Modeling of bottom crevasse and undercutting on Thwaites Glacier, West Antarctica

Abstract:

Calving is an important process that accounts for a significant share of the mass loss of Antarctica. Recently, some studies have suggested that calving is caused by the penetration of bottom crevasses rather than surface crevasses. There is also a debate on whether undercutting can change the stress regime significantly to cause calving.

Thwaites Glacier (TG) is one of the largest and broadest ice streams in West Antarctica, and is undergoing rapid thinning and mass loss. Its ice shelf has reduced significantly in size due to calving in 2015. Observations from satellites and airborne radar have revealed dense distribution of surface and bottom crevasses that play a critical role in the current processes of calving of this glacier. The current trend of mass loss will possibly be enhanced if large calving events take place, as TG will become even wider when its ice shelf gets shortened.

Here, we use the Ice Sheet System Model (ISSM) and a linear elastic fracture mechanics model to investigate 1) the penetration depth of a bottom crevasse and 2) the influence on glacier stress regime of undercutting. A 2D full Stokes model is applied on a flowline of TG to best capture the stress field near the grounding line and ice front. We show that the bottom crevasse can penetrate the whole ice thickness to cause calving near the grounding line, where the ice is tens of meters below hydrostatic equilibrium. We also show that undercutting can change the stress regime near the ice front and make the ice shelf more prone to calve. We conclude on the importance of undercutting and bottom crevasses on driving changes in speed and mass balance of the Thwaites Glacier, West Antarctica, and how these processes may evolve in a warmer environment and as the glacier retreats farther inland into a deeper bed.

This work has been performed at UC Irvine and Caltech's Jet Propulsion Laboratory under a contract with NASA's Cryospheric Science Program.