From high friction zone to frontal collapse: dynamics of an ongoing tidewater glacier surge, Negribreen, Svalbard

Odin Næss Haga,Andreas Kääb,Robert Mcnabb,Bas Altena,Christopher Nuth,Thomas Schellenberger

doi:10.1017/jog.2020.43

Abstract

AbstractNegribreen, a tidewater glacier located in central eastern Svalbard, began actively surging after it experienced an initial collapse in summer 2016. The surge resulted in horizontal surface velocities of more than 25 m d−1, making it one of the fastest-flowing glaciers in the archipelago. The last surge of Negribreen likely occurred in the 1930s, but due to a long quiescent phase, investigations of this glacier have been limited. As Negribreen is part of the Negribreen Glacier System, one of the largest glacier systems in Svalbard, investigating its current surge event provides important information on surge behaviour among tidewater glaciers within the region. Here, we demonstrate the surge development and discuss triggering mechanisms using time series of digital elevation models (1969–2018), surface velocities (1995–2018), crevasse patterns and glacier extents from various data sources. We find that the active surge results from a four-stage process. Stage 1 (quiescent phase) involves a long-term, gradual geometry change due to high subglacial friction towards the terminus. These changes allow the onset of Stage 2, an accelerating frontal destabilization, which ultimately results in the collapse (Stage 3) and active surge (Stage 4).

Highlights

Glacier surges are cyclic phenomena whereby glaciers switch between periodic phases of low activity with slow ice flow during a century- to decadal-long ‘quiescent’ phase, and rapid flow during a short-lived peak (‘surge’ phase) where velocities increase by a factor of 10–1000 times (Meier and Post, 1969; Murray and others, 2003a)
We discuss in detail the basal friction, geometry change and spread of crevasses, all important processes occurring in Stages 1 and 2 which led towards the final onset of this surge event
We have investigated the ongoing surge of Negribreen, a tidewater glacier on the east coast of Svalbard

Summary

Introduction

Glacier surges are cyclic phenomena whereby glaciers switch between periodic phases of low activity with slow ice flow during a century- to decadal-long ‘quiescent’ phase, and rapid flow during a short-lived peak (‘surge’ phase) where velocities increase by a factor of 10–1000 times (Meier and Post, 1969; Murray and others, 2003a). Additional velocity measurements from offset tracking in 2008 RADARSAT data show no real difference to the 1995/ 1997 measurements, with very low velocities (< 0.05 m d−1) at the glacier front, increasing to ∼0.12 m d−1 in the ablation area All of this suggests the presence of high basal friction near the glacier front, a likely factor in the bulge development as the zone of higher friction may have been acting as a barrier for the mobile ice coming from the accumulation area, forcing the surface to ‘pile up’. By 2015–16, the yearly thinning rate reached a maximum of 25 m a−1, and a significant bulge break-up had occurred, since the surface areas affected by thinning expanded 5 km further up-glacier from the terminus It is here where we observed a shift towards greater acceleration in velocities, and the speed at the glacier front increased from 0.5 to 2±0.6 m d−1 over the melt-season of 2015.

Discussion

Conclusion