Formation and failure of the Tsatichhu landslide dam, Bhutan

At 00:30 (local time) on the loth September 2003 a joint and foliation defined wedge of material with an estimated volume of 7-12 x 10(6) m(3) slid into the narrowTsatichhu River Valley, in Jarrey Geog, Lhuentse, eastern Bhutan. The Tsatichhu River, a north-easterly flowing tributary of the Kurichuu River, was completely blocked by the landslide. During its movement, the landslide transitioned into a rock avalanche that travelled 580 m across the valley before colliding with the opposite valley wall. The flow then moved down valley, travelling a total distance of some 700 m. The rock avalanche was accompanied by an intense wind blast that caused substantial damage to the heavily forested valley slopes. The resulting geomorphologically-typical rock-avalanche dam deposit created a dam that impounded a water volume of 4-7 x 10(6) m(3) at lake full level. This lake was released by catastrophic collapse of the landslide, which occurred at 16:20 (local time) on loth July 2004, after reported smaller failures of the saturated downstream face. The dam failure released a flood wave that had a peak discharge of 5900 m(3) s(-1) at the Kurichhu Hydropower Plant 35 km downstream.