Global Warming Yields “Glacial Earthquakes,” Future Sea Level Rise
Three studies published in the March 24 issue of the research journal Science warn of the events.
Two studies found that the Earth may be warm enough by 2100 for widespread melting of the Greenland Ice Sheet and partial collapse of the Antarctic Ice Sheet.
In one paper, Jonathan Overbeck at the University of Arizona in Tucson, Ariz., and colleagues wrote that based on reconstructions of past climates, conditions could be ripe to raise sea level by several meters (yards) by this century’s end.
Most scientists believe the melting is due to global warming, a gradual increase in the Earth’s temperature caused by the burning of fossil fuels.
In a third study, seismologists reported an unexpected offshoot of global warming: “glacial earthquakes,” in which Manhattan-sized glaciers lurch unexpectedly. Glaciers are normally slow-moving masses of ice.
The lurches yield temblors up to magnitude 5.1 on the moment-magnitude scale, which is similar to the Richter scale, the researchers said. Glacial earthquakes in Greenland, they added, are most common in July and August, and have more than doubled in number since 2002.
The researchers, at Harvard University in Cambridge, Mass. and Columbia University in New York, first described glacial earthquakes in 2003, but without reporting on their seasonality or changing frequency.
“People often think of glaciers as inert and slow-moving, but in fact they can also move rather quickly,” said Harvard’s Göran Ekström, one of the researchers. “Some of Greenland’s glaciers, as large as Manhattan and as tall as the Empire State Building, can move 10 meters (11 yards) in less than a minute, a jolt that is sufficient to generate moderate seismic waves.”
As glaciers and the snow on them gradually melt, water seeps downward. When enough water accumulates at a glacier’s base, it can serve as a lubricant, causing giant blocks of ice to lurch down valleys known as “outlet glaciers,” the team explained. These funnel Greenland’s glacial runoff toward the surrounding sea.
“Our results suggest that these major outlet glaciers can respond to changes in climate conditions much more quickly than we had thought,” said Meredith Nettles, a postdoctoral researcher at Columbia and member of the research team.
“Greenland’s glaciers deliver large quantities of fresh water to the oceans, so the implications for climate change are serious.”
Greenland is not a hotbed of traditional seismic activity associated with the grinding of the Earth’s tectonic plates, the traditional source of earthquakes, the scientists noted. But seismometers worldwide detected 182 earthquakes there between January 1993 and October 2005, they added.
They examined the 136 best-documented of these events, ranging in magnitude from 4.6 to 5.1. All temblors were found to have originated at major valleys draining the Greenland Ice Sheet, they said, implicating glacial activity.
While glacial earthquakes appear most common in Greenland, the scientists reported finding evidence of them also in Alaska and at the edges of Antarctica.