The icequakes in Greenland are caused by the motion of the glaciers and are most common in July and August when temperature is higher. But the seismologists from Columbia and Harvard have found that the total number of such "glacial earthquakes" have more than doubled since 2002.
Seismologists Göran Ekström and Victor C. Tsai at Harvard and Meredith Nettles at the Lamont-Doherty Earth Observatory, a member of The Earth Institute at Columbia University, first described glacial earthquakes in 2003, but that report did not recognize neither the seasonality nor the increasing frequency of the phenomenon. They have now scrutinized these aspects.
Greenland's seismic activity is completely different from the traditional seismic activity caused by the motion of the tectonic plates, the most notable difference being that the icequakes vary with seasons. A third of them occur in July and August.
"People often think of glaciers as inert and slow-moving, but in fact they can also move rather quickly," says Ekström. "Some of Greenland's glaciers, as large as Manhattan and as tall as the Empire State Building, can move 10 meters in less than a minute, a jolt that is sufficient to generate moderate seismic waves."
The glaciers can move at such speeds because as they melt water can seep beneath them, serving as a lubricant. The glaciers reeling down valleys in such a way, and eventually ending up in the surrounding sees, are called "outlet glaciers".
"Our results suggest that these major outlet glaciers can respond to changes in climate conditions much more quickly than we had thought," said Nettles. "Greenland's glaciers deliver large quantities of fresh water to the oceans, so the implications for climate change are serious. We believe that further warming of the climate is likely to accelerate the behavior we've documented."
The scientists found that icequakes' overall number increased markedly - as the graph shows. They have also found that the icequakes were not evenly distributed along Greenland. Some areas became more affected than others. A certain area of northwestern Greenland, where only one seismic event was observed between 1993 and 1999, experienced more than two dozen glacial quakes between 2000 and 2005.
This adds to the evidence that Greenland is melting at a faster pace than previously thought.
Picture credit: E. Wesker