Two lakes beneath Greenland's ice vanished over the course of only a few weeks.
One of the lakes had held billions of gallons of water, but emptied and formed a mile-wide crater in a very short period of time. The other lake has filled and emptied twice over the past two years, Ohio State University reported.
"The fact that our lake appears to have been stable for at least several decades, and then drained in a matter of weeks-or less-after a few very hot summers, may signal a fundamental change happening in the ice sheet," said Ian Howat, associate professor of earth sciences at Ohio State.
Every time the peculiar lakes fill up they store heat, which reduces the stiffness of the surrounding ice and making it more likely to flow out to sea.
"If enough water is pouring down into the Greenland Ice Sheet for us to see the same sub-glacial lake empty and re-fill itself over and over, then there must be so much latent heat being released under the ice that we'd have to expect it to change the large-scale behavior of the ice sheet," said Michael Bevis, Ohio Eminent Scholar in Geodynamics and professor of earth sciences at Ohio State.
Recent images suggest the cratered lake most likely emptied through a meltwater tunnel beneath it in a phenomenon the researchers classified as "catastrophic." These tunnels can carry heat and water to regions that were previously frozen. These types of rapidly draining lakes could be more prevalent than researchers expected.
"Until we get a good map of the bed topography where this lake was, we have no idea whatsoever how many lakes could be out there," Howat said. "There may be something really weird in the bed in this particular spot that caused water to accumulate. But, if all you need is a bumpy surface a bit inland from the coast, then there could be thousands of little lakes."
The rapid draining of the lakes suggests Greenland's ice loss has now reached a milestone.
"It's pretty telling that these two lakes were discovered back to back," Bevis concluded. "We can actually see the meltwater pour down into these holes. We can actually watch these lakes drain out and fill up again in real time. With melting like that, even the deep interior of the ice sheet is going to change."
The findings were published in a recent edition of the journals Cryosphere and Nature.