Notes on Avalanching and Dunes | Wind Erosion

This article provides a note on avalanching and dunes.

Avalanching:

On an unprotected large eroding field, the rate of flow increases with distance to leeward side. Soil flow is zero at the windward edge of an eroding field, but the rate increases leeward until the flow becomes maximum for the wind of specific velocity. This acceleration of soil flow with distance over an un­protected field is known as soil avalanching.

The maximum rate of flow is al­most the same for all soils and is equal to that of dune sand. The distance required for soil flow to reach a maximum is same for any erosive wind and varies inversely with erodibility of a field surface (Table 4.3). Thus, the more erodible the soil, the greater the rate of avalanching and the shorter the dis­tance at which maximum flow is reached.

Dunes:

The word ‘dune’ is derived from the English word ‘Dun’ emphasizing hilly char­acter of the topography.

Based on their mode of occurrence and physical fea­tures, the dunes of Rajasthan can be divided into the following types:

Longitudinal Dunes:

These types of dune develop under strong wind and are confined to the southern and western part of the Thar desert.

Traverse Dunes:

These types of dunes predominate in eastern and northern portion of the Thar and develop where south westernly wind is less strong. The existence of big trees on the leeward side of the traverse dunes is indicative of stabilisation of a considerable time.

Crescent Shaped Dunes:

Such type of dunes develop in central part of the Thar desert. While dunes develop near the core, Aeolian sand (wind deposited sand) and losses are deposited in the peripheral area of the desert. Being south westernly, the Thar desert slopes imperceptibly towards the Indus plain with general surface unevenness.

Dunes in south are higher, rising sometimes to 150 m whereas in north they are lower and rise up to the height of 15 m. The formation of sand dune depends on 3 factors; a prevailing moderate wind, plenty of sand and an obstacle like rock or a tree that acts as a nucleus around which sand may slowly collect. The sand dunes are highly deficient in organic matter and moisture.