Abstract
Glacier surges are quasi-periodic episodes of rapid ice flow that arise from increases in slip rate at the ice–bed interface. The mechanisms that trigger and sustain surges are not well understood. Here, we develop a new model of incipient surge motion for glaciers underlain by sediments to explore how surges may arise from slip instabilities within a thin layer of saturated, deforming subglacial till. Our model represents the evolution of internal friction, porosity and pore water pressure within the till as functions of the rate and history of shear deformation, and couples the till mechanics to a simple ice-flow model. Changes in pore water pressure govern incipient surge motion, with less permeable till facilitating surging because dilation-driven reductions in pore water pressure slow the rate at which till tends towards a new steady state, thereby allowing time for the glacier to thin dynamically. The reduction of overburden (and thus effective) pressure at the bed caused by dynamic thinning of the glacier sustains surge acceleration in our model. The need for changes in both the hydromechanical properties of the till and the thickness of the glacier creates restrictive conditions for surge motion that are consistent with the rarity of surge-type glaciers and their geographical clustering.
Highlights
Surges are enigmatic characteristics of glacier flow
Since shear strength of the till is the governing factor in surge motion and is defined by three variables, we present the results in three sections
We explore the full model, which allows for variations in pore water pressure, glacier geometry and internal friction coefficient for till
Summary
Surges are enigmatic characteristics of glacier flow. Broadly speaking, glacier surges are subannual to2020 The Authors. Surges are enigmatic characteristics of glacier flow. Multi-annual periods of relatively rapid flow that occur quasi-periodically, with quiescent periods between surges ranging from several years to centuries [1,2]. Flow speeds during a surge can royalsocietypublishing.org/journal/rspa Proc.
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