Introduction to Aeolian Environments

Introduction

Aeolian means wind action, and wind in areas of free vegetation can have significant effects.
Only fine particles (0.1mm) can be carried in suspension by the winds except in very high speed winds.
Vegetation reduces the amount of wind speed near the ground.
Aeolian activty is only effective in areas which lack a relatively complete vegetation cover and where surface material dries out at least occasionally.
Aeolian activity plays a very important role in landform development and in areas of massive sand accumulation within the world's major deserts, wind is by far the predominant geomorphic agent.

Global Distribution

The majority of the wind formed landscapes are contained within the worlds hot deserts.
Deserts are located in the sub tropical belts of latitudes 20°- 30°.
A hot and dry desert is a desert that recieves less than 15cm per year and a cold desert has between 15-26cm per year.
A hot and dry desert temperatures range from 40-49°C and a cold desert temperature ranges from 21-26°C.

Landforms that are produced by the wind

Depositional - landforms deposited by the wind.

Dunes are the most important Aeolian landform. They are formed as a response to the wind action and the effect on the particles.

Ripples are also formed in response to the wind and it is thought by some scholars that they are smaller versions of the wind, Bagnold, 1941 and Allen 1982, 1985. This is however controversial and not believed by all. The ripples are straight crested and asymmetric. The ripple wavelength and the height depends on the grain size and the wind strength, in particular to the length of the saltation path of the moving sand grains.

Dunes and draas have wavelengths of 10's to 100;s metres and several kilometres respectively. The sediment supply and the wind strength cause the dune type. The barchan, lunate dunes are from a sand supply that is limited and the sief dune or elongate ridge near parallel to the prevailing wind.

Sief draas are ridges of sand with smaller, commonly barchanoid dunes on them.

Ergs- Where sand is not spread evenly throughout a desert region it is concentrated into ergs. It is estimated that 85% of the sand in active sand bodies is contained in ergs greater than 32,000km squared. Relict ergs are found in the sub humid fringes of the worlds arid regions. Inactive ergs are found in North and South African deserts.

Loess - There are no loess deposits on the African continent. They are found mainly in Europe, China and America, (Pye, 1984). The loess deposits are fine grained material that is from ice sheets from the Pleistocene.

Erosional - landforms produced by two processes of wind erosion deflation and abrasion.

Deflation - removal of loose particles by the wind

Abrasion - the knocking together of rocks and particles into other rocks and particles in the airflow.