Debris flows triggered from non-stationary glacier lake outbursts: the case of the Teztor Lake complex (Northern Tian Shan, Kyrgyzstan)

One of the most far-reaching glacier-related hazards inthe Tian Shan Mountains of Kyrgyzstan is glacial lake outburstfloods (GLOFs) and related debris flows. An improved under-standing of the formation and evolution of glacial lakes and debrisflow susceptibility is therefore essential to assess and mitigatepotential hazards and risks. Non-stationary glacier lakes may fillperiodically and quickly; the potential for them to outburst in-creases as water volume may change dramatically over very shortperiods of time. After the outburst or drainage of a lake, the entireprocess may start again, and thus these non-stationary lakes are ofparticular importance in the region. In this work, the Teztor lakecomplex, located in Northern Kyrgyzstan, was selected for theanalysis of outburst mechanisms of non-stationary glacial lakes,their formation, as well as the triggering of flows and developmentof debris flows and floods downstream of the lakes. The differentTeztor lakes are filled with water periodically, and according tofield observations, they tend to outburst every 9–10 years onaverage. The most important event in the area dates back to1953, and another important event occurred on July 31, 2012. Othersmaller outbursts have been recorded as well. Our study showsthat the recent GLOF in 2012 was caused by a combination ofintense precipitation during the days preceding the event and arapid rise in air temperatures. Analyses of features in the entrain-ment and depositional zones point to a total debris flow volume ofabout 200,000 m3, with discharge ranging from 145 to 340 m3s−1and flow velocities between 5 and 7 m s−1. Results of this study arekey for a better design of sound river corridor planning and for theassessment and mitigation of potential GLOF hazards and risks inthe region