Surge dynamics and lake outbursts of Kyagar Glacier, Karakoram

Abstract

Abstract. The recent surge cycle of Kyagar Glacier, in the Chinese Karakoram, caused formation of an ice-dammed lake and subsequent glacial lake outburst floods (GLOFs) exceeding 50 and 40 million m3 in 2015 and 2016, respectively. GLOFs from Kyagar Glacier reached double this size in 2002 and earlier, but the role of glacier surging in GLOF formation was previously unrecognised. We present an integrative analysis of the glacier surge dynamics from 2011 to 2016, assessing surge mechanisms and evaluating the surge cycle impact on GLOFs. Over 80 glacier surface velocity fields were created from TanDEM-X, Sentinel-1A and Landsat satellite data. Changes in ice thickness distribution were revealed by a time series of TanDEM-X DEMs. The analysis shows that during a quiescence phase lasting at least 14 years, ice mass built up in a reservoir area at the top of the glacier tongue and the terminus thinned by up to 100 m, but in the two years preceding the surge this pattern reversed. The surge clearly initiated with the onset of the 2014 melt season, and in the following 15 months velocity evolved in a manner consistent with a hydrologically-controlled surge mechanism with dramatic accelerations coinciding with melt seasons, winter deceleration accompanied by subglacial drainage, and rapid surge termination following the 2015 GLOF. Rapid basal motion during surging is seemingly controlled by high water pressure caused by input of surface water into either an inefficient subglacial drainage system or unstable subglacial till. Over 60 m of thickening at the terminus caused potential lake volume to increase more than 40-fold since surge onset, to currently more than 70 million m3, indicating that lake formation should be carefully monitored to anticipate large GLOFs in the near future.

A Glacier Surge of Bivachny Glacier, Pamir Mountains, Observed by a Time Series of High-Resolution Digital Elevation Models and Glacier Velocities

“…Surface velocities increased from near-zero during the quiescence phase up to 3400 m year −1 in spring 2014 with superimposed seasonal variations. In contrast to what is observed at other surges (e.g., [18]), a sharp surge front developed during the surge of Bivachny Glacier, which is traceable in elevation as well as strain rate. It travelled with a mean velocity of 4400 m year −1 for a distance of 13 km down to the confluence with Fedchenko Glacier.…”

“…Most detailed studies concentrated on the evolution of ice flow velocity during the surge (e.g., [15][16][17][18], with only few examples of time series of elevation changes during a surge (e.g., [19,20]). …”

The hazardous 2017–2019 surge and river damming by Shispare Glacier, Karakoram

“…2a-d). The pre-surge acceleration duration for Shispare Glacier from November 2017 to February 2018 appears rather brief compared to other surges reported in the Karakoram 22 .…”

“…No change was observed in the terminus position. The fluctuations in surface displacement during 2013 to 2016 (acceleration and deceleration) mask or preclude a lengthy pre-surge acceleration as observed on other surge-type glaciers 6,22,26,44 (Fig. 2a-d).…”

“…Active surges pose dangerous hazards for local communities, threatening destruction of critical infrastructure when ice overrides villages, roads, bridges, and trails. Furthermore, if the glacier advances across river valleys and forms an ice-dammed lake, it may result in devastating outburst floods [21][22][23][24] . Therefore, monitoring of glacier surges, ice-dammed lake formation and drainage is essential.…”