Geomorphology of the megadunes in the Badain Jaran Desert
Introduction
The Badain Jaran Desert, part of the Alashan Desert, is the second largest dunefield in China. It features the highest megadunes on Earth Breed et al., 1979, Zhu et al., 1980, beautiful interdune lakes and mysterious booming sands. Though it has been inhabited by Mongolian herdsmen for a long time, the Badain Jaran Desert did not receive much attention until the 1980s.
The Badian Jaran Desert is a little studied area in northwest China (Wang, 1990). Early work in the desert was conducted as part of expeditions to the Alashan Desert, such as those led by Scandinavian geologists (Hörner, 1936). They mainly surveyed the physiographic formations and the archeological relics in the marginal areas of the desert. Shortly after the reunification of China, several expeditions were organized to investigate the natural resources in the Alashan Desert. In 1957, the Chinese–Soviet Central Yellow River Complex Expedition studied the aeolian processes in the Alashan Desert, and in 1958, the Qinghai-Gansu Expedition of the Chinese Academy of Sciences explored the Alashan Desert. In 1959, Chinese and Soviet investigators began a 3-year Complex Sand Expedition in the region. The expeditions in 1950s and 1960s were mainly concerned with the natural conditions, utilization of the natural resources. Survey results on the vegetation, water resources and aeolian landforms were reported by Li (1962), Lou (1962), Yu (1962), Sun and Sun (1964) and Tan (1964). Several ideas were proposed on the formation of the megadunes in some local areas Lou, 1962, Sun and Sun, 1964, Tan, 1964. Lou (1962) suggested two possible reasons why the megadunes were created. The first is that the pattern of the megadunes is controlled by underlying humps that were covered by drifting sand. The second is that the megadunes developed from the sand deposits that accumulated when the drifting sand was obstructed by local stone humping. Sun and Sun (1964) thought the megadunes were related to the morphology of the underlying formation that had been folded by tectonic movements. Tan (1964) pointed out that lacustrine deposits of the early Pleistocene occur underneath the megadunes. Old dunes, which were fixed by calcareous cementation, once existed over the lacustrine deposits. Drifting sand covered these old fixed dunes, resulting in the current megadunes.
After the 1970s, remote sensing technology was employed to recognize the general characteristics of the Badain Jaran Desert Breed et al., 1979, Walker et al., 1987, Zhu et al., 1992, Guo et al., 2000. Breed et al. (1979) made a detailed report of the dune type, height, arrangement and spacing and their relation to the local wind regime based on the interpretation of landsat imagery. Chinese and German scientists made a comprehensive survey of the Badain Jaran Desert in 1988 and compiled a 1:500,000 map of the aeolian landforms, based on landsat TM imagery (Zhu et al., 1992). The map shows the types, distribution of the aeolian landforms, as well as the alignment, height and spacing of the megadunes.
The Badain Jaran Desert witnessed increasing interest from scientists in different fields after the 1990s. Several researchers studied the formation and geological evolution of the desert Dong et al., 1995, Jakel, 1996, Yang, 2000, Yan et al., 2001. Dong et al. (1995) studied the climatic changes at the southern fringe of the Badain Jaran Desert since the Pleistocene. Jakel (1996) studied the origin and development of the desert. Yang (2000) reconstructed the change of landscape and precipitation in the desert over the last 30,000 years by dating the deposits in the megadunes. Other researchers studied the characteristics and formation of the sand dunes Wang, 1990, Lu and Guo, 1995, Yang and Jiang, 1998, Yang et al., 1999, Yan et al., 2001. Wang (1990) proposed that the Badain Jaran Desert has been developing since the early Mid-Pleistocene. Due to climatic changes (glaciation–interglaciation), the sand dunes were subjected to alternations of fixation and reactivation, which ultimately resulted into the formation of megadunes. Yang and Jiang (1998), by measuring the morphmetric parameters of dunes, concluded that dunes in the Badain Jaran Desert became higher, more complex and stable from the northwest to the southeast. Yan et al. (2001) studied the megadunes by means of TL dating method and bedding occurrence of the dunes. They concluded that the formation and growth of megadunes in the Badain Jaran Desert were dependent on the sand supply, wind regime, underlying morphology and the shrub vegetation. Recently, Qu et al. (in press) studied the fractal behavior of the Badain Jaran megadunes. They found that the compound star megadunes have greater fractal dimension than star dunes. Hofmann (1996) studied the limnology and geochemistry of the lakes in the desert. Guo et al. (2000) detected the old drainage system across the Badain Jaran Desert that existed between the mid-Tertiary and pre-early mid-Pleistocene using the spaceborne radar images.
Megadunes are the most typical landforms in the Badain Jaran Desert. However, their formation, especially the formation of the megadune-lake alternations, is open to argument. Based on a field survey and interpretation of aerial photographs, this paper examines the general characteristics of the Badain Jaran megadunes, their morphometry and formation, as well as the formation of megadune-lake alternation landscape.
Section snippets
Physiographical setting
The Badain Jaran Desert lies in the northwest of the Alashan Highland in western Inner Mongolia of China, between 39° 20′N and 42°N, and 99° 48′E and 104° 14′E (Yang, 2000), covering an area of 49,000 km2 (Yan et al., 2001). The desert is bounded to the south by the Heli Mountains, the Beidai Mountains and the Heishantou Mountains that separate it from the gobi of the Hexi Corridor. To the southeast, it is bounded by the Yabrai Mountains, which separate it from the Tengger Desert. To the west,
Sand drift potential (DP)
The surface wind circulation over the Badain Jaran Desert is controlled primarily by the central Asiatic high-pressure cell in the winter and the thermal low-pressure cell that develops over the Indian subcontinent in the summer. During the winter, subsidence from the central Asiatic high tends to produce northerly to northwesterly winds across the deserts. During the spring the central Asiatic high weakens, its center shifts 10° westward, and a thermal low begins to develop over the Indian
Sediments constituting the megadunes
Sand supply provides the material basis for the megadunes in the Badain Jaran Desert. Petrov (1966) suggested that outcropping Cretaceous sandstone and extensive Quaternary and modern alluvial-lacustrine sediments of the Heihe drainage system are the sources of the sand in the Alashan Desert, including the Badain Jaran. Field investigations, interpretation of aerial photographs and drilling records indicate that there are extensive thick alluvial-lacustrine deposits around the Baidain Jaran
Morphometry of the megadunes
Fig. 4 shows the megadunes in the Badain Jaran Desert. The aerial photograph was taken in 1960. Fig. 5 is a close-up of the lake of Badain Jaran taken in 1999. It can be seen that the landscape did not experience obvious changes over the latest 40 years. This is because the formation of general structure of the dunefield took a very long time. It is estimated that over 60% of the desert is occupied by megadunes. General height of the megadunes ranges from approximately 150 to 350 m; the highest
Formation of the megadunes
To date, there is no satisfactory explanation for the formation of the megadunes in the Badain Jaran Desert though several attempts have been made. The focus of argument is about the relief properties underneath the megadunes. A reasonable explanation of the formation of megadunes in the Badain Jaran Desert must answer four key questions: Why is the arrangement of megadunes so well organized? How can the megadunes reach such great heights? Why are the highest megadunes located near the
Conclusions
Morphometry and formation of the megadunes in the Badain Jaran Desert were studied by means of field survey and aerial photographs. The megadune area is characterized by low a wind energy environment. Two main types of megadunes occur in the Badain Jaran Desert: compound transverse megadunes, which developed in a wind regime with a directional variability similar to that of transverse (barchanoid) dunes, and compound star megadunes, which developed near the mountains where directional
Acknowledgments
We gratefully acknowledge the funding from the National Science Fund for Distinguished Young Scholars of the National Natural Science Foundation of China (40225003), and the Knowledge Innovation Project of the Chinese Academy of Sciences (KZCX3-SW-324). We also extend our thanks to Dr. Q. Sun, and J. Qu for their help in the field work, and Mr. B. He for preparing the illustrations.
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