ИСТИНА

The catastrophic Bureya rockslide about 25 million m 3 in volume collapsed on December 11, 2018 from the left-bank slope of the Bureya River valley (Far East of Russia), nowadays filled by the Bureya reservoir. The Bureya rockslide formation was predetermined by combination of several factors: – geological structure of the rock massif affected by several fault zones, thawing of the permafrost at the lower part of the slope due to warming effect of the deep reservoir, intensive precipitation during the preceding summer. The direct trigger could be associated with fast and intensive drop of the air temperature that froze the slope and blocked free seepage of the ground water. - Slope failure took place in several successive stages recorded by seismic network and characterized by variable failure mechanisms. Wedge rockslide about 12 million cubic meters occurred at the fist stage and transformed into rock avalanche about 750 m long (from the slope base) that moved in NNE direction. The planar rockslide almost of the same volume that originated at the second stage about 10 seconds later moved in the NNW direction for the same distance and also formed rock avalanche. Rock avalanches moved ~25 m/sec, locally up to ca. 60 m/sec. During the last stage about 1.2 million cubic meters of rocks collapsed and remain in the headscarp. - Rockslide that caved into deep reservoir produced the tsunami wave mixed with ice up to 50-60 m high that completely washed out the taiga forest at a distance of 3.6 km upstream the tributary valley, ~7 km upstream and ~4 km downstream the reservoir banks. It formed the dam that divided the reservoir into two parts that required special measures to make a canal through its body.