scholarly journals Crystal Orientation in Glacier and in Experimentally Deformed Ice

1960 ◽  
Vol 3 (27) ◽  
pp. 589-606 ◽  
Author(s):  
George P. Rigsby
Keyword(s):  
Crystal Orientation ◽  
Laboratory Experiments ◽  
Ice Crystals ◽  
Equal Area ◽  
Fine Grained ◽  
Planar Structures ◽  
Glacier Ice ◽  
Glacier Flow ◽  
High Shearing ◽  
Universal Stage

AbstractMore than 8,000 ice crystals have been oriented and measured for crystal fabric studies from widely separated temperate and polar glaciers, using a large universal stage and thin-section techniques. Very strong fabrics have been found and a number of laboratory experiments on deformation and recrystallization of ice were conducted in an attempt to solve some of the perplexing problems raised concerning glacier flow.In polar glaciers the c or optic axes of the ice crystals tend to be perpendicular to the foliation plane (alternating planar structures of bubbly and clear ice). In areas of high shearing stress the preferred orientation of the axes reached 39 per cent in 1 per cent of the area when plotted on a Schmidt equal-area projection. In temperate glaciers the optic axes tend to form three or four strong maxima which also appear related to the foliation.Patterns from ice deformed in the laboratory resemble some of the fabric patterns found in polar glaciers. During deformation of laboratory specimens, large crystals have been observed recrystallizing into many smaller ones, while fine-grained ice, after completion of deformation (both glacier ice and laboratory deformed ice), has been annealed at melting temperature into a few large crystals with different orientations from the original pattern.

scholarly journals Crystal Orientation in Glacier and in Experimentally Deformed Ice

1960 ◽  
Vol 3 (27) ◽  
pp. 589-606 ◽  
Author(s):  
George P. Rigsby
Keyword(s):  
Crystal Orientation ◽  
Laboratory Experiments ◽  
Ice Crystals ◽  
Equal Area ◽  
Fine Grained ◽  
Planar Structures ◽  
Glacier Ice ◽  
Glacier Flow ◽  
High Shearing ◽  
Universal Stage

Abstract More than 8,000 ice crystals have been oriented and measured for crystal fabric studies from widely separated temperate and polar glaciers, using a large universal stage and thin-section techniques. Very strong fabrics have been found and a number of laboratory experiments on deformation and recrystallization of ice were conducted in an attempt to solve some of the perplexing problems raised concerning glacier flow. In polar glaciers the c or optic axes of the ice crystals tend to be perpendicular to the foliation plane (alternating planar structures of bubbly and clear ice). In areas of high shearing stress the preferred orientation of the axes reached 39 per cent in 1 per cent of the area when plotted on a Schmidt equal-area projection. In temperate glaciers the optic axes tend to form three or four strong maxima which also appear related to the foliation. Patterns from ice deformed in the laboratory resemble some of the fabric patterns found in polar glaciers. During deformation of laboratory specimens, large crystals have been observed recrystallizing into many smaller ones, while fine-grained ice, after completion of deformation (both glacier ice and laboratory deformed ice), has been annealed at melting temperature into a few large crystals with different orientations from the original pattern.

scholarly journals A crystallographic investigation of glacier structure and the mechanism of glacier flow

1939 ◽  
Vol 172 (950) ◽  
pp. 335-360 ◽  
Keyword(s):  
Specific Gravity ◽  
Wind Erosion ◽  
Ice Crystals ◽  
Crystallographic Investigation ◽  
Glacier Tongue ◽  
Ablation Area ◽  
Glacier Ice ◽  
Glacier Flow ◽  
Dividing Line

1. Introduction ( a ) The transition of firn into glacier ice; glacier structure Glaciers are divided into two main parts: the accumulation area, firn region or névé where the annual accumulation in the form of snow exceeds the loss by melting, evaporation and wind erosion, and the ablation area or glacier tongue. The dividing line between the two regions is called the Firn Line. Granular, compacted snow called firn covers the accumulation area. Its crystals are rarely larger than 2 mm. in diameter and are mixed with a considerable volume of air, so that the specific gravity is much lower than that of ice. The surface of the tongue consists of blue or glassy ice, more or less covered with rock debris; here the diameter of the ice crystals varies between 1 and 10 cm. or even more; the specific gravity of the ice is never far below 0.90. In summer the tongue has a bluish or grey appearance, while the firn region retains its white or whitish hue.

scholarly journals The Debris-Laden Ice at the Bottom of the Greenland Ice Sheet

1979 ◽  
Vol 23 (89) ◽  
pp. 193-207 ◽  
Author(s):  
Susan Herron ◽  
Hoar ◽  
Chester C. Langway
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
High Deformation ◽  
Fine Grained ◽  
Free Zone ◽  
The Core ◽  
Oxidation Of Methane ◽  
Particle Aggregates ◽  
Glacier Ice

AbstractThe Camp Century, Greenland, ice core was recovered from a bore hole which extended 1 375 m from the surface of the Greenland ice sheet to the ice/sub-ice interface. The bottom 15.7 m of the core contain over 300 alternating bands of clear and debris-laden ice. The size of the included debris ranges from particles less than 2 μm in diameter to particle aggregates which are a maximum of 3 cm in diameter: the average debris concentration is 0.24ºº by weight. The debris size, concentration, and composition indicate that the debris originates from the till-like material directly below the debris-laden ice. The total gas concentration averages 51 ml/kg ice compared to the average of 101 ml/kg ice for the top 1 340 m. The gas composition of debris-bearing ice has apparently been modified by the oxidation of methane as reflected by traces of methane, high CO2 levels, and low O2 levels with respect to atmospheric air. Argon, which is not affected by the oxidation, shows an enrichment in samples with lower gas concentrations. Both the low gas concentrations in the debris-laden zone and the argon enrichment may be explained by the downward diffusion of gases from bubbly glacier ice into an originally bubble-free zone of refrozen debris-laden ice. Ice texture and ice-fabric analyses reveal extremely fine-grained ice and highly preferred crystal orientation in the lowermost 10 m of the core, indicating a zone of high deformation.

scholarly journals Present dynamics and future prognosis of a slowly surging glacier

2011 ◽  
Vol 5 (1) ◽  
pp. 299-313 ◽  
Author(s):  
G. E. Flowers ◽  
N. Roux ◽  
S. Pimentel ◽  
C. G. Schoof
Keyword(s):  
Mass Balance ◽  
Force Balance ◽  
Surface Velocity ◽  
Internal Dynamic ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Ice Surface ◽  
Glacier Ice ◽  
Glacier Flow ◽  
Negative Balance

Abstract. Glacier surges are a well-known example of an internal dynamic oscillation whose occurrence is not a direct response to the external climate forcing, but whose character (i.e. period, amplitude, mechanism) may depend on the glacier's environmental or climate setting. We examine the dynamics of a small (∼5 km2) valley glacier in Yukon, Canada, where two previous surges have been photographically documented and an unusually slow surge is currently underway. To characterize the dynamics of the present surge, and to speculate on the future of this glacier, we employ a higher-order flowband model of ice dynamics with a regularized Coulomb-friction sliding law in both diagnostic and prognostic simulations. Diagnostic (force balance) calculations capture the measured ice-surface velocity profile only when non-zero basal water pressures are prescribed over the central region of the glacier, coincident with where evidence of the surge has been identified. This leads to sliding accounting for 50–100% of the total surface motion in this region. Prognostic simulations, where the glacier geometry evolves in response to a prescribed surface mass balance, reveal a significant role played by a bedrock ridge beneath the current equilibrium line of the glacier. Ice thickening occurs above the ridge in our simulations, until the net mass balance reaches sufficiently negative values. We suggest that the bedrock ridge may contribute to the propensity for surges in this glacier by promoting the development of the reservoir area during quiescence, and may permit surges to occur under more negative balance conditions than would otherwise be possible. Collectively, these results corroborate our interpretation of the current glacier flow regime as indicative of a slow surge that has been ongoing for some time, and support a relationship between surge incidence or character and the net mass balance. Our results also highlight the importance of glacier bed topography in controlling ice dynamics, as observed in many other glacier systems.

The Significance of air Bubbles in Glacier Ice

1950 ◽  
Vol 1 (08) ◽  
pp. 443-451 ◽  
Author(s):  
Henri Bader
Keyword(s):  
Maximum Depth ◽  
Ice Crystals ◽  
Coarse Grained ◽  
Crystallographic Axis ◽  
Air Bubbles ◽  
Very Old ◽  
Air Bubble ◽  
Glacier Ice

Abstract The study of air bubbles in glacier ice can give valuable information on the evolution of the ice. An analysis of the relation between an air bubble and the water associated with it shows that it may be possible to determine the maximum depth from which the ice containing the bubble has emerged. The shapes of the cavities containing water and air bubbles are described. They are found to reflect the anisotropism of ice crystals and reveal that the main crystallographic axis is polar. The question of the mechanism of elimination of air bubbles from glacier ice is raised. The investigations were made on the very old and coarse-grained ice from the foot of the Malaspina Piedmont Glacier in Alaska, which is a temperate glacier.

scholarly journals Supraglacial Debris of G2 Glacier in Hidden Valley, Mukut Himal, Nepal

1979 ◽  
Vol 22 (87) ◽  
pp. 273-283 ◽  
Author(s):  
M. Nakawo
Keyword(s):  
Particle Size ◽  
Monsoon Season ◽  
Simple Relation ◽  
Laboratory Analysis ◽  
Field Investigations ◽  
Hidden Valley ◽  
Glacier Ice ◽  
Glacier Flow

AbstractField investigations of supraglacial debris were carried out during the monsoon season in 1974 on G2 glacier near Tukche Peak in Hidden Valley, Mukut Himal, Nepal. The thickness of the debris layer was observed to increase down-glacier. Laboratory analysis, however, showed a decrease in particle size in the same direction. This decrease is explained in terms of mixing of particles contained in glacier ice with the original debris as melting proceeds. A simple relation between debris mass and glacier flow is introduced to explain the observed results.

scholarly journals Boudinage in Glacier Ice — Some Examples

1975 ◽  
Vol 14 (72) ◽  
pp. 383-393 ◽  
Author(s):  
M. J. Hambrey ◽  
A. G. Milnes
Keyword(s):  
Compressive Strain ◽  
Coarse Grained ◽  
Planar Anisotropy ◽  
Fine Grained ◽  
Or Groups ◽  
First Results ◽  
Glacier Ice ◽  
Strain Axis ◽  
The Difference ◽  
Shear Planes

Boudinage structures have only rarely been reported in glacier ice, yet they seem to be widespread in Swiss glaciers. They form in debris-free, strongly foliated ice by the stretching, necking and rupture of layers or groups of layers, when the principal compressive strain axis lies at a high angle to the layering. Two main types of boudinage are distinguished. The first results from the difference in competence between fine-grained and coarse-grained ice, and indicates that the former is more resistant to flow than the latter. The second occurs in more equigranular ice which shows a strong planar anisotropy; associated with the necking of such ice is the development of shear planes, along which the layers are displaced. As in deformed rocks, it is not possible to determine the directions of the finite principal strain axes from the boudinage structures alone. Although the boudins described here all occur in longitudinal foliation, it is suggested that they are likely to form in other situations also.

scholarly journals Some Comments on Glacier Flow

1950 ◽  
Vol 1 (07) ◽  
pp. 383-388 ◽  
Author(s):  
Richard Finsterwalder
Keyword(s):  
Shear Stress ◽  
Shear Plane ◽  
Critical Value ◽  
Ice Flow ◽  
Crystalline Materials ◽  
Fundamental Point ◽  
Glacier Ice ◽  
Slow Moving ◽  
Glacier Flow ◽  
Streaming Flow

Abstract Drs. Orowan and Perutz have shown that glacier ice does not behave as a viscous fluid but is plastic like all crystalline materials. The present author discusses two observed types of ice flow:—(1) the normal, regular streaming flow in slow-moving glaciers; (2) Block-Schollen * movement in swiftly flowing ice. Mention is made of the shear plane or laminar flow theory of Philipp. lt appears that Orowan s thesis is also applicable to Block-Schollen flow. The author agrees with Orowan on the fundamental point that when ice is subjected to shear stress a critical value of the shear stress exists beyond which the ice alters its consistency. But the author disagrees with Orowan in that he believes that below this critical value ice behaves as a viscous material, and he supports this view by reference to many phenomena, measurements and calculations.

scholarly journals Pollen Analysis of Glaciers in Special Relation to the Formation of Various Types of Glacier Bands

1949 ◽  
Vol 1 (06) ◽  
pp. 325-332 ◽  
Author(s):  
H. Godwin
Keyword(s):  
Pollen Analysis ◽  
Statistical Evidence ◽  
General Nature ◽  
Special Relation ◽  
New Approach ◽  
Flow Problems ◽  
Pollen Content ◽  
Glacier Ice ◽  
Glacier Flow ◽  
Different Parts

Abstract The author describes the work of Dr. V. Vareschi on the pollen content of glacier ice. A general account of the method of analysis is given. The results of statistical evidence of the analyses on several alpine glaciers are discussed, particularly in regard to the general nature of glacier flow in different parts of the glaciers. Vareschi’s suggestions as to the modes of origin of a certain type of ogive banding and of parallel banding (Pflugfurcheneis) are dealt with in the light of his findings. It is pointed out that what appears to be a valuable new approach to the solution of glacier flow problems needs elaboration before it can be accepted in all its bearings.

scholarly journals Tidal bending of glaciers: a linear viscoelastic approach

2003 ◽  
Vol 37 ◽  
pp. 83-89 ◽  
Author(s):  
Niels Reeh ◽  
Erik Lintz Christensen ◽  
Christoph Mayer ◽  
Ole B. Olesen
Keyword(s):  
Laboratory Experiments ◽  
Viscoelastic Model ◽  
Elastic Beam ◽  
Beam Theory ◽  
Model Parameters ◽  
Beam Model ◽  
Glacier Ice ◽  
Linear Viscoelastic ◽  
Reasonable Choice ◽  
Linear Viscoelastic Model

AbstractIn theoretical treatments of tidal bending of floating glaciers, the glacier is usually modelled as an elastic beam with uniform thickness, resting on an elastic foundation. With a few exceptions, values of the elastic (Young’s) modulus E of ice derived from tidal deflection records of floating glaciers are in the range 0.9–3 GPa. It has therefore been suggested that the elastic-beam model with a single value of E ≈ 1GPa adequately describes tidal bending of glaciers. In contrast, laboratory experiments with ice give E = 9.3 GPa, i.e. 3–10 times higher than the glacier-derived values. This suggests that ice creep may have a significant influence on tidal bending of glaciers. Moreover, detailed tidal-deflection and tilt data from Nioghalvfjerdsfjorden glacier, northeast Greenland, cannot be explained by elastic-beam theory. We present a theory of tidal bending of glaciers based on linear viscoelastic-beam theory. A four-element, linear viscoelastic model for glacier ice with a reasonable choice of model parameters can explain the observed tidal flexure data. Implications of the viscoelastic response of glaciers to tidal forcing are discussed briefly.

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