bluuebunny/crossref_metadata_2025 huggingface dataset:
The Dynamics of Marine Ice Sheets
Authors: Thomas Robert H.
Published: September 2017

Marine ice sheets rest on land that, for the most part, is below sea-level. Ice that flows across the grounding line, where the ice sheet becomes afloat, either calves into icebergs or forms a floating ice shelf joined to the ice sheet. At the grounding line there is a transition from ice-sheet dynamics to ice-shelf dynamics, and the creep-thinning rate in this region is very sensitive to sea depth; rising sea-level causes increased thinning-rates and grounding-line retreat, falling sea-level has the reverse effect. If the bedrock slopes down towards the centre of the ice sheet there may be only two stable modes: a freely-floating ice shelf or a marine ice sheet that extends to the edge of the continental shelf. Once started, collapse of such an ice sheet to form an ice shelf may take place extremely rapidly. Ice shelves which form in embayments of a marine ice sheet, or which are partially grounded, have a stabilizing influence since ice flowing across the grounding line has to push the ice shelf past its sides. Retreat of the grounding line tends to enlarge the ice shelf, which ultimately may become large enough to prevent excessive outflow from the ice sheet so that a new equilibrium grounding line is established; removal of the ice shelf would allow retreat to continue. During the late-Wisconsin glacial maximum there may have been marine ice sheets in the northern hemisphere but the only current example is the West Antarctic ice sheet. This is buttressed by the Ross and Ronne Ice Shelves, and if climatic warming were to prohibit the existence of these ice shelves then the ice sheet would collapse. Field observations suggest that, at present, the ice sheet may be advancing into parts of the Ross Ice Shelf. Such advance, however, would not ensure the security of the ice sheet since ice streams that drain to the north appear to flow directly into the sea with little or no ice shelf to buttress them. If these ice streams do not flow over a sufficiently high bedrock sill then they provide the most likely avenues for ice-sheet retreat.
Ice Shelves: A Review
Authors: Thomas Robert H.
Published: September 2017

Ice shelves form where ice flows off the Antarctic ice sheet onto the sea to produce rather flat slabs of floating ice which, for the theoretician, are the simplest of all large ice masses. Boundary conditions are well defined, conditions change very slowly over distances that are large compared with ice thickness, and horizontal velocities are independent of depth. Unconfined ice shelves can be used as giant creep machines to investigate the ice flow law at low stresses. Further inland, where movement is hampered by obstructions such as grounded ice rises and by shear between the ice shelf and its sides, the ice shelf transmits a backpressure which tends to restrict drainage from the ice sheets that feed it. Wastage from ice shelves is principally by calving and by bottom melting. There has been no direct measurement of bottom-melting rates, but indirect evidence suggests that, near the seaward edges of ice shelves, bottom-melting rates may exceed one metre per year, with significant melting within about 100 km of the ice front. Further inland there may be bottom freezing, and analysis of cores taken from the Amery Ice Shelf indicate that bottom-freezing rates average 0.5 m a–1over a distance of 200 km. Such high freezing-rates are probably exceptional, and, beneath the Ross Ice Shelf, freezing appears to be insignificant even at a distance of 400 km from the ice front.

Because of their accessibility ice shelves have been studied in considerable detail, but many problems remain. In particular we need to improve our understanding of basal flux, ice-shelf dynamics near the grounding line, the calving of icebergs, and the state of equilibrium of ice rises. In addition there is a clear need for basic data from the Filchner-Ronne ice shelf.
Finite-Element Simulation of the Barnes Ice Cap
Authors: Emery J. J. , Hanafy E. A. , Holdsworth G. H. , Mirza F.
Published: September 2017

The finite-element method is being used to simulate glacier flow problems, with particular emphasis on the surge behaviour of the Barnes Ice Cap, Baffin Island. Following an advanced feasibility study to determine the influence of major factors such as bed topography and flow relationships, a refined simulation model is being developed to incorporate realistically: the thermal regime of the ice mass; large deformations during flow and sliding; basal sliding zones; a temperature and stress dependent ice flow relationship; mass balance; and three-dimensional influences. The findings of the advanced feasibility study on isothermal, steady-state flow of the Barnes Ice Cap are presented in the paper before turning to a detailed discussion of the refined simulation model and its application to surging. It is clear that the finite-element method allows necessary refinements not available to analytical approaches.
A Numerical Investigation of The Large Scale Dynamics of Sea Ice
Authors: Hibler W. D.
Published: September 2017

Several numerical simulations of the Arctic ice cover over a seasonal cycle are carried out. Two different types of constitutive laws are examined: rigid plastic and linear viscous. In both cases, the strength of the ice interaction is taken as a function of ice thickness and compactness. The thickness and compactness, in turn, evolve according to continuity equations which include thermodynamic source and sink terms. The simulations with the rigid-plastic law reproduce reasonable geographical ice-thickness variations, ice outflow, and ice-velocity characteristics. The viscous simulations (especially the Newtonian viscous case) produce less satisfactory geographical ice thickness variations, and near-shore velocity characteristics. In addition the Newtonian-viscous simulation produces highly unrealistic ice-edge effects in summer. The results are discussed in terms of the relative magnitudes of the shear and compressive strengths, and in terms of the non-linear versus linear dependence on deformation in the ice rheology. The portion of this study employing a plastic constitutive law is published in full in Journal of Physical Oceanography, Vol. 9, No. 4, 1979, p. 815–46.
Surface Contours and Flow Pattern of a Perfectly Plastic Three-Dimensional Ice Sheet With Arbitrary Bottom and Edge Topography
Authors: Reeh Niels
Published: September 2017

The differential equation determining the elevations of a perfectly plastic three-dimensional steady-state ice sheet is set up. Analytical solutions of the equation are obtained in two simple cases, viz. (1) an ice sheet on a horizontal base with an arbitrary curve as edge and (2) an ice sheet ona plane but sloping bed, with an edge composed of straight-line segments. The solutions are discussed in particular with reference to the development of ice divides and ice streams.
Basal friction of Ice Stream E, West Antarctica
Authors: MacAyeal Douglas R. , Bindschadler Robert A. , Scambos Theodore A.
Published: September 2017

We use surface velocity derived from sequential Landsat imagery and a control method to estimate the basal-friction distribution of a major West Antarctic ice stream. The area-averaged basal stress is approximately 1.4 × 104 Pa, or about 29% of the area-averaged driving stress of 4.9 × 104 Pa. Uncertainty of the derived area-averaged basal stress is difficult to assess and depends primarily on spatial variation of the flow-law rate factor in the constitutive law. Spatial variation associated with depth-averaged temperature variation gives an uncertainty of approximately ±103 Pa. Approximately 60% of the ice stream has a basal-stress magnitude less than 104 Pa, and approximately 30% has less than 103 Pa. These characteristics suggest the presence of a mechanically weak, water-charged subglacial till. Small-scale sticky spots where basal friction exceeds the area-averaged driving stress are scattered irregularly across the subglacial regime and comprise approximately 15% of the ice-stream area. Sticky spots cluster in regions where Landsat imagery suggests structural features in the underlying bedrock.
The formation and morphology of ice stalactites observed under deforming lead ice
Authors: Perovich Donald K. , Richter-Menge Jacqueline A. , Morison James H.
Published: September 2017

During the LeadEx main field experiment, held in April 1992 in the Alaskan Beaufort Sea, a number of large ice stalactites were observed growing under young lead ice. Formation of the stalactites was associated with rafting of the thin, highly saline ice. The rafting caused the brine to drain rapidly from the ice at a temperature well below the freezing point of the surrounding water, which in turn caused ice to form in a hollow cylinder around the brine plume. Within a 15 h period after the rafting event, the stalactites, which were located approximately 10 m apart in a line along the upwind edge of a 150 m wide lead, had grown to a length of 2 m. A detailed structural analysis of the upper part of one of these stalactites revealed that the interior channel, down which the brine flowed, was bounded by a zone of frazil ice that developed into a shell of columnar ice. The growth of the columnar ice was directed radially outward and the c axes of these crystals were oriented perpendicular to their growth direction. Development of the stalactites illustrates the impact ice deformation can have on the process of brine rejection in freezing leads and potentially on the thermohaline structure of the upper ocean in the immediate vicinity of the lead.
Dry-flowing avalanche run-up and run-out
Authors: Mcclung D. M. , Mears A. I.
Published: September 2017

The prediction of run-up and run-out of dry-flowing avalanches is very important for land-use planning, design of run-out zone defenses and construction of risk maps in avalanche terrain. In this paper, we present a numerical dynamics model to predict the stop position of the tip of these avalanches when friction coefficients (internal and external), initial flow depth and incoming speed are specified for known path geometry in the run-out zone. We also compare our model to that in the Swiss guidelines and to field examples. The results of these calculations clearly define model differences and the implications of different choices of friction coefficients.
A new device for the measurement of air content in polar ice
Authors: Lipenkov V. , Candaudap F. , Ravoire J. , Dulac E. , Raynaud D.
Published: September 2017

A new device for measuring air content in polar ice has been designed, built and tested with 22 samples of Antarctic ice. The new technique is based on the barometric method which implies: (1) air extraction under vacuum by melting refreezing of the ice sample placed in a calibrated cell, and (2) accurate air-pressure and temperature measurements. The new apparatus simplifies the experimental procedure, decreases the duration of measurement and can eventually be used in the field. It provides results with an accuracy equivalent to or better than other methods previously used.
A phase-changing dry snowpack model
Authors: Gray J.M.N.T. , Morland L.W. , Morris E.M.
Published: September 2017

An interacting continua framework is adopted to model a dry snow park, which is viewed as a three-constituent mixture composed of an ice matrix whose pore space is occupied by water vapour and dry air. We focus on the response of a one-dimensional vertical snowpack to changes in pressure and temperature at its surface. The time-scale of the surface forcing is assumed to be much longer than the time-scale for thermal transfers and phase change to take place. The constituents are, therefore, in thermal equilibrium with a common temperature Τ which is governed by a single bulk-energy balance. In addition, each constituent satisfies a mass and momentum balance. The constitutive postulates and external prescriptions necessary to close the system of equations are discussed in detail. Non-dimensional variables are then introduced formally to draw out the major balances in the equations and construct a reduced system that accurately models the dominant features in the snowpack. It is shown how the effects of phase change enter the leading-order balance. An iterative procedure is constructed to solve the system. Illustrations for the case of a sinusoidal annual temperature gradient imposed at the surface are presented.
Variations in snowpack melt on the Greenland ice sheet based on passive-microwave measurements
Authors: Mote Thomas L. , Anderson Mark R.
Published: September 2017

A simple microwave-emission model is used to simulate 37 GHz brightness temperatures associated with snowpack-melt conditions for locations across the Greenland ice sheet. The simulated values are utilized as threshold values and compared to daily, gridded SMMR and SSM/I passive-microwave data, in order to reveal regions experiencing melt. The spatial extent of the area classified as melting is examined on a daily, monthly and seasonal (May-August) basis for 1979–91. The typical seasonal cycle of melt coverage shows melt beginning in late April, a rapid increase in the melting area from mid-May to mid-July, a rapid decrease in melt extent from late July through mid-August, and cessation of melt in late September. Seasonal averages of the daily melt extents demonstrate an apparent increase in melt coverage over the 13 year period of approximately 3.8% annually (significant at the 95% confidence interval). This increase is dominated by statistically significant positive trends in melt coverage during July and August in the west and southwest of the ice sheet. We find that a linear correlation between microwave-derived melt extent and a surface measure of ablation rate is significant in June and July but not August, so caution must be exercised in using the microwave-derived melt extents in August. Nevertheless, knowledge of the variability of snowpack melt on the Greenland ice sheet as derived from microwave data should prove useful in detecting climate change in the Arctic and examining the impact of climate change on the ice sheet.
A fully three-dimensional finite-element model applied to velocities on Storglaciären, Sweden
Authors: Hanson Brian
Published: September 2017

A finite-element model that solves the stress-balance equations for glacier dynamics in three dimensions has been developed by extending previous flow-plane models. This model retains all terms of the stress tensor and uses a Glen-type power law for viscosity calculations. In the paper, the model is applied to Storglaciären, Sweden, to explore both the glacier’s dynamics and the model’s characteristics. Values of the stiffness parameter B of 0.20–0.22 MPa year1/n were required to match observed strain rates on Storglaciären. Overall velocities required imposition of a problematically small sliding speed. Stress fields implied by the model simulation showed that the glacier receives its largest driving force from a high-slope zone near the equilibrium line, and that a large proportion of the resistive stress comes from lateral drag. Lateral drag is enhanced on this glacier by being frozen to its sidewalls and by a turning of the main flow as it comes out of the main, or northern, cirque.
Hydraulic properties of subglacial sediment determined from the mechanical response of water-filled boreholes
Authors: Waddington Brian S. , Clarke Garry K. C.
Published: September 2017

Freezing of water-filled boreholes drives water into the subglacial bed and the associated pressure effects yield information about subglacial hydraulic properties. A numerical model describing the mechanical response of an unconnected borehole and the bed beneath it to this freezing forcing was developed, using a nonlinear transient visco-elastic ice-flow law and an approximate model of top-down freezing. The resulting system of equations was solved using the method of lines. Results agreed well with analytic solutions, when parameters were correctly chosen. Forward modelling of pressure records from three 1992 boreholes and three from other years indicated that the till underlying Trapridge Glacier has a hydraulic conductivity of 1.35-7.0 × 10−9m s−1. The model was also used to investigate the response of a borehole to sudden pressure changes. The response is very fast compared to pressure-sensor sampling rates; thus, the true basal signal is essentially unaffected by the presence of the borehole, except during the initial freeze-in.
Recession of Yanamarey Glacier in Cordillera Blanca, Peru, during the 20th century
Authors: Hastenrath Stefan , Ames Alcides
Published: September 2017

For Yanamarey Glacier in Cordillera Blanca, Peru, mostly situated between about 5000 and 4600 m, maps of the surface topography at a scale of 1: 5000 obtained by terrestrial triangulation for 1973, 1982 and 1988 and by aerial photogrammetry for 1948 and 1962 are compared with the glacier boundaries from a 1939 map and an undated maximum extent inferred from moraine morphology. The glacier length decreased from the maximum, 2800 m to 1600 m in 1948. and to 1250 m in 1988, with an accompanying decrease in area from 17 × 105 to 10 × 105 and thence to 8 × 105 m2. The shrinkage of ice volume was 35 × 106 m3 from the maximum to 1948. and 29 × 106 m3 from 1948 to 1988. compared to a total remaining ice volume of about 25 × 106 m3 in 1988. This quantitative assessment of mass-loss rates creates the observational basis for sensitivity studies of the climatic forcing.
A Three-Dimensional Polar Ice-Sheet Model
Authors: Jenssen D.
Published: September 2017

A three-dimensional model of the temperature and velocity distribution within any arbitrary-shaped ice mass is described. There is a mutual interaction in the model between the flow of the ice and its thermodynamics, since the flow law used in the model is temperature-dependent.

Ice growth in three dimensions is governed by mass accumulation through precipitation, by mass depletion through loss of ice over the ocean, and by continuity requirements. Phase changes at the base of the ice are accounted for. The model has been applied in art exploratory manner to the Greenland ice sheet. Changes in the ice shape and temperature are presented and discussed. The basic shortcoming of the model as here presented appears primarily due to the coarse finite-difference mesh used, and to an unsophisticated approach to modelling the boundary ice.
Structures in Ice Cliffs at the Snouts of Three Swiss Glaciers
Authors: Hambrey Michael J.
Published: September 2017

Three glaciers in Switzerland, Griesgletscher, Oberaargletscher and Vadrec da l’Albigna, terminate in lakes recently impounded for hydro-electricity generation. Calving at their snouts has produced excellent cross-sections which enable one to study the structures along almost complete vertical profiles when the lakes are empty. Each of the glacier cliffs displays a shallow synclinal structure which, by comparison with surface structures, is interpreted as the vertical expression of an arcuate foliation, originating in or below an ice fall or an area of transverse crevassing. Extensive minor folding of an earlier layering is associated with this foliation. Well-developed longitudinal foliation exposed at the surface is sometimes visible in these vertical sections, indicating that the structure can form at depth.
Dating of Greenland Ice Cores by Flow Models, Isotopes, Volcanic Debris, and Continental Dust
Authors: Hammer C.U. , Clausen H. B. , Dansgaard W. , Gundestrup N. , Johnsen S. J. , Reeh N.
Published: September 2017

The available methods for dating of ice cores are based on radioactive decay, ice-flow calculations, or stratigraphic observations. The two former categories are broadly outlined, and special emphasis is given to stratigraphic methods. Reference horizons are established back to A.D. 1783, in the form of elevated electrical conductivities due to fallout of soluble volcanic debris. Seasonal variations in the concentrations of insoluble microparticles and/or stable isotopes are measured over the entire 400 m lengths of three ice cores, recovered by Greenland Ice Sheet Program (GISP). The resulting absolute time scales are probably accurate within a few years per thousand. Techniques are outlined for re-establishing the approximate, original shape of heavy-isotope profiles that have been more or less smoothed by diffusion in firn and ice. Annual-layer thickness measurements on 24 increments down to 1130 m depth in the Camp Century ice core determine a flow pattern, consistent with that suggested by Dansgaard and Johnsen (1969), and a Camp Century time scale with an estimated uncertainty better than 3% back to 10000 years B.P.
The Dependence of Temperature Profiles in Ice Sheets on Longitudinal Variations in Velocity and Surface Temperature
Authors: Jones A. S.
Published: September 2017

Formulae for calculating temperature profiles in steady-state ice sheets are derived in terms of the horizontal and vertical velocities of the surface ice, and of the variation in surface temperature along the flow lines. Two models are considered: parallel flow and radial flow. In each case the result consists of a “stationary” term (equivalent to Robin's equation), a term dependent on the horizontal velocity, and a term arising from the temperature variations. This last term produces reversals in the temperature field such as are measured in practice.
Heat-Budget Measurements on the Quelccaya Ice Cap, Peruvian Andes
Authors: Hastenrath Stefan
Published: September 2017

During the June-August 1976 Quelccaya ice cap expedition, global, SW↓, and net long-wave radiation, LW↑↓, were measured through several complete day-night cycles, and for a wide range of cloudiness conditions. Field work further included albedo measurements along representative transects across the ice cap and lysimeter-type estimates of ablation. Automatic stations recording wind, temperature and sunshine duration were also installed.

Daily totals of SW↓ and LW↑↓ representative of completely clear and overcast days are derived. On this basis, empirical relationships allow the computation of monthly totals of radiation fluxes for an entire year from records of sunshine duration and temperature expected from the automatic stations.

The larger part of the plateau is situated above 5400 m and has an albedo mostly in excess of 80%. Sub-freezing temperatures essentially limit ablation to the energetically expensive sublimation. For clear sky, daily totals of SW↓and LW↑↓ are of the order of 312 and 53 W m–2, respectively. With the albedo found, net short-wave radiation SW↑↓ becomes of the same general magnitude as LW↑↓, and the energy left for ablation is near to nil. Cloudiness would reduce both SW↑↓ and LW↑↓, thus largely compensating the effect on the residual net radiation, SWLW↑↓. This is consistent with ablation measurements. Over the larger area of the ice plateau, ablation may be close to zero in a first approximation; some ablation, including melting, takes place near the lower-lying rim of the ice cap, and calving off steep cliffs seems to provide a major mechanism for the disposal of the ice mass.
Short Note on Slab-Avalanche Measurements
Authors: Perla R.
Published: September 2017

From a study of 205 slab avalanches it is concluded that failure initiates where the slope is 25° or steeper, that slab failure stress is in the range 102N m-2 to 104N m-2, and that the slab failure plane is most commonly at a temperature of -5°C or warmer. The study also indicates that the shear strength of weak layers varies approximately as the square of the density.
Simulated Glacial Abrasion
Authors: Mathews W. H.
Published: September 2017

Glacial abrasion has been simulated by turning a grindstone made of ice and crushed quartz between two stone plates within a domestic deep-freeze. Within limits, the speed of rotation, the normal loading, and the temperature of operation can be controlled. The tangential force exerted on one of the stone plates can be measured. The ratio of tangential to normal force, the effective coefficient of friction, is found to vary with the “roughness” of the grindstone, to increase gradually as abrasion proceeds, and to increase with decreasing velocity. Even at very low temperatures (to −26°C), abrasion products accumulated in a pad of ice frozen to the tablet “down-stream” from the grindstone, indicating that a water phase at least momentarily exists. The abraded surface of a fine-grained limestone displays grain-from-grain plucking dominating over abrasion of individual crystals. The abraded surface of a granite, by contrast, shows striations of crystals and rupture of cleavage along individual striae.
The Spectral Power Density and Shadowing Function of a Glacial Microrelief at the Decimetre Scale
Authors: Benoist J.-P.
Published: September 2017

Longitudinal profiles of roches moutonnées have been measured once every centimetre over a total length of more than 100 m. Only wavelengths in the range 3.6 cm < λ < 40 cm have been kept and analysed. Levels and their slopes have a symmetrical, non-Gaussian distribution. The spectral power density varies roughly as γ0ν–n (ν ═ wavenumber ═ 1/λ); n being the same for all the profiles (n ═ 2.36) and γ0 being dependent on the studied area. No significant difference has been found for the shadowing function of the different studied areas. It differs consistently from Smith’s theoretical function.
A Mathematical Approach to the Theory of Glacier Sliding
Authors: Fowler A. C.
Published: September 2017

Previous theories of glacier sliding are subject to the criticism that they are not properly formulated. Here we describe how the basal ice flow may be related to the bulk ice flow by means of the formal mathematical method of matched asymptotic expansions. A complete model of the basal sliding (involving coupled problems in ice, water film, and bedrock) may be rationally reduced by a dimensional analysis to a consideration of the ice flow only, and regelation may be neglected provided roughness is absent on the finest scales (<c. 1 mm). If the viscosity is supposed to be independent of the moisture content, then complementary variational principles exist which allow bounds on the drag to be obtained. In particular, these determine the magnitude of the basal velocity in terms of two crucial dimensionless parameters. Arguments are presented as to why realistic sliding laws should be taken as continuous functions of the temperature, and a (major) consequence of this assumption is mentioned. Finally the effect of cavitation is discussed, via an (exact) leading-order solution of the ice flow in the particular case of a Newtonian fluid and a “small” bedrock slope.
Discontinuous Flow, Ice Texture, and Dirt Content in the Basal Layers of the Devon Island Ice Cap
Authors: Koerner R. M. , Fisher D. A.
Published: September 2017

Surface-to-bedrock cores obtained with a CRREL thermal drill were taken in 1972 and 1973 from the top of the Devon Island ice cap. There are very pronounced variations in oxygen isotope, micro-particle concentration, and ice texture in the lowermost 5 m of the core. There is a section of isotopically cold, very fine bubbly ice with high micro-particle concentrations between 2.6 and 4.4 m above the bed, considered to represent the Last Ice Age. There is coarse, isotopically warm, clean ice above and below this. For 1.2 m above the bed, the ice is finer again with high micro-particle concentrations but it shows very low bubble concentration and is isotopically the warmest in the core. While the broad variations are common to both cores, in detail there are significant variations despite the fact that the cores were taken only 27 m apart. The variations, when analysed statistically, show that at least 25–30% of the originally continuous profile is missing from each core. Faulting within the near-bedrock ice may be responsible for some of the effect but bubble fabric also gives evidence for irregular non-laminar flow. Because of the strong relationship between crystal size and micro-particle concentrations in the Devon Island cores, it is suggested that the fine-grained nature of dirty layers in the Antarctic and Greenland ice sheets is due to the effect of the dirt inclusions and not of shearing. Steep isotopic gradients in the Devon Island cores are shown to be evidence for possible shearing, which does not effect any change in the crystal texture. Clear ice near the bed is considered a tectonic feature, but the lack of effect on its bed by the ice cap confirms the non-erosional nature of an ice cap frozen to its bed.

In terms of paleoclimatic history, it means that, because of bedrock effects, ice caps of intermediate depth (i.e. <400 m) can give continuous information only over the last approximate 5 000 years. Between 5 000 and 10 000 B.P. the time series becomes slightly discontinuous and beyond 10 000 B.P. so discontinuous as to allow only broad climatic inferences to be drawn.
A Sequence Of Glacial Deformation, Erosion, And Deposition At The Ice–Rock Interface During The Last Glaciation: Cranbrook, British Columbia, Canada
Authors: Broster B. E. , Dreimanis A. , White J. C.
Published: September 2017

A comparison of bedrock fractures with orientation of structures and fabric in the overlying late Pleistocene basal till indicates a sequence of common glacial origin. The deformations in bedrock and till, and the deposition of the till layer, were accomplished by two glacial flows that were part of a mountain ice sheet: the regional (moving south-south-east) and the local (moving south-south-west) along Peavine Valley.

The following sequence of events is postulated from this investigation: the initial glacial advance from the north-north-west that produced conjugate low-angle shear fractures in the bedrock was followed by competition of both the regional and the Peavine Valley glacial flows which also produced low-angle fracture systems. As the over-riding ice became thicker, high-angle conjugate fractures were formed by both glacial flows. Subsequently, south-east-dipping injection wedges were formed by the regional ice, which was concurrently eroding the down-glacier parts of the wedged blocks, depositing local till, and producing sigmoidal deformations in this till. The main deposition of the overlying lodgement till was accomplished by an interaction of both the regional and the Peavine Valley glacial flows, and the lodgement was supplemented by shearing of the till, producing fissility. Bedrock wedging, as a significant process of glacial erosion, is believed to be discussed here for the first time.
Subglacial Regelation Water Film
Authors: Hallet Bernard
Published: September 2017

Recent studies of subglacially precipitated carbonate deposits and associated solutional furrows have provided interesting new insight on subglacial water films, as well as on chemical exchange at the glacier bed. Considerable information on the film thickness and its temporal and spatial variability has been gained by analyzing several properties of subglacial carbonate deposits including: (1) the morphology of surface features aligned parallel to ice flow, (2) the laminated structure, and (3) the size distribution of fine rock fragments presumably transported in the film prior to their incorporation in the deposits. Chemical analyses of water from pro-glacial streams, together with calculations of CaCO3 solubility and mass balance, show that the channelized water is chemically distinct from the film water in which CaCO3 precipitates, and that subglacial precipitation is not possible where there is a considerable water flux through the film in excess of that associated with regelation sliding. The principal implication of these studies is that a temperate cirque glacier is characteristically separated from its bed by a thin water film, probably micrometers in thickness; however, the film appears to occasionally thicken, at least locally by as much as a hundred fold in exceptional cases. Furthermore, the water flux and/or solute concentration in the basal film undergoes periodic, probably seasonal, variations possibly related to variations in the amount of water reaching and flowing through the basal film.
Variations in Time and Space of the Velocity of Lower Columbia Glacier, Alaska
Authors: Meier Mark F.
Published: September 2017

Ice velocity, acceleration, and strain-rate are being measured at intervals of about 45 d using automated processing of aerial photographs. Preliminary results for the lowest 6 km of Columbia Glacier for the period July 1976 to November 1977 show the following:

(1)

High rates of flow (2–6 m/d) and longitudinal extension (occasionally exceeding 1/a).

(2)

A smooth, almost sinusoidal change in velocity 6 km above the terminus from about 2 m/d in August 1976 and 1977 to about 3 m/d in February–March 1977.

(3)

Very rapid increases in velocity near the terminus in October 1976 and September–October 1977 which follow embayment formation (increased iceberg calving).

(4)

A suggestion that the rapid velocity increases propagate up-glacier for 3–4 km before becoming unrecognizable.

(5)

Seasonal changes in velocity (which presumably relate to basal sliding) ranging from about 1 m/d 6 km above the terminus to about 4 m/d near the terminus.
Observations Of Glacier Seismicity On Unteraargletscher
Authors: Deichmann N. , Ansorge J. , Röthlisberger H.
Published: September 2017

Almost continuous recordings of glacier seismicity were obtained on Unteraar-gletscher (Berner Oberland, Switzerland) over a period of two weeks at the end of May 1977. The seismograph array consisted of micro-earthquake recorders, some recording directly onto smoked paper (three Sprengnether model MEQ-800) and others recording onto magnetic tape (one MARS-72 apparatus and two seismic-event recorders). The frequency range covered by the instruments lies between 1 and 85 Hz. The array spanned a relatively crevasse-free area of about 500 m by 700 m.

At the beginning of the period of observation only a few events were recorded per hour. Probably as a consequence of increased run-off of melt and rain, which acted as a lubricant or as an agent of hydraulic fracturing within or beneath the glacier, the activity rose in two days to a maximum of 120 events in one hour, and then with minor fluctuations it gradually decreased again to its initial level. The variations in activity showed signs of correlating with the velocity measurements, which however were only started after the main maximum, but did not seem to be influenced by the uplift of the glacier surface or by the diurnal meteorological fluctuations.

Most of the recorded signals could be classified according to their frequency content into three groups: 40, 20, and 5 Hz. The 40 Hz events, whose duration was less than 1 s, are located near the glacier surface and probably correspond to those attributed by Neave and Savage (1970) to the formation of crevasses. The majority of the events were of the 20 Hz type, each of about 1 s duration. Due to inadequacies in the seismometer array, only three of them could be located with sufficient accuracy: they originated in different areas of the glacier at a depth of about 150 m, which is strong evidence that icequakes are not, as previously thought, limited to the upper 40 m. The signals of the 5 Hz type, lasting several seconds, are thought to be 20 Hz events whose higher frequencies have been attenuated by a longer travel path. The lower-frequency signals from the glacier bed, reported by Bindschadler (unpublished) and by Weaver and Malone (1979), were not observed. This could indicate that a variety of mechanisms are operative at different times of year. In particular, the subglacial conduits were only poorly developed in Unteraargletscher at the time of these recordings.
Importance of Plastic Deformation in Regelation of Ice
Authors: Tusima K. , Tozuka S.
Published: September 2017

It is well known that regelation may occur by pressure-melting in front of a wire and refreezing at the rear. The velocity of the wire has been observed to have values ranging from 10–5 to 10–1 mm/s. However, there have always been large discrepancies between experiments and any theory based on this mechanism, and, when moving at a comparable velocity, hard balls slid on an ice surface leave grooves made by plastic deformation. So, we conducted experiments to test whether regelation phenomena might be explained by plastic deformation of ice around the wire.
Transient Water Flow in Subglacial Channels
Authors: St Lawrence William , Qamar Anthony
Published: September 2017

A hydraulic mechanism is postulated as the source of certain low-frequency (1-5 Hz) seismic signals that are recorded in the vicinity of temperate glaciers. To illustrate that the mechanism is a plausible seismic source, the equations of motion and continuity for transient flow in a subglacial conduit are developed. The solution to these equations is obtained for the case of the flow of water being terminated in a glacial conduit. Using reasonable values of physical parameters taken from the literature, the displacement of the conduit walls is determined as a function of time and distance along the tunnel. The spectral character of the proposed source and the period of time over which it operates is compared with seismic records of typical type II signals. The agreement in terms of these parameters is good.

To further examine the validity of the proposed seismic source a preliminary energy calculation is made which demonstrates that the proposed mechanism is energetically reasonable. Evidence of hydraulically generated seismic waves from a dam site is introduced to support the theory of a hydraulic source.

Based on the evidence presented, it is suggested that the flow of water from glaciers is modulated by an internal flow regime that is intermittent in time and space.

The substance of this paper is included in a report by the present authors entitled “Hydraulic transients: a seismic source in volcanoes and glaciers”, published in Science, Vol. 203, No. 4381, 1979, p. 654–56.
The Distribution of 10m Temperatures on the Ross Ice Shelf
Authors: Thomas R.H.
Published: September 2017

Ten-meter temperatures on the Ross Ice Shelf increased by I deg between 1958 and 1974. Surface temperatures at the “Byrd” and McMurdo stations have also risen during this period and the observed change is consistent with the 10m temperature increase. This rising trend in temperature appears to have an anti-phase relationship with northern hemisphere cooling.
On the Thermal Regime of a High-Arctic Valley Glacier
Authors: Müller Fritz
Published: September 2017

The 10 m temperatures were measured over several years at 16 sites on the White Glacier (lat. 80° N.), Axel Heiberg Island, Canadian Arctic Archipelago. At three sites deep profiles were made using a new drilling technique, reaching a maximum depth of 280 m. Large differences in the 10 m temperatures between locations and from year to year were observed. The deviations of these temperatures from the almost isothermal mean annual air temperature over the glacier are discussed. The heating effect of the melt water in the lower percolation zone was found to be very important. A conceptual model is developed to assess the influence of these irregularities in the energy input at the upper boundary on the thermal regime of the entire glacier. So far a quantitative analysis has been made only for the relatively simple 30 m temperature profile measured on the tongue of the glacier.
Impurities and their Distribution in Temperate Glacier Ice
Authors: Harrison W.D. , Raymond C.F.
Published: September 2017

Total impurity content of salt plus carbon dioxide was estimated as a function of grain size and depth in polycrystalline ice samples cored from a temperate glacier by measuring the electrical conductivity of the melt with air excluded. Conductivity decreased with increasing depth and grain size and ranged from × 10-5 to 0.4 × 10-5 Ω -1 m-1 at 0°C. The conductivity of pure water at 0°C is 0.1 × 10-5 Ω -1 m-1 Studies of the configuration of the three phases and of in situ temperature were also made. Thermodynamic constraints indicate that these impurities are probably concentrated as follows: about 5 mol m-3 in the liquid in the veins along three-grain intersections, roughly 1 × 10-6 mol m-2 associated with grain-boundary area exclusive of veins, and about 0.7 × 10-3 mol m-3 in volume exclusive of veins and grain boundaries. The last of these categories seems to account for most of the impurities in coarse ice (grain size about 20 mm), but all three categories seem significant in fine ice (grain size about 2 mm). Differences in bulk impurity content possibly indicate different histories of flushing by water.
Abstracts of Papers Accepted for the Symposium but not Presented Mathematical Models of Ice Shelves
Authors: Shumskiy P.A. , Krass M.S.
Published: September 2017

The flat form and high ice velocity of floating glaciers are explained by the absence of shear stresses at the lower surface. In orthogonal co-ordinates with one axis normal to the upper and lower surfaces shear stresses in these glaciers are absent. Another important peculiarity of ice shelves is their essential non-isothermality. Among them two dynamically different types are distinguished, which are described by different models.

A. External ice shelves join the coast at one edge and at some distance from it can expand freely in all directions. They can be considered with sufficient accuracy as flat plates without any physical differences between the directions of the horizontal plane, except that strains lead to the movement relative to the fixed edge. Thus the problem of thermodynamics becomes one-dimensional. In the affine dimensionless system of co-ordinates, the equations of the dynamics are simplified and together with the rheological equation lead to the non-linear integro-differential equation involving the reduced temperature. For the quasi-steady case, the boundary problem for this equation is solved by means of the method of sewing together of asymptotic expansions. It is shown that the stability of the thermodynamic regime in external ice shelves takes place only when the stream lines pass through both glacier surfaces, because in this case the advection removes the dissipative heat. In the case of ice coming from the upper and lower surfaces in opposite directions, the regime is unsteady because of the internal accumulation of heat.

B. Internal ice shelves are limited by coasts from various sides and interact with them dynamically. In the boundary zone coasts provide a braking action and outside it they prevent sideways spreading. The relation between horizontal stresses is conditioned by the configuration of coasts, therefore the angle between the coasts, or between the directions of ice flow from them, is included essentially into the equations of thermodynamics. Another complication is connected with the considerable change of the temperature and of the accumulation- ablation rate at the upper and lower surfaces of the glacier along flow lines. Integro-differential equation for the temperature in this case is more complicated, but its solution is analogous to the case above. In the coastal zone the thermodynamics are described by other equations in connection with the predominance of the shear stress in the plane parallel to the coast.
Temperature Distribution in a Sub-Isothermal Glacier
Authors: Krass M.S.
Published: September 2017

In sub-isothermal glaciers heat conduction plays the main role in the formation of the temperature field, and the contribution of advection is relatively small. The dependence of the strain-rate on the temperature is simplified by a linear approximation. If the whole range of the temperature change in a glacier does not exceed ≈ 3 deg, with the power rheological law the quasi-steady temperature distribution is described by a simple analytical dependence. In the upper part of the ice, the temperature varies with depth almost linearly; the deflection from the linear distribution is essentially in the lower part.
Relaxation Self-Oscillations and Processes at the Bottom of Glaciers
Authors: Shumskiy P.A.
Published: September 2017

In terms of the theory of oscillations, rapid glacier advances (glacier surges) are relaxation self-oscillation, and large glacier advances of the same character dependent on climate are the result of interaction between forced and self-exciting oscillations.

The relation is found between average shear stress and sliding velocity of pure and of moraine-containing ice along the bottom, taking into account the real thermal and kinematic boundary conditions, the different dependence of the ice melting point on hydrostatic pressure

and on normal component of the stress deviator, and dry friction against the bottom. In the regime of bottom melting, a communicating system of subglacial drainage channels is formed along (he borders of distal slopes of bottom irregularities. Variations of effective roughness lead to the forced variations of sliding velocity depending on the surface melting rate.

Relaxation self-oscillations of glaciers are caused by the alternation of “sticking” to the bottom in the phase of restoration and of rapid sliding along the bottom in the phase of relaxation because of the changes in the concentration of moraine material in the bottom layer of ice and of the force of dry friction against the bottom of a glacier.
Configurational Statistics
Authors: Nagle J. F.
Published: September 2017

Theories of the dielectric constant in ice differ in three fundamentally different ways that are often confused with each other. First, there is the choice of interactions to include in the model, notably whether to try to include long-range dipolar interactions as in the Kirkwood theory or to include only the short-range ice-rule interactions. Second, there is the choice of the kind of statistical quantity calculated, e.g. the Kirkwood correlation factor g or the polarization factor G, which Stillinger and Cotter showed to be different. Finally, there is the choice of the kind of computational tool used, and in original papers this choice often obscures the first two differences. With these distinctions in mind a review is given of current theoretical calculations of the dielectric constant and the residual entropy and how the different theories relate to each other and to experiments.
Dielectric Permittivity of Glacier Ice Measured In Situ by Radar Wide-Angle Reflection
Authors: Jezek Kenneth C. , Clough John W. , Bentley Charles R. , Shabtaie Sion
Published: September 2017

Values of relative permittivity measured by the wide-angle reflection technique on the Ross ice Shelf show substantial variations between sites, from 3.09 to 2.89, with estimated errors of ±0.03. The largest values, closest to those normally measured in the laboratory, are found nearest to the grounded ice sheet; values decrease generally in the direction of thinner ice that has been longer on the ice shelf. We believe the variation reflects some real physical phenomenon in the ice shelf, either a true variation in the permittivity of the ice or a complication of the ray-path geometry, but are not able to offer a satisfactory model at present. We hope an explanation will be forthcoming when actual ice core samples from the deep shelf ice are available for examination.
Deformation of Ice Single Crystals Close to the Melting Point
Authors: Jones Stephen J. , Brunet Jean-Guy
Published: September 2017

Constant strain-rate compression tests on ice single crystals at temperatures between –20°C and -0.2°C are described. The power-law dependence of yield stress on strain-rate gives a value of n which varies from 1.95±0.04 at –0.2°C to 2.07±0.08 at –20°C. The activation energy of deformation varies with strain-rate, but a mean value of 70±2 kJ mol–1 is obtained, with no indication of any increase close to maleting point,as has been found polycrystalline ice. An apparent work-hardening effect, at strains greater than 15%, is explained as being due to bending of the crystal changing the orientation of the basal planes.