Aeolian sand transport

Butterfield, G.R. 1999. Near-bed mass flux profiles in aeolian sand transport High-resolution measurements in a wind tunnel. Earth Surface Processes and Landforms 24(5) 393-412. 

The area of actual erg and dune formation is delimited by the 150 mm/yr isohyet. This precipitation boundary appears to have shifted strongly in the recent past. Between 20,000 and 13,000 yr BP, the southern limit of active dune formation in the Sahara desert was 800 km south of its present position and most of the now sparely vegetated Sahelian zone was an area of active dune formation at that time. These dunes, mostly of the longitudinal type, are now fixed by vegetation, but their aeolian parentage is still obvious from their well-sorted material. A similar story can be told for the Kalahari sands. Overgrazing in recent times has reactivated aeolian transport in many regions with sands. 

Though the process of wind action and transport of material is clearly recognized, it is difficult to measure its impact in the accumulation zones. Such measurements are most successful in the immediate neighborhood of the deflation zones where the thickness and volume of sand or loess deposits can easily be calculated. In the northern periphery of the Negev, aeolian deposits range from a few cm to several meters, which corresponds to an average accumulation of 10 to 100 mm/millennium since the Lower Pleistocene. 

Aeolian soils are those formed by aeolian action, that is, materials transported, eroded and deposited by winds. These soils appear as sand dunes or calcitic silt. Pavement construction on sand dunes, which are not protected by topsoil, appears to be problematic. A cut on calcitic silt may have very high gradient (slope) owing to the cohesive properties of calcium. The usage, however, of disturbed calcitic silt on embankment is problematic because cohesion has been lost. 

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