PhD Thesis Proposal: Logan Mann

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"Ice stream formation, activation, and evolution"

Abstract

While the Greenland and Antarctic ice sheets deform as slow viscous fluids, ice streams are regions of ice that flow several orders of magnitude faster than the surrounding ice ridges. Ice streams form the primary drainage networks for ice sheets and are currently responsible for the majority of discharge from the West Antarctic Ice Sheet. Many catchments like the Siple Coast of West Antarctica display a complex array of flow morphologies that are not primarily determined by bed topography. Instead, flow is primarily governed by thermal conditions along the bed and in shear margins that lead to rapid till deformation. In this thesis, we explore the causes and effects of ice stream formation, activation, and evolution, in time and space. In one chapter, we explore the thermomechanical implications of ice stream evolution, with a simple model. When friction at the bed is weak, most of the flow resistance comes from shear margins, at the boundary layer between fast and slow flow. In very cold, West Antarctic ice streams, internal heat dissipation in the shear margins can warm layers of temperate ice near the bed, producing meltwater. In the second chapter, we present direct numerical simulations of the coupled thermomechanical Stokes-kinematic problem to derive parameterizations for shear heating and temperate ice. Finally, taking a materially frame invariant view of shear margin/onset boundary layers, we explore more general implications of flow onset to the stress balance of fast flowing ice streams. In the third chapter, we derive exact solutions to the Shallow Shelf/Stream Approximation (SSA), and we demonstrate that these exact solutions can be used as quasi-Green’s functions for the nonlinear dynamics of ice flow.

Thesis Committee

• Colin Meyer (Chair)
• Helene Seroussi
• Robert Hawley (EARS)
• Martin Truffer (U Alaska, Fairbanks)

Contact

For more information, contact Thayer Registrar at thayer.registrar@dartmouth.edu.