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The Greenland Ice Sheet is Melting!
Fahnestock, M., Abdalati, W., Joughin, I., Brozena, J. and Gogineni, P.  2001.  High geothermal heat flow, basal melt, and origin of rapid ice flow in central Greenland.  Science 294: 2338-2342.

What was done
The authors used airborne ice-penetrating radar data to determine the extent and rate of basal melting for a large portion of the Greenland Ice Sheet, while employing other geophysical data to study the underlying topography of the area.

What was learned
The authors discovered a large region of rapid basal melting of the Greenland Ice Sheet in the source area of the rapidly flowing ice stream that drains the north side of the summit dome.  This melting was further shown to be occurring above a 1000-m high topographic disturbance that exhibits a dramatic increase in bed roughness, which suggests, in the words of the authors, that "it has undergone less erosion and may be younger than the surrounding bed."  Melt rates of this area are indicative of geothermal fluxes 15 to 30 times greater than the continental background rate.

What it means
The authors note that free-air gravity measurements over the primary area of basal melting and the high geothermal fluxes experienced there are comparable in magnitude and spatial extent to those of the Yellowstone caldera, and that localized peaks in gravity and rough-surfaced bed topography are suggestive of local extrusive structures.  Hence, they conclude that their "limited geophysical evidence suggests the presence of a caldera structure," which leads to "rapid and extensive basal melting in Greenland that has a direct effect on ice flow."

Will this finding take a little "heat" off the ongoing rise in the air's CO2 content when it comes to identifying something to blame - which must be done, of course - for the10-cm-per-year melting of ice above the apparent caldera?  Actually, there may not be a need to do so; for the authors note that the findings of several studies of thickening and thinning in the high interior of the ice sheet suggest that "the present ice sheet is close to being in balance with the patterns of basal melting" they discovered.  And if a natural volcano can't bring about the demise of the Greenland Ice Sheet, it's very likely the human volcano won't either.

Reviewed 12 June 2002