Here's a new article I've written based on talking to glaciologist William Colgan who studies hydrology of the Greenland ice sheet:
http://www.fairfaxclimatewatch.com/blog/2014/02/liquid-water-inside-greenlands-ice-sheet.htmlI also asked Colgan if water might start accumulating at the base of the ice sheet in the "bowl" of Greenland, instead of all routing out into the ocean, as is generally assumed with conventional thinking. He basically said that's valid hypothesis, but he wouldn't expect it to be the main issue this century, at least compared to the other issues with Greenland.
My thinking is this:
The water at the base of the sheet will go where pressure and gravity direct it, so there is a tendency for the water to get pushed towards areas of thinner ice where there is less overhead pressure, which is why - if one thinks on very large scale terms - it seems reasonable that the subglacial water will all get pushed towards the perimeter of the ice sheet where the ice is thinner. However, when one considers the fine-scale variations of the bed topography and the ice thickness overhead, it's clear that the pressure gradients in the center of the ice sheet (the "bowl" area) are quite varied. So for example, ice that reaches the ice sheet's base in the center might migrate upslope along the bedrock-ice interface, but then reach the top of a hill-like feature and stop migrating. Thus, a new subglacial lake would be born in that spot. As a consequence of having a new subglacial lake there, the ice overhead experiences less friction, and so it slides faster, thinning overhead of the lake area, thus reinforcing the tendency for water to migrate to the subglacial lake and expanding the capacity of the subglacial lake. Likewise, at the top of the ice sheet, the slight dip in surface elevation from the accelerated local ice flow will cause surface meltwater to preferentially pool in that spot, thus increasing the tendency for future rapid supraglacial lake drainage events in the location, thereby delivering more water to the subglacial lake and its "subglacial watershed."