ИСТИНА

Most powerful and disastrous debris flows are caused by lakes' breach, the glacial lakes mainly (GLOFs). However, even more adverse consequences might be caused by the rockslide-dammed lakes' outburst, whose volume can reach several cubic kilometers. Such outburst floods transport significant amount of debris eroded from the blockages, though, generally, do not have the flow density typical of the "classical" debris flows. Case studies of such debris floods that occurred in the historical times in different mountainous regions will be presented. Traces of the extremely powerful debris floods that occurred in the prehistoric times in different parts of the Central Asia region, in the Kokomeren, Sarydjaz (Aksu), Sokh, Gunt, Piandj River valleys were identified by analysis of high resolution space images and during field observations. They allow not just identify such phenomena, but assess their parameters such as height of the surge wave and peak discharge at some distances from the breached blockages. Such conclusions can be drawn based on the analyses of rivers' thalweg profiles, of the specific landforms left by debris floods on river terraces and of the deposits accumulated downstream of the breached dams. These data, along with observations made during historical outburst floods that occurred in last 200 years, can be considered as analogues applicable for assessing possible effects of the outburst of both the existing dammed lakes and those lakes that could originate in future.