Ice Sliding and Friction Experiments

AbstractWe are interested in studying the processes of sliding of ice over a variety of rock surfaces with the object of determining an empirical relation for the basal shear stress appropriate for glaciers. The variables to be considered include: normal stress Ν, shear stress Ƭ, surface roughness r, sliding velocity V, temperature θ, water at the interface, and the presence of debris. The roughness is considered to be a function of two variables; the scale or wavelength λ, and the shape or slope of the roughness a / λ, where ais the amplitude of the variations of that scale.

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Basal Sliding and Bed Separation: Is There a Connection?

Journal of Glaciology ◽

10.1017/s0022143000030045 ◽

1979 ◽

Vol 23 (89) ◽

pp. 407-408 ◽

Cited By ~ 1

Author(s):

Robert Bindschadler

Keyword(s):

Shear Stress ◽

Normal Stress ◽

Water Pressure ◽

Simple Relationship ◽

Sliding Velocity ◽

Separation Parameter ◽

Basal Sliding ◽

Bed Separation ◽

Image Position ◽

Basal Shear

Abstract Analysis of field data from Variegated Glacier supports the conclusion of Meier (1968) that no simple relationship between basal shear stress and sliding velocity can be found. On the other hand, an index of bed separation is defined and evaluated that correlates very well with the longitudinal variation of summer sliding velocity inferred for Variegated Glacier. This bed separation parameter is defined as where τ is the basal shear stress and is proportional to the drop in normal stress on the down-glacier side of bedrock bumps and N eff is the effective normal stress equal to the overburden stress minus the subglacial water pressure. The water-pressure distribution is calculated assuming water flow to be confined in subglacial Röthlisberger conduits. The excellent agreement between the longitudinal profiles of I and sliding velocity suggests that calculations of the variation of bed separation can be used to deduce the variation of sliding velocity in both space and time. Further, it is possible that a functional relationship can be developed that adequately represents the geometric controls on basal sliding to permit accurate predictions of sliding velocities.

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Basal Sliding and Bed Separation: Is There a Connection?

Journal of Glaciology ◽

10.3189/s0022143000030045 ◽

1979 ◽

Vol 23 (89) ◽

pp. 407-408

Author(s):

Robert Bindschadler

Keyword(s):

Shear Stress ◽

Normal Stress ◽

Water Pressure ◽

Simple Relationship ◽

Sliding Velocity ◽

Separation Parameter ◽

Basal Sliding ◽

Bed Separation ◽

Image Position ◽

Basal Shear

AbstractAnalysis of field data from Variegated Glacier supports the conclusion of Meier (1968) that no simple relationship between basal shear stress and sliding velocity can be found. On the other hand, an index of bed separation is defined and evaluated that correlates very well with the longitudinal variation of summer sliding velocity inferred for Variegated Glacier. This bed separation parameter is defined as where τ is the basal shear stress and is proportional to the drop in normal stress on the down-glacier side of bedrock bumps and Neff is the effective normal stress equal to the overburden stress minus the subglacial water pressure. The water-pressure distribution is calculated assuming water flow to be confined in subglacial Röthlisberger conduits. The excellent agreement between the longitudinal profiles of I and sliding velocity suggests that calculations of the variation of bed separation can be used to deduce the variation of sliding velocity in both space and time. Further, it is possible that a functional relationship can be developed that adequately represents the geometric controls on basal sliding to permit accurate predictions of sliding velocities.

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The role of bed separation and friction in sliding over an undeformable bed

Journal of Glaciology ◽

10.1017/s0022143000009618 ◽

1992 ◽

Vol 38 (128) ◽

pp. 77-92 ◽

Cited By ~ 32

Author(s):

Jürg Schweizer ◽

Almut Iken

Keyword(s):

Shear Stress ◽

Functional Relationship ◽

Water Pressure ◽

Important Variable ◽

Sliding Velocity ◽

Sliding Motion ◽

Basal Ice ◽

Bed Separation ◽

Basal Shear

AbstractThe classic sliding theories usually assume that the sliding motion occurs frictionlessly. However, basal ice is debris-laden and friction exists between the substratum and rock particles embedded in the basal ice. The influence of debris concentration on the sliding process is investigated. The actual conditions where certain types of friction apply are defined, the effect for the case of bed separation due to a subglacial water pressure is studied and consequences for the sliding law are formulated. The numerical modelling of the sliding of an ice mass over an undulating bed, including the effect of both the subglacial water pressure and the friction, is done by using the finite-clement method. Friction, seen as a reduction of the driving shear stress due to gravity, can be included in existing sliding laws which should contain the critical pressure as an important variable. An approximate functional relationship between the sliding velocity, the effective basal shear stress and the subglacial water pressure is given.

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Surface Roughness Tuning at Sub-Nanometer Level by Considering the Normal Stress Field in Magnetorheological Finishing

Micromachines ◽

10.3390/mi12080997 ◽

2021 ◽

Vol 12 (8) ◽

pp. 997

Author(s):

Xiaoyuan Li ◽

Qikai Li ◽

Zuoyan Ye ◽

Yunfei Zhang ◽

Minheng Ye ◽

...

Keyword(s):

Surface Roughness ◽

Shear Stress ◽

Stress Field ◽

Normal Stress ◽

Fused Silica ◽

Fine Tuning ◽

Magnetorheological Finishing ◽

Optical Surfaces ◽

The Impact ◽

The Relationship

Although magnetorheological finishing (MRF) is being widely utilized to achieve ultra-smooth optical surfaces, the mechanisms for obtaining such extremely low roughness after the MRF process are not fully understood, especially the impact of finishing stresses. Herein we carefully investigated the relationship between the stresses and surface roughness. Normal stress shows stronger impacts on the surface roughness of fused silica (FS) when compared with the shear stress. In addition, normal stress in the polishing zone was found to be sensitive to the immersion depth of the magnetorheological (MR) fluid. Based on the above, a fine tuning of surface roughness (RMS: 0.22 nm) was obtained. This work fills gaps in understanding about the stresses that influence surface roughness during MRF.

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Evolution of Variegated Glacier, Alaska, U.S.A., Prior to its Surge

Journal of Glaciology ◽

10.3189/s0022143000032184 ◽

1988 ◽

Vol 34 (117) ◽

pp. 154-169 ◽

Cited By ~ 5

Author(s):

C. F. Raymond ◽

W. D. Harrison

Keyword(s):

Shear Stress ◽

Seasonal Variation ◽

Normal Stress ◽

Deformation Rate ◽

Surface Slope ◽

Thickness Increase ◽

Effective Normal Stress ◽

Inverse Effect ◽

Basal Sliding ◽

Basal Shear

AbstractDuring the decade prior to its 1982–83 surge, Variegated Glacier experienced progressive changes in geometry and velocity. It thickened in the upper 60% and thinned in the lower 40% of its 20 km length. Thickness changes were up to 20%. Annual velocity increased by up to 500%, reaching a maximum of 0.7 m d−1 in the year before surge onset. Amplitude of seasonal variation in velocity increased up to 0.3 m d−1 by 1978, but did not increase markedly after that. The changes in velocity were larger than predicted from changes in deformation rate caused by changes in shear stress and depth. This anomalous velocity was especially large after 1978 in the zone of thickening on the upper glacier. If it is assumed to arise from basal sliding, the inferred pattern of sliding shows qualitative features consistent with a direct effect from basal shear stress and an inverse effect from effective normal stress. A drop in effective normal stress in a zone of decreasing surface slope up-glacier from the largest thickness increase may have been significant in the initiation of surge motion in 1982.

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The role of bed separation and friction in sliding over an undeformable bed

Journal of Glaciology ◽

10.3189/s0022143000009618 ◽

1992 ◽

Vol 38 (128) ◽

pp. 77-92 ◽

Cited By ~ 2

Author(s):

Jürg Schweizer ◽

Almut Iken

Keyword(s):

Shear Stress ◽

Functional Relationship ◽

Water Pressure ◽

Important Variable ◽

Sliding Velocity ◽

Sliding Motion ◽

Basal Ice ◽

Bed Separation ◽

Basal Shear

AbstractThe classic sliding theories usually assume that the sliding motion occurs frictionlessly. However, basal ice is debris-laden and friction exists between the substratum and rock particles embedded in the basal ice. The influence of debris concentration on the sliding process is investigated. The actual conditions where certain types of friction apply are defined, the effect for the case of bed separation due to a subglacial water pressure is studied and consequences for the sliding law are formulated. The numerical modelling of the sliding of an ice mass over an undulating bed, including the effect of both the subglacial water pressure and the friction, is done by using the finite-clement method. Friction, seen as a reduction of the driving shear stress due to gravity, can be included in existing sliding laws which should contain the critical pressure as an important variable. An approximate functional relationship between the sliding velocity, the effective basal shear stress and the subglacial water pressure is given.

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The Sliding Velocity of Athabasca Glacier, Canada

Journal of Glaciology ◽

10.1017/s0022143000026794 ◽

1970 ◽

Vol 9 (55) ◽

pp. 55-63 ◽

Cited By ~ 19

Author(s):

W. S. B. Paterson

Keyword(s):

Shear Stress ◽

Strain Rate ◽

Longitudinal Strain ◽

Shear Stresses ◽

Sliding Velocity ◽

Flow Law ◽

Basal Shear ◽

Longitudinal Strain Rate

AbstractA method of estimating siding velocity is presented. It rests on few assumptions, one of which is that longitudinal strain-rate varies linearly with depth. The flow law of ice is not used. To apply it, the sliding velocity at one point must be known. The method is used to calculate the sliding velocity at twelve points on Athabasca Glacier. These values are not related to calculated basal shear stresses. Thus one or more of the following statements must be true: (1) basal shear stress cannot be calculated by the conventional formula, (2) the roughness of the glacier bed varies from place to place, (3) sliding velocity does not obey Weertman's formula. Analysis of seven published measurements of sliding velocity leads to the same conclusion.

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Evolution of Variegated Glacier, Alaska, U.S.A., Prior to its Surge

Journal of Glaciology ◽

10.1017/s0022143000032184 ◽

1988 ◽

Vol 34 (117) ◽

pp. 154-169 ◽

Cited By ~ 56

Author(s):

C. F. Raymond ◽

W. D. Harrison

Keyword(s):

Shear Stress ◽

Seasonal Variation ◽

Normal Stress ◽

Deformation Rate ◽

Surface Slope ◽

Thickness Increase ◽

Effective Normal Stress ◽

Inverse Effect ◽

Basal Sliding ◽

Basal Shear

Abstract During the decade prior to its 1982–83 surge, Variegated Glacier experienced progressive changes in geometry and velocity. It thickened in the upper 60% and thinned in the lower 40% of its 20 km length. Thickness changes were up to 20%. Annual velocity increased by up to 500%, reaching a maximum of 0.7 m d−1 in the year before surge onset. Amplitude of seasonal variation in velocity increased up to 0.3 m d−1 by 1978, but did not increase markedly after that. The changes in velocity were larger than predicted from changes in deformation rate caused by changes in shear stress and depth. This anomalous velocity was especially large after 1978 in the zone of thickening on the upper glacier. If it is assumed to arise from basal sliding, the inferred pattern of sliding shows qualitative features consistent with a direct effect from basal shear stress and an inverse effect from effective normal stress. A drop in effective normal stress in a zone of decreasing surface slope up-glacier from the largest thickness increase may have been significant in the initiation of surge motion in 1982.

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Surging Glaciers—The Dilemma Continues

Journal of Glaciology ◽

10.1017/s0022143000015112 ◽

1979 ◽

Vol 24 (90) ◽

pp. 502-503 ◽

Cited By ~ 1

Author(s):

M. F. Meier

Keyword(s):

Shear Stress ◽

Phenomenological Approach ◽

Sliding Velocity ◽

Recent Interest ◽

Normal Behavior ◽

Rapid Flow ◽

Basal Sliding ◽

Ice Velocity ◽

Glacier Flow ◽

Basal Shear

AbstractA glacier surge, according to most definitions, is a short-lived phase of unusually rapid glacier flow, after which the glacier returns to more normal behavior, with the surge–non-surge phases recurring on a regular or periodic basis. Recent interest is largely directed toward analyzing the effect of water at the bed on the periodic change in flow regime and on the rapid flow during a surge phase. For instance, study of a local depression of basal shear stress that dependson a “friction lubrication factor” which becomes important as the ice velocity increases, is one promising phenomenological approach. An important physical approach focuses on a water “collection zone” that occurs where and when the longitudinal pressure gradient in the subglacial wtaer film approaches zero. The data necessary for properly verifying these and other similar theories do not yet exist. Computer modeling of rapidly-surging glaciers based on a “friction lubrication factor” has been quite successful in duplicating their major features. Once rapid movement (102–103m a–1) has begun, sufficient water is generated at the bed, from ice melted by heat dissipated in sliding, to produce some decoupling of the glacier from its bed and to maintain the surge, but only if this water is not lost by rapid drainage. Some glaciers exhibit periodic pulses in which the basal sliding velocity during the fastest part of the pulses appears to be in the range for “normal” glaciers (<102m a–1). Some evidence suggests a continuum of behavior from steady (normal) glaciers through these “mini-surges” to classic surges. This continuum and the “mini-surges” seem to be difficult to explain quantitatively by existing theories. A few glaciers flow continuously at surging speeds (>103m a–1) in certain reaches. The up-glacier transition reaches show speeds decreasing to “nonrmal” with no indication of intermediate surging regime, but the down-glacier transition reaches may be areas where surges are triggered.

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