Buoyant flexure and basal crevassing in dynamic mass loss at Helheim Glacier

Abstract

Iceberg calving accounts for a significant proportion of annual mass loss from marine-terminating glaciers1,2 and may have been a factor in the rapid demise of ancient ice sheets3. The largest contributions from the main outlet glaciers of the Greenland ice sheet to sea-level rise over the next two centuries have been projected to be dynamic in origin, that is, driven by glacier flow and calving4. However, present physical models remain a coarse approximation of real calving mechanisms because models are poorly constrained by sparse glacier geometry observations5. Here we present a record of daily digital elevation models from the calving margin of Greenland’s Helheim Glacier at a high spatial resolution. Our digital elevation models are derived from stereo terrestrial photography taken over the summers of 2010 and 2011. We find that during these two summers dynamic mass loss at Helheim Glacier was dominated by calving events exceeding 1 km3 that were the result of buoyant flexure and the propagation of basal crevasses. We suggest that this buoyancy-driven mechanism for calving may be common elsewhere in Greenland and could be a first-order control on the ice sheet’s future contribution to sea-level rise.

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Figure 1: Camera locations with differenced DEMs.
Figure 2: Elevation profiles along Helheim’s central flowline.
Figure 3: Image feature tracking before 12 July 2010 18:30 UTC calving event.
Figure 4: Surface profiles and bed topography.

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Acknowledgements

T.D.J. was supported by The Leverhulme Trust Research Leadership Award GLIMPSE Project (F/00391/J) and the Climate Consortium for Wales (C3W). N.S. is supported by NERC (NE/I007148/1). N.S. and K.S. were also supported by The Leverhulme Trust. M.O. was supported by the Welsh Institute for Sustainable Environments (WISE). Field work was funded by The Leverhulme Trust, a Royal Geographical Society-Institute of British Geographers EPSRC Geographical Research Grant (20IGC 01/10), NERC (NE/I007148/1) and the European Union Seventh Framework Programme [FP7/2007–2013] under grant agreement number 262693 [INTERACT]. ASTER imagery were acquired through NASA’s Land Processes Distributed Active Archive Center (LP DAAC) with thanks to Operation IceBridge and B. Krabill. The authors would also like to acknowledge software support from TerraDat Geophysics (ImageMaster) and F. Ayoub (COSI-Corr). We acknowledge the use of bed data from CReSIS generated with support from NSF grant ANT-0424589 and NASA grant NNX10AT68G and their assistance with data analysis.

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T.D.J. developed the methodology, undertook the analysis and interpretation and prepared the manuscript. T.M. was the grant-holder and contributed to data collection and interpretation. N.S. and K.S. contributed to methodological development and data collection. M.O. contributed to the interpretation. All authors contributed to the manuscript preparation.

Correspondence to Timothy D. James.

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James, T., Murray, T., Selmes, N. et al. Buoyant flexure and basal crevassing in dynamic mass loss at Helheim Glacier. Nature Geosci 7, 593–596 (2014). https://doi.org/10.1038/ngeo2204

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