Abstract:

Recent research has raised concerns about the potential influence of rapid climate change on the stability of major ice sheets. The behaviour of glaciers is determined largely by the processes and conditions operating at their base. Technological advances have allowed these factors to be examined and their contribution to ice flow constrained. This study investigated the rapid disintegration of an aquatic based Norwegian glacier, through the study of boreholes, video, ground-penetrating radar, differential global positioning system, bathymetry and Glacsweb wireless probes. Briksdalsbreen retreated dramatically between 2000 and 2007, with c. 56 × 105 m3 of ice lost from the glacier tongue, equivalent to a rate of 70 m a−1. This was due to the combined effect of higher summer temperatures, decreased precipitation (resulting from a negative phase of the North Atlantic Oscillation) and increased fracturing of the glacier tongue. The enlargement of a proglacial lake played a key role in Brikdalsbreen's rapid retreat, allowing calving events and promoting crevassing and fluctuating water contents at the glacier margin. We suggest that hydro-fracturing was the dominant mechanism responsible for generating more crevasses each year, which facilitated the development of an efficient englacial drainage system. This fed increasing quantities of water to the bed, where it was stored in subglacial cavities and transferred through a distributed (‘slow') drainage system. However, despite this increase in subglacial water content, ice velocities remained constant during the break-up. Comparisons are made between the processes observed at Briksdalsbreen and those associated with the acceleration and rapid retreat of Greenland's tidewater glaciers.

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