Giant earthquakes are shaking Greenland — and scientists just figured out the disturbing reason why

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7. Glacial Earthquakes May Help Forecast Sea-Level Rise

https://www.ldeo.columbia.edu/news-events/glacial-earthquakes-may-help-forecast-sea-level-rise

[font face=Serif][font size=5]Glacial Earthquakes May Help Forecast Sea-Level Rise[/font]

June 25, 2015

[font size=3]It is only recently that scientists learned of the existence of glacial earthquakes–measurable seismic rumblings produced as massive chunks fall off the fronts of advancing glaciers into the ocean. In Greenland, these quakes have grown sevenfold over the last two decades and they are advancing northward, suggesting that ice loss is increasing as climate warms. But exactly what drives the quakes has been poorly understood. Now, a new study elucidating the quakes’ mechanics may give scientists a way to measure ice loss remotely, and thus refine predictions of future sea-level rise. The study appears this week in the early online edition of the leading journal Science.

It shows that as the glacier front falls off into the water, or calves, there is a kickback. The rest of the glacier moves rapidly downward and backward–something like a skateboard that slips out from under a rider’s feet and goes backward as the rider falls forward. This is what produces the quake, say the researchers. The force of that kickback can be so great, it can reverse the glacier’s flow for a few minutes, from the equivalent of about 95 feet per day forward to about 130 feet per day backward. Earlier studies have shown that glaciers often speed up after calving, but did not show the more immediate backward motion that apparently produces the quakes.

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“We were really surprised to see the glacier flowing backwards in our GPS data,” said lead author Tavi Murray of Swansea University. “The motion happens every time a large iceberg is calved and a glacial earthquake is produced.”

Glacial earthquakes in Greenland have increased from only 6 detected in 1993 to 42 in 2013. Understanding how they work is a crucial step toward measuring glaciers’ contributions to sea-level change, said the researchers. It could eventually provide global near-real time estimates of iceberg loss from ice sheets, they said.

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