The influence of basal-ice debris on patterns and rates of glacial erosion

Ugelvig, Sofie V.; Egholm, David Lundbek

doi:10.1016/j.epsl.2018.03.022

Cited by 17 publications

(16 citation statements)

References 50 publications

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“…In subsequent years, Hallet's model (1979b, 1981) has been widely implemented in glacier erosion models (Herman and others, 2011; Anderson, 2014; Beaud and others, 2014; Egholm and others, 2017; Ugelvig and Egholm, 2018), and available experimental data support a linear relationship between F c and u v as predicted (Iverson, 1990; Byers and others, 2012). Although Hallet's model identified key controls on debris-bed friction, numerous lines of evidence indicate the problem remains unresolved.…”

Section: Introductionmentioning

confidence: 85%

Experimental constraints on subglacial rock friction

Hansen

Zoet

2019

Ann. Glaciol.

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Subglacial rock friction is an important control on the sliding dynamics and erosive potential of hard-bedded glaciers, yet it remains largely unconstrained. To explore the relative influence of basal melt rate, effective stress and ice temperature on frictional resistance, we conducted abrasion experiments in which limestone beds were slid beneath a fixed slab of ice laden with granitic rock fragments. Shear stress scales linearly with melt rate and cryostatic stress, confirming that both viscous drag and effective stress are first-order controls on the contact force in drained conditions. Furthermore, temperature gradients in the ice increase the contribution of viscous drag on basal shear stress. In all experiments, the relationship between melt rate and shear stress is best explained by a model that accounts for the effects of regelation and viscous creep on the bed-normal drag force. We interpret this to mean fluid flow around entrained clasts contributed to basal drag even at subfreezing temperatures. Incorporating premelting dynamics into the Watts/Hallet model for subglacial rock friction, we find that the predicted debris-bed drag decreases by approximately an order of magnitude, with a corresponding ~3.5 × increase in the transition radius. This is lower than we observe for ice slightly below the pressure melting point.

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Section: Introductionmentioning

confidence: 85%

Experimental constraints on subglacial rock friction

Hansen

Zoet

2019

Ann. Glaciol.

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“…In efforts to better include the well‐documented influence of effective pressure

N

(defined as the ice pressure minus basal water pressure,

p_{i} - p_{w}

) on slip velocity (e.g., Iken & Bindschadler, ; Jansson, ), several contrasting modifications to equation have been proposed (Budd et al, ; Schoof, ; Tsai et al, ). Numerical ice‐flow models (e.g., Brondex et al, ) indicate that ice fluxes can be highly sensitive to these modifications; sensitivity of bedrock erosion rates to the form of the slip relation of landscape evolution models is only beginning to be explored (Ugelvig & Egholm, ).…”

Section: Introductionmentioning

confidence: 99%

Sliding Relations for Glacier Slip With Cavities Over Three‐Dimensional Beds

Helanow

Iverson

Zoet

et al. 2020

Geophysical Research Letters

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Results of glacier flow models and associated estimates of future sea level rise depend sensitively on the prescribed relation between shear stress and slip velocity at the glacier bed. Using a fully three‐dimensional numerical model of ice flow, we compute steady‐state sliding relations for where ice slips over a rock bed with three‐dimensional, periodic topography. In agreement with studies of two‐dimensional beds, water‐filled cavities that form down‐glacier from bedforms cause basal shear stress to peak at a threshold slip velocity and decrease at higher velocities (i.e., rate‐weakening drag). However, the shear stress magnitude and extent of rate‐weakening drag depend systematically on lateral topographic variations not considered previously. Moreover, steep up‐glacier‐facing slopes of bedforms can result in shear stress that increases monotonically over a wide range of slip velocity, helping to stabilize slip. These results highlight the potential variability of sliding relations and their likely sensitivity to the morphological diversity of glacier beds.

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“…These kinds of effects represent complex feedbacks between erosion rates and glaciological variables. However, capturing such feedbacks would require modeling of debris transport and comminution (MacGregor et al, ; Ugelvig & Egholm, ), which is outside the scope of the present contribution.…”

Section: Discussionmentioning

confidence: 99%

Glacial Erosion Driven by Variations in Meltwater Drainage

et al. 2018

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The subglacial processes of abrasion and quarrying are thought to be primarily responsible for bedrock erosion by glaciers. While theory points to sliding speed as the dominant control on abrasion, rates of quarrying are likely scaled by a more complex combination of sliding speed, effective pressure, bed roughness, and short‐term water‐pressure fluctuations. Here we pair a model for quarrying based on statistical characterization of bedrock strength with a model for subglacial hydrology that describes the temporal evolution of cavities under the influence of variations in sliding speed and effective pressure. Using a finite element model, we simulate the evolution of the hydrological system at the base of a glacier and compute rates of abrasion and quarrying. Cavity lengths and channel cross sections evolve through time, causing temporal shifts in ice‐bed contact area, which in turn govern the differential stress that influences erosion over the course of a year. Our results demonstrate how variations in meltwater production amplify rates of subglacial erosion relative to the case of steady meltwater generation. The level of amplification depends on how the variations control the ice‐bed contact area. Seasonal variations are most effective in boosting mean rates of basal sliding and hence subglacial abrasion, whereas shorter‐term variations (monthly‐weekly) most strongly influence rates of subglacial quarrying through temporal amplification of differential bedrock stress around cavities. This influence of transient hydrology on subglacial erosion processes may explain why glaciers in temperate climates with strong variations in temperature and precipitation erode faster than similar‐type glaciers in polar environments.

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The influence of basal-ice debris on patterns and rates of glacial erosion

Cited by 17 publications

References 50 publications

Experimental constraints on subglacial rock friction

Experimental constraints on subglacial rock friction

Sliding Relations for Glacier Slip With Cavities Over Three‐Dimensional Beds

Glacial Erosion Driven by Variations in Meltwater Drainage

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