scholarly journals Ice Fabrics in a Vertical Flow Plane, Barnes Ice Cap, Canada

1980 ◽  
Vol 25 (92) ◽  
pp. 195-214 ◽  
Author(s):  
Roger Leb. Hooke ◽  
Peter J. Hudleston
Keyword(s):  
Crystal Size ◽  
Thick Layer ◽  
Stability Diagram ◽  
Independent Variables ◽  
Fine Grained ◽  
Ice Cap ◽  
Single Maximum ◽  
Cumulative Strain ◽  
Ice Fabrics ◽  
Flow Plane

AbstractAt a depth of about 75 m in the lower part of the accumulation area of the Barnes Ice Cap there is a change from fine-grained ice with a weakly-orientedc-axis fabric to coarser ice with a broad single-maximum fabric. At a depth of about 150 m the single maximum becomes elongate perpendicular to the direction of bubble elongation, and then splits into two distinct maxima making an angle of about 40–45° with respect to one another. At greater depths a third and finally a fourth maximum appear, forming the well known diamond pattern. Mean crystal size does not seem to increase in the transitions from one to two and thence to three maxima, but it may become more uniform. Crystal size does increase in the transition from three to four maxima, however. At the base of the glacier there is a 10–20 m thick layer of unusually-bubbly, fine-grained white ice with a strong single-maximum fabric.The depths to the transitions increase up-glacier and in place of the single-maximum fabric a small-circle pattern is found. Down-glacier the depths to the transitions decrease, systematically eliminating the higher zones. Thus in the lower part of the ablation area, ice with a four-maximum fabric appears at the surface.The independent variables governing these fabric transitions appear to be temperatureT, stressτ, and cumulative strain³oc. In a tentative stability diagram showing the fields in which given fabrics are stable inT–τ–³ocspace, multiple-maximum fabrics occur at high temperatures (> —10°C) and at moderate to high stresses, weakly-oriented fabrics at low stresses or low cumulative strains, broad single-maximum fabrics at moderate stresses or moderate cumulative strains, and strong single-maximum fabrics at high stresses or large cumulative strains.

scholarly journals Ice Fabrics in a Vertical Flow Plane, Barnes Ice Cap, Canada

1980 ◽  
Vol 25 (92) ◽  
pp. 195-214 ◽  
Author(s):  
Roger Leb. Hooke ◽  
Peter J. Hudleston
Keyword(s):  
Crystal Size ◽  
Thick Layer ◽  
Stability Diagram ◽  
Independent Variables ◽  
Fine Grained ◽  
Ice Cap ◽  
Single Maximum ◽  
Cumulative Strain ◽  
Ice Fabrics ◽  
Flow Plane

AbstractAt a depth of about 75 m in the lower part of the accumulation area of the Barnes Ice Cap there is a change from fine-grained ice with a weakly-oriented c-axis fabric to coarser ice with a broad single-maximum fabric. At a depth of about 150 m the single maximum becomes elongate perpendicular to the direction of bubble elongation, and then splits into two distinct maxima making an angle of about 40–45° with respect to one another. At greater depths a third and finally a fourth maximum appear, forming the well known diamond pattern. Mean crystal size does not seem to increase in the transitions from one to two and thence to three maxima, but it may become more uniform. Crystal size does increase in the transition from three to four maxima, however. At the base of the glacier there is a 10–20 m thick layer of unusually-bubbly, fine-grained white ice with a strong single-maximum fabric.The depths to the transitions increase up-glacier and in place of the single-maximum fabric a small-circle pattern is found. Down-glacier the depths to the transitions decrease, systematically eliminating the higher zones. Thus in the lower part of the ablation area, ice with a four-maximum fabric appears at the surface.The independent variables governing these fabric transitions appear to be temperature T, stress τ, and cumulative strain ³oc. In a tentative stability diagram showing the fields in which given fabrics are stable in T–τ–³oc space, multiple-maximum fabrics occur at high temperatures (> —10°C) and at moderate to high stresses, weakly-oriented fabrics at low stresses or low cumulative strains, broad single-maximum fabrics at moderate stresses or moderate cumulative strains, and strong single-maximum fabrics at high stresses or large cumulative strains.

scholarly journals Ice Fabrics and Petrography, Meserve Glacier, Antarctica

1974 ◽  
Vol 13 (68) ◽  
pp. 285-306 ◽  
Author(s):  
P.W. Anderton
Keyword(s):  
Steady State ◽  
Stress Level ◽  
Optic Axis ◽  
Near Surface ◽  
Fine Grained ◽  
Basal Ice ◽  
Single Maximum ◽  
Fabric Analysis ◽  
Rock Interface ◽  
Ice Fabrics

Results of petrographic and fabric analysis of fine-grained cold ice from the tongue of Meserve Glacier, Antarctica, are described. Most of the basal ice is remarkably uniform in texture and shows an optic-axis fabric with a single strong maximum, which is consistent with the steady-state conditions of flow. Within 0.5 m of the ice–rock interface, irregularities in the bed cause flow perturbations which are correlated with recrystallization and changes in fabric of the ice. Optic-axis fabrics in the basal ice show close symmetry relationships with dimensional fabric and deformation symmetry. Grain-size of the ice increases towards the surface of the glacier and the single maximum of the optic-axis fabric undergoes a rotation about the flow vector. In the near surface, where strain-rates are relatively much lower, the optic-axis fabric symmetry is not closely related to either deformation symmetry or the dimensional fabric. Syntectonic recrystallization of ice throughout the glacier tongue characteristically produces a strong single-maximum fabric, the orientation of which in relation to the stress field is apparently determined by stress level. Under steady-state conditions of flow, the strength of the maximum also appears to be a function of stress level.

scholarly journals Development of the Crystal Structure within the Law Dome Ice Cap, Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 222-222
Author(s):  
Neal W. Young
Keyword(s):  
Internal Structure ◽  
Crystal Size ◽  
Flow Line ◽  
Layer Structure ◽  
Ice Cores ◽  
Complex Stress ◽  
Crystal Anisotropy ◽  
Ice Cap ◽  
Single Maximum ◽  
The Law

Fourteen shallow and medium-depth cores have been drilled from the Law Dome ice cap, between the summit and the coast near Casey Station. Measurements of their crystal and other physical properties are reviewed briefly. The variations along the cores in crystal size, orientation, fabric type and strength, and bubble dimensions, are used to define the internal structure of the ice cap locally at the bore-hole sites. Surveys of bore-hole deformation and the shape and movement of the ice cap are used to define relations between the structure and the variables: stress, temperature, strain-rate and accumulated strain. The relations and the survey data are incorporated in a numerical model in order to deduce the internal structure of the ice cap along a flow line linking the bore-hole sites. The results of the model in turn depend on the crystal anisotropy of the calculated structure.The main results are provided by the medium-depth bore holes located at the summit, near the margin, and about half-way along the flow line. The major features of the internal structure are determined by the predominant shear deformation in the ice cap. There is horizontal continuity in the properties and structure within the group of bore holes near the margin of the ice cap. There are distinct differences, between the coastal and the inland ice cores, in the changes in properties with depth. Near the margin a strong single-maximum fabric develops within the upper 60% of the ice thickness; crystal size initially increases with depth, then shows a marked decrease at about 50% thickness. For the inland cores, a strong single-maximum fabric also develops, but at a greater total depth and a much shallower fraction of the thickness. A similar decrease in crystal size was not observed.The broad-scale trends of the properties are reproduced by the model. The finer-scale deviations in the properties can be explained by the effects of longitudinal strain and of past changes in surface conditions, such as the effect of surface melting. A complex stress distribution, related to flow over rough bedrock, needs to be invoked to explain the pronounced multi-layer structure in the lower part of the ice cores from near the margin. A series of time lines is modelled, following the flow along the ice-particle trajectories, to produce the stress, temperature and deformation histories of the ice in the cores. These provide the basic data for a reconstruction of past changes in the ice cap.

scholarly journals Development of the Crystal Structure within the Law Dome Ice Cap, Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 222
Author(s):  
Neal W. Young
Keyword(s):  
Internal Structure ◽  
Crystal Size ◽  
Flow Line ◽  
Layer Structure ◽  
Ice Cores ◽  
Complex Stress ◽  
Crystal Anisotropy ◽  
Ice Cap ◽  
Single Maximum ◽  
The Law

Fourteen shallow and medium-depth cores have been drilled from the Law Dome ice cap, between the summit and the coast near Casey Station. Measurements of their crystal and other physical properties are reviewed briefly. The variations along the cores in crystal size, orientation, fabric type and strength, and bubble dimensions, are used to define the internal structure of the ice cap locally at the bore-hole sites. Surveys of bore-hole deformation and the shape and movement of the ice cap are used to define relations between the structure and the variables: stress, temperature, strain-rate and accumulated strain. The relations and the survey data are incorporated in a numerical model in order to deduce the internal structure of the ice cap along a flow line linking the bore-hole sites. The results of the model in turn depend on the crystal anisotropy of the calculated structure. The main results are provided by the medium-depth bore holes located at the summit, near the margin, and about half-way along the flow line. The major features of the internal structure are determined by the predominant shear deformation in the ice cap. There is horizontal continuity in the properties and structure within the group of bore holes near the margin of the ice cap. There are distinct differences, between the coastal and the inland ice cores, in the changes in properties with depth. Near the margin a strong single-maximum fabric develops within the upper 60% of the ice thickness; crystal size initially increases with depth, then shows a marked decrease at about 50% thickness. For the inland cores, a strong single-maximum fabric also develops, but at a greater total depth and a much shallower fraction of the thickness. A similar decrease in crystal size was not observed. The broad-scale trends of the properties are reproduced by the model. The finer-scale deviations in the properties can be explained by the effects of longitudinal strain and of past changes in surface conditions, such as the effect of surface melting. A complex stress distribution, related to flow over rough bedrock, needs to be invoked to explain the pronounced multi-layer structure in the lower part of the ice cores from near the margin. A series of time lines is modelled, following the flow along the ice-particle trajectories, to produce the stress, temperature and deformation histories of the ice in the cores. These provide the basic data for a reconstruction of past changes in the ice cap.

scholarly journals Ice Fabrics and Petrography, Meserve Glacier, Antarctica

1974 ◽  
Vol 13 (68) ◽  
pp. 285-306 ◽  
Author(s):  
P.W. Anderton
Keyword(s):  
Steady State ◽  
Stress Level ◽  
Optic Axis ◽  
Near Surface ◽  
Fine Grained ◽  
Basal Ice ◽  
Single Maximum ◽  
Fabric Analysis ◽  
Rock Interface ◽  
Ice Fabrics

Results of petrographic and fabric analysis of fine-grained cold ice from the tongue of Meserve Glacier, Antarctica, are described. Most of the basal ice is remarkably uniform in texture and shows an optic-axis fabric with a single strong maximum, which is consistent with the steady-state conditions of flow. Within 0.5 m of the ice–rock interface, irregularities in the bed cause flow perturbations which are correlated with recrystallization and changes in fabric of the ice. Optic-axis fabrics in the basal ice show close symmetry relationships with dimensional fabric and deformation symmetry. Grain-size of the ice increases towards the surface of the glacier and the single maximum of the optic-axis fabric undergoes a rotation about the flow vector. In the near surface, where strain-rates are relatively much lower, the optic-axis fabric symmetry is not closely related to either deformation symmetry or the dimensional fabric. Syntectonic recrystallization of ice throughout the glacier tongue characteristically produces a strong single-maximum fabric, the orientation of which in relation to the stress field is apparently determined by stress level. Under steady-state conditions of flow, the strength of the maximum also appears to be a function of stress level.

Preparation of Fine-Grained Corundum Powders with Given Properties: Crystal Size and Habit Control

2018 ◽  
Vol 52 (5) ◽  
pp. 879-886 ◽  
Author(s):  
G. P. Panasyuk ◽  
L. A. Azarova ◽  
V. N. Belan ◽  
E. A. Semenov ◽  
M. N. Danchevskaya ◽  
...  
Keyword(s):  
Crystal Size ◽  
Fine Grained

scholarly journals Thermal Response of a Small Ice Cap to Climatic Forcing

1990 ◽  
Vol 36 (122) ◽  
pp. 49-56 ◽  
Author(s):  
Brian Hanson
Keyword(s):  
Response Times ◽  
Thermal Response ◽  
Warming Trend ◽  
Temperature Fields ◽  
Ice Cap ◽  
Dimensional Finite Element ◽  
Order Of Magnitude ◽  
Sensitivity Studies ◽  
Strain Heating ◽  
Flow Plane

AbstractTwo-dimensional finite-element calculations of velocity and temperature fields have been applied to the energy balance of a cross-section of Barnes Ice Cap, Baffin Island, Canada. The flow plane currently is cooling near the ice divide and warming near the margin. Long-term simulations show a net warming trend followed by a cooling trend with a steady-state average temperature similar to the present. Sensitivity studies on an idealized version of the flow plane show that the overall temperature responds less than surface-temperature forcing, because a negative feedback in temperature advection is substantially larger than a positive feed-back in strain heating. The response times of the flow plane by itself are somewhat faster but of the same magnitude as response times that would be estimated from one-dimensional modeling. When bedrock-temperature calculations are included, response times increase an order of magnitude, but these do not substantially affect the short-term response.

scholarly journals A Comparison of Ice Fabrics and Textures at Camp Century, Greenland and Byrd Station, Antarctica

1982 ◽  
Vol 3 ◽  
pp. 118-124 ◽  
Author(s):  
Susan L. Herron ◽  
Chester C. Langway
Keyword(s):  
Short Interval ◽  
Ice Cores ◽  
Remarkable Similarity ◽  
Single Maximum ◽  
Crystal Orientations ◽  
Degree Of Orientation ◽  
Break Up ◽  
Ice Fabrics ◽  
High Degree

A comparison of the crystalline texture and fabric of the two deep cores to bedrock from Camp Century, Greenland, and Byrd station, Antarctica, reveals striking similarities. Each core exhibits a fabric profile which progresses from depositional fabrics at shallow depths through multi-maxima transitional stages into single maximum distributions. The major difference between the two cores occurs near the base where the Camp Century fabrics maintain a high degree of orientation while the Byrd station fabrics break up into a diamond pattern. The most remarkable similarity between the two profiles occurs at the glacial-interglacial transition where crystal sizes decrease and crystal orientations strengthen significantly over a very short interval. Similar changes occur in other deep ice cores, thus indicating the possibility that the late Wisconsin ice has a unique crystallographic signature.

scholarly journals Ice-Fabric Study of the Mawson Region, East Antarctica

1969 ◽  
Vol 8 (53) ◽  
pp. 253-276 ◽  
Author(s):  
K. Kizaki
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Ice Sheet ◽  
Secondary Recrystallization ◽  
East Antarctica ◽  
Strain Rates ◽  
Fine Grained ◽  
Single Maximum ◽  
Multiple Maxima

Attempts are made to test the relation predicted by Brace (1960) between strain-rates and the ice-fabric patterns obtained at Mawson station, east Antarctica. These orientation fabrics not only are hardly related to the prediction by Brace (1960) or Kamb (1959) but also change easily within a strain grid with 100m diagonals.Stable patterns of two- and three-maximum fabrics are confirmed. The latter is common and stable in the coarse ice at the surface of the ice sheet. It is apparent that the fabric patterns are generally related to the grain-size. The single-maximum fabric always occurs in fine-grained ice, then more maxima are formed in the course of grain growth.It appears that syntectonic-secondary recrystallization is effective in producing the orientation fabrics with two, three and multiple maxima. Also, the maxima always shift away from the pole of foliation as grain-size increases and there are several stable positions of maximum such as 0°, 17°, 23° and 30°. It is expected that further stable angles would occur with coarser crystals as found in temperate glaciers.

scholarly journals Structure and Flow in the Margin of the Law Dome Ice Cap. Antarctica (Abstract)

1988 ◽  
Vol 10 ◽  
pp. 222
Author(s):  
Neal W. Young
Keyword(s):  
Physical Properties ◽  
Crystal Size ◽  
Flow Line ◽  
Ice Core ◽  
Ice Cores ◽  
Crystallographic Structure ◽  
Proxy Records ◽  
Ice Cap ◽  
Radio Echo Sounding ◽  
The Law

The internal structure of the Law Dome ice cap is being investigated by studying ice cores obtained from several sites along the summit-Cape Folger line. Profiles of measured physical properties for four of the ice cores from near the margin of the ice cap are presented. A comparison of the profiles shows a gradual increase and then decrease in crystal size, and the development of strong crystal anisotropy in the upper half of the ice thickness. But in the lower part there is a complex multi-layer crystallographic structure, with an interleaving of ice which has markedly different physical properties. The development of the physical properties in the ice cores is discussed in terms of the deformation in the ice cap in the neighbourhood of the bore holes and the movement of the ice over the rough bedrock. The interdependence of the physical properties and the flow within the ice cap and their effect on other proxy records obtained from the ice cores are also explored. The Law Dome is a small ice cap, about 200 km in diameter, adjoining the main Antarctic ice sheet. It is being studied as a model ice cap, using surface surveys and ice-core drilling. It is large enough to have most of the features of larger ice sheets but small enough to be investigated in considerable detail. The four cores were drilled within 10 km of the coast at Cape Folger and lie approximately along a flow line. Each of the cores covers the Holocene and at least the later part of the Last Glacial Maximum. Two of the cores are within 40 m of bedrock and the remaining two, in thinner ice nearer the coast, are within a few metres of bedrock. Physical properties which were measured include: crystal size, texture and orientation; bubble size, orientation and distribution; and visible stratigraphy. The stratigraphy in the upper layers is related mainly to the occurrence of surface melting during the warmer months of the year. Additional supporting information is available from measurements of the physical properties on shallow cores up-stream of the four bore holes, from radio echo-sounding profiles and from other studies on the ice cores. This data is used in the discussion of the velocity field in the ice cap.

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