DESERTSAEOLIAN AND FLUVIAL PROCESSES AND FEATUERS

Transportation processes - WindWind transports rubble near the surface by ‘saltation’. Saltation refers to short jumps of grains displaced from the surface caused by the force of wind. As the grains fall back to the surface they may disturb other grains that then get carried by wind until they collide with ground. This then leads to the process continuing on, leading to dislodge of other particles. 

DEFLATION

Deflation is the lowering of the land surface due to removal of fine-grained particles by the wind. Deflation concentrates the rougher grained particles at the surface, eventually resulting in a surface composed only of the coarser grained remains that cannot be transported by the wind. This type of surface created is called a desert pavement.

DUNES - LINEAR 

LINEAR DUNES are long straight dunes that form in areas with a limited sand supply and converging wind directions.

DUNES - PARABOLIC

PARABOLIC DUNES are "U" shaped dunes with an open end facing upwind. They are usually stabilized by vegetation, and occur where there is abundant vegetation, a constant wind direction, and an abundant sand supply. They are common in coastal areas.

SAND DUNES

Sand dunes form when there is 

1.     a large supply of sand

2.     a steady wind 

3.     Some kind of obstacle such as vegetation, rocks, or fences, to trap some of the sand. 

Sand dunes form when moving air slows down on the downwind side of an obstacle. The sand grains drop out and form a mound that becomes a dune. 

LANDFORMS SHAPED BY WINDAreas where there is little or no vegetation are usually the most effected places that experience shaping due to wind. This happens when the wind picks up weathered rock materials and uses them to sand-blast larger rock structures on the zone closet to the ground. The formation of rock-strewn reg surfaces has resulted in the removal of finer material by wind. The wind also plays an important role in moving and reshaping dunes. Examples of landforms that are obvious in deserts are rock pedestals, Yardangs, Desert pavements, Deflation hollows, Oasis and Sand dunes. 

ROCK PEDESTALS

Rock pedestals are landforms created by abrasion in which grains cut away the base of rock structures but leaves their tips intact. This is due to wind-borne sand grains following bouncing trajectories that carry sand as high as 1m above the ground. 

DEFLATION HOLLOWS

When the sand is carried away over long distances by the wind, depressions are formed. These depressions are called deflation hollows and are commonly found in non-mountainous arid regions. Deflation hollows are an example of wind erosion causing

deflation yet these depressions also tend to collect rainwater and hold this water for a time depending on evaporation rates through the stones. E.g. Qattara Depression, Eygpt.

OASIS

Oasis' are found in the middle of deserts as fertile spots containing one or more springs surrounded by vegetation. This is caused by a variety of different temperature extremes causing islands of life. This outcome is due to oasis usually been located in parts of the desert where the elevation is low enough meaning the water table is underneath the

surface, allowing life to grow through their roots extending into the moist land. Water is able to run right through the sand as it is holey hence why the water can stay underneath the surface especially when large quantities of sand is moved due to wind erosion. 

SAND DUNES

There are two different types of sand dunes which are the barchan dunes and seif dunes. These are differentiated as barchan dunes are produced by the action of wind predominately convex facing from one direction forming crescent-shaped dunes, whereas the seif dunes are long

and narrow or can be a chain of dunes. These dunes are generally orientated in a direction parallel to the wind or in a direction in which have been the result of two or more winds blowing at acute angles to each other. Wind directions can also alter the series of peaks, gaps, steepness and the face of the sides. These sand dunes are mostly found in open deserts and rest on a base of a sand sheet.  Sand dunes are a result of deposition processes. 

YARDANGS 

Similarly Yardangs are also the result of sand grains pushed by persistent winds to form low ridges of sand carved in soft rock. This is commonly found in flat deserts where steady winds blow away dust and silt. Higher front faces of Yardangs are undercut as erosion is concentrated in the lower areas because wind driven sand stays near the ground. These are an example of erosional landforms

DESERT PAVEMENTS 

Desert pavements are commonly covered with stones rather than sand. This may be due to the wind blowing away the finest material leaving the stones behind as they are the bigger particles and remain as a lag deposit or may be through various physical processes including the soil in the ground as the fine materials are moved down beneath the pebbles. This results in the stones remaining on top. Desert pavements can be used as mulch for plants or as a shelter for ants and rodents

Water Erosion

Wadi: An arabic term that refers to a valley. In some cases it can also refer to a dry riverbed that only experiences water when there is a heavy rain fall. Unlike other valleys a wadi has been cut and eroded by water however because it is in desert it rarely experiences any constant water except for during the rainy season. Deposition is very common in a feature such as this because of the fact that the water dries up and is no longer able to carry a load of sediment that it has.

Playas: An area of very dry land that is found below the sea level. Flats like this often consist of fine grained sediments such as salts. During the dry season the surface of the lake is usually hard and rough, where as in the rainy season it gets wet and soft. The water usually creates a small hole meaning there is a very shallow lake in the desert.

Alluvial Fans: Often found in the desert

where periodic flash floods occur. They often have a large funnel shaped basin at the top which then creates a very narrow stream which then opens into an alluvial fan at the end of its course. These alluvial fans are often home to much more life and plants then the rest of the desert due to the fact that any nutritional sediment and water will end up here.

Bajada: When many alluvial fans all come together in one place, or deposit in the same area it creates a bajada. Because of the gathering of all the fans it means that there is much more water and sediment then usual, and it is quite evenly spread out throughout the whole bajada.

Mesa: An elevated area of land that has a very steep sides and a flat top. They are formed by the weathering and erosion of horizontally layered rocks that are lifted by the tectonic activity of the area. Due to the fact that some rocks erode faster then others, or others are stronger it means that stronger rocks usually make it to the top and the weaker rock is at the bottom.

Butte: An isolated hill with very steep sides, and a small somewhat flat top. Typically they say that a mesa has a top wider then its height and a butte has a height larger then its width.

Canyon: A deep ravine between cliffs, often carved into the landscape by a river. They are formed when there is stronger rock on either side of where the water is eroding. This means that the water is able to cut vertically but not horizontally.