A theory of glacier dynamics and instabilities Part 1: Topographically confined glaciers

Hsien-Wang Ou

doi:10.1017/jog.2021.20

Abstract

AbstractWe present a theoretical framework that integrates the dynamics of glaciers with and without the topographic confinement. This Part 1 paper concerns the former, which may exhibit surge cycles when subjected to thermal switches associated with the bed condition. With the topographic trough setting the glacier width and curbing the lateral drainage of the meltwater, the problem falls under the purview of the undrained plastic bed (UPB) formalism. Employing the UPB, we shall examine the external controls of the glacial behavior and test them against observations. Through our non-dimensionalization scheme, we construct a 2-D regime diagram, which allows a ready prognosis of the glacial properties over the full range of the external conditions, both climate- and size-related. We first discern the boundaries separating the glacial regimes of steady-creep, cyclic-surging and steady-sliding. We then apply the regime diagram to observed glaciers for quantitative comparisons. These include the Svalbard glaciers of both normal and surge types, Northeast Greenland Ice Stream characterized by steady-sliding, and Hudson Strait Ice Stream exhibiting cyclic surges. The quantitative validation of our model containing no free parameters suggests that the thermal switch may unify the dynamics of these diverse glaciers.

Highlights

Some glaciers are known to surge periodically, a phenomenon that has long intrigued glaciologists and is the subject of extensive studies and reviews (Meier and Post, 1969; Clarke, 1987; Raymond, 1987; Harrison and Post, 2003)
It is seen that because of its greater width than the Northeast Greenland Ice Stream (NEGIS), the Hudson Strait Ice Stream (HSIS) falls in the cyclicsurging regime, and the underlying physics is that the greater width strongly augments the sliding flux of the HSIS, which may no longer be accommodated by the catchment, resulting in cyclic surges
Through our non-dimensionalization scheme, we construct a 2-D diagram depicting the glacial regimes of steadycreep, cyclic-surging and steady-sliding, and from which the glacial properties can be prognosed over the full range of the external conditions – both climate- and size-related

Summary

Introduction

Some glaciers are known to surge periodically, a phenomenon that has long intrigued glaciologists and is the subject of extensive studies and reviews (Meier and Post, 1969; Clarke, 1987; Raymond, 1987; Harrison and Post, 2003). For a quantitative simulation the critical element is the sliding velocity where primary uncertainty arises In some models, this sliding velocity is imposed as a jump or triple-valued function of the basal stress (Payne, 1995; Calov and others, 2002; Sayag and Tziperman, 2009; Kyrke-Smith and others, 2013), and in others, it has evolved into a sliding flow law (Budd and others, 1984; Bentley, 1987) that remains in wide use to this date (Dunse and others, 2011; Feldmann and Levermann, 2017; Smith-Johnsen and others, 2020). As the latter directly impacts the amplitude and period of the surge cycles, it renders such models practically unfalsifiable by observations

Objectives

Discussion

Conclusion