Ice on the Greenland Sheet doesn’t just melt. The ice actually slides quickly across its bed towards the ice sheet’s edges. As a result, because ice motion is from sliding as opposed to ice deformation, ice is being moved to the high-melt marginal zones extra rapidly than previously thought.
Neil Humphrey, a College of Wyoming professor of geology and geophysics, and Nathan Maier, a UW geology Ph.D. scholar from Morristown, N.J., headed the latest analysis group that discovered that you do not need beds with till or mud, which acts as a lube, to have high rates of sliding. Rather, they discovered that it’s over hard bedrock where ice slides more rapidly. Additionally, the ice slides over the bedrock much more than earlier theories predicted of how ice on the Greenland Ice Sheet moves.
“That is the kicker. The Greenland Ice Sheet is happily sliding over a surface that theory says it shouldn’t be able to quickly slide over,” Humphrey says. “What’s important is that, because of this, you get a lot of ice to the oceans or low altitudes where it could melt really fast. It is like a lump of molasses sliding off the continent. It just doesn’t soften. It slides toward the ocean.”
“Our measurements of sliding-dominated flow over a hard bed in a slow-moving region were quite surprising as a result of people do not usually associate these areas with high sliding,” Maier provides. “Generally, people associate lots of sliding motion with regions that have soft beds (mud) or exceptionally high-sliding velocities, such as ice streams. But, on this relatively boring area, we found the highest fraction of sliding measured to date.”