Ice loss and glacial earthquakes in Greenland and Antarctica (Invited)

Ice-mass fluctuations on a large scale are known to influence the occurrence of tectonic earthquakes, primarily as a result of loading and unloading of the Earth's lithosphere. Smaller-scale ice-mass fluctuations, in the form of large calving events at marine-terminating outlet glaciers, are now also known to generate seismic signals directly, in the form of ``glacial earthquakes''. A strong seasonal signal in earthquake occurrence, and a general increase in numbers of glacial earthquakes during periods of calving-front retreat at Greenland's largest outlet glaciers, suggests that the glacial earthquakes may be used as indicators of changes in glacier dynamics. In particular, the earthquakes provide information on the nature of glacier calving, itself an important control on outlet-glacier flow speed. Observations of interannual variability in earthquake numbers at individual glaciers in turn suggest the importance of local conditions, such as bedrock topography and current location of the calving front, in controlling glacial-earthquake occurrence. Here, we present recent results from studies of glacial earthquakes in Greenland and Antarctica, in the context of changes in glacier dynamics that may affect mass balance within the ice sheets.