Experimental determination of a double-valued drag relationship for glacier sliding

Zoet, Lucas K.; Iverson, Neal R.

doi:10.3189/2015jog14j174

Cited by 34 publications

(69 citation statements)

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“…The frictional interface on which glaciers slide is in many ways similar to a tectonic fault, and ice sliding over the glacier bed should follow the same rate-and statedependent behaviour as tectonic faults, albeit with the temperature dependences appropriate to the rate-limiting micromechanisms at glacier conditions. Previous experimental studies have elucidated important physics related to the velocity and temperature dependences of laboratory grown and natural ice-on-ice friction [8][9][10][11][12][13][14], ice-on-rock friction [15][16][17] and till friction [18] over a broad range of conditions. However, only a few studies [12,14,16] utilize the formalism of rate-and state-dependent frictional behaviour that is common in rock mechanics, and which may provide a useful framework for assessing stability and sliding behaviour of glaciers.…”

Section: Introductionmentioning

confidence: 99%

Temperature dependence of ice-on-rock friction at realistic glacier conditions

McCarthy

Savage

Nettles

2017

Phil. Trans. R. Soc. A.

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One contribution of 11 to a theme issue 'Microdynamics of ice'. Using a new biaxial friction apparatus, we conducted experiments of ice-on-rock friction in order to better understand basal sliding of glaciers and ice streams. A series of velocity-stepping and slidehold-slide tests were conducted to measure friction and healing at temperatures between −20°C and melting. Experimental conditions in this study are comparable to subglacial temperatures, sliding rates and effective pressures of Antarctic ice streams and other glaciers, with load-point velocities ranging from 0.5 to 100 µm s −1 and normal stress σ n = 100 kPa. In this range of conditions, temperature dependences of both steady-state friction and frictional healing are considerable. The friction increases linearly with decreasing temperature (temperature weakening) from μ = 0.52 at −20°C to μ = 0.02 at melting. Frictional healing increases and velocity dependence shifts from velocity-strengthening to velocityweakening behaviour with decreasing temperature. Our results indicate that the strength and stability of glaciers and ice streams may change considerably over the range of temperatures typically found at the ice-bed interface. Subject Areas: glaciology KeywordsThis article is part of the themed issue 'Microdynamics of ice'.

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Section: Introductionmentioning

confidence: 99%

Temperature dependence of ice-on-rock friction at realistic glacier conditions

McCarthy

Savage

Nettles

2017

Phil. Trans. R. Soc. A.

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“…Recent theoretical models neglect regelation, both for convenience and because the small wavelengths of bedrock undulations for which regelation tends to be dominant -less than a few decimeterstend to be rare on deglaciated bedrock, presumably because these small wavelengths are most susceptible to being smoothed by abrasion (Hooke, 2005). Thus, in experiments, in which bed wavelengths larger than a few decimeters are impractical (Iverson and Petersen, 2011;Zoet and Iverson, 2015), regelation is inhibited by using a bed material with a thermal conductivity approximately an order of magnitude smaller than that of most rocks. Ice, therefore, in these experiments moves past bed undulations by enhanced creep, rather than by melting Fig.…”

Section: Scaling Problemsmentioning

confidence: 96%

“…To date, however, bed undulations have been used with heights that are smaller, by a factor of~6, than the thickness of the ice ring. Thus, the boundary layer where ice flow past undulations occurs is a small fraction of the total ice thickness (Iverson and Petersen, 2011;Zoet and Iverson, 2015).…”

Section: Scaling Problemsmentioning

confidence: 99%

“…2B), provided the first test of this hypothesis (Zoet and Iverson, 2015). Experiments were conducted at constant sliding speeds or shear stresses and carried out until the other of these variables became steady, together with the development of cavities of steady size (Fig.…”

Section: Slip Across a Hard Bedmentioning

confidence: 99%

“…2) aimed at testing the double-valued drag relationship for glacier slip (Zoet and Iverson, 2015), a fundamental scaling problem involves the wavelengths of bed undulations. Recent theoretical models neglect regelation, both for convenience and because the small wavelengths of bedrock undulations for which regelation tends to be dominant -less than a few decimeterstend to be rare on deglaciated bedrock, presumably because these small wavelengths are most susceptible to being smoothed by abrasion (Hooke, 2005).…”

Section: Scaling Problemsmentioning

confidence: 99%

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Experiments on the dynamics and sedimentary products of glacier slip

Iverson

Zoet

2015

Geomorphology

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Experimental work in glacial geomorphology is focused almost entirely on processes in the thin shear zone at the beds of sliding glaciers, where ice at its pressure-melting temperature moves over either rigid rock or deformable till. Experiments with rotary shear devices illuminate constitutive behavior there, central to the dynamics of fastmoving glaciers, and provide a foundation for interpreting the sedimentary record of glacier slip and associated sediment transport. Results from experiments designed to study ice sliding over a rigid wavy bed, shear deformation of till, and plowing of clasts across the surface of a till bed point to a common conclusion: drag at the bed can decrease with increasing slip velocity, thereby concentrating driving stress elsewhere and promoting rapid glacier flow. This rate-weakening behavior at glacier beds is in contrast to the viscous slip resistance assumed in ice-sheet models and most efforts to determine distributions of basal drag from glacier surface velocities. Ring-shear experiments in which various basal tills and more idealized materials are sheared to high strains provide quantitative insight into grain size evolution, mixing at contacts between basal tills, microstructure development, particle-fabric development, and development of anisotropy of magnetic susceptibility. Preferred orientations of principal magnetic susceptibilities provide the most dependable and complete description of till shear patterns. When applied to basal tills of the geologic record, magnetic till fabrics measured along thick till sections and calibrated experimentally indicate that deformation of the bed by two lobes of the Laurentide ice sheet was shallow (b1 m), patchy, and occurred as till progressively accreted. Rates of sediment transport by bed shear were thus significantly less than estimates based on models that invoke deep, pervasive shear of the bed. The lack of an experimental tradition in glacial geomorphology leaves many research avenues open for exploration but also increases the challenge of demonstrating the relevance of experimental results to theoretical and field-based studies.

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Heterogeneity in Karakoram glacier surges

et al. 2015

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Many Karakoram glaciers periodically undergo surges during which large volumes of ice and debris are rapidly transported downglacier, usually at a rate of 1-2 orders of magnitude greater than during quiescence. Here we identify eight recent surges in the region and map their surface velocities using cross-correlation feature tracking on optical satellite imagery. In total, we present 44 surface velocity data sets, which show that Karakoram surges are generally short-lived, lasting between 3 and 5 years in most cases, and have rapid buildup and relaxation phases, often lasting less than a year. Peak velocities of up to 2 km a À1 are reached during summer months, and the surges tend to diminish during winter months. Otherwise, they do not follow a clearly identifiable pattern. In two of the surges, the peak velocity travels down-ice through time as a wave, which we interpret as a surge front. Three other surges are characterized by high velocities that occur simultaneously across the entire glacier surface, and acceleration and deceleration are close to monotonic. There is also no consistent seasonal control on surge initiation or termination. We suggest that the differing styles of surge can be partly accounted for by individual glacier configurations and that while some characteristics of Karakoram surges are akin to thermally controlled surges elsewhere (e.g., Svalbard), the dominant surge mechanism remains unclear. We thus propose that these surges represent a spectrum of flow instabilities and the processes controlling their evolution may vary on a glacier by glacier basis.

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Experimental determination of a double-valued drag relationship for glacier sliding

Cited by 34 publications

References 57 publications

Temperature dependence of ice-on-rock friction at realistic glacier conditions

Temperature dependence of ice-on-rock friction at realistic glacier conditions

Experiments on the dynamics and sedimentary products of glacier slip

Heterogeneity in Karakoram glacier surges

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