金沙江上游超大古堰塞湖及其相关问题

历史大型堵江滑坡研究不仅是认识区域构造背景和河流演变规律的重要工作，而且对山区河流工程安全亦有十分重要的意义。以金沙江上游河段的王大龙古滑坡为研究对象，基于野外调查与资料分析，对其成因与演变过程进行了分析。主要结论如下：（1）王大龙滑坡位于金沙江缝合带，源区基岩主要为三叠系中心绒群下段板岩 (T1-2zh1)，其次为二叠系嘎金雪山群下段石英砂岩 (Pgj1)，滑坡总体上为王大龙断裂与中心绒群板理面切割形成的楔形体，前缘受雄松-苏洼龙活动断裂切割，方量约4.0×108m3；（2）诱发滑坡的内动力为地震，外动力为河流凹岸侵蚀，滑坡时间应为晚更新世大理冰期；（3）堰塞坝长约1700m，宽约3000m，高度超过450m，形态右高左低，右岸高程约2770m，左岸垭口高程约2735m；（4）堰塞湖规模约266×108m3，干流库尾到达叶巴滩水电站坝址的降曲河口，长度约176 km；（5）堰塞坝发生过3次溃决，溃口底面高程分别为2460m、2400m和2358m（现河面高程）；（6）第一次溃决极有可能雄松-苏洼龙断裂错动导致的，时间早于1900 a BP，估算溃口流量21.0~39.8×104m3/s，远远大于长江历史洪水记录。

A Gigantic Paleo-dammed Lake in the Upper Reaches of Jinsha River and Its Relevant Issues

Investigations of historical landslide dams are of great significance both for in-depth understanding of regional tectonics and river evolution, and for the safety of mountain river engineering. Based on detailed field survey and data analysis of Wangdalong paleo-landslide in the upper reaches of Jinsha River, its formation and evolution are analyzed and major conclusions are summarized as follows. (1) Wangdalong landslide is located in the suture area of Jinsha River and its main rocks comprise of slate in the lower Zhongxinrong Formation (T1-2zh1) and quartz sandstone in the lower Gajin Formation (Pgj1). Its source zone is a rock wedge confined by two discontinuities, i.e. the slate foliation of T1-2zh1 and fracture surface of the Wangdalong Fault, which form an intersection line plunging towards the west. Xiongsong-Suwalong active Fault cuts through the toe of the wedge and the wedge volume thus formed is estimated to be ~ 400×106 m3. (2) The landslide was probably triggered endogenically by an earthquake and exenogenically by lateral erosion due to its location on the concave-bank of the river. And the slide should occur in the Dali glaciations of the Late Pleistocene. (3) The dimensions of the landslide dam are ~1700 m in length, ~3000 m in width and ~450 m in height. The left side of the dam is lower than the right side, the elevation of the left side is ~2735 m, while the right side can reach as high as ~2770 m. (4) The dammed lake has a volume of ~26.6×109 m3, which extends upstream for ~176 km and to the estuary of Jiangqu creek, i.e. the damsite of Yebatan hydropower station. (5) The dam experienced three beaching events and the corresponding elevation of sluice bed are ~2460 m, ~2400 m and ~2358 m ( the present river level) respectively. (6) The first dam-break should most likely be induced by the dislocation of Xiongsong-Suwalong Fault, earlier than 1900 a BP, and its empirically estimated flood is 210×103 to 398×103m3/s, much larger than any historical records available in the reaches of Yangtze river.