10/25/2017 - Flow, Friction and Fracture in Iceberg Mélange: Earth’s Largest Granular Material


12:00 PM - 12:50 PM
Geology 1707

Presented By:
Alexander Robel - Caltech


Iceberg mélange is a dense granular aggregation of icebergs and sea ice that is found floating in the ocean in front of many marine-terminating glaciers in Greenland and Antarctica. Recent observations indicate that the decline of local sea ice cover within mélange has been accompanied by an increase in nearby iceberg calving and associated ice sheet mass loss. The leading for this association is that mélange exerts a mechanical force directly on the glacier, lowering extensional stresses, preventing fracture propagation and iceberg calving near the glacier terminus. In this talk, I will show how sea ice thickness and concentration play a critical role in setting the material strength of mélange. I adapt a discrete element model to simulate mélange as a cohesive granular material. In these simulations, mélange laden with thick, dense, landfast sea ice can produce enough resistance to shut down calving at the terminus. When sea ice thins, mélange weakens, reducing the mechanical force of mélange on the glacier terminus, and increasing the likelihood of calving. When calving events occur, jamming waves are initiated within mélange, propagating away from the glacier and causing the fracture of the sea-ice matrix that bonds mélange, increasing the likelihood of subsequent calving events. I compare these simulations to observations of mélange from ground-based photogrammetry and interferometric synthetic aperture radar. I then discuss whether longer periods of sea-ice-free conditions in winter may lead to a transition from currently slow calving, predominantly occurring in the summer, to rapid calving, occurring throughout the year, accelerating ice sheet mass loss and sea level rise. The results in this talk can mostly be found in the following paper from earlier this year: LINK TO PAPER

Thinning sea ice weakens buttressing force of iceberg mélange and promotes calving

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