Abstract
AbstractWe present a highly detailed study of calving dynamics at Tunabreen, a tidewater glacier in Svalbard. A time-lapse camera was trained on the terminus and programmed to capture images every 3 seconds over a 28-hour period in August 2015, producing a highly detailed record of 34 117 images from which 358 individual calving events were distinguished. Calving activity is characterised by frequent events (12.8 events h−1) that are small relative to the spectrum of calving events observed, demonstrating the prevalence of small-scale calving mechanisms. Five calving styles were observed, with a high proportion of calving events (82%) originating at, or above, the waterline. The tidal cycle plays a key role in the timing of calving events, with 68% occurring on the falling limb of the tide. Calving activity is concentrated where meltwater plumes surface at the glacier front, and a ~ 5 m undercut at the base of the glacier suggests that meltwater plumes encourage melt-under-cutting. We conclude that frontal ablation at Tunabreen may be paced by submarine melt rates, as suggested from similar observations at glaciers in Svalbard and Alaska. Using submarine melt rate to calculate frontal ablation would greatly simplify estimations of tidewater glacier losses in prognostic models.
Highlights
IntroductionThe loss of ice from the termini of marine-terminating glaciers (i.e. frontal ablation) occurs by both submarine melting and iceberg calving
The loss of ice from the termini of marine-terminating glaciers occurs by both submarine melting and iceberg calving
It is likely that this style of calving event would be undetected by remote seismic monitoring (e.g., Köhler and others, 2015; How, 2018), requiring multiple seismic installations at the glacier terminus in order to increase the chance of detection (e.g., Bartholomaus and others, 2015)
Summary
The loss of ice from the termini of marine-terminating glaciers (i.e. frontal ablation) occurs by both submarine melting and iceberg calving. Calving from tidewater glaciers can occur by a number of mechanisms, including longitudinal stretching, buoyant instability and under-cutting of the front by submarine melt (Van Der Veen, 2002; Benn and others, 2007). Submarine melting can influence calving by under-cutting and destabilising the subaerial part of the ice front. Where melt-under-cutting is the dominant driver of calving, frontal ablation rates depend on the relationship between two fundamental factors: (1) the temporal and spatial evolution of subaqueous cavities by melting; and (2) the mechanical response of the ice to the evolving geometry and associated stresses (Joughin and others, 2008; Howat and others, 2010). Our understanding of the relationship between under-cutting and calving is, heavily reliant on modelling at present
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