Calving icequakes are recorded over 100 km from the termini of tidewater glaciers, all the world over. We show that the spectra of these events (recorded nearly once per minute) are distinct from tectonic earthquakes. By synchronizing video with locally-recorded seismic signals, we demonstrate that these icequakes are produced through the interaction between icebergs and the sea. Peak icequake amplitudes are produced seconds after the icebergs impact the sea, and coincide with the cavitation events beneath sea level. These results are supported by a model of the forces acting on decelerating icebergs following impact with the sea.
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