In a recent collaboration with University of Montana, University of Wyoming (UW) researchers headed out to explore a little-studied area of the Greenland ice sheet. The team was headed by Neil Humphrey, a UW professor of geology and geophysics, and his graduate student, Nathan Maier.
"The region that we did [our research] in is a region that this has never been measured before. We did it in these slow-moving, land-terminating regions. These are generally seen to be the more 'boring' regions of ice sheets because they're not the fast-moving outlet glaciers or the regions that calve into the ocean," Maier said. "But they're really important because they represent a large part of the margins of ice sheets."
But these so-called boring regions of the ice sheet turned out to be a bit of a surprise.
Ice flows from the higher, colder sections of Greenland to the lower, warmer sections, pulled along by its own weight. Its movement can be broken down into two parts: sliding, or deforming. Ice that's on a slippery bed like till, a mud-like substance, can slide relatively easily. Ice that’s on a harder surface, like bedrock, doesn't typically slide – it deforms. When ice deforms, it moves along similar to a thick liquid like molasses.
To figure out the ratio of sliding to deforming, an important factor in how the ice can respond to climate change, the researchers drilled a grid of holes through the ice, all the way to the bed underneath.
They used a hot water drill – basically a huge pressure washer with superheated water – to drill through the ice in about 8 hours. Tilt sensors were then frozen along the hole.
The amount that the sensors tilted allowed the researchers to calculate the deformation of the ice. After that, they could calculate how much of the surface motion is due to sliding.
Their results were "super weird" said Maier, since these sites that were supposed to be moving primarily by deformation were actually doing most of their movement by sliding.
"So that kind of redefines where we can think of as these high sliding areas. So usually we think of these till bedded regions or these marine terminating glaciers to have these high rates of sliding. But we found that in these relatively slow moving and boring regions of ice sheet, we also have the motion that’s just completely dominated by sliding," Maier said.
These results are fundamental parameters to creating accurate ice sheet models to determine how Greenland is going to respond to increases in air temperatures and how it may melt in the future.
Greenland is currently experiencing its second heat wave of this year. Heat waves like this have become more common, and the ice sheet has seen an increase in melting rate over the past three decades.
"As far as the overall fate of the Greenland ice sheet, it's not looking good. But that being said, Greenland is really, really big. But even with these really, really high rates of melting and increased rates of melt that's going to continue through the next decades, it’s still going to be around for another millennia," Maier said. "Greenland is a really, really large system, but right now, as far as we can tell, it's still being melted at an unprecedented rate."
The Greenland ice sheet is the second largest in the world, after Antarctica. If it melts, then sea levels are predicted to rise by nearly 25 feet.
