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Thwaites Glacier, West Antarctica, nicknamed the "Doomsday Glacier," is currently the largest single-glacier contributor to sea level rise and is poised to increase its contribution significantly due to the dynamic instability inherent as it retreats into a deep marine basin.
Predictions of eustatic sea level rise over the next decades relies on predicting future retreat of this glacier, which depends on ocean circulation and glacier dynamics near the grounding zone. At present, two thirds of the glacier flows across the grounding zone at 2000m per year and into the ocean as a weak ice melange. The other third of the glacier, flows into a floating ice shelf, which slows the ice to 600m per year. This Thwaites Eastern Ice Shelf, however, is vulnerable to collapse, which will trigger upstream stress changes and acceleration of the glacier. Here we use ice-penetrating radar and remote sensing to assess the changing patterns of flow and fractures that lead to potential weaknesses, instability, and collapse of the floating ice shelf. We find three weaknesses are the most likely to trigger collapse:
1) a submarine bedrock ridge that provides structural stability is losing contact with the ice; 2) changes in the stress regime over the last 18 years have opened new bands of crevasses in a localized shear zone; and 3) a new set of rift fractures are propagating into a region of thin vulnerable ice. At the current rate of change, these weaknesses are likely to cause ice shelf collapse in as little as 5 years, but such an extrapolation of non-linear interacting processes is highly uncertain. Collapse of the floating ice shelf will not directly cause sea level to rise, but it will relieve backstress and allow acceleration of the slower third of Thwaites Glacier that currently flows into the Eastern Ice Shelf. If this ice accelerates to match the speed of the rest of the glacier, this would increase the ice discharge across the grounding zone from 180km3 to 240km3 per year, which would more than double its current contribution to sea level rise (from 50km3 per year to 110km3 per year ~0.5mm sea level rise per year).