Three dimensional monitoring of a major calving event at Helheim Glacier using stereo terrestrial photography

The Greenland Ice Sheet is losing mass to the oceans at an accelerating rate due to increased runoff and changes in ice dynamics. This will have important implications for global sea-level, ocean circulation, and regional climate. A wide variety of evidence, including GRACE data, and both satellite and airborne altimetry show that losses from the south-east have been the primary cause of these changes. Beginning in the late 1990s, flow velocities of many tidewater outlet glaciers increased to as much as double their former speed, coupled with rapid retreat of calving front positions. Overall, calving is responsible for about 50% of the annual mass discharge from Greenland. However, calving is a challenging process to understand and its controls are not well understood. Calving fronts are very dynamic environments, difficult to access, large in scale and often the majority of the calving activity occurs underwater. Our aim is to measure calving rates, glacier flow speeds and ice mélange behaviour using terrestrial photography and hence to improve understanding of their relationship to fjordic conditions. In July 2010, we recorded a major calving event at Helheim Glacier, in stereo and ten second time-lapse photography. The calved ice measured approximately 4000 - 5000 m wide, 200 - 500 m deep and appeared to be the full depth of the glacier terminus (~600-700 m). The stereo imagery collected before, during and after the event enables the production of three-dimensional elevation models of the calving face and near-terminus glacier surface. From this quantitative measurements of calving volume and changes in glacier velocity are possible. The imagery also captured the ice mélange, which provides quantitative information about ice transport through the fjord.