A team of international researchers has shown for the first time how 18 meltwater lakes in Greenland collapse during winter, causing the edges of the ice to flow faster. This new knowledge is essential for understanding how climate change influences the flow of ice masses in the Arctic.
In the middle of winter in 2018, an almost 50 year old meltwater lake disappeared from the western Greenland ice sheet. The lake was covered by ice and snow when it collapsed but stored water inside. The water drifted down through the newly formed cracks into the approximately 2km thick layer of ice. The water hit the rock bed below the ice and flowed out from under the ice sheet toward the sea.
The meltwater acts as a lubrication between the rock bed and the thick ice on top. As a result, the large mass of ice could slide faster toward the coast, accelerating a substantially large region of inland ice. The drainage of this lake caused several neighboring lakes to collapse too. In total, the collapsed lakes released approximately 180 million tons of meltwater that ended up in the ocean.
“The meltwater lakes on the ice sheet form in the summer when the ice on the surface melts. It is well known that these lakes can collapse and drain during summer. But, surprisingly, this takes place in the winter too. This is the first time that it has been shown that these specific lake drainages cause large ice accelerations during winter when temperatures are very low,” says lead author Nathan Maier.
“We have only investigated a limited area, but we have good reason to assume that similar events take place in many more places in Greenland. If this applies to larger parts of the ice sheet, it could be quite large amounts of meltwater that disappear in this way and cause the ice sheet to slide faster towards the sea,” says co-author Jonas Kvist Andersen.
“Right now, our understanding of how surface melting will affect mass loss from Greenland in the future is based entirely on the assumption that melting only affects the speed of the ice flow during summer. Our discovery, that large accelerations in the ice flow caused by stored meltwater that drains during winter, significantly changes how we understand ice sheet hydrology over annual time scales,” says Nathan Maier.
https://phys.org/news/2023-02-lakes-collapse-meltwater-winter-inland.html