关键词: 地貌学, 风蚀形态, 雅丹, 罗布泊

Abstract:

Yardang is a typical, aeolian erosion landform widely distributed on Earth and discovered on other planets (Venus and Mars) too. Because of its various forms and volatility, yardang's morphological characteristics have attracted attention for generations. Lop Nur is located in the eastern part of the Tarim Basin in Xinjiang, China. Although there are many yardangs with various types in the area of Lop Nur, there is a lack of study about this impressive landform there. On the basis of field investigation, the authors found that UAV drones can efficiently and effectively collect yardang morphology data. Based on collected yardang morphology data (including field survey and DEM from UAV), using the terrain digital extraction method, after measuring the morphological parameter data of yardang, this article attempts to clarify the morphological characteristics of yardangs in the Lop Nur area, and to discuss its formation processes. The main conclusions are as follows: (1) The lengths of yardangs in the Lop Nur area are often < 20 m, although a few of them are even > 160 m. The widths of yardangs in our study area are mainly < 8 m, with a height of mostly < 2 m. It shows that the sizes of yardangs in the study area are generally small, although some large ones occur too. The ratio of length vs. width (R) of yardangs ranges from 2:1 to 4:1, and even > 10:1. The orientations of the yardangs in our study area are mainly toward 22.5°-67.5°, consistent with the predominant wind directions. Our observations suggest that the morphology of yardangs in the study area initiated from a dome-shaped form and then changed to drop-shaped, and finally to linear forms. The number of yardangs occurring nearby is often 3-4, and the distance between them is often < 20 m but occasionally 40-80 m. (2) The most likely evolution processes of yardangs in the Lop Nur area can be summarized into four stages: embryonic, juvenile, mature and decay periods. However, due to the influence of various controlling factors such as stratum sediment characteristics, wind erosion, and flowing water, yardang's morphology in the Lop Nur area become quite complex. (3) The developments of yardangs in the Lop Nur area have multiple periods. Since the Quaternary, there have been four main development periods in late Pleistocene (ca. 90 ka B.P.), early Holocene (8-9 ka B.P.), late Holocene (after 1.6 ka B.P.) and Little Ice Age (around 0.5 ka B.P.). According to morphological characteristics and environmental evolution, we infer that yardangs in Longcheng and Bailongdui were formed in the late Pleistocene, the northern Loulan grand yardangs formed in the Early Holocene, yardangs in central and northern Loulan formed in the late Pleistocene and the small yardangs in Loulan area formed probably during the Little Ice Age. Based on the chronology and yardangs' height, the average wind erosion rate near the Loulan site after 0.5 ka B.P. was calculated to be 6.2 mm a^-1. Accurately describing the morphological characteristics of yardangs in the Lop Nur area and understanding its evolution procession is of great significance for analyzing the morphological development of yardangs and the regional wind erosion process.

Key words: geomorphology, wind-eroded landform, Yardang, Lop Nur