EOS - "Diagnosing Thwaites" And The Pancake Batter Analogy For Antarctic Glacier Collapse
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Despite its remoteness, researchers have flagged Thwaites as a scientific priority. It already contributes roughly 4% to the global sea level rise rate, currently 3.4 millimeters per year, and recent simulations suggest that it could start collapsing very quickly, within as little as 200 years, potentially adding at least 1 additional millimeter every year. Moreover, airborne and satellite observations have revealed that a huge cavity—two thirds the size of Manhattan Island and roughly 300 meters tall—is forming beneath the glacier, vacating a volume within the past 3 years that would have held 14 billion tons of ice.
Given its position amid the WAIS, were Thwaites to disappear, it could also hasten the demise of surrounding parts of the ice sheet that it helps buttress. In short, as important as Thwaites is individually, it may also be a linchpin for accelerated ice sheet collapse and melting on a much broader scale. But without a better understanding of the glacier’s past, present, and potential futures, it’s difficult to tell how the entire WAIS might respond to changes in Thwaites.
One of the reasons why Thwaites Glacier is potentially unstable is the great depth of the underlying bedrock below sea level. Glaciers flow under their own weight, slowed by floating ice shelves, which act like dams for the grounded ice sheets behind, and by friction between grounded ice and the rock beneath. As Thwaites loses mass—from above and below—its ice shelf faces a greater risk of failing. In addition, the weight holding the ice sheet against bedrock lightens and ocean water can get below the ice more easily, reducing the friction and allowing the glacier to flow more freely into the ocean.
Typically, glaciers behave “like pancake batter on a frying pan,” Scambos said. If you put a big blob of it on the surface it settles from the top toward the edge. “But what you get in West Antarctica is a situation where the pancake batter is on an oiled frying pan, so [the whole blob] slides over the frying pan rather than just deforming under its own weight.” If Thwaites starts thinning and flowing faster, it may begin calving—or losing large pieces of ice—at a faster rate, potentially getting into a runaway situation called marine ice sheet instability. In this scenario, the glacier’s grounding line, the edge where the bottom of the ice is in contact with bedrock, retreats due to warming and the loss of ice mass. While the current grounding line is 600 meters below sea level, the bedrock farther inland is even deeper, so as the grounding line retreats, a thicker portion of the glacier will be afloat—and flow even faster under its own weight.
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https://eos.org/features/diagnosing-thwaites
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