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

Abstract

Negribreen, 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).

Complementary Approaches Towards a Universal Model of Glacier Surges

“…The mechanism further resonates as valid in instances where (enthalpy driven) propagation speeds exceed ice flow velocities (e.g. Murray et al, 2003) and in situations where the lower reaches of the glacier are subject to sudden destabilisation after basal water intrusions (Haga et al, 2020). Nevertheless, examples of up-glacier propagation (e.g.…”

“…Since the 1980s, a growing body of research describes a wide range of observed surge behavior that does not fit neatly within one of the two originally suggested categories of surges (e.g. Fowler et al, 2001;Murray et al, 2003;Dunse et al, 2015;Lovell et al, 2018;Haga et al, 2020). Perhaps as a result, the various additions and revisions to initial surging theories suggested by these newer studies often transcend the boundaries between the initially proposed mechanisms; and the once clear distinction between two separate surging regimes somewhat wanes.…”

Brief Communication: Detection of glacier surge activity using cloud computing of Sentinel-1 radar data

“…After the 2017 peak in surface velocity, they find a gradual slowdown in which the crevassing of the glacier surface, though, further intensified during the years 2018 and 2019. Haga et al (2020) explain this from flow velocity being still high after the peak, which in turn led to continued stretch in the glacier ice. This indicates we can observe increase in backscatter even after the surge velocity peak.…”

“…As a detailed example we discuss results for Negribreen and Sonklarbreen on the east coast of Spitsbergen, Svalbard. Fig 2a shows a clear increase in radar backscatter between winter 2018 and winter 2019 for Negribreen, which started to surge in late summer 2016 and had surface velocities peak in the melt season of 2017 (Haga et al, 2020). After the 2017 peak in surface velocity, they find a gradual slowdown in which the crevassing of the glacier surface, though, further intensified during the years 2018 and 2019.…”

open discussion short comments

“…A final short remark is that in a recent paper, Haga et al (2020) mention the potential importance of an efficient drainage system in the partial freezing of the Negribreen glacier terminus to its bed surface. The rapid erosion in response to surface events in this study could indicate the capacity of a drainage system to adjust rapidly to changes, even in permafrost.…”