During summer, melt water pools into lakes on the ice sheet's surface, and when the water pressure gets high enough the ice fractures beneath the lake and "a huge burst of water quickly pulses through to the bed of the ice sheet," University of Colorado Boulder researcher William Colgan said.
As global climate warms such catastrophic lake drainages are increasing in frequency, the researchers said in a university release.
During a typical drainage, they said, about 35 million cubic feet of melt water -- roughly the volume of 4,000 Olympic swimming pools -- funnels to the ice sheet's underside within a day or two, turning the ice-bed surface into a Slip 'N Slide.
Such lake drainage may move enough of the ice sheet's glaciers into the ocean to affect sea-level rise, with implications for coastal communities, the researchers said.
Climate warming is accelerating the phenomenon, they said, as catastrophic lake drainage was 3.5 times more likely to occur during the warmest years than the coldest years.