Showing papers in "Journal of Glaciology in 1971"
TL;DR: In this article, the authors measured the distribution of the velocity vector and the strain-rate tensor over a nearly complete cross section of a valley glacier, and made it possible to test the applicability of experimental and theoretical concepts in the analysis of glacier flow.
Abstract: 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 boreholes (depth about 300 m, eight holes essentially to the bottom) was measured with a newly developed electrical inclinometer, which allows a great increase in the speed and accuracy with which borehole configurations can be determined, in comparison with earlier methods. The measurements define the distribution of the velocity vector and the strain-rate tensor over 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 centerline (about 40 m yr(-1)), (3) marginal shear strain rate near the valley walls two to three times larger than the basal shear strain rate near the centerline (0.1 yr(-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 11% than the average flow velocity seen at the glacier surface, whereas it would be 2% smaller if the theoretical prediction were correct. These differences are caused to a large extent by the constant sliding velocity assumed in the theoretical analysis, which contrasts strongly with the actual distribution of sliding. 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 yr(-1) at the surface) decreases with depth, becoming nearly 0 at the bed in the center of the glacier. 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 marginward 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 yr(-1)) are compatible with the lateral flux required to maintain equilibrium of the marginal portions of the glacier surface under ablation (3.7 m yr(-1)) and are driven by the convex transverse profile of the ice surface.
When the measured strain-rate field is analyzed on the basis of the standard assumption that the shear stress parallel to the glacier surface varies linearly with depth, the rheological behavior in the lower one-half to two-thirds of the glacier is found compatible with a power-type flow law with n = 5.3. However, the upper one-third to one-half of the glacier constitutes an anomalous zone in which this treatment gives physically unreasonable rheological behavior. In a new method of analysis, rheological parameters are chosen so as to minimize the fictitious body forces that appear as residuals in the equilibirum equations when evaluated for the measured strain-rate field. This new method requires no a priori assumptions about the stress distribution, although for simplicity in application, the mean stress is assumed constant longitudinally. This treatment shows that the anomalies in the near-surface zone are due to significant departures from linear dependence of shear stress on depth, and gives a flow-law exponent of n = 3.6, which is closer than n = 5.3 to values determined by laboratory experiments on ice.
127 citations
TL;DR: In this article, the authors defined a temperate glacier as a glacier containing liquid inclusions in which the concentration of salts is not too high, and explained why firn, at a depth which the annual cold wave does not reach, is nevertheless transformed relatively suddenly into practically impermeable ice.
Abstract: A temperate glacier is defined as a glacier containing liquid inclusions in which the concentration of salts is not too high. Nevertheless these salts suffice to produce a depression in temperature comparable with that due 10 the pressure, and much greater than that due to interfacial energies. Because of this a large part of the liquid water present in the ice is not mobile, contrary to the theory of Nye and Frank. Deformation and recrystallization is bound to close off capillary intergranular channels, for glacier ice is usually impermeable. An explanation is given of why firn, at a depth which the annual cold wave does not reach, is nevertheless transformed relatively suddenly into practically impermeable ice. Saline inclusions will migrate with a velocity inversely proportional to the potential temperature (difference from the melting point of pure ice at the pressure in question) and proportional to the gradient of this potential temperature. This velocity, the salinity, the liquid water content, and the ice temperature, parameters which are all functions of the depth, are calculated for a steady state in a stagnant or moving glacier. Under the action of anisotropic stresses, isolated inclusions perpendicular to the maximum compressive stress will enlarge at the expense of their neighbours. If however the two inclusions are connected by a capillary channel, no enlargement occurs, but instead the salt content decreases, evacuated to the other inclusion. This process would constitute an objection to the theory of glacier sliding by melting and refreezing around small obstacles, unless new subglacial mechanisms were to occur.
116 citations
TL;DR: In this article, field observations during a journey through the arid regions of the South American Andes in June-July 1969 are evaluated in conjunction with available air photographs and reports from adjacent areas of the High Andes.
Abstract: Field observations during a journey through the arid regions of the South American Andes in June-July 1969 are evaluated in conjunction with available air photographs and reports from adjacent regions of the High Andes. Results indicate an increase of the Pleistocene snow-line depression in the western Cordillera from about 700 m at lat. 12° S. to more than 1 500 m at lat. 30° S. The Pleistocene snow-line depression decreases from the Pacific to the Atlantic side of the Andes, but particularly strongly so on the poleward fringe of the arid region. From this geomorphic evidence it is suggested that the atmospheric circulation during the glacial period was characterized by an Equatorward displacement of the boundary between tropical easterlies and temperate-latitude westerlies.
86 citations
TL;DR: Two Kipp hemispherical radiometers mounted back to back and suspended by an 18 m cable from a helicopter flying at an altitude of about 90 m were used to make measurements of incident and reflected short-wave radiation as mentioned in this paper.
Abstract: Two Kipp hemispherical radiometers mounted back to back and suspended by an 18 m cable from a helicopter flying at an altitude of about 90 m were used to make measurements of incident and reflected short-wave radiation. The helicopter was brought to a hovering position at the instant of measurement to ensure that the radiometers were in the proper attitude and a photograph of the ice cover was taken at the same time. The observations were made in 1969 during 16 flights out of Tuktoyaktuk, Northwest Territories (lat. 69° 26’N., long. 133° 02’W.) over the fast ice extending 80 km north of Tuktoyaktuk. Values of albedo of the ice cover were found to decrease during the melting period according to the equation A = 0.59 —0.32P where P is the degree of puddling of the surface.
75 citations
TL;DR: In this article, the generalized Glen's law is used to calculate die horizontal and vertical velocity profiles and from these the temperature and age profiles of cold ice sheets are obtained, by substituting for θ a function increasing linearly with height, velocity profiles for all ice sheets were obtained which represent excellent approximations to the true ones.
Abstract: The generalized Glen’s law έ = έ0Tn exp (kθ ) is used to calculate die horizontal and vertical velocity profiles and from these the temperature and age profiles of cold ice sheets. It is shown that, by substituting for θ a function increasing linearly with height, velocity profiles for all ice sheets are obtained which represent excellent approximations to the true ones, since, above a critical height he where the deviation from linearity becomes large, the influence of temperature on ice flow becomes negligible. In a comparison of the present theory with Robin’s (1955) treatment a larger temperature difference ΔT of up to 30% is obtained. Furthermore the present theory yields an age considerably increased compared with Nye’s model; e.g. more than 50% at a relative height of h\H = 0·1.
64 citations
TL;DR: In this paper, a spectral analysis of the surface and bedrock profiles along a flow line of the Wilkes ice cap and the surface along the Greenland E.I.G. profile is presented.
Abstract: : Results are presented of spectral analyses of the surface and bedrock profiles along a flow line of the Wilkes ice cap and the surface along the Greenland E.G.I.G. profile. Although the bedrock appears irregular over all wavelengths studied, the ice-cap surface is typically characterized by a smooth curve with small-scale surface undulations superimposed on it. The following relations of Budd (1969, 1970) are confirmed. (Author)
57 citations
TL;DR: In this paper, the analysis of steady-state flow over bedrock perturbations of Budd(1970[a]) is extended to evaluate the stress variations associated with the flow, in particular the four separate terms of the fundamental one-dimensional (longitudinal) stress equation (Budd,1968) are examined to show explicitly how the longitudinal stress gradient G, the base stress τ, the surface slope stress s, and the integrated second derivative of the shear stress T all vary over a given wave.
Abstract: The analysis of steady-state flow over bedrock perturbations of Budd(1970[a]) is extended to evaluate the stress variations associated with the flow. In particular the four separate terms of the fundamental one-dimensional (longitudinal) stress equation (Budd,1968) are examined to show explicitly how the longitudinal stress gradient G, the base stress τ, the surface slope stress s, and the integrated second derivative of the shear stress T all vary over-a given wave. The result shows an error of a factor of 2 in some earlier studies relating longitudinal stress variations to the slope. This error resulted from the erroneous assumption that remains constant at its regional value. In fact the basal stress varies over the undulations in a similar way to the longitudinal stress gradient, and this is the same as the surface slope stress for long waves, but for short waves or less) requires the addition of the fourth term T, which then becomes dominant.
48 citations
46 citations
TL;DR: Oxygen-isotope and chlorinity determinations, as well as petrographie observations, indicate that the basement we of the Ward Hunt Ice Shelf is largely composed of a unique brackish ice, which interdigitates with sea ice as mentioned in this paper.
Abstract: Oxygen-isotope and chlorinity determinations, as well as petrographie observations, indicate that the basement we of the Ward Hunt Ice Shelf is largely composed of a unique brackish ice, which interdigitates with sea ice Some iced firn occurs near the top of the Basement Ice, below an unconformity stratification in brackish and sea ice represents annual increments to the bottom of the ice shelf The c-axis vertical orientation and small-angle grain-boundary relations in brackish ice are explained by nucleation and floating of ice dendrites from the undercooled brackish water zone to the bottom of the ice shelf, where they attach themselves sub-parallel to the plane of the undersurface Ice island T-3 did not come from a break-up of the main part of the Ward Hunt Ice Shelf, but probably originated in a nearby area to the west
43 citations
TL;DR: The presence of 49 cirques on the Falkland Islands indicates that glacial conditions were prevalent during the Pleistocene as mentioned in this paper, and periglacial landforms such as stone runs, stone terraces and stone lobes also developed during the Pliocene and attained very large dimensions because of the lithology, the relatively small scale of glacierization and the presence of rotted bedrock.
Abstract: The presence of 49 cirques on the Falkland Islands indicates that glacial conditions were prevalent during the Pleistocene. Cirque moraines and glacially eroded valleys also occur. There appear to have been three phases: a period of cirque formation, the growth of local ice caps and subsequent cirque development. Periglacial landforms such as stone runs, stone terraces and stone lobes also developed during the Pleistocene and attained very large dimensions because of the lithology, the relatively small scale of glacierization and the presence of rotted bedrock.
39 citations
TL;DR: The formation of these moraines seems to be more complex than simple upwarping of the foliation bands at the margin of the ice cap as discussed by the authors, and the time required to obtain the quantity of debris forming the moraine at the ice surface is estimated to be between 65 and 200 years.
Abstract: The north-west margin of the main ice cap in south-western Ellesmere Island is fringed by ice-cored moraines. The formation of these moraines seems to be more complex than simple upwarping of the foliation bands at the margin of the ice cap. At one locality, where outer and inner zones can be distinguished on the basis of lithological composition, debris in the outer zone is composed of material from farther back under the ice cap than debris in the inner zone. In another locality, localized ridges cross each other independently of the trend of the main ridge.The time required to obtain the quantity of debris forming the moraine at the ice surface is estimated to be between 65 and 200 years.
TL;DR: In this article, 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.
Abstract: 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.
TL;DR: In this paper, it was calculated that lake water temperatures of 0.25, 0.9 and 0.15°C are required to account for the November 1965, September 1967 and November 1968 drainings, respectively.
Abstract: Testing of a water-balance equation for the Summit Lake basin in July and August 1968 indicated that, 2½ months before its fourth known draining, there existed a leak through or under the damming glacier that may have been as large as 3–5 m3/s. Lake temperatures recorded during the same period indicate water at 0.5–0.8°C near the ice dam and up to 2.6°C 4–5 km from the dam. These observations support the proposal of Liestol (1956) and Mathews (in press) of tunnel enlargement by melting. It is calculated that lake water temperatures of 0.25, 0.9 and 0.15°C are required to account for the November 1965, September 1967 and November 1968 drainings, respectively.
TL;DR: In this article, the authors used mass-balance data and a slightly different method for computing the datum state to predict the future movement of the glacier in the next 25 years.
Abstract: Untersteincr and Nye (1968) calculated the possible future movement of Berendon Glacier, B.C. These calculations are repeated using much improved data and a slightly different method for computing the datum state. The predictions that result are very similar to those found in the earlier work. It is concluded, however, from mass-balance data, that the chance of the glacier rising sufficiently in the next 25 years to be a danger to the mining installations situated near the snout of the glacier is much greater than was previously considered. The sensitivity of the theory to changes in input data is discussed.
TL;DR: In the Cairngorm Mountains of the UK, measurements of widths, diameters and boulder sizes indicate that fine polygons are produced by heave and their sizes are dependent upon the frequency of boulders large enough to be resistant to heave, which in turn depends upon climatic severity as mentioned in this paper.
Abstract: Measurements of widths, diameters and boulder sizes of patterned ground in the Cairngorm Mountains indicate two sorts of stripes and polygons (fine and coarse). Pipkrake and boulder-inclination observations and measurements suggest that fine polygons are produced by heave and their sizes are dependent upon the frequency of boulders large enough to be resistant to heave, which in turn depends upon climatic severity. The lack of orientation, angle of boulder inclination, hemispherical shape, high relative size dispersion and lithological dependence of coarse polygons indicate a selective weathering origin. The frequency of low inclination of boulders in stripes suggests an origin due to solifluction, whereby large immobile or relatively slower-moving boulders impede soil (and smaller boulder) movements and control stripe spacing. Movement observation and lichenometry indicate that fine polygons and stripes and bare coarse polygons are active at the present time and that coarse stripes and vegetated coarse polygons probably date from the Little Ice Age.
TL;DR: In this paper, the thermal conductivity and diffusivity of natural snow computed from Fourier-type analyses of annual snow temperature variations are shown to be strongly temperature dependent, and the computed temperature coefficients of-0.007 and -0.012 deg-1 respectively, agree well with older laboratory experiments carried out on polycrystalline ice.
Abstract: The thermal conductivity and diffusivity of natural snow computed from Fourier-type analyses of annual snow temperature variations are shown to be strongly temperature dependent. The computed temperature coefficients of-0.007 and -0.012 deg-1 respectively, agree well with older laboratory experiments carried out on polycrystalline ice.
TL;DR: In this article, a record of sedimenta tion from pro-glacia l sa ndur d eposits th rough p ro-glacia l lake deposits to fi na l deposition of till is used to interpre t cha nging environ menta l conditions, a nd d epositiona l processes.
Abstract: ABSTR ACT. A record of sedimenta tion from pro-glacia l sa ndur d eposits th rough p ro-glacia l lake deposits to fi na l deposition of till is used to interpre t cha nging environ menta l conditions, a nd d epositiona l processes. during the development of the \" Little Welsh Advance\" in the Shrewsbury a rea, Engla nd . The rela tionship between lacustrine sediments a nd till es tablishes till depos ition by flowage. H owever, the mos t important conclusions are d erived from the d eduction tha t lac ustrine sediments were incorpora ted into the basa l pa rt of the ice shee t a nd transported across previously d epos ited end mora ines. A discussion of this dedu ction, based on the findings of W eertman ( 196 1), es ta blishes that during the advancing phase the ice shee t was of the polar type. Final melting is thought to have occurred by both top-melt and under-melt as a result of cl ima tic a meliora tion.
TL;DR: In this article, the movement at a marginal location on the Ward Hunt Ice Shelf, northern Ellesmere Island, was determined by repeated survey measurements with theodolite and geodimeter, and the purpose and duration of the field work, and reduction of the observational data are described, and resulting mean ice velocity of 0.53 m year-1 is discussed.
Abstract: The movement at a marginal location on the Ward Hunt Ice Shelf, northern Ellesmere Island, was determined by repeated survey measurements with theodolite and geodimeter. The purpose and duration of the field work, and reduction of the observational data are described, and the resulting mean ice velocity of 0.53 m year-1 is discussed. Strain-rates of a 1 km by 1 km deformation figure are determined. The parameters n and B of Glen’s power flow law are determined by using the equations given by Nye and Weertman. The results are compared with experimental data. Computed ice stresses show that the “ridge-and-trough" structure on the ice shelf surface is not originated by internal ice forces. The elevations of all survey markers have been determined from vertical-angle measurements, and the peculiarities of atmospheric refraction in near-surface layers are discussed.
TL;DR: The Howorka steam-operated ice drill as discussed by the authors uses a double-walled flexible hose and a straight guide tube with an exchangeable nozzle at the end, which is mounted on a pack frame for easy transportation in rugged terrain.
Abstract: A further development of the Howorka steam-operated ice drill is given. It is mounted on a pack frame for easy transportation in rugged terrain. A propane flame is used to vaporize water in a single-pass fire-tube boiler. The steam is delivered to the ice through a double-walled flexible hose and a straight guide tube with an exchangeable nozzle at the end. One hole, 25 mm in diameter and 8 m deep, can be drilled in 15 min; four such holes can be drilled with one tank of water and 10 with one tank of propane. Holes deeper than 16 m are impractical as heat losses in the hose become too large. Sturdy construction has been used and the drill has been tested and found to work satisfactorily under both temperate and arctic conditions.
TL;DR: In this paper, surface deformations in the neighborhood of a crevasse field were measured over short (3 m) gage lengths in order to study flow conditions associated with crevse formation, and the results obtained were unusual in that they were inconsistent with large-scale results found by previous workers.
Abstract: Surface deformations in the neighborhood of a crevasse field were measured over short (3 m) gage lengths in order to study flow conditions associated with crevasse formation. The results obtained were unusual in that they were inconsistent with large-scale results found by previous workers. It was concluded that the presence of small-scale surface effects, such as fractures, pot-holes and healed crevasses give rise to small-scale deformation fields with large spatial and temporal variations and that there is a lower limit of gage length below which deformation measurements pertinent to regional (low phenomena cannot be made. This lower limit is apparently an order of magnitude greater than the spacing of the features which give rise to localized effects.