Date of Award

Summer 8-23-2019

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Peter Koons

Second Committee Member

Christopher Gerbi

Third Committee Member

Seth Campbell

Abstract

The Ross Ice Shelf (RIS), a floating mass of ice tethered to the continent, is integral to the stability of the interior West Antarctic Ice Sheet. Its collapse could lead to an acceleration of land ice toward the ocean and a direct contribution to sea level rise. Rifts, or pull apart fractures in ice shelves, have been linked to ice shelf disintegration in other parts of Antarctica in recent decades. The rifts of interest for this study are on the western lateral margin of the RIS and have been active for at least the past five decades, as documented in historical optical imagery, and probably longer considering evidence of older rifts visible downstream. The rifting process appears to follow a pattern in which rifts open with apparent spatial and temporal periodicity and stop propagating at some predictable length, but the mechanisms behind the pattern have not been fully characterized. This study aims to understand the origin of rifts through characterization of the evolution of material strength across the RIS. I use numerical modeling to evaluate the hypothesis that deformation initiated at the grounding zone leads to formation of basal crevasses with rough periodicity which define zones of material weakness as they advect across RIS and in turn define the spacing of rifts at my study site. I created several numerical models to evaluate the kinematic structure and stability of the RIS, both on whole ice shelf and localized scales. The goal of these models is to capture deformation and shelf stability patterns that may influence rifting at my study site. A model created using the Ice Sheet System Model (ISSM) evaluates the whole shelf kinematic structure and stability and reveals that with the most likely scenarios for changes in surface accumulation and basal melt, the RIS will gain ice mass rather than lose it. Though these results project stability, there are several notable processes not captured, including locally scaled deformation at the margin. Three smaller scale numerical models explore ice shelf flexure, stretching, and lateral drag against a bedrock constriction. These models confirm that deformation of inflowing ice is likely to localize at a grounding zone due to buoyancy forces and the zone of deformation subsequently enlarged as a result of ice shelf stretching. Furthermore, the models illustrate localization of extensional strain with drag along a bedrock margin which is amplified when vertical zones of weakness are present. Model results support the overarching hypothesis, but more thorough sensitivity analysis needs to be done due to model sensitivity to rheological material properties. Results of this study point to the plausibility of localized deformation as a consequence of the inherent physics on the RIS leading to existing weak zones across the ice shelf. Based on the modeling presented, it is likely that these weak zones influence rift periodicity not only at my study site, but on other Antarctic ice shelves as well. With projected widespread ice shelf thinning, weak zones will be inherently more likely to produce full thickness rifts, which could lead to destabilization of entire systems of ice shelves and glaciers. This phenomenon leads to destabilization of the greater Antarctic ice sheet system and global sea level rise.

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