Little tectonic activity takes place on Earth’s ice-covered, southernmost continent. That makes the area around David Glacier (shown in the figure and located on the inset map) especially interesting because a lot of low-level seismic events have been detected there over the years. Those detections prompted Stefania Danesi and Andrea Morelli of the National Institute of Geophysics and Volcanology in Bologna, Italy, and Stephen Bannister of GNS Science in Lower Hutt, New Zealand, to deploy a portable seismographic array for three months during the austral summer of 2003-04. They recorded more than 6000 events, most of which originated within the ice layer; the remaining 121 were induced by ice-rock interactions as the outlet glacier flowed over the underlying terrain. Those 121 events—all with magnitudes from 1.1 to 2.2—had unusual but similar waveforms and occurred in three main clusters, labeled and shown with stars in the figure. Two loose clusters are...

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