File:Shades of Blue on the Greenland Ice Sheet.jpg

English: By mid-summer each year, vibrant blue meltwater lakes dot the surface of the Greenland Ice Sheet. These lakes, also known as melt ponds, store a large amount of fresh water throughout the season, and they are an important part of the ice sheet’s surface hydrology.

The images above were acquired on July 15, 2015, by the Operational Land Imager (OLI) on Landsat 8. They show meltwater lakes on the ice near Greenland’s west coast, about 100 kilometers (60 miles) southeast of Ilulissat. Dark debris coats the ice surface in some areas.

“One reason we’re interested in the lakes is because they might be important for speeding up the ice sheet,” said Allen Pope, a glaciologist at the National Snow and Ice Data Center. Once the lakes grow large enough, Pope notes, they can force open crevasses in the ice. The melt water can then move through the crevasse to the base of the glacier and temporarily speed up ice flow across the bedrock below.

So how large are these lakes? As the image shows, size varies. Some lakes have a greater surface area than others, but that’s not the only difference. Their depth can vary dramatically too, which becomes apparent in the various shades of blue.

According to Pope, some lakes are shallow and lagoon-like, while others are as much as 9 meters (30 feet) deep. Pope and colleagues have been working on a technique to determine the depth of meltwater lakes based on information contained in Landsat 8 images. To do that, they need to know three pieces of information: how much light the water absorbs, how much it scatters, and the reflectance of the bottom of the lake.

Download full resolution and read more at earthobservatory.nasa.gov/IOTD/view.php?id=86564&src=...

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