bluuebunny/crossref_metadata_2025 huggingface dataset:
The spatial variability of snow resistance on potential avalanche slopes
Authors: Birkeland K. W. , Hansen K.J. , Brown R. L.
Published: September 2017

Since snow avalanches are believed to release from zones of localized weakness, knowledge of snow-strength patterns is important for determining slope stability and for applying effective avalanche-control measures. In this study, the spatial variability of snow resistance (an index of snow strength) and depth were measured and compared with terrain features on two inclined slopes. A refined instrument allowed the strength of an entire snow slab to be characterized in a short time. The spatial pattern of trees appeared to affect the pattern of snow depth at one site, where a significant linear relationship was found between snow depth and average snow resistance. These results suggest that localized snow-depth variations may be important in snow-strength genesis. Although a linear relationship existed at that site, additional factors may be critically relevant. A second site with more complex terrain features and less localized wind drifting did not show a linear relationship between depth and average resistance. Instead, complex patterns of resistance demonstrated that many factors contribute to snow resistance. In particular, die snow overlying rocks was found to have significantly weaker resistance than that in adjacent areas not over rocks.
Plasticity Solution for a Glacier Snout
Authors: Nye J. F.
Published: September 2017

The flow near the end of a glacier in a steady state is investigated by using a theoretical model: a plastic–rigid material with a constant flow stress resting on a rough horizontal bed. Starting from an appropriately chosen slip-line far from the end, the slip-line field is constructed numerically and continued to the end of the glacier. The field rapidly settles down to a form independent of the precise starting conditions. In the region of small surface slope it agrees with the approximate analytical solution reported earlier (Nye, 1951). To avoid a breakdown in the method it is found necessary to modify the bed by a trivial amount over the final 3 m. In practice the ice can lose contact with the bed very near the end, and the effect of this on the solution is discussed.

The velocity field is computed for a uniform ablation-rate. Other distributions of ablation-rate could be accommodated, but there appears to be a critical gradient of ablation-rate beyond which the slip-line field fails.
Temperature profiles for the barnes ice cap surge zone
Authors: Classen D. F.
Published: September 2017

Thermal drilling and deep ice-temperature measurements along a flow line in a surge area of the Barnes Ice Cap, Baffin Island, N.W.T., Canada revealed a layer of basal temperate ice 30 m thick. Marginal areas were determined to be frozen to bedrock and geothermal heat flow estimated to be 1.02 μcal/cm2s (42 mW/m2).
Artificially Induced Thermokarst in Active Glacier Ice: An Example from North-West British Columbia, Canada
Authors: Eyles N. , Rogerson R. J.
Published: September 2017

Warm waste water, at 30°C, has been discharged from a copper concentrater on to the active terminal ice of Berendon Glacier, British Columbia, since 1970. As a result, rapid basal ice melt causes the formation of caverns and subsequent collapse features referred to as glacier thermokarst. A review of the literature reveals that such features have been described elsewhere from active ice, and the usual conditions assumed for the development of glacier thermokarst (stagnant, heavily debris-covered ice) should be redefined to include these examples.
Superimposed Drumlins
Authors: Rose J. , Letzer J. M.
Published: September 2017

Drumlins in parts of central Scotland and east Cumbria form two populations according to their size. In certain cases the small features are superimposed on the large. Drumlins, superimposed drumlins, and megadrumlins are considered to be part of a continuum of glacier bed forms, which is the product of changes in the stress applied by glaciers and the strength of bed material. Glacier behaviour can be inferred on the basis of this interpretation.

Drumlins in parts of central Scotland and east Cumbria form two populations according to their size. In certain cases the small features are superimposed on the large. Drumlins, superimposed drumlins, and megadrumlins are considered to be part of a continuum of glacier bed forms, which is the product of changes in the stress applied by glaciers and the strength of bed material. Glacier behaviour can be inferred on the basis of this interpretation.
An inverse problem in glacial geology: The reconstruction of glacier thinning in glacier bay, alaska between A.D. 1910 and 1960 from relative sea-level data
Authors: Clark James A.
Published: September 2017

Inverse theory is applied to relative sea-level data to reconstruct a glacial history that is consistent with the emergence data near Glacier Bay, Alaska over the past half century. A comparison between the predicted glacial thinning and observed thinning indicates that a combination of elastic uplift of the ground and a fall in the geoid defining the ocean surface, causes 25% to 35% of the observed emergence of the coast line. Because of errors in the sea-level data, inverse theory cannot provide a unique solution in terms of glacier response, and, in fact, the least-squares fit is very inaccurate. However, by considering (1) the error of fit to the data, (2) the accuracy of the model, (3) the variation in the model, and (4) the model resolution, a physically realistic glacial history can be deduced. The advantage of inverse calculations is not only in its efficient means of finding a model that fits the data, but more importantly, it provides a means of assessing the reliability of the model by indicating the accuracy of the model and the range of other glacial histories that also fit the data. This approach also allows an estimate of the extent to which each data point constrains the model, independent of the actual data values. From this information, the most useful areas for additional data collection may be delimited.
Plane-Strain Compressive Strength of Columnar-Grained and Granular-Snow Ice
Authors: Frederking R.
Published: September 2017

An ice cover impinging on a long straight structure is assumed to be under a condition of plane strain. A technique is described for performing plane-strain compression tests, and results are presented for the strain-rate dependence of strength. The plane-strain compressive strength of ice having anisotropic structure (columnar-grained ice) is at least two and a half times the uniaxial compressive strength, whereas the plane-strain compressive strength of ice having an isotropic structure (granular-snow ice) is at most 25% greater than the uniaxial case. The greater plane-strain compressive strength of columnar grained ice when the loading and confining directions are in the plane of the ice cover, can be attributed to its anisotropic structure, which leads to a different failure mechanism for the plane-strain case.
Short Note: Preliminary Observations on the Daily Variation of Ice Albedo
Authors: Bolsenga S. J.
Published: September 2017

A preliminary assessment of the daily variation of ice albedo in the 285-2 800 nm range was made using field data collected over snow ice and refrozen slush. Significant diurnal variations could be attributed to changing low solar altitude under clear skies or to decay of the ice surface. Changes in albedo due to changes in cloud cover were observed for the most part to be slight. The measurements provide a base for a program of wider scope which would consider other types of ice under a variety of natural conditions.
Structures and Ice Deformation in the White Glacier, Axel Heiberg Island, Northwest Territories, Canada
Authors: Hambrey M.J. , Müller F.
Published: September 2017

The major structures in the long, narrow tongue of a sub-polar valley glacier are described: namely, longitudinal foliation, crevasses, clear-ice layers related to crevasses, debris-rich layers (frequently referred to as thrust or shear planes in the past), and folds. The foliation is vertical, is as well-developed in the centre of the glacier as at the margins, and does not, apparently, form perpendicular to the principal compressive strain-rate axis, nor exactly parallel to a line of maximum shearing strain-rate, although it sometimes approximately coincides with the latter. The intensity of foliation development is not related to the magnitude of the strain-rates, but the structure consistently lies parallel to flow lines through the glacier. There is no critical extending strain-rate, as such, associated with the development of new crevasses. Some crevasses have formed where the principal extending strain-rate is as low as 0.004 a-1while, in other areas, extending strain-rates of 0.163 a-1have not always resulted in fracturing. Prominent clear-ice layers, referred to as crevasse traces as displayed at the glacier surface, have formed in crevasse belts parallel to the main fracture directions. These are interpreted either as tensional veins or as the result of the freezing of water in crevasses. Extension parallel to the layering occurs during flow and, near the snout, the surface dip decreases rapidly. The fact that the crevasse traces can be followed to the snout implies that fracture occurs almost to the bottom of the glacier in the source area of the traces. Near the snout, debris-rich layers have developed parallel to the crevasse traces; frequently these are marked by prominent ridge-like ice-cored moraines. It is suggested that these structures are formed by a combination of basal freezing and thrusting. Isoclinal and tight similar folds on all scales are present. Some may be formed by the passive deformation of clear-ice layers as a result of differential flow; others may arise from the lateral compression of the original stratification in areas where ice flow becomes constricted by the narrowing of the valley. An axial plane foliation sometimes is associated with these folds.
A Framework for the Investigation of Medial Moraine Formation: Austerdalsbreen, Norway, and Berendon Glacier, British Columbia, Canada
Authors: Eyles N. , Rogerson R. J.
Published: September 2017

Morphology of medial moraines on Austerdalsbreen, Norway, and Berendon Glacier, British Columbia, depends upon englacial debris supply. Major sub-types of this "ablation-dominant" model are related to the zone of debris entrainment relative to the firn line, and the manner of entrainment.

On Austerdalsbreen, debris derived from extraglacial bedrock slopes is entrained via crevasses at the confluence of two ice-cap outlet glaciers below the firn line. Revelation of crevasse-bound debris generates a distinct ice-cored morphology which is destroyed as crevasse bottoms are revealed down-glacier.

On Berendon Glacier ice streams coalesce above and below the firn line. Above the firn line, debris from extraglacial rock outcrops, subnival and subglacial zones, undergoes seasonal sedimentation with snowfall, and extends throughout the ice depth. Distinct moraine morphology in the terminal zone is related to continuing debris supply. Most debris is transported at depth near the glacier base.

An "ice-stream interaction" model where medial moraines formed below the firn line from the confluence of ice streams with large lateral moraine load are morphologically controlled by flow, explains morphology on the Berendon Glacier in the main confluence zone only. Down-glacier, this moraine becomes "ablation dominant". A minor "avalanche-type" model is also recognized.
The Glacial Record in Southern County Dublin, Eire
Authors: Hoare Peter
Published: September 2017

Early work by Farrington at the northern end of the Leinster mountains established a framework for glacial episodes throughout Ireland. The recent excavation of a small pit in commercial gravel workings in southern County Dublin has confirmed the relationship between four of the five events described by Farrington.
Processes of Glacier Erosion on Different Substrata
Authors: Boulton G.S.
Published: September 2017

Most theories of glacier movement and subglacial erosion have assumed that glaciers rest on rigid bedrock surfaces. Whilst this is probably correct for much of the bed area of most modern glaciers, deformable sediments do occur beneath them and formed a substantial area of the beds of large ice sheets during glacial periods. Observations and theories are presented and reviewed about the processes of glacier erosion of rock and unlithified sediment beds both when they are frozen and unfrozen.

Erosional bedrock landforms, such as roches moutonnées, indicate two principal subglacial erosional processes, plucking and abrasion. Where supraglacially derived debris is unimportant, plucking provides the tools which abrade the bed, and must be a quantitatively more important process than abrasion, though more localized. Where plucking is suppressed, erosion rates must be slow. Subglacial measurements of abrasion rates beneath a temperate glacier are used to test an earlier abrasional theory (Boulton, [C1974]). The form of the predicted abrasion-rate curve for changing ice velocity and pressure is verified. This theory successfully simulates two-dimensional erosional bedforms. Subglacial observations demonstrate how flow basal ice around the flanks of bedrock obstacles causes streaming of debris to occur. It is suggested that this streaming process is primarily responsible for the longitudinally lineated form of large-scale surfaces typical of glacially eroded bedrock.

Plucking and abrasion also occur beneath cold ice, though at slow rates, and are probably restricted to places where the ice thickness is small.

Where the glacier bed is composed of unlithified sediment, subglacial measurements show that deformation can produce very large discharges of subglacial material, which makes this a potential agent of very rapid subglacial landform production. The heterogeneity of subglacial sediment leads to spatially variable rates of deformation, and it is suggested that relatively stronger parts of the sediment body may form the nuclei for drumlin and mega-flute formation.

Whereas unlithified unfrozen sediment deforms beneath the glacier rather than being incorporated within it, ice-cemented subglacial sediments can behave like bedrock, because of their relative rigidity, and are readily plucked and incorporated englacially. They may also deform beneath the glacier.
A Theoretical Model of Glacial Abrasion
Authors: Bernard Hallet
Published: September 2017

Preliminary results of a quantitative model of glacial abrasion are presented. The analysis, which is constructed within a framework of modern glaciological views of processes near to the bed, is aimed at modeling abrasion under a temperate glacier whose basal layers contain only occasional rock fragments. It does not simulate abrasion by debris-rich ice or by subglacial drift. Calculations of abrasion-rates reduce to evaluations of the forces pressing rock fragments against the glacier bed and of the rates at which they are moved along the bed. The estimated viscous drag induced by ice flow toward the bed due to basal melting is generally the dominant contribution to this contact force. Although the analysis shares several important elements with the pioneering study of Boulton ([c1974]), sufficient fundamental differences in the modeling lead to distinctly different conclusions. Several new results are noteworthy: (1) other parameters being equal, abrasion will tend to be fastest where basal melting is most rapid, (2) glacier thickness does not affect abrasion through its influence on basal pressures, and (3) lodgement of rock fragments is only possible if the sliding velocity is very low, equivalent to the rate of basal melting.
The Flow of Ice, Treated as a Newtonian Viscous Liquid, around a Cylindrical Obstacle Near the Bed of a Glacier
Authors: Morris E. M.
Published: September 2017

This paper describes an analytical solution of the equations of motion and heat conduction for ice flowing around a cylindrical solid inclusion and over a solid plane boundary. This is intended to be a simplified representation of the flow of clean glacier ice around a stone and over a rigid rock bed. The ice is treated as a Newtonian viscous liquid and the equations are solved in two dimensions. Regelation boundary conditions are applied at both ice–rock interfaces. It is found that finite solutions for the temperature and stream function only exist for the special cases in which two dimensionless critical wavelengths are zero. That is, unless the stone is very far from the glacial bed, the classical regelation boundary conditions cannot be obeyed over the whole of its surface.
Simulated Glacier Sliding over an Obstacle
Authors: Brepson R.
Published: September 2017

The sliding of temperate ice over two obstacles with sine-wave profiles (wavelength, 0.53 m; maximum slope, 0.22) and low thermal conductivity has been reproduced at full scale within a steel chamber. As expected, large cavities form between the ice and the obstacles so that the drag is limited. However, the delayed elasticity of bubbly ice modifies the expected behaviour. At the base of the ice a fine-grained, bubble-free blue ice layer develops. The shear strain concentrates on the up-stream side of bumps and in the blue ice layer. Tap-water ions enhance tertiary creep-rates.
On the Origin of Stratified Debris in Ice Cores from the Bottom of the Antarctic Ice Sheet
Authors: Gow A. J. , Epstein S. , Sheehy W.
Published: September 2017

Cores from the bottom 4.83 m of the Antarctic ice sheet at Byrd Station contain abundant stratified debris ranging from silt-sized particles to cobbles. The nature and disposition of the debris, together with measurements of the physical properties of the inclosing ice, indicate that this zone of dirt-laden ice originated by “freezing-in” at the base of the ice sheet. The transition from air-rich glacial ice to ice practically devoid of air coincided precisely with the first appearance of debris in the ice at 4.83 m above the bed. Stable-isotope studies made in conjunction with gas-content measurements also confirm the idea of incorporation of basal debris by adfreezing of melt water at the ice―rock interface. It is suggested that the absence of air from basal ice may well constitute the most diagnostic test for discriminating between debris incorporated in a melt―refreeze process and debris entrapped by purely mechanical means, e.g. shearing. We conclude from our observations on bottom cores from Byrd Station that “freezing-in” of basal debris is the major mechanism by which sediment is incorporated into polar ice sheets.
The Debris-Laden Ice at the Bottom of the Greenland Ice Sheet
Authors: Herron Susan , Hoar  , Langway Chester C.
Published: September 2017

The 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 0.24ººby 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 CO2levels, and low O2levels 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.
Depolarization of Radio Waves can Distinguish between Floating and Grounded Ice Sheets
Authors: Woodruff A. H. W. , Doake C. S. M.
Published: September 2017

Polar ice is now thought to be marginally birefringent at radio echo-sounding frequencies. An experiment on the polarization behaviour of 60 MHz radio echoes from the bed of both ice shelf and land ice in Antarctica showed a marked difference in the returned polarization. It appears that differences in electrical properties or roughness of the reflecting boundary cannot explain our results. We suggest that there is a large change in the birefringence of the ice sheet at the hinge zone, caused by the effect of tidal strain on crystal orientation. This would imply a minimum value of the radio-frequency anisotropy in permittivity for the single crystal of (0.52±0.8)%. Therefore polarization changes could allow floating and grounded ice to be distinguished.
Energy Dissipation During Subglacial Abrasion at Nisqually Glacier, Washington, U.S.A.
Authors: Metcalf Richard C.
Published: September 2017

This study examines the effect of subglacial abrasion on the basal sliding term of the gravitational energy balance of the dynamic, temperate Nisqually Glacier on Mount Rainier, Washington, U.S.A. Subglacial water flux is estimated as 3 × 107 m3 a–1 and suspended sediment flux as 3 × 107 kg a–1. Suspended-sediment flux is assumed to represent, within an order of magnitude, the annual mass eroded by subglacial abrasion.

Subglacial abrasion involves both brittle fracture and plastic deformation. Field observations of bas-relief and grooved depression striations appear to have exact counterparts in rock mechanics experiments approximating subglacial velocities and normal stresses. Boulton's ([Cl974]) abrasion model and a new attritivity model proposed herein are shown to predict subglacial abrasion-rates within the limits of natural variability and the error range of measurements. The first crude gravitational energy balance for lower Nisqually Glacier (1.96 km2) is attempted and probably has only order-of-magnitude accuracy. The importance of subglacial abrasion in dissipating basal sliding energy at Nisqually Glacier is confirmed.
Pressure-Melting Effects in Basal Ice of Temperate Glaciers: Laboratory Studies and Field Observations Under Glacier D’Argentière
Authors: Goodman D. J. , King G. C. P. , Millar D. H. M. , Robin G. de Q.
Published: September 2017

The suggestion that patches of basal ice may freeze to the bed of a glacier due to certain regelation effects has been tested in the laboratory by applying high hydrostatic pressures to ice samples at the pressure-melting point. During compression, ice temperatures follow the pressure-melting point closely, but after rapid decompression the ice temperature at first returns only half to three-quarters of the way to the pressure-melting point, after which it appears to warm by thermal conduction from outside the ice sample. If the moving ice at the base of a glacier behaves in the same way as it is exposed to changing pressure fields, frozen patches at bedrock are to be expected.

Records of strain variations in a tunnel beneath Glacier d’Argentière show two types of strain events. The first is a rapid jump or offset in the recorded strain, while the second are strain excursions, initiated by a change in strain over a period up to ten seconds, followed by a gradual recovery to the original strain over some minutes. It is suggested that the offset events are due to nearby stress release due to fracturing of frozen patches of ice at the bedrock while the strain-excursion events show the more distant adjustment of the glacial bed to the former events due to the time lags associated with changes of water-film thickness and regelation heat flow.
Observations Within Cavities at the Bed of the Glacier Østerdalsisen, Norway
Authors: Theakstone Wilfred H.
Published: September 2017

Basal ice at the glacier Østerdalsisen commonly deforms under stress within cavities at the glacier bed. Some ice subject to rapid strain, however, fails in a brittle manner. The creep-rate of basal ice is influenced by sediment particles within it, and by ice grain-size and structural anisotropy; a flow law for such ice has not been derived experimentally. Near the glacier bed, particles enclosed in ice may migrate as a result of stress concentration, bubbles may be flattened, and anisotropic structures may develop. Recrystallization leads to grain-size changes. Both regelation spicules and layers of regelation ice, generally thin, form within subglacial cavities but their occurrence is limited. Regelation-ice formation has a significant influence on the distribution of rock debris at the ceilings of subglacial cavities.
Geometry of Former Subglacial Water Channels and Cavities
Authors: Walder Joseph , Hallet Bernard
Published: September 2017

The spatial pattern of the formerly active processes of water flow, cavitation, abrasion, dissolution, and precipitation at the base of a small cirque glacier has been reconstructed by detailed mapping of surficial features on recently deglaciated limestone bedrock near the glacier terminus. Our interpretation of these features, which reflect basal conditions averaged over a period of several or several tens of years, leads us to the following conclusions:

1.

A nearly continuous, non-arborescent network of cavities and incised channels existed and probably acted as the primary drainage of melt waters. This network evolved through time as many channels were filled, perhaps intermittently, by basal ice.

2.

At least 20% of the glacier sole was separated from the bed by water-filled cavities. The rest of the glacier–rock interface characteristically comprises a very thin water film.

3.

Abrasion was locally intensified, relative to chemical alteration, in 5–10 m wide zones paralleling the ice-flow direction, perhaps as a result of locally enhanced sheet flow of subglacial water.
Subglacial Constructions and Investigations At Bondhusbreen, Norway
Authors: Wold B. , Østrem G.
Published: September 2017

For the construction of a hydro-electric power station in western Norway, a diversion tunnel was made to collect subglacial melt water under an outlet glacier from the Folgefonni ice cap. Many investigations were carried out by glaciologists and engineers before the project could begin, and several unexpected problems arose during the completion of the project. This paper deals with some of the problems and how they were solved.

To avoid coarse glacier-carried material from being flushed into the water-collecting tunnel system, a large sedimentation chamber was constructed in the bedrock under the glacier. The dimensions of this huge chamber were decided from sediment-transport studies in the glacier stream and from studies of old bottom deposits in a lake close to the glacier front.

Ice-velocity measurements were made on the glacier surface and similar studies were attempted in sub-glacial ice caves made by spraying hot water near the glacier bed, where the ice is 170 m thick.

The subglacial water-drainage system was studied from a horizontal tunnel constructed in the bedrock under the glacier. Some preliminary conclusions are drawn from these studies.

In future, it will still be possible to undertake subglacial studies because inspection tunnels have been left in the bedrock, and the accessibility is relatively good.
Erosion by Continental Ice Sheets
Authors: Whillans I. M.
Published: September 2017

Some of the problems with earlier theories for erosion and transport by ice sheets are discussed, and it is noted that those theories cannot simply account for the often-reported finding that most till is derived from bedrock only a few tens of kilometers up-glacier. Considerations of the mass balance of debris in transport lead to the conclusion that ice sheets are capable of transporting most debris only a short distance.

The theory that the break-up of bedrock is mostly a preglacial process is developed. The advancing ice sheet collects the debris and then deposits it after a short travel. As the ice sheet first advances over the regolith, debris is frozen onto the base and is carried until basal melting due to geothermal and frictional heat causes lodgment till deposition. Most debris is deposited during the advance of the ice sheet and is carried only a short distance. A generally small amount of debris is carried at higher levels and is deposited during ice standstill and retreat as melt-out and ablation tills.

The present theory makes many predictions, among them, that most till units are not traceable over long distances, that thick till sequences represent unstable glacier margins and not necessarily long periods of glacier occupation, and that lodgment tills are to be interpreted in terms of ice advances and ablation tills in terms of ice retreats.

This paper is published in full in Journal of Geology, Vol. 86, No. 4, 1978, p. 516–24.
Ice-Sheet Erosion—A Result of Maximum Conditions?
Authors: Sugden D. E.
Published: September 2017

Understanding the relationship between the morphology of former ice-sheet beds and glaciological processes is handicapped by the difficulty of establishing which stage of a cycle of ice-sheet growth and decay is responsible for most erosion. Discussions at this conference and in the literature display a variety of opinions, some favouring periods of ice-sheet build up, others periods of fluctuations, and still others steady-state maximum conditions. Here it is suggested that there is geomorphological evidence which points to the dominance of maximum conditions.

Along the eastern margins of the Laurentide and Greenland ice sheets there is a sharp discontinuity between Alpine relief which stood above the ice-sheet surface at the maximum and plateau scenery which was covered by the ice sheet. Often the two types of relief are adjacent and yet separated by an altitudinal difference of only 100–200 m. The existence of an abrupt rather than gradual transition from one relief type to the other suggests that most glacial sculpture must have taken place while the ice sheet was at its maximum extent. In other geomorphological situations where high mountains were submerged by ice sheets, the major erosional landforms are frequently found to relate to ice sheets rather than to local mountain glaciers, again suggesting the dominance of erosion during full ice-sheet conditions. Finally, the identification of patterns of glacial erosion on an ice-sheet scale in North America and Greenland points to erosion when the ice sheets were fully expanded, rather than to the variable flow conditions associated with growth or decay.

If ice-sheet erosion is accepted as being a result of maximum conditions, then it places certain constraints on glacial theory, for example the need to develop theories of glacial erosion which apply beneath ice thicknesses of several thousand metres. It also suggests that the use of steady-state models of ice sheets is likely to be a profitable way of relating glaciological processes to the morphology of former ice-sheet beds.
Estimation of Basal Heat Flux Over Ice-Covered Areas From Radio Echo-Sounding
Authors: Drewry David J.
Published: September 2017

Two fundamental boundary conditions for basal ice may be recognized by radio echo-sounding: ice–rock and ice–water interfaces. The latter is identified on the basis of horizontal echoes displaying slow fading, high persistent returned power, and with a reflection coefficient lying between –1 and –3 dB. Such water, located beneath an ice sheet, provides a known limiting condition to the vertical temperature profile and allows more precise calculation of the basal temperature gradient and estimation of the heat flux through the sole.
Pressure-Melting Within The Basal Ice of an Alpine Glacier Indicated by The Chemical Composition of Regelation Ice
Authors: Souchez R. , Lemmens M. , Lorrain R. , Tison J.-L.
Published: September 2017

In the heat-pump effect developed by Robin (1976), pressure-melting within the basal ice mass, as distinct from processes at the ice–bedrock interface, can be responsible for the formation of excess water in zones of high-pressure ice up-stream of obstacles. This water is squeezed out of the ice by the pressure and can refreeze at the interface to form regelation ice down-stream.

The peculiar chemical characteristics of regelation ice at the base of Glacier de Tsijiore Nouve in the Swiss Alps can only be explained by refreezing of this squeezed water. Melting at the interface up-stream of bed protuberances and refreezing of these melt waters downstream, as implied in weertman’s theory, can be excluded in this case.

This paper is published in full in Nature, Vol. 273, No. 5662, 1978, p. 454–56,
Characteristics and Origins of the Debris and Ice, Matanuska Glacier, Alaska
Authors: Lawson D.E.
Published: September 2017

The physical characteristics of the ice and debris of the Matanuska Glacier, Alaska (lat. 61° 47’, long. 147° 45’) and their consistent variation in a vertical stratigraphic column of the glacier indicate multiple origins for both. The two zones of ice recognized in the glacier are the upper englacial zone, which comprises the bulk of the glacier (est. 300 m thick), and the thin (3 to 15 m thick) basal zone, which contains an estimated 97% of the sediment transported in the glacier. The physical characteristics of the ice and the quantity and mode of distribution of debris in it define two ice facies in each zone. The englacial zone consists mainly of the debris-poor (0.002 volume per cent) diffused facies. White coarse-bubbly ice and blue coarse-clear ice (2 to 10 cm diameter) comprise most of this facies. The bubble-rich banded facies (debris bands) contains abundant debris (25 to 50 volume per cent), varies in lateral and vertical extent, and occurs randomly in the diffused facies.
On the Temperature Response in Ice Sheets to Radioactive Waste Deposits
Authors: Philberth K.
Published: September 2017

Disposal of the the radioactive waste from the peaceful use of nuclear energy in the central region of the ice sheet of Greenland or Antarctica has been proposed. This paper demonstrates that an area only 100 km2 on the ice divide is sufficient to dispose of the high-level waste of the whole world for the next 30 years without hazard. The thermal power of the radioactive decay makes the waste containers melt down to a depth of 2 km. Thus the total disintegration heat is spread through a volume of 100 km2 × 2 km. The mean temperature increase in this volume is a few degrees. The temperature increase does not influence the rheology of the ice sheet at any time: for a few ten-thousand years after the dumping the area concerned is too small; later the temperature increase is too small.
Measured and Computed Temperature Distributions in the Law Dome Ice Cap, Antarctica
Authors: Budd W.F. , Young N.W. , Austin C.R.
Published: September 2017

By 1969 considerable data had been collected over Law Dome from surface measurements. These included surface elevation, ice thickness, accumulation rates, ice movement and strain-rates, surface mean temperatures, and several temperature-depth gradients. Since then core drilling up to 380 m in depth has been carried out from the summit to the coast where the cores reached close to the bed. The bore holes have been concentrated on two main flow lines: one to Cape Folger and the other to Cape Poinsett. The bore-hole temperatures give a clear indication of the temperature distribution throughout the ice cap.

Numerical modelling shows that the measured deep temperatures closely match the steady-state temperature distribution calculated from the present regime. The variations in the temperature profiles over the dome are primarily associated with the flow regime.

The Cape Folger line has low accumulation rates and low velocities which results in positive surface temperature-depth gradients increasing towards the coast. By contrast the Cape Poinsett line has high accumulation rates and high velocities which result in a large negative temperature-depth gradient there. The profile at the Dome summit is close to isothermal primarily due to the high accumulation rates and lack of horizontal motion.
Some Thermal Effects of Bubbles in Temperate Glacier Ice
Authors: Raymond C.F.
Published: September 2017

Gas bubbles in core samples from the Blue Glacier, Washington, were observed to be partially filled with liquid. The time and spatial dependence of liquid content in the bubbles demonstrates that the in situ liquid content of the bubbles was small and liquid appeared in the bubbles as a consequence of heat flow into the sample after collection. An effective bulk heat capacity for wet bubbly ice is derived and used to analyze the relaxation process and it is shown that the warming of samples is controlled by an effective heat capacity two or more orders of magnitude larger than for pure ice. The relaxation process presents a practical difficulty for measurement of in situ water content from core samples and the behavior of the bubbles indicates that at positions in a temperate glacier where bubbles have pressure in excess of the ice stress, bubbles may control the ice temperature and significantly restrict water flow through veins.
Is the Basal Ice of a Temperate Glacier at the Pressure Melting Point?
Authors: Robin G. de.Q.
Published: September 2017

Certain aspects of the flow of glaciers suggest that molecular adhesion contributes to basal friction of glaciers sliding at speeds below those of surging glaciers. Laboratory experiments indicate that this will only occur if some part of the ice-rock contact is “cold”, that is below the pressure melting point (p.m.p.), a few tenths of a degree being sufficient. Field evidence is scanty, but suggests that such cold patches may exist at the base of a temperate glacier.

Discussion of pressure-melting within the basal ice mass, as distinct from processes at the ice-rock contact, indicate that excess water is formed in zones of high-pressure ice up-stream of obstacles. If this water is squeezed out of the ice by the pressure, we have a simple heat pump that will tend to cool the basal ice. The ice will warm again as the result of thermal conduction and internal friction, but before reaching the p.m.p. it can produce "cold" patches of the ice-rock contact, roughly estimated to be from 0. 1 to 1.0 m in extent.

Another factor that could cause intermittent cold patches at the ice-rock interface arises from changes of basal water pressures with time beneath a glacier. If a major part of the weight of a glacier is supported by a thin water film at a relatively low pressure and by a small proportion of water film in which pressures are high, then over a large area the water pressures must balance the weight of ice. If however the pressure in the low-pressure film rises, the smaller high-pressure areas of stress concentration will suffer a proportionately greater decrease of pressure to maintain the total balance between pressure and weight, If changes take place rapidly, in a matter of hours, then in areas of stress concentration of the order of a metre or more across, the water film will freeze to the bed as stresses are relieved. This could cause stick-slip motion in a temperate glacier.

Pressure-temperature effects at the ice-rock interface can help to explain certain features of glacial erosion, such as intense grinding on the top surface of a roche moutonée and plucking on the down-stream side.
15m Deep Temperatures in the Glaciers of Mont Blanc (French Alps)
Authors: Lliboutry L. , Briat M. , Creseveur M. , Pourchet M.
Published: September 2017

The top of Mont Blanc is a dry snow zone. The cold infiltration zone extends between about 4 300 and 3 800 m. Its lower limit is lined by large cracks and ice cliffs, similar to bergschrunds. Near rock faces this limit is the bergschrund, which can descend as far as the 0°C isotherm of the mean annual air temperature, 3 100-3 200 m- At Col du Dôme (c, 4 250 m), 15 m deep temperature has increased 1.8 deg between the years 1911 and 1973, probably due to infiltration which happened there in the last few years. The ice in the ablation area is entirely temperate, while in dryer areas of the Alps it may be at 1°C to — 3°C in the vicinity of the firn line.
Thermal Regulation of Glacier Surging
Authors: Clarke Garry K.C.
Published: September 2017

A necessary condition for a glacier to surge by thermal instability is that the glacier be cold with basal ice at or near the melting point. Deep temperature measurements show that two small surge-type glaciers in the Yukon Territory meet this requirement, but shallow measurements in three other surge-type glaciers suggest a temperate regime. If the latter observations are accepted, not all surges are thermally controlled: if a single mechanism accounts for all surges it cannot be thermal instability.

In this paper it is argued that thermal instability remains a viable mechanism for explaining surges of many cold glaciers, and that regardless of the underlying mechanism, thermal processes must at least have a major influence on the surge behavior of cold glaciers.

Two numerical modelling experiments are described. The first involves a one-dimensional model which shows that thermal control can account for the remarkably constant surge cycle found in some glaciers. The second, a two-dimensional model of the time-dependent temperature structure of a surge-type glacier, shows that the relative amounts of temperate and cold basal ice can change considerably as the surge cycle progresses. This variation alone may be sufficient to explain surges, but even if this is not the case, thermal processes must affect the timing of surges in many cold glaciers.

A compelling feature of the thermal instability mechanism is that it offers an explanation of the factors controlling the non-random geographical distribution of surge-type glaciers. For a glacier to have a cold surface and near-temperate bed, the ice thickness, temperature, and geothermal flux must be fortuitously related.
Post-Surge Temperatures in Steele Glacier, Yukon Territory, Canada
Authors: Clarke Garry K.C. , Jarvis Gary T.
Published: September 2017

Deep ice temperatures measured at four widely spaced sites on Steele Glacier show that the thermal regime was profoundly influenced by the 1965-66 surge advance. Three of four measured temperature profiles are "anomalous" in that the upper 100 m of ice is far from thermal equilibrium. Water penetration during the surge is the probable cause of these anomalies. Insufficient data are available to predict the basal ice temperature.
Reports on Current Work Temperatures in the Devon Island Ice Cap, Arctic Canada
Authors: Paterson W.S.B.
Published: September 2017

Temperatures have been measured in a 299 m bore hole that reaches the base of the ice near the divide of the main ice cap on Devon Island in the Canadian Arctic Archipelago. Temperature ranges from — 23.0°C at a depth of 20 m to — 18.4°C at the bottom. The difference between surface and bottom temperatures is about 1.5 deg less than expected for a steady state. Recent climatic warming seems the most likely explanation of the discrepancy. The temperature gradient in the lowest 50 m is approximately linear and corresponds to a geothermal heal flux of 1.5 h.f.u. This value may be invalid, however, because temperatures at and below this depth have probably been perturbed by changes of surface temperature during the past several thousand years, particularly by the warming at the end of the last glaciation. A detailed analysis of the results is in progress.
Creep Instability of Ice Sheets
Authors: Clarke Garry K.C.
Published: September 2017

The equation governing the growth or decay of a temperature perturbation T’ in an ice slab under shear stress σxy is

where K and k are respectively the thermal conductivity and diffusivity of ice, KB-v is the advection velocity normal to the bed and

is the rate of increase of strain heating with temperature assuming a power law for flow. For a slab of infinite thickness under constant stress and at constant ambient temperature, T Fourier analysis gives -k2+a/k < o as the condition for stability where k is the wave number of a sinusoidal perturbation. When the slab has finite thickness the stability depends on the sign of the eigenvalues λm of the perturbation equation and on the boundary condition at the ice-rock interface. In general the eigenfunctions and eigenvalues must be found by approximate methods such as the Rayleigh-Ritz procedure but in the case where the stress and ambient temperature are constant over the slab thickness and there is no advection the eigenfunctions are either sines or cosines depending on the boundary conditions.

In this special case the stability condition is

if the bed is frozen and

if it is at the melting point. The eigenvalue associated with the smallest value of m is the least stable so the maximum stable thickness is thus h = ½ π(a/K)1/2 if the bed is frozen or h = π (a/K)1/2 if it is at the melting point. For typical flow-law parameters these depths are around 250 m and 500 m respectively. The eigenvalues are related in a simple way to the growth or decay rates of the eigenfunctions: (K λm)–1 is the time constant for the mth eigenfunction.

Depth-dependent stress, temperature, and advection have a marked effect on stability. A slab in which stress and temperature increase to values B and TB at the bed is considerably more stable than a slab held at constant stressσB and a constant temperature TB. Advection normal to the bed also has a major influence on stability. If the advection velocity is taken to vary linearly with depth and the bed is frozen, the effect of upward advection is to decrease stability and of downward advection to increase it. When the bed is temperate the effect of advection is more complex: downward advection increases stability but upward advection may increase or decrease it depending on the magnitude of the advection velocity.
Abstracts of Papers Presented at the Symposium but not Published in Full in this Volume Computer: Modelling of Temperature Distributions in Polar Ice Sheets
Authors: Budd W.F. , Young N.W.
Published: September 2017

It is now practicable to construct complete three-dimensional primitive- equation models of ice flow in which all the input may be time dependent. The input consists of bedrock and ocean distribution, accumulation net balance, ice-surface elevation- temperature relation, and the thermal and flow parameters of the ice. The main limitations on this type of model is the extensive demand of computation time. Thus simplified two-dimensional models have been developed for detailed flow-line studies, and single-column models have been used extensively for analysing the few deep bore-hole temperature profiles.

The main feature of the measured temperature profiles reflect the current steady-state regime at each location. Deviations from the steady state are caused by time variations of any of the variables such as surface temperature, accumulation rate, ice thickness, velocity, etc.

Measurements of stable-isotope ratios in the ice cores provide an indication of past temperatures which has been confirmed by the analysis of the temperature profiles. However the temperature changes could be either due to surface elevation changes or climate changes. Gas volumes in the core show promise of providing an indication of past elevations. Annual variations of the isotopes give indications of past accumulation rates. The determination of past velocities, however, requires velocity-temperature coupled models with more precise flow-law information.

Three-dimensional models are necessary to study past variations of the flow-line pattern. Finally the sliding and surging models recently developed need to be incorporated into the cold ice-sheet models.