Scientists have been well aware of how glaciers melt faster than they build up, and how that contributes to the rise of the sea levels. Now, they’ve added the other half of the equation to how all the rest of the water leaving the glaciers also get there.
This part of the mystery involves supra glacial lakes that are drained of all their 12 billion gallons of water in a couple of hours. In 2006, Greenland’s North Lake did exactly that, being a 2.2 square-mile (5.6 square kilometers) large meltwater lake on top of a glacier.
Previous studies of the lakes with the help of GPS stations, did not contribute to the understanding of the sudden drainage. But now, there are 16 stations positioned to monitor certain areas of the Greenland Northlake, as opposed to the handful of GPS stations that had been used before, back in 2008. This has resulted in a much more detailed look at how the glacier behaves, right before dropping that cold lake of water somewhere.
Laura Stevens, a glaciology doctoral candidate with the MIT/Woods Hole Oceanographic Institution Joint Program explains the process: “We found that before we get the main expression of the lake drainage, there is a period of time (about six to 12 hours) where uplift and slip increase. That motion is enough to take the surface of the ice sheet and put portions of it in high tension that allows cracks to start forming.”
Satellite images have shown that almost 13 percent of the supraglacial lakes vanish quickly, in less than 24 hours. Where the common drainage is slow and occurs by water leaving through permanent shafts and conduits, the “suddenly gone”-ones experience temporary hydro-fractures that are basically cracks leading all the way down to the bottom of the ice sheet.
By understanding this process a lot better, which is now possible thanks to the increase in monitoring satellites, scientists can begin to add these events into calculations that predict the rise in sea levels due to melting glaciers.
Image: Laura A. Stevens