Glacier sliding, seismicity and sediment entrainment

Lipovsky, B. P.; Meyer, Colin R.; Zoet, Lucas K.; McCarthy, Christine; Hansen, Dougal; Rempel, A. W.; Gimbert, Florent

doi:10.1017/aog.2019.24

Cited by 51 publications

(56 citation statements)

References 88 publications

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“…Röthlisberger and Lang, 1987; Alley and others, 1998; Lawson and others, 1998; Creyts and Clarke, 2010). Evidence has been given that the thermo-mechanical feedbacks made possible by premelting and variations in effective stress are instrumental in limiting both the range of observed glacier driving stresses (Meyer and others, 2018) and the occurrence of regions amenable to stick-slip behavior (Lipovsky and others, 2019). This adds further emphasis to the importance of basal liquid transport for understanding glacier dynamics (e.g.…”

Section: Discussionmentioning

confidence: 99%

Premelting increases the rate of regelation by an order of magnitude

Rempel

Meyer

2019

J. Glaciol.

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Glacier sliding over small obstacles relies on melting on their upstream sides and refreezing downstream. Previous treatments have appealed to ‘pressure melting’ as the cause of the spatial variations in melting temperature that drive thisregelationprocess. However, we show that typical liquid pressure variations across small obstacles are negligible and therefore variations in ice pressure closely approximate variations in effective stress. For a given change in effective stress, the equilibrium melting temperature changes by an order of magnitude more than when the pressure of ice and liquid both change by an equal amount. In consequence, the temperature gradients that drive heat flow across small obstacles are larger than previously recognized and the rate of regelation is faster. Under typical conditions, the transition wavelength at which ice deformation and regelation contribute equally is of m-scale, several times longer than previous predictions, which have been reported to underestimate field inferences.

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Section: Discussionmentioning

confidence: 99%

Premelting increases the rate of regelation by an order of magnitude

Rempel

Meyer

2019

J. Glaciol.

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“…Waveforms of microseismic basal earthquakes are generally of short duration because the path effects that distort the source signal as it moves through the glacial ice are minimal. A possible source mechanism for basal earthquakes is the slip of debris-laden ice over bedrock highs protruding through the till (or large clasts embedded in the till) (Zoet and others, 2012; Lipovsky and others, 2019), though hydraulic fracturing (Zoet and others, 2013b), tensile failures (Walter and others, 2009, 2010), and shear events in the till have also been proposed as possible sources. Detection of these events automatically is often done by comparing a running short-term average to a long-term average (STA/LTA) of the seismic energy (Allen, 1978), which becomes large when impulsive signals occur.…”

Section: Introductionmentioning

confidence: 99%

Basal seismicity of the Northeast Greenland Ice Stream

2020

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Seismic studies of glaciers yield insights into spatio-temporal processes within and beneath glaciers on scales relevant to flow and deformation of the ice. These methods enable direct monitoring of the bed in ways that complement other geophysical techniques, such as geodetic or ground penetrating radar observations. In this work, we report on the analysis of passive seismic data collected from the interior of the North East Greenland Ice Stream, the Greenland ice sheet's largest outlet glacier. We record thousands of basal earthquakes, many of which repeat with nearly identical waveforms. We also record many long-duration glacial tremor episodes that migrate across the seismic network with slow velocities (e.g. ~4–12 m s−1). Analysis of the basal earthquakes indicates a transition between times of individual event activity and times of tremor activity. We suggest that both processes are produced by shear slip at localized asperities along the bed. The transition between discrete and quasi-continuous slipping modes may be driven by pore-water pressure transients or heterogeneous strain accumulation in the ice due to strength contrasts of the underlying till.

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“…For micron sized pore throats and γ iw = 0.034 N/m, the entry pressure is p f ∼ 70 kPa (Rempel, 2008;Meyer et al, 2018;Lipovsky et al, 2019). The ice that enters the pore space to form a frozen fringe partially saturates the available porosity, meaning that there is both water and ice between sediment grains.…”

Section: Premelting and Ice Infiltrationmentioning

confidence: 99%

Frozen fringe explains sediment freeze-on during Heinrich events

Meyer¹,

Robel²,

Rempel³

2019

Preprint

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Anomalous coarse-grained sediment layers beneath the North Atlantic likely originated from sediment freeze-on to the base of ice sheets during the last glacial period. These layers represent periods of extreme ice discharge, called Heinrich events, and are variously attributed to ice stream flow instability, ice shelf collapse, or enhanced terminus melting due to ocean warming. In this paper, we study the processes controlling how sediment freezes on to the base of ice streams and predict the volume of sediment conveyed by icebergs during a Heinrich event. The local thickness of frozen sediment is sensitive to the heat flux at the ice-bed interface and the water pressure, both of which also contribute to the controls on basal friction; as the basal water pressure increases, both the frozen sediment thickness and the basal friction decrease. The sediment discharged during a Heinrich event must have frozen on to the ice during the inter-Heinrich period. As the Heinrich event proceeds, the frozen sediment melts off the base of the ice stream, indicating that the thickness of sediments deposits in the North Atlantic may not reliably constrain Heinrich event duration. Choosing reasonable parameters corresponding to the Hudson Strait Ice Stream, our model of sediment freeze-on and discharge is consistent with observational estimates of Heinrich event sediment discharge volume.

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Glacier sliding, seismicity and sediment entrainment

Cited by 51 publications

References 88 publications

Premelting increases the rate of regelation by an order of magnitude

Premelting increases the rate of regelation by an order of magnitude

Basal seismicity of the Northeast Greenland Ice Stream

Frozen fringe explains sediment freeze-on during Heinrich events

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