A new observation from Science - seismic detection of surges in glaciers:

Glacial Earthquakes

Göran Ekström, Meredith Nettles, Geoffrey A. Abers
Harvard University, Boston University

We have detected dozens of previously unknown, moderate earthquakes beneath large glaciers. The seismic radiation from these earthquakes is depleted at high frequencies, explaining their non-detection by traditional methods. Inverse modeling of the long-period seismic waveforms from the best-recorded earthquake, in southern Alaska, shows that the seismic source is well represented by stick-slip, downhill sliding of a glacial ice mass. The duration of sliding in the Alaska earthquake is 30-60 seconds, about 15-30 times longer than for a regular tectonic earthquake of similar magnitude.