Like any other landform, desert landforms are also the result of erosional and depositional processes. These landforms are mainly formed due to the weathering of rocks, action of wind and water. Exfoliation (Mechanical weathering) is the process which is mainly responsible for weathering in the desert while chemical weathering plays less role here. In upland regions of tropical deserts and in the most interior regions of the continental deserts, the frost in winter season is also an important factor involved in weathering.
Although wind is also responsible for erosion but in deserts it is mainly associated with the transportation and deposition processes. Wind carries large fine particles to great distances and bounces the coarser particles over the surface. The bouncing movement of these particles is called saltation.
Wind erosion is composed of:
- Abrasion – Very small particles of rocks are hit against the rock surfaces which lead to the formation of some characteristic features of desert like Zeugens, Rock pedestals and Yardangs.
- Deflation – The depressions are formed when wind blows away the wastes of rocks to distant areas. The movement of particles causes the surface to get lowered and forms depressions.
- Attrition – When rock particles rub against each other and wear down and break down into much smaller particles, it is called attrition.
Dunes – These are the result of deposition of rock wastes which get deposited in the form of large mounds. These mounds are either ridge shaped or crescent shaped.
The presence of water is quite low in desert but still when combined with the power of wind, it forms various shapes and landforms in the desert.
Some of those features are given below:
1. Sandy desert or erg – When the undulating plain of sand surface is blown into the wavy ripples and sand dunes, it is called an erg. Example – The sand desert of the Great Sand Sea. The sand seas of Libya and Egypt are also good example of this type of feature.
Note: Koum is the term used for this in Turkestan.
2. Stony desert or reg – The desert goes through up and downs in the temperature as the day shifts from light to dark. Thus this temperature change also contributes in the formation of gravels, boulders and angular pebbles. These are called serir in Libya and Egypt.
3. Rocky desert or Hamada – When all the fine material is removed by deflation while abrasion polishes and smooth out the rock surface, a large-scale areas of bare rocks are formed which is called Hamada. Hamada-el-Hamra is the largest Hamad in the Sahara of Libya.
4. Badlands – Sudden violent rainstorms are experienced by semi-desert regions which breaks the land and lead to the formation of extensive gullies divided by steep-sided ridges. The stretch of land from Alberta to Arizona and into the Dakota, in the U.S.A is the best example of the badlands.
Features produced by wind erosion
When the wind attacks the big rocks in the desert, it abrades these big rocks and lead to formation of sculptures or strange looking shapes. Some of these shapes look like pedestal and hence are called rock pedestals.
Formation of rock pedestals
The weaker region in the rocks are easily worn out by the abrasion activity of the wind and lead to tower like structures with many types of shapes. The Tibesti Mountain of Central Sahara provides good example of these structures. These structures can also be witnessed in the desert land of Saudi Arabia.
A furrow and ridge landscape is formed when the wind abrase the soft and less resistant part of the rock and the hard resistant part is left. The ridges thus formed are called zeugens and can be of varying sizes, some even 30 m high.
These ridges wear away eventually through constant undercutting by winds.
When the bands of soft and hard rocks lie parallel to the winds, the wind forms another type of furrow and ridged landscape. The sloping ridges of resistant rocks varies in size from five meters to fifteen meters in height. These ridges are known as Yardangs. Further, these abrasions causes undercutting of these ridges. Salah in central Algeria and the regions near the Kom Ombo (Egypt).
Deflation give origin to hollows which reach down the water-carrying rocks. This leads to the formation of Oasis or a swamp. A good example of these hollows is Qattara Depression in the south west of Alexandria, Egypt. This hollow is about 120 m below the sea level. It consist of salt marshes and belt of dunes on the leeside which is formed by the sand excavated from these hollows.
The rounded top isolated masses which are formed due to almost complete erosion of original surface are called inselberg. Some of these can be the remains of the edges of plateaus which have gone through extensive weathering and further sheet wash has removed the weathered debris from its surface.