西藏东南雅鲁藏布大峡谷入口处 第四纪多次冰川阻江事件*

在第四纪的末次冰期、新冰期和小冰期期间,位于大峡谷入口处的则隆弄跃动冰川发生多次的快速前进,多次发生阻塞雅鲁藏布江事件,在大峡谷以上河段形成4期(Ⅳ~Ⅰ)的林芝古堰塞湖。¹⁴ C测年结果指示第2次、第3次和第4次堰塞湖分别发生在9760~11300aB.P.,1220±40~1660±40aB.P.和287±93~394±83aB.P.。估计Ⅳ~Ⅱ期堰塞湖库容量约2150km³,835km³和81km³。冰川阻塞湖坝的溃决释放突发性洪水,对下游的雅鲁藏布大峡谷河段及下游地区的环境产生巨大的影响。

QUATERNARY GLACIER BLOCKING EVENTS AT THE ENTRANCE OF YARLUNG ZANGBO GREAT CANYON,SOUTHEAST TIBET

There are four sets of lacustrine terraces and sediments distributing along the upstream of the Yarlung Zangbo River and its tributary Nyang River in Southeast Tibet.Researches on lacustrine sediments and glacier activities which were located near the entrance of the Yarlung Zangbo Great Canyon,combined with ¹⁴ C dating have confirmed glacier blocking events and dammed lakes along the upstream of the Yarlung Zangbo River in Quaternary.The Zelunglung glacier which was located at the entrance of the Yarlung Zangbo Great Canyon and the west slop of the Mt.Namche Barwa (7782m) is an active oceanic as well as surge glacier.In Quaternary along the Yarlung Zangbo Great Canyon the India oceanic water vapor supplied enough precipitation to form oceanic glaciers distributing in East Tibetan Plateau,including the Zelunglung Glacier.Ancient lakes dammed by moraines from the Zelunglung Glacier were formed in the upstream of the Yarlung Zangbo Great Canyon at the eastern Himalayan Syntaxis.At least four damming events were recorded in the lacustrine and alluvial terraces and sediments distributed in that area; the first and second events happened during the Last Glaciation,the third and fourth occurred in the New Glaciation and the Little Glaciation respectively.Radiocarbon dating of wood and charcoal yields ages of 9760~11300aB.P.for the second damming,1220±40~1660±40aB.P.for the third damming,and 287±93 ~ 394±83aB.P.for the fourth damming.Estimated volumes of the ancient glacier dammed lakes (named Linzhi Ancient Lakes) were 2150km³,835km³,and 81km³ respectively.During interglacial phases the outburst floods down to the gorge of the Yarlung Zangbo River were estimated at peak discharge of up to 1×10⁶ to 9×10⁶m³／s.The erosive intensity represented by the estimation for such a catastrophic lake breakout implies that the post-glacial megafloods down to the Yarlung Zangbo River were likely among the most erosive events in recent Earth history.