Dilatant till facilitates ice-stream flow in northeast Greenland

Christianson, Knut; Peters, L. E.; Alley, Richard B.; Anandakrishnan, S.; Jacobel, R. W.; Riverman, K. L.; Muto, Atsuhiro; Keisling, B. A.

doi:10.1016/j.epsl.2014.05.060

Cited by 86 publications

(188 citation statements)

References 72 publications

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“…This is in agreement with previous studies, which have also found a potential for changes in drainage pattern (Livingstone et al, 2013;Christianson et al, 2014).…”

Section: Subglacial Water Outfluxsupporting

confidence: 94%

Response of the large-scale subglacial drainage system of Northeast Greenland to surface elevation changes

Karlsson

Dahl-Jensen

2015

The Cryosphere

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Abstract. The influence of subglacial water on the dynamics of ice flow has been the object of increasing interest in the past decade. In this study we focus on large-scale, longterm changes in surface elevation over Northeast Greenland and the corresponding changes in subglacial water routeways. Our results show that over timescales ranging from decades to millennia the area may experience redistribution of and fluctuation in subglacial water outflux under the main glacier outlets. The fluctuations in subglacial water routing occur even in the absence of external forcing. Based on these results we conclude that changes in the subglacial water routeways are an intrinsic part of the drainage basin dynamics, where the subglacial system is likely always in a transient state. The results also imply that fluctuations at the margins observed at present might originate from changes several hundred kilometres upstream. Since surface elevation changes may propagate upstream over timescales much longer than the observational period, the cause of the fluctuations may not be present in current observational records.

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“…This is in agreement with previous studies, which have also found a potential for changes in drainage pattern (Livingstone et al, 2013;Christianson et al, 2014).…”

Section: Subglacial Water Outfluxsupporting

confidence: 94%

Response of the large-scale subglacial drainage system of Northeast Greenland to surface elevation changes

Karlsson

Dahl-Jensen

2015

The Cryosphere

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“…A growing number of glaciological applications have been using amplitude v. offset (AVO) data as powerful diagnostics of acoustic impedance -the product of seismic velocity and density -and Poisson's ratio -a measure of material stiffness calculated from compressional and shear wave velocities -as proxies for subglacial till deformation (Nolan & Echelmeyer 1999;Anandakrishnan 2003;Peters et al 2007Peters et al , 2008Booth et al 2012;Dow et al 2013;Christianson et al 2014;Kulessa et al In review). For example, lower acoustic impedances and higher Poisson's ratios diagnose weaker higher-porosity tills that dilate to Fig.…”

Section: Hydrological and Mechanical Conditions At The Ice-sheet Bedmentioning

confidence: 99%

Antarctic subglacial groundwater: a concept paper on its measurement and potential influence on ice flow

Siegert

Kulessa

Bougamont

et al. 2017

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Is groundwater abundant in Antarctica and does it modulate ice flow? Answering this question matters because ice streams flow by gliding over a wet substrate of till. Water fed to icestream beds thus influences ice-sheet dynamics and, potentially, sea-level rise. It is recognized that both till and the sedimentary basins from which it originates are porous and could host a reservoir of mobile groundwater that interacts with the subglacial interfacial system. According to recent numerical modelling, up to half of all water available for basal lubrication, and time lags between hydrological forcing and ice-sheet response as long as millennia, may have been overlooked in models of ice flow. Here, we review evidence in support of Antarctic groundwater and propose how it can be measured to ascertain the extent to which it modulates ice flow. We present new seismoelectric soundings of subglacial till, and magnetotelluric and transient electromagnetic forward models of subglacial groundwater reservoirs. We demonstrate that multifaceted and integrated geophysical datasets can detect, delineate and quantify the groundwater contents of subglacial sedimentary basins and, potentially, monitor groundwater exchange rates between subglacial till layers. The paper thus describes a new area of glaciological investigation and how it should progress in future.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license. Water beneath the ice sheetAntarctic ice-sheet flow is fundamentally affected by water at the bed, as it reduces basal friction to encourage sliding and weakens till to enable bed deformation. Subglacial hydrology -the flow of water beneath the ice -is therefore a key element of the ice-sheet system. Studies to date on subglacial hydrology, and its impact on ice flow, have concentrated on water at or very near to the bed of the ice sheet.Basal water modulation of ice flow can be achieved in a number of ways. Over an impermeable bed, water can flow through channels cut either downwards into the substrate or upwards into the ice. Enhanced basal water pressures may occur where the channels and their linkages are distributed, increasing overriding ice flow through a reduction in the substrate's effective pressure. Conversely, where a well-organized channel system is formed, water pressures are lower and the hydrological effect on ice flow is reduced. If the ice stream rests on permeable subglacial till, its strength can affect ice flow as controlled by porewater pressures. High pressures lead to a reduction in material strength by pushing till grains apart, reducing bed friction and thus

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“…A modern example of such an ice stream may be the NEGIS Fahnestock et al, 2001). While there is topographic steering near its outlet glaciers, topographic steering is weak over much of its length Christianson et al, 2014). Seismic and radio-echo sounding have shown the base of the NEGIS to be rough (e.g.…”

Section: Relevance For Ice Streaming and Ice-sheet Modellingmentioning

confidence: 99%

“…Seismic and radio-echo sounding have shown the base of the NEGIS to be rough (e.g. Christianson et al, 2014) and also suggest the possible presence of water-rich till. However, the presence of soft, deformable till below the NEGIS is not proven and, if existent, may not be the rate-controlling factor, as deforming till will not help in moving ice over bedrock humps.…”

Section: Relevance For Ice Streaming and Ice-sheet Modellingmentioning

confidence: 99%

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Sliding of temperate basal ice on a rough, hard bed: creep mechanisms, pressure melting, and implications for ice streaming

Krabbendam

2016

The Cryosphere

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Abstract. Basal ice motion is crucial to ice dynamics of ice sheets. The classic Weertman model for basal sliding over bedrock obstacles proposes that sliding velocity is controlled by pressure melting and/or ductile flow, whichever is the fastest; it further assumes that pressure melting is limited by heat flow through the obstacle and ductile flow is controlled by standard power-law creep. These last two assumptions, however, are not applicable if a substantial basal layer of temperate (T ∼ T melt ) ice is present. In that case, frictional melting can produce excess basal meltwater and efficient water flow, leading to near-thermal equilibrium. High-temperature ice creep experiments have shown a sharp weakening of a factor 5-10 close to T melt , suggesting standard power-law creep does not operate due to a switch to melt-assisted creep with a possible component of grain boundary melting. Pressure melting is controlled by meltwater production, heat advection by flowing meltwater to the next obstacle and heat conduction through ice/rock over half the obstacle height. No heat flow through the obstacle is required. Ice streaming over a rough, hard bed, as possibly in the Northeast Greenland Ice Stream, may be explained by enhanced basal motion in a thick temperate ice layer.

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Dilatant till facilitates ice-stream flow in northeast Greenland

Cited by 86 publications

References 72 publications

Response of the large-scale subglacial drainage system of Northeast Greenland to surface elevation changes

Response of the large-scale subglacial drainage system of Northeast Greenland to surface elevation changes

Antarctic subglacial groundwater: a concept paper on its measurement and potential influence on ice flow

Sliding of temperate basal ice on a rough, hard bed: creep mechanisms, pressure melting, and implications for ice streaming

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