The formation of loess deposits in the Tashkent region and parts of Central Asia; and problems with irrigation, hydrocollapse and soil erosion

Abstract

There are large problems of irrigation, hydrocollapse and soil erosion associated with the loess deposits of Central Asia. To get to grips with these we need a clear view of the nature and formation of the loess, and in this region there are still disputes and disagreements and controversies. Important events in the loess deposit formation process can be identified and studied, and relative significances assigned. There are large loess deposits in the vicinity of Tashkent, in the north-east of Uzbekistan. These were mapped and studied for many years by G.A. Mavlyanov and associates; they used a terminology which appears to be based on Pavlov's nineteenth century usage and developed a ‘polygenetic’ formation theory for loess deposits. This was a formation theory very much associated with Central Asia and essentially favouring a ‘proluvial’ mechanism. A speculative look at the deposits near Tashkent allows alternative terminologies and formation mechanisms to be considered. In particular the widespread Soviet antipathy to aeolian deposition can be examined. The deposits associated with the Chirchik river, upstream of Tashkent, might be affected by the Pavlov mechanisms, but could be topped by aeolian deposits. The collapse of loess when wetted is controlled by the nature of the ground and is a very significant interaction of soil and water, in particular in Central Asia. Hydrocollapse and water erosion are closely related and are controlled by the complex nature of loess ground. Dust clouds in eastern Uzbekistan are largely loess related, but in the west dust material is raised from the drying Aral Sea bed; this is often clay mineral agglomerate material and can carry dangerous pollutants.