Antarctic Glaciers Accelerate in Wake of Ice Shelf Breakup:
In Antarctica, glaciers flowing to the coast form ice shelves thick platforms of ice that float on the ocean. Together, the glacier and ice shelf form a stable system, but this system can lose its stability in response to warmer temperatures.
Warmer summer temperatures sometimes result in glacier acceleration as melt water percolates through the glacier to its base. Here the water lowers the friction between the glacier and the underlying rock. This effect is seasonal, and with the ice shelf in place, the glacier returns to a lower flow speed once summer (and surface melting) ends.
Warmer summer temperatures can also lead to rapid ice shelf disintegration. As temperature rises, melt water accumulates on the shelf surface. Although only a tiny fraction of the ice shelf melts, the water infiltrates the shelf through small cracks in the ice. Over time, the weight of the melt water in the cracks shatters the shelf. This happened in the Antarctic Peninsula in 1995 and again in 2002. To read more about these events, see Larsen Ice Shelf Breakup Events.
Removal of the ice shelf causes much more dramatic glacier acceleration by reducing two forces that counteract glacier flow. One counteracting force is "backstress" produced by islands or coastline underlying the original shelf. Another is the buoyant (hydrostatic) force of the seawater against the front of the shelf or glacier. A full explanation will require numerical modeling of glacier flow, but observations to date suggest that ice shelves act as "braking" systems on the glaciers behind them.
Stress on the high ice cliff enhances fracturing of the Hektoria Glacier near the grounding line in this March 2002 aerial photo. (Photo courtesy of Pedro Skvarca, Glaciology Division, Instituto Antártico Argentino)
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