Thermal Stresses near the Surface of a Glacier

AbstractStresses occur in the uppermost 10 m of a glacier as a result of temperature fluctuations at the surface. A model is set up of a typical year's surface temperature variation, and the progress of temperature waves through the glacier is calculated using Fourier theory of heat conduction. Short-period fluctuations are rapidly attenuated, and at 10 m depth the annual cycle is reduced to 5% of its surface amplitude. As the temperature of the ice varies it undergoes small volume changes; stresses are calculated on the assumption that any tendency of the ice to expand or contract laterally results in the creation of just enough stress to cause the ice to remain unstrained. It is found that in the top 2 or 3 m stresses of thermal origin are generally in excess of those due to gross deformation or overburden pressure. For the case of high-density ice Glen's flow law is used, and conditions are found to be favourable for the formation of surface rumples of wavelength about 10 m. For the case of firm or snow a Newtonian flow law is assumed, and it is found that under cold conditions fracture under tension can occur. Cracks of thermal origin may be responsible for the initial formation of crevasses, and they also provide an explanation for background noise encountered when seismic shooting at low temperatures. Calculations are made of the strain-rate field surrounding a crack and it is found that thermal effects can lead to appreciable Strain-rate anomalies for strain-rate measurements near cracks. The magnitude of the effect is easily sufficient to account for anomalous fluctuating strain-rates found by workers using wire strainmeters on the Barnes Ice Cap.

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Thermal Stresses near the Surface of a Glacier

Journal of Glaciology ◽

10.3189/s0022143000013836 ◽

1978 ◽

Vol 20 (83) ◽

pp. 257-283 ◽

Cited By ~ 1

Author(s):

T. J. O. Sanderson

Keyword(s):

Strain Rate ◽

Thermal Stresses ◽

Overburden Pressure ◽

Ice Cap ◽

Short Period ◽

Thermal Origin ◽

Fourier Theory ◽

Flow Law ◽

Set Up ◽

Strain Rate Field

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Derived Characteristics of the Ross Ice Shelf, Antarctica (Abstract only)

Annals of Glaciology ◽

10.3189/s0260305500003220 ◽

1982 ◽

Vol 3 ◽

pp. 349-349 ◽

Cited By ~ 1

Author(s):

R.H. Thomas ◽

D.R. Macayeal

Keyword(s):

Steady State ◽

Strain Rate ◽

Equivalent Stress ◽

Ice Cores ◽

Melting Rate ◽

Ice Shelf ◽

Data Set ◽

Ross Ice Shelf ◽

Flow Law ◽

Strain Rate Field

Results of the Ross Ice Shelf Geophysical and Glaciologlcal Survey (RIGGS) provide the most complete data set available for any large portion of the polar ice sheets. In this paper, we use RIGGS data to calculate some ice-shelf characteristics. These include steady-state particle trajectories through the ice shelf and the depth of isochronous surfaces, which are of particular importance in choosing a drilling site where ice from the grounded West Antarctic ice sheet is likely to be near the surface. Our estimates for depth to ice originating from the 500 m elevation contour show good agreement with depths to a glaciochemical transition in four ice cores that is believed to be associated with this elevation. This suggests that, for much of the ice shelf, there have been no dramatic and sustained departures from steady state during the past 1.5 to 2.5 ka. With the RIGGS data and an assumed bottom melting rate distribution we calculate steady-state temperature profiles at each of the measurement stations. Then, adopting an ice-flow law deduced from laboratory experiments and ice-shelf measurements, we obtain an effective flow-law parameter for each of these sites. Using these values, the measured strain rate field is transformed to an equivalent stress field over the ice shelf. The stresses are determined by the ice-shelf freeboard and by the force field exerted on the ice shelf by its sides and by ice rises, and our analysis yields estimates of these restraining forces F for the Ross Ice Shelf. An apparent increase in F very close to the ice front suggests that the ice shelf possesses a narrow seaward fringe of anomalously stiff ice. We suspect that this represents the effects of increased bottom-melting rates (and therefore colder and stiffer ice) very close to the ice front.In order to illustrate the role of the restraining forces in controlling ice-shelf behavior, we calculate the strain-rate field for an unrestricted Ross Ice Shelf, i.e. one that is detached from its sides and contains no ice rises. Currently the creepthinning rate for most of the ice shelf is 0.5 to 1m a−1 for an unrestricted ice shelf, but it would increase to 1 to 10 m a −1, with values up to 60 ma− 1 up-stream of the ice risesThis paper has been accepted for publication in the Journal of Glaciology.

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Structure and Flow in the Margin of the Barnes Ice Cap, Baffin Island, N.W.T., Canada

Journal of Glaciology ◽

10.1017/s0022143000031841 ◽

1973 ◽

Vol 12 (66) ◽

pp. 423-438 ◽

Cited By ~ 77

Author(s):

Roger Leb. Hooke

Keyword(s):

Flow Field ◽

Strain Rate ◽

Effective Strain ◽

The Other ◽

Baffin Island ◽

Glacier Surface ◽

Effective Strain Rate ◽

Ice Cap ◽

Single Maximum ◽

Flow Law

The structure and flow field in the margin of the Barnes Ice Cap was determined through observations on the ice-cap surface, in four bore holes, and in a 125 m ice tunnel. A band of fine bubbly white ice with a single maximum fabric appears at the glacier surface about 160 m from the margin. This band is overlain by coarse blue ice with a four-maximum fabric, and underlain by alternating bands of fine ice with a single-maximum fabric and moderately coarse ice with a two or three-maximum fabric. The effective strain rate was determined from the bore-hole and tunnel deformation data, and possible variations in the other three parameters in Glen’s flow law, , were studied. It appears that τ xy is independent of depth near the surface, and that relative to the coarse blue ice, A is 40 to 50% lower in the white ice and possibly 10% lower in the fine blue ice. Dips of foliation planes decrease rapidly with increasing depth and distance from the margin. This foliation is assumed to have developed near and parallel to the bed some distance from the margin. An analysis based on this assumption predicts the observed change in dip, but suggests that it did not develop under the present flow field. The ice cap was probably thicker a few tens of years ago, and the observed foliation pattern may be a relict from that time.

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Structure and Flow in the Margin of the Barnes Ice Cap, Baffin Island, N.W.T., Canada

Journal of Glaciology ◽

10.3189/s0022143000031841 ◽

1973 ◽

Vol 12 (66) ◽

pp. 423-438 ◽

Cited By ~ 2

Author(s):

Roger Leb. Hooke

Keyword(s):

Flow Field ◽

Strain Rate ◽

Effective Strain ◽

The Other ◽

Baffin Island ◽

Glacier Surface ◽

Effective Strain Rate ◽

Ice Cap ◽

Single Maximum ◽

Flow Law

The structure and flow field in the margin of the Barnes Ice Cap was determined through observations on the ice-cap surface, in four bore holes, and in a 125 m ice tunnel. A band of fine bubbly white ice with a single maximum fabric appears at the glacier surface about 160 m from the margin. This band is overlain by coarse blue ice with a four-maximum fabric, and underlain by alternating bands of fine ice with a single-maximum fabric and moderately coarse ice with a two or three-maximum fabric.The effective strain rate was determined from the bore-hole and tunnel deformation data, and possible variations in the other three parameters in Glen’s flow law, , were studied. It appears that τxy is independent of depth near the surface, and that relative to the coarse blue ice, A is 40 to 50% lower in the white ice and possibly 10% lower in the fine blue ice.Dips of foliation planes decrease rapidly with increasing depth and distance from the margin. This foliation is assumed to have developed near and parallel to the bed some distance from the margin. An analysis based on this assumption predicts the observed change in dip, but suggests that it did not develop under the present flow field. The ice cap was probably thicker a few tens of years ago, and the observed foliation pattern may be a relict from that time.

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Derived Characteristics of the Ross Ice Shelf, Antarctica (Abstract only)

Annals of Glaciology ◽

10.1017/s0260305500003220 ◽

1982 ◽

Vol 3 ◽

pp. 349

Author(s):

R.H. Thomas ◽

D.R. Macayeal

Keyword(s):

Steady State ◽

Strain Rate ◽

Equivalent Stress ◽

Ice Cores ◽

Melting Rate ◽

Ice Shelf ◽

Data Set ◽

Ross Ice Shelf ◽

Flow Law ◽

Strain Rate Field

Results of the Ross Ice Shelf Geophysical and Glaciologlcal Survey (RIGGS) provide the most complete data set available for any large portion of the polar ice sheets. In this paper, we use RIGGS data to calculate some ice-shelf characteristics. These include steady-state particle trajectories through the ice shelf and the depth of isochronous surfaces, which are of particular importance in choosing a drilling site where ice from the grounded West Antarctic ice sheet is likely to be near the surface. Our estimates for depth to ice originating from the 500 m elevation contour show good agreement with depths to a glaciochemical transition in four ice cores that is believed to be associated with this elevation. This suggests that, for much of the ice shelf, there have been no dramatic and sustained departures from steady state during the past 1.5 to 2.5 ka. With the RIGGS data and an assumed bottom melting rate distribution we calculate steady-state temperature profiles at each of the measurement stations. Then, adopting an ice-flow law deduced from laboratory experiments and ice-shelf measurements, we obtain an effective flow-law parameter for each of these sites. Using these values, the measured strain rate field is transformed to an equivalent stress field over the ice shelf. The stresses are determined by the ice-shelf freeboard and by the force field exerted on the ice shelf by its sides and by ice rises, and our analysis yields estimates of these restraining forces F for the Ross Ice Shelf. An apparent increase in F very close to the ice front suggests that the ice shelf possesses a narrow seaward fringe of anomalously stiff ice. We suspect that this represents the effects of increased bottom-melting rates (and therefore colder and stiffer ice) very close to the ice front. In order to illustrate the role of the restraining forces in controlling ice-shelf behavior, we calculate the strain-rate field for an unrestricted Ross Ice Shelf, i.e. one that is detached from its sides and contains no ice rises. Currently the creepthinning rate for most of the ice shelf is 0.5 to 1m a−1 for an unrestricted ice shelf, but it would increase to 1 to 10 m a −1, with values up to 60 ma− 1 up-stream of the ice rises This paper has been accepted for publication in the Journal of Glaciology.

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Derived Characteristics of the Ross Ice Shelf, Antarctica

Journal of Glaciology ◽

10.3189/s0022143000005025 ◽

1982 ◽

Vol 28 (100) ◽

pp. 397-412 ◽

Cited By ~ 7

Author(s):

R. H. Thomas ◽

D. R. MacAyeal

Keyword(s):

Steady State ◽

Strain Rate ◽

Equivalent Stress ◽

Ice Cores ◽

Melting Rate ◽

Ice Shelf ◽

Data Set ◽

Ross Ice Shelf ◽

Flow Law ◽

Strain Rate Field

AbstractResults of the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS) provide the most complete data set available for any large portion of the polar ice sheets. In this paper, we use the RIGGS data to calculate some of the ice-shelf characteristics. These include steady-state particle trajectories through the ice shelf and the depth of isochronous surfaces, which are of particular importance in choosing a drilling site where ice from the grounded West Antarctic ice sheet is likely to be near the surface. Our estimates for depth to ice originating from the 500 m elevation contour show good agreement with depths to a glaciochemical transition in four ice cores that is believed to be associated with this elevation. This suggests that, for much of the ice shelf, there have been no dramatic and sustained departures from steady state during the past 1500 to 2500 years. With the RIGGS data and an assumed bottom melting rate distribution we calculate steady-state temperature profiles at each of the measurement stations. Then, adopting an ice flow law deduced from laboratory experiments and ice-shelf measurements, we obtain an effective flow-law parameter for each of these sites. Using these values, the measured strain-rate field is transformed to an equivalent stress field over the ice shelf. The stresses are determined by the ice-shelf freeboard and by the force field exerted on the ice shelf by its sides and by grounded ice rises, and our analysis yields estimates of these “restraining” forces F for the Ross ice Shelf. An apparent increase in F very close to the ice front suggests that the ice shelf possesses a narrow seaward fringe of anomalously stiff ice. We suspect that this represents the effects of increased bottom melting rates (and therefore colder and stiffer ice) very close to the ice front. In order to illustrate the role of the restraining forces in controlling ice-shelf behavior, we calculate the strain-rate field for an unrestricted Ross Ice Shelf—one that is detached from its sides and contains no ice rises. Currently the creep-thinning rates for most of the ice shelf is (0.5–1) m year−1; for an unrestricted ice shelf, they would increase to ( 1–10) m year−1, with values up to 60 m year up stream of the ice rises.

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Derived Characteristics of the Ross Ice Shelf, Antarctica

Journal of Glaciology ◽

10.1017/s0022143000005025 ◽

1982 ◽

Vol 28 (100) ◽

pp. 397-412 ◽

Cited By ~ 87

Author(s):

R. H. Thomas ◽

D. R. MacAyeal

Keyword(s):

Steady State ◽

Strain Rate ◽

Equivalent Stress ◽

Ice Cores ◽

Melting Rate ◽

Ice Shelf ◽

Data Set ◽

Ross Ice Shelf ◽

Flow Law ◽

Strain Rate Field

AbstractResults of the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS) provide the most complete data set available for any large portion of the polar ice sheets. In this paper, we use the RIGGS data to calculate some of the ice-shelf characteristics. These include steady-state particle trajectories through the ice shelf and the depth of isochronous surfaces, which are of particular importance in choosing a drilling site where ice from the grounded West Antarctic ice sheet is likely to be near the surface. Our estimates for depth to ice originating from the 500 m elevation contour show good agreement with depths to a glaciochemical transition in four ice cores that is believed to be associated with this elevation. This suggests that, for much of the ice shelf, there have been no dramatic and sustained departures from steady state during the past 1500 to 2500 years. With the RIGGS data and an assumed bottom melting rate distribution we calculate steady-state temperature profiles at each of the measurement stations. Then, adopting an ice flow law deduced from laboratory experiments and ice-shelf measurements, we obtain an effective flow-law parameter for each of these sites. Using these values, the measured strain-rate field is transformed to an equivalent stress field over the ice shelf. The stresses are determined by the ice-shelf freeboard and by the force field exerted on the ice shelf by its sides and by grounded ice rises, and our analysis yields estimates of these “restraining” forcesFfor the Ross ice Shelf. An apparent increase inFvery close to the ice front suggests that the ice shelf possesses a narrow seaward fringe of anomalously stiff ice. We suspect that this represents the effects of increased bottom melting rates (and therefore colder and stiffer ice) very close to the ice front. In order to illustrate the role of the restraining forces in controlling ice-shelf behavior, we calculate the strain-rate field for an unrestricted Ross Ice Shelf—one that is detached from its sides and contains no ice rises. Currently the creep-thinning rates for most of the ice shelf is (0.5–1) m year−1; for an unrestricted ice shelf, they would increase to ( 1–10) m year−1, with values up to 60 m year up stream of the ice rises.

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Tension and Compression Behavior of Pre-Stressed Steel Strands at High Strain Rate

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.82.154 ◽

2011 ◽

Vol 82 ◽

pp. 154-159 ◽

Cited By ~ 1

Author(s):

Anatoly M. Bragov ◽

Ezio Cadoni ◽

Alexandr Yu. Konstantinov ◽

Andrey K. Lomunov

Keyword(s):

High Strain Rate ◽

Strain Rate ◽

High Strain ◽

Split Hopkinson Pressure Bar ◽

High Strength ◽

Gauge Length ◽

Hopkinson Pressure Bar ◽

Dog Bone ◽

Tension And Compression ◽

Set Up

In this paper is described the mechanical characterization at high strain rate of the high strength steel usually adopted for strands. The experimental set-up used for high strain rates testing: in tension and compression was the Split Hopkinson Pressure Bar installed in the Laboratory of Dynamic Investigation of Materials in Nizhny Novgorod. The high strain rate data in tension was obtained with dog-bone shaped specimens of 3mm in diameter and 5mm of gauge length. The specimens were screwed between incident and transmitter bars. The specimens used in compression was a cylinder of 3mm in diameter and 5mm in length. The enhancement of the mechanical properties is quite limited compared the usual reinforcing steels.

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