Abstract:Investigations of historical landslide dams are of great significance for both in-depth understanding of regional tectonics and river evolution, and the safety of mountain river engineering. A section of the upper Jinsha River runs among the Jinsha River suture belt from the estuary of Baqu stream to the estuary of Maiqu stream. Due to the alpine and gorge geomorphy and active tectonics in the section, historical landslide dams are highly developed, among which Wangdalong paleo-landslide is characterized by the highest dam height, the largest volume of dammed lake and the longer silt history. 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 the major conclusions are summarized as follows: 1) Wangdalong landslide is located in the suture area of Jinsha River and its main rocks comprise slate in the lower Zhongxinrong Formation (T_1–2zh¹) 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 T_1–2zh¹ and fracture surface of the Wang-dalong 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 is estimated to be about 4.0×10⁸ 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 approximately 1 700 m in length, 3 000 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 about 2 735 m, while the right side can reach as high as about 2 770 m. 4) The dammed lake has a volume of about 26.6×10⁹ m³, which extends upstream for about 176 km and to the estuary of Jiangqu creek, i.e. the damsite of Yebatan hydropower station. 5) The dam experienced three breaching events and the corresponding elevation of sluice bed are approximately 2 460 m, 2 400 m and 2 358 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 21.0×10⁴ to 39.8×10⁴ m³/s, much larger than any historical records available in the reaches of Yangtze River.