Remote-sensing-based monitoring the dynamics of Kyagar Glacial Lake in the upstream section of Yarkant River, north Karakoram

Long-term monitoring of ice-dammed lakes is important for understanding the process of lake storage, development, and glacial outburst flood (GLOF). Based on remote sensing observations for the period 1972-2020, we obtained what is so far the most detailed reconstruction of the filling and draining of Kyagar Lake, a typical annually ice-dammed lake in the north Karakoram. We show that annually repeated lake fillings-drainings were detected by satellite observations during two periods: 1996-2009 and 2015-2020, while between 2009 and 2015 no obvious cycle occurred. These two intermitted periods with regular annual revival of lake outburst were likely related to the long-term cycle of glacier surge dynamics, namely two remarkable surge-induced terminus accelerations during 1995-1997 and 2014-2016. Following each surge, the maximum lake areas decreased by about 33% from 1996 to 2009 and by about 88% from 2015 to 2020. Combined with climatic warming and the thinning of the ice-dam, the storage capacity of Kyagar Lake will likely continue to decrease in the future, and the risk of lake outburst flood thus becomes lower. Repeated drainage following filling exacerbates the depletion of mass at the glacier terminal, leading to the cessation of storage and creating the conditions for the next glacial surge to occur, creating a long-term iteration of the surge process. Considering the uncertainty and intensified climate changes, it suggests that a close monitoring of the glacial lake development and glacier dynamics would be still important.