High-Stress Ice Fracture and Friction

Rist, M. A.

doi:10.1021/jp963175x

Cited by 40 publications

(30 citation statements)

References 12 publications

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“…The maximum overburden pressure is set by the depth to the brittleeductile transition, probably a few kilometers depth . The friction coefficient of ice at the low temperatures appropriate to the brittle region is similar to that for rock (Kennedy et al, 2000), although friction is reduced at higher temperatures or strain rates (Rist, 1997). Based on these results and the values obtained in Section 3, we will assume s f ¼1 MPa, a conservatively low value.…”

Section: Displacement: Length Ratiomentioning

confidence: 65%

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Normal faulting on Europa: implications for ice shell properties

Nimmo¹,

Schenk²

2006

Journal of Structural Geology

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We identify two likely normal faults on Europa, of lengths z30 and 11 km. A simple flexural model of fault-related topography gives effective elastic thicknesses of 1.2 and 0.15 km, respectively, and the resulting inferred fault strength is of order 1 MPa. The maximum fault displacement: length ratio for each fault is z0.02, comparable with values on silicate planets. We combine this observation with a modified linear elastic fracture mechanics model to conclude that the shear modulus of the Europan surface must be significantly less than that for unfractured ice. The low value of the modulus is probably due to near-surface fracturing or porosity, which will affect the material's radar properties and seismic velocities. For a likely reduction in shear modulus of an order of magnitude, the driving stresses inferred are about 6e8 MPa, much higher than present-day diurnal tidal stresses. However, stresses approaching these values can be generated by non-synchronous rotation or polar wander, while stresses exceeding these values arise during ice shell freezing. If the entire larger fault breaks, it will generate an event of seismic magnitude M s z5.3.

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Section: Displacement: Length Ratiomentioning

confidence: 65%

“…(2)). This range is spanned by experimentally determined shear strengths, which typically vary with both pressure and strain rate (Rist, 1997).…”

Section: Displacement: Length Ratiomentioning

confidence: 99%

Normal faulting on Europa: implications for ice shell properties

Nimmo¹,

Schenk²

2006

Journal of Structural Geology

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“…However, our investigation of the structure of the multiyear floe suggests that existing flaws have healed, so preexisting cracks in the ice cover would be on a still larger scale. Rist [1997] • [Paterson, 1978]. So a fracture angle of 45 ø would require that the coefficient of friction for any Coulombic fracture theory is zero.…”

Section: Shear Fault Formation In Icementioning

confidence: 99%

Fracture of multiyear sea ice

Sammonds¹,

Murrell²,

Rist³

1998

J. Geophys. Res.

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Abstract. The fracture and flow of multiyear sea ice was investigated under triaxial compression and uniaxial tension in the temperature range -40 ø to -3.5øC, for strain rates from 10 -7 to 10 -2 s -1, and for confining pressures up to 30 MPa using 40 mm diameter specimens. Specimens both in the horizontal plane of the multiyear floe and perpendicular to this plane were tested. The results of short-rod fracture toughness tests on multiyear and first-year sea ice at temperatures -20øC are also reported. The multiyear sea ice came from an unridged portion of a single floe about 7 m thick, which was found to be massive and not blocky with large voids. The ice had low salinity and high porosity. The inelastic deformation of multiyear sea ice was found to be strongly dependent upon strain rate, temperature, and confining pressure. In compression, four main types of deformation were observed. (4) However, at still higher confining pressures, cracking was completely inhibited and deformation was entirely plastic. At -20øC, shear fracture occurred according to a maximum shear stress criterion and hence was pressure independent, with crack nucleation dominating the fracture behavior. At -40øC, however, the shear fracture stress was found to be strongly pressure dependent up to 14 MPa and could be described in terms of a Coulombic failure envelope. The unusual 45 ø orientation of ice shear fractures, together with the unusual pressure dependencies of ice peak strengths, may be explained by the fact that low-stress slip and cleavage occurs in the basal planes of ice crystals. Characterization of Multiyear Sea IceThe physical properties of sea ice have been reviewed by Gow and Tucker [1991]. First-year sea ice has been well characterized. An undeformed, first-year Arctic sea ice sheet is typically less than 2 m thick and consists of a thin granular layer and a fairly uniform lower layer of columnar grains. In the columnar zone the crystallographic c axes of grains are to within a few degrees in the horizontal plane and in some locations are aligned within that plane owing to ocean currents. Significantly less work has been done on multiyear sea ice. Richter-Menge and Cox [1986] and Tucker et al. [1987] found multiyear ridges to be structurally complex with low salinity. Weeks and Mellor [1984] suggested that ridges are composed of massive ice, where all voids present in newly formed ridges are 21,795

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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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High-Stress Ice Fracture and Friction

Cited by 40 publications

References 12 publications

Normal faulting on Europa: implications for ice shell properties

Normal faulting on Europa: implications for ice shell properties

Fracture of multiyear sea ice

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

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