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SAN FRANCISCO, Feb. 12 (Xinhua) -- Researchers at the University of Washington (UW) in the U.S. Pacific Northwest and the University of Edinburgh in the United Kingdom have used data from the European Space Agency's CryoSat-2 satellite to identify a sudden drainage of large pools below Thwaites Glacier.
Thwaites Glacier on the edge of West Antarctica as part of the larger West Antarctic Ice Sheet, already one of the planet's fastest-moving glaciers, is sliding unstoppably into the ocean, mainly due to warmer seawater lapping at its underside, speeding up by about 10 percent from June 2013 and January 2014.
In a study published in The Cryosphere, the researchers report finding four interconnected lakes drained during the eight-month period.
"This was a big event, and it confirms that the long-term speed-up that we're observing for this glacier is probably driven by other factors, most likely in the ocean," said corresponding author Ben Smith, a glaciologist with the UW's Applied Physics Laboratory. "The water flow at the bed is probably not controlling the speed."
The authors used a new technique to discover drops at the glacier's surface of up to 70 feet, or 20 meters, over a 20 kilometer by 40 kilometer area. Calculations show it was likely due to the emptying of four interconnected lakes far below. The peak drainage rate was about 8,500 cubic feet, or 240 cubic meters, per second, the largest meltwater outflow yet reported for subglacial lakes in this region.
"This lake drainage is the biggest water movement that you would expect to see in this area, and it didn't change the glacier's speed by that much," Smith was quoted as saying in a news release. The reason is likely that Thwaites Glacier is moving quickly enough, that friction is heating up its underside to ice's melting point. The glacier's base is already wet and adding more water doesn't make it much more slippery.
The study supports previous UW research from 2014 showing that Thwaites Glacier will likely collapse within 200 to 900 years to cause seas to rise by 2 feet, or 0.6 meter. Those calculations were made without detailed maps of how water flows at the glacier's underbelly.
The new findings suggest that doesn't really matter. "If Thwaites Glacier had really jumped in response to this lake drainage, then that would have suggested that we need a more detailed model of where water is flowing at the bed," Smith said. "Radar data from NASA's Operation Ice Bridge program has told us a lot about the shape of Thwaites Glacier, but it's very difficult to see how water is moving. Based on this result, that may not be a big problem."
Melting at the ice sheet base would refill the lakes in 20 to 80 years, Smith said. Over time meltwater gradually collects in depressions in the bedrock. When the water reaches a certain level it breaches a weak point, then flows through channels in the ice. As Thwaites Glacier thins near the coast, its surface will become steeper, he said, and the difference in ice pressure between inland regions and the coast may push water coastward and cause more lakes to drain.
