Science Times Liu Yingnan
Recent research by Fang Xiaomin and Han Yongxiang of Lanzhou University discovers that the Tibetan Plateau have all the conditions for the happening of sand-dust storms. It’s not only a dust-source field comparable to the arid regions in northern China, but possibly one that affords the most efficient remote dust transport in the world.
Prof. Fang Xiaomin, director of the Key Lab of Western China’s Environment of Lanzhou University, said that the surrounding and marginal regions of the Tibetan Plateau abounded in loess, whose origin and sources had always been a remarkable scientific issue. Latest geological evidences show that loess on the Tibetan Plateau is “cold loess”, different from that on the Loess Plateau, whose granularity is coarser than that of the latter. West wind at medium and high altitudes and the alpine monsoon are probably the major makers and carriers of the dust. The possibility of their coming from the northern deserts was lately ruled out, which showed that the Tibetan Plateau must have been an important source of sandstorms in geological history. Besides, the times and frequency of sand-dust storms happening in China in the last 30 years do not match with the records of loess (floating dust) from Japan and Korea at the lower reaches. Loess observed in Japan displays a marked multilayer structure, which cannot be explained by the single dust-source region of north China and thus indicates that the high-altitude Tibetan Plateau could be the cause of the difference.
“Whether the Tibetan Plateau is an important dust-source region is not merely a regional scientific issue, but a significant one involving the cognizance of the formation and source of loess on the Plateau, the uplift of the Plateau, and the global ocean-land-atmosphere coupling process. It’s necessary to conduct further and deeper research.” Prof. Fang Xiaomin said that loess over and around the Tibetan Plateau was mainly formed 0.8~1.15 Ma, and was probably closely related to a series events of that time such as the global cooling down, the sharp desertification in inland China, and the large-scale expansion of loess from the Loess Plateau to the middle and lower reaches of Changjiang Drainage Area in eastern China.
Prof. Fang said that to decide whether the Tibetan Plateau was a major dust-source field, the frequency of the sand-dust storms as well as the capacity of the sand to reach the west wind jet zone should be counted on besides inspection of related geological reality. Through analysis of the sand-dust storm in Lhasa during March 3 to 5, 2003, Fang and his colleagues found that the Tibetan Plateau had all the conditions needed for the happening of a sand-dust storm. It has strong ascending motion to raise the dust of different grain sizes to different altitudes; the coarser dust deposit at east of the Plateau and form loess, while finer dust is carried by the west wind jet to Far East region. Through comparative study of the sand-dust storm elements of the Tibetan Plateau and of other dust-source regions in China, they believe that the Tibetan Plateau is a dust-source field comparable to the arid regions in northern China.
Follow-up research shows that on the Tibetan Plateau dust needs to ascend merely 1000-2000 meters to reach the west wind jet zone and undergo remote transport. Compared to dust-source deserts at low altitude (Takelamagan Desert, Badanjilin Desert and Tenggeli Desert), dust raised in sandstorms on the plateau enters the west wind jet zone and travels to north Pacific more easily, with an efficient sand transport mechanism. Prof. Fang and his colleagues stressed that due to the high frequency of sand-dust storms on the plateau (more than 30 times per year), it was not only a main source of remote transported dust, but was probably the most efficient dust-source region for remote dust transport in the world .
Prof. Fang finally indicated that what they had got was merely a preliminary conclusion. The final conclusion could not be drawn before further research was conducted.
