"How deep is that icy blue water on Greenland's ice sheet? Dr. Allen Pope, of the National Snow and Ice Data Center, is using data from the NASA/USGS Landsat 8 satellite to find out. In this video, Dr. Pope shares what he sees when he looks at a Landsat image of the Greenland ice sheet just south of the Jakobshavn Glacier.
Because the lakes are darker than the ice around them, they absorb more energy from the sun. A little bit of melt concentrates in one place, and then melts more, establishing a feedback mechanism accelerating the growth of the lake. When the lakes get big enough they can force open fractures that then drill all the way down to the bed of the glacier, transporting this water to the base where it can temporarily speed up the flow of the ice."