Athabasca Glacier Research Articles

Flow in a Transverse Section of Athabasca Glacier, Alberta, Canada

Measurements of ice deformation at the surface and at depth in the Athabasca Glacier, Canada, reveal for the first time the pattern of flow in a nearly complete cross-section of a valley glacier, and make it possible to test the applicability of experimental and theoretical concepts in the analysis of glacier flow. Tilting in nine bore holes (eight holes essentially to the bottom at depth about 300 m) was measured with a newly developed electrical inclinometer. The new instrument permitted bore-hole configurations to be determined with greater speed and accuracy than possible with earlier methods. The measurements define the distribution of the velocity vector and the strain-rate tensor over about 70% of the area of the glacier cross-section.The main longitudinal component of flow has the following general features: (1) basal sliding velocity which exceeds 70% of the surface velocity over half of the width of the glacier, (2) marginal sliding velocity (not more than a few meters per year) much less than basal sliding velocity at the center-line (about 40 m a-1), (3) marginal shear strain-rate near the valley walls two to three times larger than the basal shear strain-rate near the center-line (0.1 a-1).The observed longitudinal flow is significantly different from that expected from theoretical analysis of flow in cylindrical channels (Nye, 1965). The relative strength of marginal and basal shear strain-rate is opposite to that expected from theory. In addition, the longitudinal flow velocity averaged over the glacier cross-section (which determines the flux of ice transported) is larger by 12% than the average flow velocity seen at the glacier surface, whereas it would be essentially the same if the theoretical prediction were correct. These differences are caused to a large extent by the contrast between the actual distribution of sliding velocity and the constant sliding velocity for which the theoretical analysis holds. The observed relation between marginal and basal sliding velocity is probably a general flow feature in valley glaciers, and may be caused by lateral variation of water pressure at the ice-rock contact. The observed pattern of longitudinal velocity over the section also shows in detail certain additional features incompatible with the theoretical treatment, even after the difference in boundary conditions (distribution of sliding velocity) is taken into account.Longitudinal strain-rate (a compression of about 0.02 a-1at the surface) decreases with depth, becoming nearly o at the bed in the center of the glacier, which confirms a prediction by Savage and Paterson (1963). The depth variation cannot be explained completely by overall bending of the ice mass as a result of a longitudinal gradient in the curvature of the bed, and is at variance with existing theories, which require the longitudinal strain-rate to be constant with depth.Motion transverse to the longitudinal flow occurs in a roughly symmetric pattern of diverging margin-ward flow, with most of the lateral transport occurring at depth in a fashion reminiscent of extrusion flow. The observed lateral velocities averaged over depth (up to 1.9 m a-1) are compatible with the lateral flux required to maintain equilibrium of the marginal portions of the glacier surface under ablation (about 3.7 m of ice per year) and are driven by the convex lateral profile of the ice surface.

Flow in a Transverse Section of Athabasca Glacier, Alberta, Canada

AbstractMeasurements of ice deformation at the surface and at depth in the Athabasca Glacier, Canada, reveal for the first time the pattern of flow in a nearly complete cross-section of a valley glacier, and make it possible to test the applicability of experimental and theoretical concepts in the analysis of glacier flow. Tilting in nine bore holes (eight holes essentially to the bottom at depth about 300 m) was measured with a newly developed electrical inclinometer. The new instrument permitted bore-hole configurations to be determined with greater speed and accuracy than possible with earlier methods. The measurements define the distribution of the velocity vector and the strain-rate tensor over about 70% of the area of the glacier cross-section.The main longitudinal component of flow has the following general features: (1) basal sliding velocity which exceeds 70% of the surface velocity over half of the width of the glacier, (2) marginal sliding velocity (not more than a few meters per year) much less than basal sliding velocity at the center-line (about 40 m a-1), (3) marginal shear strain-rate near the valley walls two to three times larger than the basal shear strain-rate near the center-line (0.1 a-1).The observed longitudinal flow is significantly different from that expected from theoretical analysis of flow in cylindrical channels (Nye, 1965). The relative strength of marginal and basal shear strain-rate is opposite to that expected from theory. In addition, the longitudinal flow velocity averaged over the glacier cross-section (which determines the flux of ice transported) is larger by 12% than the average flow velocity seen at the glacier surface, whereas it would be essentially the same if the theoretical prediction were correct. These differences are caused to a large extent by the contrast between the actual distribution of sliding velocity and the constant sliding velocity for which the theoretical analysis holds. The observed relation between marginal and basal sliding velocity is probably a general flow feature in valley glaciers, and may be caused by lateral variation of water pressure at the ice-rock contact. The observed pattern of longitudinal velocity over the section also shows in detail certain additional features incompatible with the theoretical treatment, even after the difference in boundary conditions (distribution of sliding velocity) is taken into account.Longitudinal strain-rate (a compression of about 0.02 a-1at the surface) decreases with depth, becoming nearly o at the bed in the center of the glacier, which confirms a prediction by Savage and Paterson (1963). The depth variation cannot be explained completely by overall bending of the ice mass as a result of a longitudinal gradient in the curvature of the bed, and is at variance with existing theories, which require the longitudinal strain-rate to be constant with depth.Motion transverse to the longitudinal flow occurs in a roughly symmetric pattern of diverging margin-ward flow, with most of the lateral transport occurring at depth in a fashion reminiscent of extrusion flow. The observed lateral velocities averaged over depth (up to 1.9 m a-1) are compatible with the lateral flux required to maintain equilibrium of the marginal portions of the glacier surface under ablation (about 3.7 m of ice per year) and are driven by the convex lateral profile of the ice surface.

Determination of the Three-Dimensional Velocity Field in a Glacier

A method for the determination of the three-dimensional velocity field in a glacier is described, Measurements in three or more bore holes arranged in an appropriate array are needed for its application. Surface motion measured by triangulation and tape measure, bore-hole profiles given by inclinometry, and the geometry of the bed are all considered simultaneously in order to determine the velocity field. The basic assumption is that velocity between the bore holes can be represented by suitable interpolation based on the measurements in the holes. Ice displacement parallel to bore holes is calculated indirectly from incompressibility and the constraint that velocity normal to the bed be zero. As an example, the method is applied to an array of 9 bore holes in Athabasca Glacier.

Icequakes on the Athabasca Glacier

Icequakes have been recorded with an eight-geophone array on an active glacier. All the events appear to originate from extensional faulting near the surface of the glacier. The absence of events occurring at depth suggests that the creep-instability mechanisms proposed for shear faulting are not operative at depth in the glacier. Most icequakes occurred as single events within the zone of marginal crevasses. Swarms of icequakes were occasionally recorded. The individual events in a swarm were distributed along a straight line several hundred meters long. The activity seemed to progress from one end of this line to the other at a velocity of about 30 m/sec. The line often extended through a crevasse-free section of the glacier.

Excess Pressure Observed in a Water-filled Cavity in Athabasca Glacier, Canada

Abstract During drilling in the Athabasca Glacier in April 1968, a cavity containing water was punctured at a depth of 9.2 m below the ice surface. Upon removing the drill, water gushed from the bore hole for about 55 s indicating an excess pressure of at least 0.25 bar within the cavity. The surrounding ice was slightly below the pressure melting point, and the excess pressure was apparently generated by the reduction in volume of the cavity caused by freezing of some of the water within it.

Excess Pressure Observed in a Water-filled Cavity in Athabasca Glacier, Canada

AbstractDuring drilling in the Athabasca Glacier in April 1968, a cavity containing water was punctured at a depth of 9.2 m below the ice surface. Upon removing the drill, water gushed from the bore hole for about 55 s indicating an excess pressure of at least 0.25 bar within the cavity. The surrounding ice was slightly below the pressure melting point, and the excess pressure was apparently generated by the reduction in volume of the cavity caused by freezing of some of the water within it.

The Sliding Velocity of Athabasca Glacier, Canada

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.

The Sliding Velocity of Athabasca Glacier, Canada

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.

Internal Deformation and Thermal Anomalies in Lower Blue Glacier, Mount Olympus, Washington, U.S.A.

AbstractIn 1957 through 1962 six deep holes were drilled by means of specially developed electrically powered hotpoints, 4 cm diameter aluminum pipes were placed in them, and annual inclinometer surveys were made to investigate the deformation field and flow law of the ice at depth. Although a strongly maritime climate with moderate temperatures implies that lower Blue Glacier should be temperate, freezing at depths as great as 200 m, sometimes even in summer, seriously hindered inclinometer surveys. This freezing cannot be due solely to chilling by winter cold and to leakage into initially dry pipes, but may also be due to wintertime changes of water Table in the glacier and to contamination of the ice by antifreeze. Another possibility, residual subfreezing zones carried down from the ice fall, seems unlikely.Because the relatively inextensible pipe slips lengthwise in the deforming hole, observations of pipe motion at best give only the two components of ice velocity perpendicular to the hole. Thus, a single hole gives two independent equations connecting the nine unknown derivatives of the velocity components; two holes give four equations: and three or more give at most six. Incompressibility of the ice, when applicable gives another. The remaining unknowns must be either neglected or estimated from assumptions about the flow field. At the Blue Glacier holes the longitudinal strain-rate is less than about 0.01 per year, becoming more extensional down-glacier and more compressional at depth, because the holes were moving through a reach in which the surface steepens and the bed becomes more steep-sided and flat-bottomed. Although the effective strain-rates are only about 0.01 to 0.1 per year, so that errors are relatively large, they are in reasonable agreement with flow laws deduced from laboratory experiments by Glen, from tunnel contraction by Nye, and from deformation of Athabasca Glacier bore holes by Paterson and Savage, except that in the range of strain-rates covered the viscosities found for Blue Glacier are about half those derived from the other studies.

Internal Deformation and Thermal Anomalies in Lower Blue Glacier, Mount Olympus, Washington, U.S.A.

AbstractIn 1957 through 1962 six deep holes were drilled by means of specially developed electrically powered hotpoints, 4 cm diameter aluminum pipes were placed in them, and annual inclinometer surveys were made to investigate the deformation field and flow law of the ice at depth. Although a strongly maritime climate with moderate temperatures implies that lower Blue Glacier should be temperate, freezing at depths as great as 200 m, sometimes even in summer, seriously hindered inclinometer surveys. This freezing cannot be due solely to chilling by winter cold and to leakage into initially dry pipes, but may also be due to wintertime changes of water Table in the glacier and to contamination of the ice by antifreeze. Another possibility, residual subfreezing zones carried down from the ice fall, seems unlikely.Because the relatively inextensible pipe slips lengthwise in the deforming hole, observations of pipe motion at best give only the two components of ice velocity perpendicular to the hole. Thus, a single hole gives two independent equations connecting the nine unknown derivatives of the velocity components; two holes give four equations: and three or more give at most six. Incompressibility of the ice, when applicable gives another. The remaining unknowns must be either neglected or estimated from assumptions about the flow field. At the Blue Glacier holes the longitudinal strain-rate is less than about 0.01 per year, becoming more extensional down-glacier and more compressional at depth, because the holes were moving through a reach in which the surface steepens and the bed becomes more steep-sided and flat-bottomed. Although the effective strain-rates are only about 0.01 to 0.1 per year, so that errors are relatively large, they are in reasonable agreement with flow laws deduced from laboratory experiments by Glen, from tunnel contraction by Nye, and from deformation of Athabasca Glacier bore holes by Paterson and Savage, except that in the range of strain-rates covered the viscosities found for Blue Glacier are about half those derived from the other studies.

Internal friction in ice near its melting point

The internal friction of ice near its melting point has been measured in the Athabasca glacier for Rayleigh waves from 0.025 to 0.18 kHz, for P waves from 0.12 to 1.0 kHz, and for S waves from 0.12 to 0.68 kHz. The mean Q for Rayleigh waves was 28., for S waves 23., and for P waves 65. From the attenuation data, it is shown that the internal friction in pure dilatation is much less than in pure shear. On this basis the Rayleigh and S-wave data may be reduced to equivalent P-wave attenuation coefficients, yielding an attenuation spectrum that extends from 0.025 to 1.0 kHz. Additional measurements by Westphal extend the spectrum to 5.0 kHz. These measurements supplement the work of Kuroiwa and permit one to conclude that the attenuation mechanism is most probably grain-boundary slip.

TEST OF CONTOUR ACCURACY ON A PHOTOGRAMMETRIC MAP OF ATHABASCA GLACIER

An independent survey of the positions and elevations of 59 surface markers set in the lower part of Athabasca Glacier permits assessment of the accuracy of contours on a large-scale map of the glacier. The root mean square difference between the elevation at each marker as determined from the survey and from the map was 49 cm. This is an upper limit to the standard error of the contours. It is less than three times the theoretical error and about 15% of the contour interval.

New Bryophytes for Colorado

Mnium ambiguum H. Miill., M. andrewsianum Steere, and M. trichomanes Mitt. are reported from Colorado, and their known ranges thereby significantly extended. The moss genus Mnium has been known in Colorado by the species M. arizonicum, M. blyttii, M. cuspidatum, M. lycopodioides, M. marginatum, M. medium, M. orthorrhynchum, M. pseudopunctatum, M. punctatum, M. punctatum var. elatum, and M. rugicum (Grout 1940). In connection with cytotaxonomic studies of the genus (Bowers 1966), three species previously unknown for the state have been discovered, namely M. ambiguum, M. andrewsianum, and M. trichomanes. These additions are of a considerable phytogeographic significance, widely extending the known distribution of the species. The specimens cited were collected in 1963 to 1965, and they are preserved in the University of Colorado Museum. MNIUM AMBIGUUM H. Mill. The distribution of forms referable to this species has previously been limited to two localities in the United States: Rockland County, New York, and Bergen County, New Jersey (Grout 1903). The species also occurs in Europe (Miiller 1866). The present Colorado collections were all made above an elevation of 8,500 feet and they represent the first report of the species from the southern Rocky Mountains. Perhaps the species has been overlooked in North America and, if definitely searched for, will be found better represented than the present literature indicates. COLORADO. GRAND CO.: West St. Louis Creek, Fraser, Bowers bb-553. Berthoud Pass, Bowers bb-556. W of Berthoud Pass on U.S. 40, Bowers bb-559. EL PASO CO.: Pike's Peak, W of Colorado Springs, Bowers bb-624. MNIUM ANDREWSIANUM Steere. This taxon is distributed throughout Alaska, Canada, and Greenland. It is also reported for Michigan (Mazzer & Sharp 1963). The Colorado collections constitute the second report from the United States outside of Alaska and the first report from the southern Rocky Mountains. The closest known locality is at the edge of the tundra near Athabasca Glacier, Columbia Icefields, Jasper National Park, Alberta, Canada (Steere 1958). Dr. W. C. Steere suggested to me that this species be looked for at high altitudes in Colorado, and collections were subsequently made at altitudes from 8,500 to 11,300 feet. This report extends the range to a new southern limit in western North America. The Colorado specimens differ from the typical M. andrewsianum only in being more robust. COLORADO. GRAND CO.: West St. Louis Creek, Fraser, Bowers bb-185. Berthoud Pass, Bowers bb-554. W of Berthoud Pass on U.S. 40, Bowers 1 Department of Biology, University of Colorado, Boulder, Colorado. Present address: Department of Biology, Northern Michigan University, Marquette, Michigan. This content downloaded from 157.55.39.255 on Wed, 25 May 2016 06:37:29 UTC All use subject to http://about.jstor.org/terms 1966] BOWERS: BRYOPHYTES FROM COLORADO 369 bb-557. LARIMER CO.: Poudre Lake, Rocky Mountain National Park, Bowers bb-194. BOULDER CO.: Jenny Lake, Rollins Pass, Bowers bb-194. MNIUM TRICHOMANES Mitt. The distribution of forms referable to this species has previously been limited to two localities in the United States: Florida (Lowry 1948) and Illinois (Andrews 1959). It is widespread in Asia (Noguchi 1960). The Colorado specimens are the first report from the southern Rocky Mountains. It has probably been overlooked in North America and Europe. COLORADO. DOUGLAS CO.: Jackson Creek Road, 11.5 mi from the junction of Colorado 105, Bowers bb-200. Jackson Creek Road, 10 mi from the junction of Colorado 105, Bowers bb-204.

Additional borehole measurements in the Athabasca glacier

Savage and Paterson [1963] have discussed measurements of inclination made in boreholes in the Athabasca glacier during the years 1960 to 1962. A further set of measurements has been made in one borehole. The results, which are consistent with the earlier ones, are given in this letter. We also take this opportunity of listing corrections to this paper and an associated paper [Paterson and Savage, 1963].

Reply to Meier’s letter on “Variations in velocity of Athabasca Glacier with time”

Reply to Meier’s letter on “Variations in velocity of Athabasca Glacier with time”

Comments on Paterson’s paper “Variations in velocity of Athabasca Glacier with time”

Comments on Paterson’s paper “Variations in velocity of Athabasca Glacier with time”

Comments on Paterson’s paper “Variations in velocity of Athabasca Glacier with time”

Comments on Paterson’s paper “Variations in velocity of Athabasca Glacier with time”

Reply to Meier’s letter on “Variations in velocity of Athabasca Glacier with time”

Reply to Meier’s letter on “Variations in velocity of Athabasca Glacier with time”

Variations in Velocity of Athabasca Glacier with Time

AbstractThe physical setting of the Athabasca Glacier is described. Ablation of ice from the glacier contributes roughly 40 per cent of the annual outflow from the lake at the terminus. Variations of ice velocity, measured over periods ranging from a week to four months, are discussed. Few if any of these variations can be explained by changes of ice thickness. Variations in the amount of water at the glacier bed provide a plausible explanation however, and the data lend some support to Weertman’s ideas on this subject. Variations in annual velocity of the glacier are not correlated with stream flow, but passage of a kinematic wave provides an explanation of these variations. The wave is attributed to a climatic change which began about 1938.

Variations in Velocity of Athabasca Glacier with Time

AbstractThe physical setting of the Athabasca Glacier is described. Ablation of ice from the glacier contributes roughly 40 per cent of the annual outflow from the lake at the terminus. Variations of ice velocity, measured over periods ranging from a week to four months, are discussed. Few if any of these variations can be explained by changes of ice thickness. Variations in the amount of water at the glacier bed provide a plausible explanation however, and the data lend some support to Weertman’s ideas on this subject. Variations in annual velocity of the glacier are not correlated with stream flow, but passage of a kinematic wave provides an explanation of these variations. The wave is attributed to a climatic change which began about 1938.