March 24, 2006

Falling apart.

Big white place

Southern Greenland during mid-winter, looking toward the pole from the US space shuttle. The only difference you'd notice during the summer is that ice and snow cover would disappear from very narrow bands in some coastal areas. [Photo: NASA].

That's what's happening to Greenland's ice sheet, which is being rocked by 'glacial earthquakes' as meltwater seeps to the bottom of the ice and speeds the progress of glaciers to the sea. What this new finding means is that Greenland's ice sheet will disappear faster than scientists had expected.

The 'glacial earthquakes' were discovered by a scientific team led by Harvard University seismologist Göran Ekström. According to Ekström, these earthquakes differ from 'regular' quakes in that they are caused by slips within the ice sheet, rather than along an earthquake fault. Glacial quakes can be quite large — a slip of just 10 meters by an ice slab the size of Manhattan can generate a magnitude 5 quake.

Ekström's team found that the number of glacial quakes has been increasing. Between 1993 and 2002, there were between six and fifteen per year prior to 2003. However, the number has increased to the point that 32 glacial quakes were detected during the first 10 months of 2005 alone.

The new findings show that temperature increases can affect Greenland's ice sheet far more reapidly than han had been believed:

Models that treated glaciers like giant ice cubes had predicted very slow melting. But recent studies of Greenland glaciers have shown much faster effects when meltwater causes glaciers to slip easily over rock.

"Within a few years after temperature warms, you get a big increase in discharge," says Ian Joughin of the polar science center at the University of Washington in Seattle, US. "If temperature rises two or three degrees in Greenland, things are going to start falling apart," Joughin told New Scientist. Antarctica is not as sensitive to rising air temperature because it is too cold for surface melting, which accounts for about half the mass lost from the Greenland ice sheet. [Emphasis added]

Via New Scientist.

Posted by Magpie at March 24, 2006 04:37 PM | Environment | Technorati links |