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Fast-draining lakes atop Greenland ice sheet could accelerate sea level rise
http://www.whoi.edu/oceanus/feature/scientists-find-trigger-that-cracks-lakes[font face=Serif][font size=5]Scientists Find Trigger That Cracks Lakes[/font]
[font size=4]Fast-draining lakes atop Greenland ice sheet could accelerate sea level rise[/font]
By Lonny Lippsett :: Originally published online June 3, 2015
[font size=3]…
The scientists theorize that meltwater had begun to drain through a nearby system of moulins, or vertical conduits through the ice, which connected the surface to the base of the ice sheet. This accumulating water eventually created a bulge between the bedrock and the base of the ice, which floated the entire ice sheet. That exerted tension at the surface, underneath the lake. The stress built up until it was relieved by a sudden large crack in the ice below the lake.
“In some ways, ice behaves like Silly Putty,” Stevens said. “If you push up on it slowly, it will stretch; if you do it with enough force, it will crack. Ordinarily, pressure at the ice sheet surface is directed into the lake basin, compressing the ice together. But if you push up on the ice sheet and create a dome instead of a bowl, you get tension that stretches the ice surface apart. You change the stress state of the surface ice from compressional to tensional, which promotes crack formation.”
Once the tension initiates the crack, the volume of water in the lake does play a critical role. It surges into the opening with thunderous force, widening and extending the crack, and keeping it filled with water all the way to base of the thick ice sheet.
“You need both conditions—tension to initiate the crack and the large volume of water to amplify it—for hydrofractures to form,” Stevens said. The key finding of the study is that without the former, even large supraglacial lakes will retain their water.
…[/font][/font]
[font size=4]Fast-draining lakes atop Greenland ice sheet could accelerate sea level rise[/font]
By Lonny Lippsett :: Originally published online June 3, 2015
[font size=3]…
The scientists theorize that meltwater had begun to drain through a nearby system of moulins, or vertical conduits through the ice, which connected the surface to the base of the ice sheet. This accumulating water eventually created a bulge between the bedrock and the base of the ice, which floated the entire ice sheet. That exerted tension at the surface, underneath the lake. The stress built up until it was relieved by a sudden large crack in the ice below the lake.
“In some ways, ice behaves like Silly Putty,” Stevens said. “If you push up on it slowly, it will stretch; if you do it with enough force, it will crack. Ordinarily, pressure at the ice sheet surface is directed into the lake basin, compressing the ice together. But if you push up on the ice sheet and create a dome instead of a bowl, you get tension that stretches the ice surface apart. You change the stress state of the surface ice from compressional to tensional, which promotes crack formation.”
Once the tension initiates the crack, the volume of water in the lake does play a critical role. It surges into the opening with thunderous force, widening and extending the crack, and keeping it filled with water all the way to base of the thick ice sheet.
“You need both conditions—tension to initiate the crack and the large volume of water to amplify it—for hydrofractures to form,” Stevens said. The key finding of the study is that without the former, even large supraglacial lakes will retain their water.
…[/font][/font]
