Geodetic observations of short-time-scale changes in glacier flow at Helheim and Kangerdlugssuaq Glaciers, East Greenland

Evidence obtained by several workers during the past few years has shown that the major outlet glaciers in Greenland can both accelerate and decelerate more rapidly than previously appreciated. Some abrupt accelerations at the largest outlet glaciers, including Jakobshavn Isbrae and Helheim and Kangerdlugssuaq Glaciers, have been linked to large-scale calving events and glacial earthquakes (Nettles et al., 2008; Amundson et al., 2008). Many questions regarding the dynamics of these glaciers remain unresolved, including the nature and cause of rapid deceleration events and the influence of surface melting and hydrology on variations in glacier speed. We have operated a GPS network on the surface of Helheim Glacier during the four summers of 2006--2009, as well as during the fall of 2008, late spring of 2009, and fall of 2009. Several auxiliary geophysical sensors have also been operated nearby. This short four-year period has revealed both glacier acceleration and deceleration, occurring on interannual to sub-hour timescales. The number of glacial earthquakes observed during this time period has also varied significantly. During the summer of 2009, we also operated a GPS network on Kangerdlugssuaq Glacier, obtaining a full season of high-time-resolution observations of glacier motion and deformation. The GPS data acquired during 2009 come primarily from a low-cost GPS receiver system designed by the authors to provide data security and near-real-time data delivery via a combination of radio and satellite telemetry. Here, we present results from the extended 2008/2009 seasons at Helheim and Kangerdlugssuaq in the context of our previous observations and longer-term observations of other workers.