Surge dynamics and lake outbursts of Kyagar Glacier, Karakoram
Vanessa Round1, Silvan Leinss2, Matthias Huss1,3, Christoph Haemmig4, and Irena Hajnsek21Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zurich, 8093 Zurich, Switzerland 2Institute of Environmental Engineering, ETH Zurich, 8093 Zurich, Switzerland 3Department of Geosciences, University of Fribourg, 1700 Fribourg, Switzerland 4GEOTEST AG, Zollikofen, Switzerland
Received: 22 Oct 2016 – Accepted for review: 02 Nov 2016 – Discussion started: 10 Nov 2016
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.
Round, V., Leinss, S., Huss, M., Haemmig, C., and Hajnsek, I.: Surge dynamics and lake outbursts of Kyagar Glacier, Karakoram, The Cryosphere Discuss., doi:10.5194/tc-2016-236, in review, 2016.