TC The Cryosphere TC 1994-0424 Copernicus GmbH Göttingen, Germany 10.5194/tc-7-129-2013 Ice tectonic deformation during the rapid in situ drainage of a supraglacial lake on the Greenland Ice Sheet Doyle S. H. 1 Hubbard A. L. 1 Dow C. F. 2 Jones G. A. 1 2 Fitzpatrick A. 1 Gusmeroli A. 2 5 Kulessa B. 2 Lindback K. 3 Pettersson R. 3 Box J. E. 4 Centre for Glaciology, Institute of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, SY23 3DB, UK Glaciology Group, College of Science, Swansea University, Swansea, SA2 8PP, UK Earth Sciences, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden Department of Geography, The Ohio State University, 1036 Derby Hall, 154 North Oval Mall, Columbus, Ohio 43210–1361, USA now at: International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, Alaska, USA 28 01 2013 7 1 129 140 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.the-cryosphere.net/7/129/2013/tc-7-129-2013.html The full text article is available as a PDF file from http://www.the-cryosphere.net/7/129/2013/tc-7-129-2013.pdf

We present detailed records of lake discharge, ice motion and passive seismicity capturing the behaviour and processes preceding, during and following the rapid drainage of a 4 km<sup>2</sup> supraglacial lake through 1.1-km-thick ice on the western margin of the Greenland Ice Sheet. Peak discharge of 3300 m<sup>3</sup> s<sup>−1</sup> coincident with maximal rates of vertical uplift indicates that surface water accessed the ice–bed interface causing widespread hydraulic separation and enhanced basal motion. The differential motion of four global positioning system (GPS) receivers located around the lake record the opening and closure of the fractures through which the lake drained. We hypothesise that the majority of discharge occurred through a 3-km-long fracture with a peak width averaged across its wetted length of 0.4 m. We argue that the fracture's kilometre-scale length allowed rapid discharge to be achieved by combining reasonable water velocities with sub-metre fracture widths. These observations add to the currently limited knowledge of in situ supraglacial lake drainage events, which rapidly deliver large volumes of water to the ice–bed interface.

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