What is Ya Dan landform?

Ya Dan landform refers to the fragmented ridge and gully landform formed by lake deposition or wind erosion of alluvial plain in arid areas. Ya Dan is called in Uyghur, which means a mountain with steep walls. The raised wind erosion hills are long, and the arrangement direction is parallel to the main wind direction. Recent research shows that the erosion of temporary running water and lake water is also one of the important reasons for the formation of Ya Dan. The landform of Ya Dan is most typical near Loulan in the northwest of Lop Nur. (Information provided by the Ministry of Land and Resources)

In the inland desert of China, there are a series of long mounds and grooves extending intermittently, which is the landform of Ya Dan. During the joint inspection in Lop Nur in the 20th century, junior high school and foreign scholars discovered this peculiar landform near Guloulan in the northwest of Lop Nur, and named it according to the Uighur appellation, and then translated it back into Chinese as "Ya Dan".

Ya Dan can be found in many arid areas in the world, not only in Xinjiang, China. The road from You Xiang in Qinghai to southern Xinjiang is very desolate. Ya Dan can be seen between Nanbaxian and Yiliping Highway, which is the largest distribution area of Ya Dan in the northwest inland. However, Ya Dan landform is the most widely distributed landform in Xinjiang. Besides Ya Dan and Guloulan in Lop Nur, the ghost town in Karamay and the windy city in Qitai are also typical Ya Dan landforms.

Formation mechanism of Ya Dan landform

There are two key factors in the formation of Ya Dan. First, the geological basis for the development of this landform, that is, lacustrine sedimentary strata; The second is external force erosion, that is, strong directional wind erosion and flowing water erosion in the desert.

Lakes in arid areas often include repeated water inflow and water withdrawal in their formation history, thus developing overlying mudstone layers and sandy soil layers. Wind and running water can take away loose sandy soil layer, but it has limited effect on hard mudstone layer and gypsum cementation layer. However, the dense mudstone layer is not indestructible, and the expansion and contraction effect caused by severe temperature difference in desert area will eventually lead to the disintegration of mudstone layer, and the exposed sandy soil layer will be carried away by wind and running water and evolved into a groove shape; The part still covered by mudstone is relatively stable, forming large or small strip mounds, and the landform of Ya Dan gradually appears.

The external factors that form Ya Dan are usually considered as the dominant factors of strong prevailing winds, but this is not a single dominant factor. For example, in the east of Acic Valley, the direction of Sanlongshayadan is southeast, perpendicular to the prevailing northwest wind direction and consistent with the flow direction of mountain torrents, indicating that floods play a leading role in this Ya Dan; In addition, some Ya Dan are formed by the interaction of wind and flowing water, such as Ya Dan in Longcheng.