserts -

1) Continentality - the desert is far from a body of water or the influence of a
body of water - e.g. Gobi desert

2) High Pressure - in subtropical regions descending air in high pressure belts
prevents moist air masses from entering the area and bringing rainfall
e.g. Sahara

3) Rainshadow- regions on the leeward side of mountains experience dry
conditions due to adiabatic heating of descending air masses e.g. Mojave

4) Cold Ocean currents - on the west coasts of S. America and S. Africa cold
currents create stable air masses that hold very little water vapour - as the
air mass meets the warmer land mass fog forms but there is not enough
water vapour to create precipitation - e.g. Atacama

5) Polar deserts - created by sinking of cold dry air masses - ice is present
on the land although there is little precipitation


DESERT LANDFORMS

Despite the lack or limited amount of precipitation in deserts, water is the major agent of erosion. Rainfall when it comes is brief and intense, and due to the hard rocky surface and limited vegetation tends to quickly run off,
creating flash floods.

Landforms created by water include: (define and draw)

Wadis – Common water-formed features in desert regions. They have steep sides, and don't usually contain flowing water. Most of the damage is done by flash floods.
Playas – Dry lake beds imbedded with clays and silts. After a rainfall, as the water evaporates, it leaves behind remnants of solid salts and such. These dry lake beds are usually found in the centre of inland basins.




Alluvial fans – This is where large sediments previously carried by running water has built up abruptly on level plains, valleys or basins. This usually occurs between mountains, and causes a drop in stream velocity and depth.




Bahada – Linked closely to alluvial fans, this is a gently sloping surface of alluvial materials from the foot of a mountain to the centre of a basin. These are formed by build up of alluvial fans.




Mesa/ Butte – A butte is smaller than a mesa, a flat topped hill with steep sloped sides. A mesa is a bigger version of this, with escarpments marking the sides.




Canyon – A ravine caused by a river, in an area of seldom rainfall.





Because of limited precipitation physical weathering is dominant.
The main physical processes are heating-cooling, freezing-thawing,
and exfoliation.