Glacier Undercutting in Action

In this aerial view, a glacier along Greenland's craggy coastline is actively undergoing undercutting, a process in which meltwater flowing out from the bottom of the glacier enters the fjord. The brown water in front of the glacier is caused by sediment being dredged up from the base of the glacier by meltwater plumes reaching the surface of the fjord.

Because the meltwater contains no salt, it is lighter and rises through the saltier ocean water, dragging the warm ocean water into contact with the ice at the glacier's base. The result is increased melting at the bottom of the glacier, which creates and overhanging layer of ice that breaks off (or calves) as icebergs. As the climate warms, the ocean water temperature and the amount of meltwater both increase, combining to hasten this undercutting process and speed up the ice loss from Greenland's Ice Sheet.

The image was taken on Aug. 25, 2019 by a probe-dropping airplane as part of the Oceans Melting Greenland (OMG) mission. OMG has been studying glaciers that plunge into Greenland's steep-sided inlets, or fjords, for the past five years, gathering precise measurements of fjord depth and water salinity from probes dropped by plane, supplemented by measurements made by boat. The aim is to better understand how the warming ocean water around Greenland is hastening ice melt and calving of these marine-terminating glaciers.

For more information about the OMG mission: https://omg.jpl.nasa.gov/portal/