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Friday, September 21, 2012

Greenland’s ‘ice quakes’ on track to break record set in 2005

Greenland’s ‘Ice Quakes’ May Set a Record

The previous record for ice quakes was set in 2005, but at the current pace it is likely to be broken in 2012.Meredith Nettles, Lamont-Doherty Earth ObservatoryThe previous record for ice quakes was set in 2005, but at the current pace it is likely to be broken in 2012.
Green: Science
One of the more amazing facts about the ongoing destruction of the Greenland ice sheet is that it is producing earthquakes that can be detected worldwide. Now, fresh evidence is at hand to show that these “ice quakes” are spreading to previously quiescent parts of Greenland. We’re only in September, but it seems increasingly likely that 2012 will set a record for such quakes.
Some readers may remember my article from 2010 about the acceleration of Greenland’s outlet glaciers, which carry ice from the middle of the great ice sheet and dump it into the sea. Their speedup, in fits and starts over the past decade, has coincided with a lot of other evidence that the ice sheet is deteriorating at an accelerating clip.
And it is the calving of huge icebergs from these sped-up glaciers that is producing the earthquakes. They are many times weaker than, say, the earthquake off the coast of Japan last year, but they are strong enough to be detected by the worldwide network of seismometers.
One of the scientists I quoted two years ago was Meredith Nettles, a seismologist at the Lamont-Doherty Earth Observatory, a unit of Columbia University that is just outside New York City. With her colleagues Goran Ekstrom and Geoffrey A. Abers, she discovered the glacial earthquakes in 2003.
Now, with a student collaborator, Stephen Veitch, she has produced an update of the earthquake situation. Their paper, recently accepted for publication in the Journal of Geophysical Research, shows that earthquakes have been spreading northward, from the warmer southern parts of Greenland to the colder northern parts. (A synopsis of the paper is available here, and for those with access to the journal, the full preprinted version can be found here.)

Dr. Nettles and Mr. Veitch show that, after becoming more active earlier in the decade, some of the southerly glaciers have quieted down to a degree. That is consistent with other science on the behavior of Greenland glaciers, showing that they can speed up and start dumping more ice into the ocean, apparently in response to melting near their fronts caused by warmer ocean water.
But that breakneck pace is usually not maintained for many years. They tend to slow down again, though rarely back to their starting speed.
The striking thing about this paper is the evidence that glacial earthquakes, and the ice loss they represent, have spread to one of the coldest parts of Greenland, in the far northwest. From 2000 to 2010, 66 glacial earthquakes occurred at northwestern glaciers that in previous decades had produced virtually none. The paper describes this as “a major expansion in the number of glaciers producing glacial earthquakes and the geographic range of those glaciers.”
While the analysis in the paper stops in 2010, Dr. Nettles is keeping count, and she sent me the plot above, showing that for all of Greenland, 2011 had the second-highest number of glacial earthquakes, after the record year of 2005. And, as is obvious from the graph, it now seems quite likely that 2012 will surpass the 2005 record.
Coupled with recent news about the loss of Arctic sea ice and the possible long-term effect that will have on the Greenland ice sheet, this paper is a sobering reminder that all is not well in the Arctic region.

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