Landforms of Hot Arid and Semi-Arid Environments

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.

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.

A furrow and ridge landscape is formed when the wind abrade 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.

Wind erodes the Earth's surface by deflation (the removal of loose, fine-grained particles by the turbulent action of the wind). Dune deflation hollows occur where wind removes fine particles down to a level where a layer of particles too heavy for the wind to move stabilises the sand and prevents the surface being eroded further. They often form between a series of sand dunes.

Deflation hollows are sometimes refered to as 'blowouts'. They are generally small, but in some instances they can be up to several kilometers in diameter.

Deflation may give rise to hollows which reach down to the water-table. Leading to formation of a desert oasis.

An oasis can be formed by an underground aquifer or river that creates enough pressure for water to seep to the surface, forming the oasis. These aquifers and natural springs allow for life to exist in harsh climates like the desert and are often well known to local herders, farmers, and travelers in the region.

Geological factors influence how an oasis gets its water. Rock layers under the surface of the Earth help trap and channel water in pockets and along fault lines, leading to water seeping into an oasis via the surface or into a nearby aquifer. Certain rocks are suited for water retention or passage and can help facilitate the creation and maintenance of an oasis. In some cases where an aquifer might not have enough pressure to break through to the surface, wells can be the catalyst for drawing water to the surface.

Yardangs are formed in environments where water is scarce and the prevailing winds are strong, uni-directional, and carry an abrasive sediment load. The wind cuts down low-lying areas into parallel ridges which gradually erode into separate hills that take on the unique shape of a yardang.

Yardangs are cut into softer rock running in the direction of the wind, separated by ridges. The direction of the yardangs can indicate the direction of the prevailing wind.

They are more commonly created from softer rock types like siltstone, sandstone, shale and limestone, but have also been observed in crystalline rocks such as schist and gneiss.

Generally speaking, there are five types of sand dunes: transverse, linear/longitudinal, star, barchan, and parabolic. Sand dune types are determined by shape.

The shape of a sand dune is dependent on the strength of the wind and on the sand type. Wind coming from all directions generates star dunes. Barchan and parabolic dunes can look very similar but the main difference is the direction of the wind in relation to the top of the crescent shape.

The direction of the wind also creates the main difference between transverse and linear dunes.

The percolation of infrequent precipitation tends to cause lateral and downslope movement of silt particles beneath the surface of the ground. This leads to the concentration of gravel, a process enhanced by the constant removal of fine sediment at the surface by wind action. Thus, pavements are produced by the combined effects of water and wind. Evaporation and capillary action draw soil moisture to the surface and may precipitate calcium carbonate, gypsum, and other salts that cement the pebbles together to form a desert conglomerate. The pebbles often are so packed and smooth that no more wind deflation can occur. Desert pavement forms on level or gently sloping desert flats, fans, or bajadas and lake and river terraces often dating to the Pleistocene Epoch.