Usoi Rockslide Dam and Lake Sarez, Pamir Mountains, Tajikistan

The Usoi blockage, 2.2 km3 in volume formed a World-highest natural dam and the Lake Sarez containing about 16 km3 of water can pose a threat to the downstream Bartang – Pianj – Amu-Daria River valleys. Different view-points on the dams’ stability exist. Modern data on the dam and the potentially unstable lakeside are presented that are used for the Lake Sarez outburst flood risk assessment. The conclusion has been drown that at present the Usoi Dam is stable and can not be completely destroyed either by the internal erosion or by overtopping owing to its huge dimensions, composition and structure. Regarding the existence of the Right Bank Landslide 0.9 km3 in volume, which simultaneous collapse has been considered as the most hazardous phenomena capable for dams’ breach, no sufficient evidences of such scenario have been found out. This slope is undergoing typical post-glacial evolution and only relatively small failures that can not cause the Usoi Dam destruction are expected. Even Lake level raise caused by dams’ body compaction due to strong earthquakes and decrease of seepage or by increasing inflow due to climate changes should not lead to the immediate catastrophic consequences, since composition of the dams’ surface covered by blocky carapace prevents its rapid destruction.