Formation of a hazardous ice-dammed glacier lake: a case study of anomalous behavior of Hassanabad glacier system in the Karakoram

Abstract

Formation of glacier lakes and glacier lake outburst floods (GLOF) are not a new phenomenon in the Karakoram Himalaya. This case study focuses on sudden expansion of Shishper glacier termini and subsequent formation of an ice-dammed glacier lake occupying ~ 3 km moraine following Mochuwar glacier retreat in the Karakoram. A method based on a combination of space (remote sensing) and ground observations is applied to reconstruct spatio-temporal glacier termini change and lake extent. Moreover, the likely glacier-mass losses are determined above and below the Equilibrium Line Altitude (ELA) contours based on recommended values of Accumulation-Area-Ratio and Accumulation-Area-Balance-Ratio for mountain glaciers. Potential implications of glacier surge and ice-dammed glacier lake on downstream infrastructure and hydrological system are assessed. The results show that the Shishper glacier termini advanced 90% from 1980s to 1999 and 78.7% from 1999 to 2019 as compared to 188% and 421% retreat in the Mochuwar glacier termini for the same years, respectively. The current unusual surge of debris-covered Shishper glacier termini created a ~ 152 m deep ice-dammed glacier lake representing a total area increase of 500% over 6 months. The ratio of glacier accumulation to ablation is low for the Hassanabad glacier system, therefore there is a significant influence on forward movement of Shishper glacier termini. Water discharge from the glacier lake increased with increase in summer temperatures causing inundation of part of the Karakoram Highway at Hassanabad village. The current unusual surge of the Shishper glacier can be characterized as type-I as it involves an in-built unsteadiness without any regular intervals due to an unknown mechanism producing very high movement of debris-covered glacial ice and sediments.