YARDANGS AND DOME DUNES NORTHEAST OF TAVAN HAR, GOBI, MONGOLIA

A variety of eolian landforms characterizes a 5-km² area in a region of the Gobi where dunes and yardangs are otherwise uncommon. The yardangs are eroded from Upper Cretaceous weakly consolidated sandstone and mudstone, and are oriented along a northwest-southeast axis. Many have a steep northwest side with a moat, relatively steep northeast and southwest sides, and a gently sloping southeast side, but there is significant variation in shape and slopes. The yardangs with strange and grotesque shapes, attributed in part to variation in the cross-bedded strata, are more accurately called demoiselles. Abrasion, deflation, fluvial erosion, and mass wasting are all processes sculpting the yardangs. The yardangs range in size from 4 m long and 1 m high to 11 m long and 3 m high. The average length-to-width ratio of the yardangs is 1.8:1. Yardangs usually indicate uni- or bidirectional winds. However, abutting the yardangs are dome dunes indicating highly variable wind directions. Pits dug around two of the dome dunes show beds dipping outward in all directions. Their heights vary from 2.3 to 5.9 m with side slopes of 2.3° to 12.5 °. The dome dunes are transitional to other types of dunes, such as longitudinal dunes with long axes in a northwest-southeast direction. The longitudinal dunes display slip faces characteristic of both transverse and barchan dunes. Other wind-related landforms include: coppice dunes, or vegetated sand mounds, which are positive feedback features; vegetation-anchored sand pedestals, probably originally formed as coppice dunes; inactive, semi-consolidated dunes undergoing erosion; and desert pavements. The yardangs and longitudinal dunes indicate dominant winds from the northwest, but the dome dunes suggest highly variable winds.