Characterizing Sediment Flux of Deforming Glacier Beds

Hansen, Dougal; Zoet, Lucas K.

doi:10.1029/2021jf006544

Cited by 20 publications

(13 citation statements)

References 76 publications

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“…As the ice approaches flotation, we would expect an increasing degree of slip between the ice and till, so that the basal motion of the ice is not fully transmitted to the till. This could lead to a non-monotonic till flux relationship with pressure, such as observed in [49]. Given the importance of understanding till fluxes when explaining the formation of subglacial bedforms, an extension to this work would be to consider the three-layer system that incorporates an increasingly deep film of water at the ice–till interface, to more fully understand the transition from deep till deformation to sliding over a water-filled cavity.…”

Section: Discussionmentioning

confidence: 99%

Shear dilation of subglacial till results in time-dependent sliding laws

2023

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The dynamics of glacial sliding over water-saturated tills are poorly constrained and difficult to capture realistically in large-scale models. Experiments characterize till as a plastic material with a pressure-dependent yield stress, but the subglacial water pressure may fluctuate on annual to daily timescales, leading to transient adjustment of the till. We construct a continuum two-phase model of coupled fluid and solid deformation, describing the movement of water through the pore space of a till that is itself dilating and deforming. By forcing the model with time-dependent effective pressure at the ice–till interface, we infer the resulting relationships between basal traction, solid fraction and rate of deformation. We find that shear dilation introduces internal pressure variations and transient dilatant strengthening emerges, leading to hysteretic behaviour in low-permeability materials. The result is a time-dependent effective sliding law, with permeability-dependent lag between changes in effective pressure and the slidingspeed. This deviation from traditional steady-state sliding laws may play an important role in a wide range of transient ice-sheet phenomena, from glacier surges to the tidal response of ice streams.

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Section: Discussionmentioning

confidence: 99%

Shear dilation of subglacial till results in time-dependent sliding laws

2023

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“…This apparatus better approximates subglacial drainage conditions compared to the direct shear and effectively allows unlimited displacement. (For a detailed description of this device refer to Hansen and Zoet, 2022. ) We slid rings of debris-laden temperate ice over marble beds at prescribed normal stresses, basal melt rates, and slip speeds (see Table 1 for boundary conditions).…”

Section: S2 Ring Shear: Experimental Protocolmentioning

confidence: 99%

A power-based abrasion law for use in landscape evolution models

Hansen

Brooks

Zoet

et al. 2023

Geology

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Subglacial abrasion drives erosion for many glaciers, inundating forefields and proglacial marine environments with glaciogenic sediments. Theoretical treatments of this process suggest that bedrock abrasion rates scale linearly with the energy expended through rock-on-rock friction during slip, but this assumption lacks an empirical basis for general implementation. To test this approach, we simulated abrasion by sliding debris-laden ice over rock beds under subglacial conditions in a cryo-ring shear and a direct shear device. Miniscule volumes of erosion that occurred during each run were mapped with a white-light profilometer, and we measured the rock mechanical properties needed to constrain the energy expended through abrasion. We find that abraded volume per unit area increases linearly with average shear force at the bed and that abrasion rates increase linearly with basal power for plane beds. Lastly, only a small percentage (1%) of the energy partitioned to basal slip is dissipated by abrasion. These results confirm the basal-power abrasion rule is viable to implement in landscape evolution models.

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“…Our model design assumes that subglacial sediment transport is dominated by water flow. While this is a common assertion (e.g., Alley et al, 1997;Riihimaki et al, 2005), the role of further sediment transport processes under debris-covered ice like the entrainment of sediment in the glacier sole (e.g., Iverson, 1993) or subglacial till deformation (e.g., Hansen & Zoet, 2022) should be explored. Additionally, we neglect seasonal variations in melt, yet, the subglacial water velocities in the model are high compared to those observed in other studies (e.g., Werder & Funk, 2009).…”

Section: Experimental Limitationsmentioning

confidence: 99%

Debris Cover Limits Subglacial Erosion and Promotes Till Accumulation

Delaney

Anderson

2022

Geophysical Research Letters

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Glaciers are efficient agents of erosion, which sculpt some of the most iconic landscapes on Earth. Glaciers modify mountain landscapes primarily by eroding their beds through the processes of abrasion and plucking (Herman et al., 2021;Iverson, 2012;Ugelvig et al., 2018). These processes are closely linked to ice dynamics through the sliding of glacial ice at the bed. The role of basal sliding and erosion has been elegantly explained for clean glaciers producing explanations for U-shaped valleys and flattened longitudinal profiles (Egholm et al., 2009;Harbor et al., 1988;Herman et al., 2011).Glaciers also tend to steepen the headwalls above them through basal erosion (MacGregor et al., 2009) and also by encouraging processes such as frost cracking at the base of headwalls (Heimsath & McGlynn, 2008;Sanders et al., 2012). Hillslope erosion in mountain settings is mostly accomplished via landslides, rock falls, and avalanches all of which deposit loose rock (or debris) on glaciers below (e.g., Sanders et al., 2013;Scherler, 2014). Debris deposited high on glaciers is buried by accumulating snow and is then transported passively through the interior emerging low on the glacier (Figure 1). Where hillslope erosion rates are high, enough debris can melt out onto glacier surfaces that a nearly continuous mantle of debris forms.Debris-covered glaciers are especially common in mountains steepened by active tectonics, like High Mountain Asia, Alaska, or the Andes (Herreid & Pellicciotti, 2020;Scherler et al., 2018). The most important effect of debris on glacier surfaces is that it insulates glacier ablation zones from melt (Östrem, 1959). Some features scattered on debris-covered glaciers like ponds, ice cliffs, and streams enhance surface melt locally (e.g., Benn

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Characterizing Sediment Flux of Deforming Glacier Beds

Cited by 20 publications

References 76 publications

Shear dilation of subglacial till results in time-dependent sliding laws

Shear dilation of subglacial till results in time-dependent sliding laws

A power-based abrasion law for use in landscape evolution models

Debris Cover Limits Subglacial Erosion and Promotes Till Accumulation

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