Greenland’s glaciers are rivers of ice that transport billions of tons of frozen water to the ocean each year. In the past few decades, these glaciers have been flowing faster, releasing more ice into the ocean.
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As the planet warms, glacier melt will continue to contribute to global sea-level rise, but not all melt happens at the surface. In a process called undercutting, warm cold meltwater from the surface drives the warmer ocean into contact with the glacier’s base.
When warm summer air melts the surface of a glacier, the meltwater bores holes down through the ice. It makes its way all the way down to the bottom of the glacier, where it runs between the ice and the glacier bed and eventually shoots out in a plume at the glacier base and into the surrounding ocean.
The meltwater plume is lighter than the surrounding ocean water because it doesn’t contain salt. So it rises toward the surface, mixing the warm ocean water upward in the process. The warm water then rubs up against the bottom of the glacier, causing even more of the glacier to melt. This often leads to calving – ice cracking and breaking off into large ice chunks (icebergs) – at the front end or terminus of the glacier.