SUBMERGED KALUTS IN SOUTHWESTERN AFGHANISTAN

Asian yardangs were first described by Hedin (1903) in NW China, and extensive kaluts (Persian word for yardangs) in Iran’s Dasht-e Lut were described by Gabriel (1938). Mega yardangs are dominant in several Central Asian deserts and yardang slopes are commonly characterized by strong wind and water erosion patterns that developed over multiple climate cycles, and has resulted in fantastic, irregular-carved kaluts across basin floors. The Lut desert contains over 7200 km² of spectacular wind eroded landforms that extend for tens of kilometers. Less than 280 km east of the southern Lut yardangs is the relatively unknown Zirreh Kalut, a 700 km² field of yardangs in the Gaud-i Zirreh (GZirreh) of southwestern Afghanistan. The surfaces of these yardangs exhibit much less wind and water erosion and, in some areas, kalut slopes appear continuously smooth and rounded, covered by silty gypsiferous crusts. These kaluts have been and still are occasionally submerged by lakes (hamuns) that have filled by 1) exceptionally large floods on the Helmand River, 2) by past Holocene(?) deeper lakes whose gravel shorelines, visible across the basin, lie above the kaluts, and 3) by rising ground waters in the present climate. For over a century it was assumed that the GZirreh only filled from the spillover from upstream hamuns. Satellite images of the past 42 years, however, indicate that nearly full lakes in the GZirreh exist when upstream hamuns are only partially filled or are drying out. The Zirreh Kalut were carved from lakebeds during the last cold, dry and very windy conditions of the last glacial episode, and have been submerged by increased waters available in the basin during the warmer and wetter interglacial conditions of the Holocene. Although extreme arid conditions pervade at present, increased water availability, including the recently recognized role of ground waters, has supported several past civilizations in the Helmand basin for over 6000 years.