In the 1960s, the network of seismometers around the world expanded rapidly. It wasn’t because seismology became a fad—it was because seismometers could detect underground nuclear weapons tests anywhere in the world. Shifting gears from a cold war to the cold science of glaciology, there’s another phenomenon seismometers can pick up: seismic booms from the melting end of glaciers. These “glacial earthquakes” have become increasingly frequent as parts of the Greenland and Antarctic ice sheets shed mass and shrink in volume, contributing to sea level rise.
Glacial earthquakes have much longer periods than actual tectonic earthquakes, with minutes passing between peaks in the wave. As a result, researchers actually have to analyze seismometer data in a different way in order to pick them up. The quakes aren’t trivial in strength though; most release a similar amount of total energy as a magnitude 5 earthquake.
The weird thing is that, even as we've tracked them, we haven’t actually figured out precisely what a glacial earthquake was. They seemed to be related to calving events, where large icebergs break off the floating front of a glacier that reaches the ocean, but what actually shakes the earth? Was the iceberg scraping along bottom? Did it have something to do with the sudden acceleration of the iceberg as it peels away from the rest of the glacier?
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