Step‐wise changes in glacier flow speed coincide with calving and glacial earthquakes at Helheim Glacier, Greenland

Nettles, M.; Larsen, Tine B.; Elósegui, P.; Hamilton, G. S.; Stearns, L. A.; Ahlstrøm, Andreas P.; Davis, J. L.; Andersen, M.; Juan, J. de; Khan, Shfaqat Abbas; Stenseng, Lars; Ekström, Göran; Forsberg, R.

doi:10.1029/2008gl036127

Cited by 102 publications

(175 citation statements)

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“…The effect of calving events on glacier speed must therefore be quantified and removed from the velocity signals in order to study the effect of melt on speed variations. The largest changes in daily glacier velocity are associated with calving events for which glacial earthquakes are detected (Nettles and others, 2008) and these changes appear in the velocity record as step-like offsets. To identify the times when calving-related velocity offsets may occur, we use the list of glacial earthquakes from Nettles and others (2008) for events in 2007, and a list of events for 2008 identified in a similar manner, using the algorithm of Ekström (2006).…”

Section: Glacier Surface Velocitymentioning

confidence: 99%

“…The largest changes in daily glacier velocity are associated with calving events for which glacial earthquakes are detected (Nettles and others, 2008) and these changes appear in the velocity record as step-like offsets. To identify the times when calving-related velocity offsets may occur, we use the list of glacial earthquakes from Nettles and others (2008) for events in 2007, and a list of events for 2008 identified in a similar manner, using the algorithm of Ekström (2006). In 2008, we identify two M $ 4.8 seismic events at Helheim Glacier on day 214 and one event of M $ 4.7 on day 232, as well as several smaller events (Fig.…”

Section: Glacier Surface Velocitymentioning

confidence: 99%

“…The velocity estimates have uncertainties of $0.1 m d -1 . The loss of ice from the glacier terminus during largescale calving events has been shown to change the flow speed by as much as 20% at Helheim Glacier (Nettles and others, 2008) and elsewhere (Amundson and others, 2008). The effect of calving events on glacier speed must therefore be quantified and removed from the velocity signals in order to study the effect of melt on speed variations.…”

Section: Glacier Surface Velocitymentioning

confidence: 99%

“…The networks extended from within a few km of the calving front to $20 km upstream along the flowline in 2007 and $30 km in 2008. Daily velocities were calculated by fitting a linear model to position estimates determined kinematically at 15 s intervals, as described by Nettles and others (2008). The velocity estimates have uncertainties of $0.1 m d -1 .…”

Section: Glacier Surface Velocitymentioning

confidence: 99%

“…Howat and others, 2005), seasonal (e.g. Joughin and others, 2008a) and shorter (Amundson and others, 2008;Nettles and others, 2008) timescales.…”

Section: Introductionmentioning

confidence: 99%

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Quantitative estimates of velocity sensitivity to surface melt variations at a large Greenland outlet glacier

et al. 2011

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ABSTRACT. The flow speed of Greenland outlet glaciers is governed by several factors, the relative importance of which is poorly understood. The delivery of surface-generated meltwater to the bed of alpine glaciers has been shown to influence glacier flow speed when the volume of water is sufficient to increase basal fluid pressure and hence basal lubrication. While this effect has also been demonstrated on the Greenland ice-sheet margin, little is known about the influence of surface melting on the large, marine-terminating outlet glaciers that drain the ice sheet. We use a validated model of meltwater input and GPS-derived surface velocities to quantify the sensitivity of glacier flow speed to changes in surface melt at Helheim Glacier during two summer seasons (2007-08). Our observations span $ $55 days near the middle of each melt season. We find that relative changes in glacier speed due to meltwater input are small, with variations of $ $45% in melt producing changes in velocity of $ $2-4%. These velocity variations are, however, of similar absolute magnitude to those observed at smaller glaciers and on the ice-sheet margin. We find that the glacier's sensitivity to variations in meltwater input decreases approximately exponentially with distance from the calving front. Sensitivity to melt varies with time, but generally increases as the melt season progresses. We interpret the time-varying sensitivity of glacier flow to meltwater input as resulting from changes in subglacial hydraulic routing caused by the changing volume of meltwater input.

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Section: Glacier Surface Velocitymentioning

confidence: 99%

Section: Glacier Surface Velocitymentioning

confidence: 99%

Section: Glacier Surface Velocitymentioning

confidence: 99%

Section: Glacier Surface Velocitymentioning

confidence: 99%

“…Howat and others, 2005), seasonal (e.g. Joughin and others, 2008a) and shorter (Amundson and others, 2008;Nettles and others, 2008) timescales.…”

Section: Introductionmentioning

confidence: 99%

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Quantitative estimates of velocity sensitivity to surface melt variations at a large Greenland outlet glacier

et al. 2011

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Quantifying flow regimes in a Greenland glacial fjord using iceberg drifters

Sutherland

Roth

Hamilton

et al. 2014

Geophysical Research Letters

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Large, deep-keeled icebergs are ubiquitous in Greenland's outlet glacial fjords. Here we use the movement of these icebergs to quantify flow variability in Sermilik Fjord, southeast Greenland, from the ice mélange through the fjord to the shelf. In the ice mélange, a proglacial mixture of sea ice and icebergs, we find that icebergs consistently track the glacier speed, with slightly faster speeds near terminus and episodic increases due to calving events. In the fjord, icebergs accurately capture synoptic circulation driven by both along-fjord and along-shelf winds. Recirculation and in-/out-fjord variations occur throughout the fjord more frequently than previously reported, suggesting that across-fjord velocity gradients cannot be ignored. Once on the shelf, icebergs move southeastward in the East Greenland Coastal Current, providing wintertime observations of this freshwater pathway.

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Avalanching glacier instabilities: Review on processes and early warning perspectives

Faillettaz

Funk

Vincent

2015

Reviews of Geophysics

103

102

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Avalanching glacier instabilities are gravity-driven rupture phenomena that might cause major disasters, especially when they are at the origin of a chain of processes. Reliably forecasting such events combined with a timely evacuation of endangered inhabited areas often constitute the most efficient action. Recently, considerable efforts in monitoring, analyzing, and modeling such phenomena have led to significant advances in destabilization process understanding, improving early warning perspectives. The purpose of this paper is to review the recent progress in this domain. Three different types of instabilities can be identified depending on the thermal properties of the ice/bed interface. If cold (1), the maturation of the rupture is associated with a typical time evolution of surface velocities and passive seismic activity. A prediction of the final break off is possible using these precursory signs. For the two other types, water plays a key role in the development of the instability. If the ice/bed interface is partly temperate (2), the presence of meltwater may reduce the basal resistance, which promotes the instability. No clear and easily detectable precursory signs are known in this case, and the only way to infer any potential instability is to monitor the temporal evolution of the thermal regime. The last type of instability (3) concerns steep temperate glacier tongues switching for several days/weeks during the melting season into a so-called "active phase" followed in rare cases by a major break-off event. Although the prediction of such events is still far from being achievable, critical conditions promoting the final instability can be identified.

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Step‐wise changes in glacier flow speed coincide with calving and glacial earthquakes at Helheim Glacier, Greenland

Cited by 102 publications

References 22 publications

Quantitative estimates of velocity sensitivity to surface melt variations at a large Greenland outlet glacier

Quantitative estimates of velocity sensitivity to surface melt variations at a large Greenland outlet glacier

Quantifying flow regimes in a Greenland glacial fjord using iceberg drifters

Avalanching glacier instabilities: Review on processes and early warning perspectives

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