Mechanism of an ancient river-damming landslide at batang hydropower station, Jinsha river basin, China

Abstract

An ancient, large-scale river-damming landslide, located 4 km on the upper stream of the dam site of the Batang Hydropower Station, southeastern Tibetan Plateau, China, was investigated herein. We used an unmanned aerial vehicle (UAV) survey, field investigations, geology and topography maps, borehole surveys, basic laboratory testing, and geological dating to reveal evidence of this river-damming landslide and its cause mechanism. The studied landslide had an estimated volume of 3.5 × 107 m3, blocked the valley, and formed a dam > 170 m in height. A large quantity of lacustrine sediments was discovered on both banks upstream of the residual landslide dam; this had a maximum thickness of 30 m, mainly comprised of fine sand and silt, with particle sizes of 0.01–0.25 mm, and demonstrated that the landslide blocked the Jinsha River. There was a clear geological structural dependence of the slope failure in the landslide area, dominated by a combination of sliding-toppling failure on cataclinal slopes. The slope instability mode was slip-controlled toppling failure within a thin-layered biotite quartz schist that exhibited inferior mechanical properties. The head scarp developed along a bedding plane that dipped steeply in the same direction as the slope. The upstream and downstream lateral scarps formed along the joint sets J2 and J3, respectively, which intersected with the bedding plane, forming a wedge and facilitating slope instability. Rapid river incision, intense tectonic activity, a high and steep slope, and thin-layered steeply dipping strata were the controlling factors for the occurrence of this landslide, all contributing to slope failure. On the basis of our comprehensive analysis of paleoearthquakes, paleoclimate, and geological dating of the landslide, we conclude that this ancient river-damming landslide event was likely triggered by a strong earthquake related to activity on the Xiongsong‒Suwalong fault in the Late Holocene.