bluuebunny/crossref_metadata_2025 huggingface dataset:
The Flow of Ice Over a Till Bed
Authors: Jones A. S.
Published: September 2017

This paper considers the contribution made to overall glacier flow by deformation of an unlithified bed. The flow pattern in deforming till beneath a glacier is determined for the case of a uniform ice slab resting on a uniform thick till bed. The results obtained show that, once the till is saturated, very little surplus water is needed to produce high velocities in the till near the ice−till interface, the interface velocity varying as the 5/2 power of the surplus water concentration. This sensitivity to water content suggests that this may be a mechanism inducing glacier surging.
Patterned Ground on an Active Medial Moraine, Jotunheimen, Norway
Authors: Ballantyne C. K.
Published: September 2017

Sorted circles and nets formed on the surface of the principal medial moraine on Storbreen, Jotunheimcn, Norway, are described. These consist of “islands” of coarse sand, granules, and small pebbles, surrounded by pebbles and cobbles and underlain by small domes of glacier ice. It is suggested that patterned ground formation on the moraine results from differential ablation in areas of thin (<200 mm) debris cover near the glacier snout, where melting is relatively rapid. It is unlikely that supraglacial patterned ground could survive deposition.
Flow separation and diurnal variability in the hydrology of Conness Glacier, Sierra Nevada, California, U.S.A.
Authors: Lecce Scott A.
Published: September 2017

A mass-balance approach using hourly discharge and electrical conductivity values measured over a 10 d period during the ablation season was used to separate englacial and subglacial components of the total meltwater discharge from a small alpine glacier in the Sierra Nevada, California, U.S.A. Symmetrical diurnal hydrographs indicate that little delay occurred as water was tranferred through the drainage system. Electrical conductivity (which varied inversely with proglacial discharge) increased abruptly at each daily conductivity maximum, and cross-correlation analysis indicated that subglacial discharge peaked on the rising limb of the englacial hydrograph (about 2 h prior to the englacial peak). This suggests that a translatory flow process operates in which increased water pressure in the englacial system on the rising limb of the diurnal-discharge cycle forced subglacial water from beneath the glacier in advance of short residence-time meltwater. Net radiation dominated the energy balance at the glacier surface, explaining 86% of the variance in proglacial discharge, which was dominated by the englacial flow component.
Firn-core study from the southern Patagonia ice cap, South America
Authors: Aristarain Alberto J. , Delmas Robert J.
Published: September 2017

A shallow firn core, recovered from the southern Patagonia ice cap (elevation 2680 m a.s.I.), has been analyzed for H stable isotope composition and for major soluble chemical compounds. The temperature measurement at 13.17 m depth (bottom of the core) shows that the ice cap is temperate. The chemical profiles indicate that some soluble impurities have been partly washed out by percolation, but seasonal deuterium content variations are relatively well preserved down to the bottom of the core, which allows the net accumulation rate of the site to be calculated (1.2 m water equivalent). The mean concentrations measured in the most recent year recorded (Cl−:4.85, nssSO42−: 0.65, NO3−:0.32, Na+:4.30, K+:0.64 and NH4+: 0.77, in μeq. 1−1) serve as a reference for the background chemical composition of precipitation at mid-southern latitudes under South Pacific meteorological conditions.
Relating the occurrence of crevasses to surface strain rates
Authors: Vaughan David G.
Published: September 2017

The presence of crevasses on the surface of ice masses indicates that a fracture criterion has been met. Understanding how crevasses form will provide information about the stress and strain-rate fields in the ice. This study derives a relationship between measurements of strain rate and observations of crevassing on the surface of ice masses. A literature search yielded 17 polar and alpine locations where strain rates had been measured and crevassing recorded. By plotting strain rates (converted to stresses using a creep law) using axes representing the surface-parallel principal stresses, failure envelopes were derived by enclosing measurements where surface crevassing was absent. The derived failure envelopes were found to conform well to theoretical ones predicted by the Coulomb and the maximum octahedral shear stress (von Mises) theories of failure. The derived failure envelopes were scaled by the tensile strength, which was found to vary from 90 to 320 kPa. There was no systematic variation of tensile strength with either temperature at 10 m depth or the method used to locate the crevasses. The observed variation in tensile strength could result from variations in ice properties (e.g. crystal size, impurity content or density) or could be related to uncertainty in the constitutive relation. Creep flow and fracture share a very similar temperature dependence, suggesting similar crystal-scale processes are responsible for both. The observed relationship will provide a supplementary tool with which to verify and test models of ice dynamics against remotely sensed imagery. The study also indicates that a temperature rise of a few degrees throughout the ice column will not result directly in any increase in calving rates from the large Antarctic ice shelves such as the Filchner–Ronne or Ross Ice Shelves.
Debris entrainment at the ice-bedrock interface in sub-freezing temperature conditions (Terre Adélie, Antarctica)
Authors: Tison J. -L , Petit J. -R. , Barnola J. -M. , Mahaney W. C.
Published: September 2017

The debris-rich ice from the bottom 6 m of the 82 m deep CAROLINE (Coastal Antarctic Record of Last Interglacial Natural Environment) ice core reaching bedrock, and from five 2 m long surface cores at Moraine Prudhomme in Terre Adélie (Antarctica) is described and compared to debris-laden ice from the core-drilling site DIO. Isotopic, total-gas content, CO2 concentration and SEM investigations of embedded particles, together with ice textures and fabrics, rule out “pressure-melting” regelation around bed obstacles or “freezing-on” as possible mechanisms for the debris entrainment at the ice-bedrock interface. It is suggested that the debris entrapment by purely mechanical means (e.g. shearing) is an efficient process in forming basal ice layers (BIL) at sub-freezing temperatures. This process might be dominant at the margin of the Antarctic ice sheet where no ice shelf exists and where a ramp terminus or a buttressing coastal relief induces compressive flow.
Characteristics of avalanching: Kootenay Pass, British Columbia, Canada
Authors: McClung D. M. , Tweedy John
Published: September 2017

Individual variables found to be significant from a correlation analysis are analyzed as a function of probability of avalanching for data from Kootenay Pass, British Columbia. The analysis is compared with a similar study for data from Alta, Utah, U.S.A. The results show that the variable significance is very similar for the two areas. Primary variables include: snowfall rate, weight of new snow, water equivalent of new precipitation, total storm snow and new snow depth. Secondary variables include wind speed and direction, and new-snow density.
Micro-earthquakes beneath Ice Streams Β and C, West Antarctica: observations and implications
Authors: Anandakrishnan S. , Bentley C. R.
Published: September 2017

Micro-earthquakes have been monitored at two locations on Ice Stream Β and one on Ice Stream C using a seismographic array built specifically for that purpose. Subglacial micro-earthquakes arc 20 times more abundant beneath Ice Stream C than beneath Ice Stream B, despite the 100 times more rapid movement of Ice Stream B. Triangulation shows the foci beneath Ice Stream C, like those beneath Ice Stream B, to be within a few meters of the base of the ice, presumably within the uppermost part of the bed, and fault-plane analysis indicates slips on horizontal planes at about a 30° angle to the presumed direction of formerly active flow. Source parameters, computed from spectra of the arrivals, confirmed that the speed of slip is three orders of magnitude faster beneath Ice Stream C than beneath Ice Stream Β which means that a five orders-of-magnitude greater fraction of the velocity of Ice Stream C is contributed by the faulting, although that fraction is still small. We attribute the difference in activity beneath the two ice streams to the loss of dilatancy in the till beneath Ice Stream C in the process that led to its stagnation.
The detailed net mass balance of the Ice plain on Ice Stream B, Antarctica: a geographic information system approach
Authors: Bindschadler Robert , Vornberger Patricia L. , Shabtaie Sion
Published: September 2017

Field data of ice thickness, velocity and accumulation of the ice plain region of Ice Stream B, Antarctica, are organized into a geographic information system (GIS) and used to calculate the spatial pattern of net mass balance. Overall, the ice plain is thickening at a rate of 0.13 ± 0.05 m a−1. Large uncertainties of the high-resolution calculations are reduced by spatial averaging, revealing a number of areas significantly out of balance. Ice in the broad diverging flow field is mostly thinning but a thinner region of the ice plain which includes ice raft “a” is thickening. Thickening is also indicated farther downstream on the ice plain, matching the thickening already calculated to be occurring upstream of Crary Ice Rise. The patterns of net mass balance for the two major tributaries of Ice Stream Β are asymmetric, demonstrating a real difference in the current dynamics of these two tributaries.
New and improved determinations of velocity of Ice Streams B and C, West Antarctica
Authors: Whillans I. M. , Van Der Veen C.J.
Published: September 2017

Measurements of velocity have been made on and next to Ice Streams Β and C, West Antarctica. The results are more precise than previous work and constitute a 93% increase in the number of values. These velocities are used to describe the confluence of flow into the ice streams and the development of fast ice-stream flow. The onset of fast-streaming flow occurs in many separate tributaries that coalesce down-glacier into the major ice streams. For those inter-stream ridges that have been studied, the flow is consistent with steady state. Along Ice Stream B, gradients in longitudinal stress offer little resistance to the ice flow. The transition from basal-drag control to ice-shelf flow is achieved through reduced drag at the glacier base and increased resistance associated with lateral drag. Velocities in the trunk of Ice Stream C are nearly zero but those at the up-glacial head are similar to those at the head of Ice Stream B.
Siple Coast Project research of Crary Ice Rise and the mouths of Ice Streams B and C, West Antarctica: review and new perspectives
Authors: Bindschadler Robert
Published: September 2017

Satellite imagery is used as a basis to review and critique the results of studies at the mouths of Ice Streams Β and C and Crary Ice Rise. In many cases, these past analyses are extended by taking advantage of the broad coverage within each image. New perspectives are provided by the image data and some longstanding controversies are resolved. The grounding line is easily delineated and mapped in areas covered by imagery. Extensive areas of grounded ice with complex patterns of flow stripes are identified on the flanks of Crary Ice Rise. The imagery also allows a corrected map of surface topography in the vicinity of the Downstream Β camp. New questions are posed by hitherto unseen features. Data from the IGY traverse of the Ross Ice Shelf in 1957 are included to demonstrate that large changes have occurred in the past almost 30 years in the area upstream of Crary Ice Rise. These changes include modifications in the surface topography, elimination of crevasses and increases in the ice thickness by approximately 60 m.
Timing of stagnation of Ice Stream C, West Antarctica, from short-pulse radar studies of buried surface crevasses
Authors: Retzlaff Rory , Bentley Charles R.
Published: September 2017

Five short-pulse radar profiles were run across the edge of inactive Ice Stream C, one of the “Ross” ice streams that flows from the West Antarctic inland ice sheet into the Ross Ice Shelf. Scatter from buried crevasses, which we presume were at the surface of the ice stream when it was active, creates hyperbolae on the radar records. A density-depth curve and local accumulation rates were used to convert the picked travel times of the apices of the hyperbolae into stagnation ages for the ice stream. Stagnation ages are 130 ± 25 year for the three profiles farthest downstream and marginally less (100 ± 30 year) for the fourth. The profile farthest upstream shows a stagnation age of only ~30 year. We believe that these results indicate a “wave” of stagnation propagating at a diminishing speed upstream from the mouth of the ice stream, and we suggest that the stagnation process involves a drop in water pressure at the bed due to a conversion from sheet flow to channelized water flow.
The interaction between an ice sheet and its atmospheric boundary layer
Authors: Hall Alison , Weston Keith
Published: September 2017

The importance of the atmospheric boundary layer for the coupling between the climate and an ice sheet is investigated using a slab model of the atmospheric boundary layer. The model is shown to give reasonable agreement with observations over Antarctica and it is used to look at the effect of different ice-sheet shapes on the boundary layer. The importance of entrainment in bringing heat to the surface is highlighted and is shown to be particularly significant when the ice profile becomes steeper. The model could be used as part of an energy-balance model of snow in order to incorporate the interplay of the boundary layer and ice-sheet shape in the ablation process. The slab model could also be used in a GCM as a parameterization of these sub-grid scale processes which are at present ignored in models on a global scale.
Snow stability during rain
Authors: Conway H. , Raymond C. F.
Published: September 2017

The mechanical response of snowpacks to penetrating liquid water was observed over two winter seasons in the central Cascade Mountains, Washington, U.S.A. Following the onset of rain, three evolutionary regimes of snow behavior were identified: immediate avalanching, delayed avalanching, and return to stability. Immediate avalanching occurred within minutes to an hour after the onset of rain and the time of release could be predicted with an accuracy of less than an hour from meteorological forecasts of the transition from snow to rain. These avalanches usually slid on surfaces substantially deeper than the level to which water or associated thermal effects had penetrated. The mechanism by which alteration of a thin skin of surface snow can cause deep slab failure has not been identified, but several possibilities involving a redistribution of stress are discussed. Delayed avalanches released several hours after rain started. The delay varied, depending on the rate of increasing stress associated with the additional precipitation, and on the time taken for water to penetrate and weaken a potential sliding layer. It is difficult to define accurately the evolving distribution of liquid water in snow which makes it difficult to predict accurately the time of avalanching. Depth profiles of the rate of snow settlement showed that a wave of increased strain rate propagated into the snow in response to penetrating water. This type of measurement could prove useful for predicting when snow stability is reaching a critical condition. Avalanche activity was rare after continuation of rain for 15 h or more. This return to stability occurred after drainage structures had evolved and penetrated the full depth of the snowpack. Established drain channels route water away from potential sliding surfaces and are also relatively strong structures within a snowpack.
Rutschblock precision, technique variations and limitations
Authors: Jamieson J. B. , Johnston C. D.
Published: September 2017

The Swiss rutschblock test provides practical information about the stability of snow slabs. However, its use by avalanche workers and ski guides is limited by the time required to perform the test and recommended minimum slope inclination (30°). The present study shows how time requirements can be reduced by cutting rutschblocks with cords or specialized saws — faster techniques that do not appear to affect the results. Comparing the rutschblock results with a stability index developed in Switzerland shows that the recommended minimum slope inclination can be reduced to 20°, provided a second person is present to observe the small block displacements associated with slope inclinations below 30°. Sets of rutschblocks on slopes that vary in inclination by 8° or more are used to determine the effect of slope inclination on rutschblock scores. Also, the frequency distributions of six large sets of repeated tests are used to estimate the precision of one or two tests on a uniform slope.
Snow Forces
Authors: Salm Bruno
Published: September 2017

Snow forces are understood as forces originating from a very slow motion of the seasonal snow cover and acting on boundaries confining it. They depend on the total water-equivalent (a statistical magnitude with a certain probability of occurrence) and on mechanical characteristics of snow. The approximation of considering of snow as a Newtonian liquid fits the requirements for applications best. In this the only mechanical characteristics to be taken into account, besides density, are shear viscosity and Poisson’s ratio. They depend strongly on the snow structure. Generalizations are shown in which the snow cover is subdivided into layers having constant (Newtonian) properties. Non-Newtonian behaviour is also mentioned.
Approximate Solutions for the Interruption of Creep and Glide by Avalanche Defenses
Authors: Evans R. J. , Langdon J. A.
Published: September 2017

This paper presents a numerical calculation procedure for the stress and deformation analysis of a snow mass which is creeping and gliding on an inclined surface and which may, in addition, be restrained by rigid obstacles. The analysis is based on the assumption that the velocity profile at any position in the snow-pack is linear, that is, that sections initially plane remain plane during deformation. Such motion has been observed to occur in the neutral zone and is certainly true at a rigid barrier; accordingly, it appears to be reasonable to restrict the velocity field to be plane everywhere. A constitutive law for steady creep is used which is consistent with the observed neutral zone motion. The solution procedure is illustrated by its application to some problems of avalanche defense barriers. The cases investigated include: continuous barriers, cylindrical barriers, and barriers of finite width. Barrier forces and the extent of back-pressure zones are given.
Propagation of a Plastic Wave in Snow
Authors: Wakahama Gorow , Sato Atsushi
Published: September 2017

When snow is pushed very fast by a moving body a plastic wave is generated at the head of the body. If the velocity of the moving body becomes close to that of the plastic wave, the snow may exert a great resistive force against the body as predicted by Yosida. It is, therefore, very important to study the dynamic behaviour of snow at a high rate of deformation, such as takes place when a snow plough is used on the highway, a train runs on a railroad covered with snow, or an avalanche occurs. Hence, this study is concerned with the safety and maintenance of winter traffic and transportation, and also with the generation and propagation of an avalanche. In order to clarify the detailed processes of the deformation of snow at high rates, laboratory experiments were made by compressing snow at high speed. The propagation of a plastic wave through snow was observed by using a high-speed camera and a pressure-detecting device. Analyses of the data obtained gave the velocity of the plastic wave for various kinds of snow whose density ranged from 0.17 to 0.46 Mg m-3 and free-water content from o to 17%, whereby studies were made into the dependences on the density and free-water content of the velocity of the plastic wave. When the impact velocity was 4.3 ± 0.2 m s-1, the wave velocity ranged from 5 m s-1 for a new snow to 12 m s-1 for a fine-grained, well-settled snow. The plastic-wave velocity in wet snow was, in general, smaller than that in dry snow of the same density. Changes in density and structure of snow associated with the passage of a plastic wave were studied and discussed. The pressure at the wave front was measured; values of 0.1-0.3 bar were obtained, these are of the same order as the value estimated from theoretical formulae. The plastic-wave velocity was also observed for a confined snow, which showed a larger velocity and plastic strain than an unconfined snow.
Expected Snow Loads on Structures from Incomplete Hydrological Data
Authors: Martinec J.
Published: September 2017

An assessment of snow loads in Switzerland was required for a revision of the building code. Settling curves of snow are used to compute water equivalents of snow if direct measurements are not available. Based on a frequency analysis, relations between the snow load and the altitude are given for various return periods. Problems of regional effects and of converting the snow-cover data to roof loads are outlined.
Measuring the Uniaxial Compressive Strength of Ice
Authors: Haynes F. D. , Mellor M.
Published: September 2017

An attempt was made to develop a simple but accurate method for making compressive strength tests on right circular cylinders. Compliant loading platens were designed to apply uniform normal stress without introducing significant interface radial shear stresses. The compliant platens gave reproducible results that agree well with results obtained by a precise conventional technique. Accurate results were obtained with simple specimen preparation, and with short specimens where the length-to-diameter ratio was less than unity. Platens were made from a rubber-like urethane which was molded in aluminum cylinders to provide lateral restraint. Uniaxial compression tests on cylindrical polycrystalline ice specimens were made to determine the characteristics of the platens. For 21 specimens with ends prepared on a lapping plate to obtain a mirror finish, the measured strength showed a variation of only 13% for length-to-diameter ratios from 0.74 to 2.5, with no systematic trend. Another 21 specimens with length-to-diameter ratios of about 2.35 were tested with various platens and various methods of specimen end preparation. The strength for specimens with saw-cut ends and for those with ends lapped showed very little difference when tested with the rubber platens.
Friction of a Steel Ball on a Single Crystal of Ice
Authors: Tusima Katutosi
Published: September 2017

This paper presents the results of a study carried out to explain the low friction on ice. Friction of a steel ball on a single crystal of ice was measured as a function of load, velocity, temperature, and diameter of slider. It was found that even when the velocity was very small (1.5 - 10-7 to 1.8-10–3 m/s) the coefficient of friction was very small ranging from 0.005 to 0.2, although friction on the prismatic plane was twice as large as that on the basal plane. The coefficient of friction increased with load, which means that Amonton’s classical law of friction is not applicable to ice. The coefficient of friction increased with decreasing velocity, which may result from the creep of ice in the contact area. The friction strongly increased as the temperature became close to °C. A minimum friction was observed for a definite temperature. It was found that the explanation of the results obtained is given satisfactorily neither by the classic pressure-melting theory nor by the friction-melting theory, but only by adhesion theory.
Ice-Structure Interaction with Artificially Generated Force Records
Authors: Swamidas A. S. J. , Reddy D. V. , Purcell G.
Published: September 2017

The paper describes the dynamic ice-structure interaction study of monopod platforms (fixed type) which are of considerable interest to the off-shore oil industry in cold regions. In view of the scantiness of continuous ice-force records, artificial-force records are generated from available small-scale field ice-force records using stochastic concepts. The method, based on the similarity between the fluctuating parts of randomly varying ice-force records and the seismic records uses a non-stationary random process obtained from filtering a shot noise through a second-order filter. The dynamic response analysis of a monopod structure located at Cook Inlet, Alaska, is carried out by hybridizing the relevant sub-routines of the computer programmes, SAP IV (Structural Analysis Programme) and EATSW (Earthquake response of Axisymmetric Tower Structures surrounded by Water). The work includes a study of the influence of soil properties on the frequencies and responses, and a comparison between the responses of fixed and elastically supported (by the soil foundation) monopod platforms.
Wave Pattern of Flowing Snow Slabs
Authors: Lang T. E.
Published: September 2017

Equations are derived, using a total potential-energy formulation, which predict the wavelength of the dominant wave pattern of a flowing snow slab. Account is taken of the visco-elastic properties of an assumed surface layer of snow which overlays a distinct visco-elastic foundation layer of snow. The predicted wave pattern is recognized as a precursory mechanism which influences the characteristics of the sawtooth flank fracture pattern that may remain following a snow avalanche, particularly on broad, uniform slopes. The parameters that influence the wave pattern are determined by an order-of-magnitu de reduction of the terms in the governing differential equation for visco-elastic slab response.
Strong Snow-Storms, their Effect on Snow Cover and Snow Accumulation
Authors: Dyunin A.K. , Anfilofiyev B.A. , Istrapilovich M. G. , Mamayeva N.T. , Kvon YA. D.
Published: September 2017

Snow-drifts have been studied by many researchers both in field and laboratory conditions, however these investigations have been carried out mostly at wind speeds up to 20 m/s whereas in many areas of our planet snow-storms occur at winds up to 40 m/s and more. During the winter seasons of 1972-76 the authors carried out a great number of experiments with an artificial snow-storm in a special wind tunnel 27 m long. The wind speeds reached 40 m/s (60-65 m/s at the 10 m anemometer height). The existing theories and hypotheses of snow-drifting, and in particular the “diffusion" model, were tested in a series of the experiments. These have not confirmed the assumption of the Australian scientists on the decisive role of diffusion in drift mechanism at large wind speeds. The problem of strong snow-storm effect on snow accumulation on avalanche-danger slopes, in particular, wind redistribution of snow is no less important.

The results obtained may be used for the determination of snow accumulation in avalanche starting zones due to deflation. This is especially important for forecasting very dangerous and frequently-occurring avalanches due to snow-storms. The investigations performed enable us to estimate the snow deposition produced by strong and superstrong snow-storms, to account for the peculiarities of such snow-storms and the means of protection, to forecast snow distribution in mountainous regions, and to define the role of snow-storms in glacier mass balance.
Studies of the Movement of Coastal Sea Ice Near Prudhoe Bay, Alaska, U.S.A.
Authors: Weeks W. F. , Kovacs A. , Mock S. J. , Tucker W. B. , Hibler W. D. , Gow A. J.
Published: September 2017

During March-May 1976, a combination of laser and radar ranging systems was used to study the motion of both the fast ice and the pack ice near Narwhal and Cross Islands, two barrier islands located 16 and 21 km offshore in the vicinity of Prudhoe Bay, Alaska. Laser measurements of targets on the fast ice near Narwhal Island indicate small net displacements of approximately 1 m over the period of study (71 d) with short-term displacements of up to 40 cm occurring over 3 d periods. The main motion was outward normal to the coast and was believed to be the result of thermal expansion of the ice. The radar records of fast-ice sites farther offshore show a systematic increase in the standard deviation of the displacements as measured parallel to the coast, reaching a value of ±6.6 m at 31 km. The farthest fast-ice sites show short-term displacements of up to 12 m. There are also trends in the records that are believed to be the result of the general warming of the fast ice with time.

Radar targets located on the pack ice showed large short-term displacements (up to 2.7 km) but negligible net ice drift along the coast. There was no significant correlation between the movement of the pack and the local wind, suggesting that coastal ice prediction models can only succeed if handled as part of a regional model which incorporates stress transfer through the pack. The apparent fast-ice-pack-ice boundary in the study area was located in 30-35 m of water.
Horizontal Movement of Fast Ice in the North Water Area
Authors: Ito Hajime , Müller Fritz
Published: September 2017

The understanding of the horizontal movement of fast ice is important for applied sea-ice mechanics. A case study, carried out in conjunction with a polynya known as North Water, is presented in this paper. The displacements of the fast-ire arches which separate the polynya from the surrounding ice-covered sea, were measured and found to be small. It is, therefore, confirmed that these arches prevent the influx of large quantities of sea ice into the polynya. The results are then explained in terms of the external forces (wind and current), the stress- strain situations and some physical characteristics (temperature and thickness) which were measured simultaneously.
Influence of Friction on Ice Forces Acting Against Sloped Surfaces
Authors: Danys J. V. , Bercha F. G. , Carter D.
Published: September 2017

On the basis of crushing and flexural failure theories, in conjunction with the assumption that ice˗structure interface friction conforms to classical Coulomb friction laws, it is shown that effects of friction can be significant. Generally, the resultant force on the structure will increase very rapidly due to increases in the coefficient of interface friction. This increase in force is attributable to two analytically tractable phenomena; namely, that involving the resistance to sliding caused by the generation of tangential force at the interface, referred to as the primary effect, and that involving propagation of this primary-effect force into the ice failure zone increasing resistance to failure, referred to as the secondary effect.

Next, a non-classical theory of friction is reviewed. It admits the possibility of the coefficient of friction being a function of the normal force, velocity, and temperature for certain materials while still admitting Coulomb-type behaviour for other materials. Effects of replacing the classical theory with the non-classical one are considered, but it is concluded that further work is necessary before they can be realistically evaluated.

Finally, it is concluded that current design practice of neglecting the effects of friction on a certain class of structures is likely to lead to conservative results. Future work necessary to better predict the actual margin of safety resulting from current design practice is identified.
The Short-Range Forecasting of Discharge from a Glaciated Region and its use for Optimizing the Grande Dixence S.A. Pumping Plants
Authors: Dayer G.
Published: September 2017

The economical operation of the Grande Dixence S.A. pumping plants involves an optimal utilization of the electrical energy for pumping the discharges of five glacierized basins. For each basin, a short-range forecasting model (3 d) has been implemented in order to determine, at any time, the future evolution of the hourly discharge curve. The forecasting model is based on multiple regressions and involves following variables: discharge, air temperature, global radiation, precipitation and the altitude of the snow-cover limit. The selection of the variables not only depends on the physical laws of the melting of glaciers but also on the possibilities of measuring them accurately. The melt-water run-off is not a stationary process, but this difficulty can be by-passed by introducing the altitude of the snow-cover limit and by subdividing the melt season into intervals. The model must automatically choose the equations corresponding to the actual interval. The quality of the forecasts essentially depends on the weather forecast; some difficulties, such as the precipitation in the forecasted period, have not yet been resolved. The utilization of discharge forecasts in an optimizing model for the operation of a pumping plant with a compensation basin is compulsory and, further, enables the maximum usage of low-price electrical energy, limits water losses, and guarantees operational security.
Utilization of Dynamic and Physical Properties of Ice in Underground Mining Operations
Authors: Fangel Henning
Published: September 2017

In sub-level caving mining operations, the lateral walls cave in. This results in dilution of the mineral content of the produced ore by 15%-20% waste rock. Also 15%-20% of the valuable ores are lost in the caved wall material that is left behind in the mined-out rooms. Placing ice, in the form of a small glacier, in the mine-room before the lateral walls start to cave, permit complete recovery of ore reserves without dilution. The glacier will advance at a rate permitted by ore extraction processes, in accordance with glaciological theories and laws.

Volumes of ice that are required may be calculated from ore extraction rates, power consumed in the mine, ventilating air volumes and temperatures, specific heat and thermal conductivity of the lateral rock. The required ice volumes can be produced through natural freezing of water, where the winter temperatures regularly fall below 0°C for a predictable period every winter. Use of ice as a mining aid reduces costs of the ore extraction process by about one-third and increases value of the produced ore by about 20%. Thus, the value of a given orebody is increased by about 30% relative to the values experienced in the most efficient mines of today.
Characteristics of Processes of Electrical Relaxation in Frozen Soils
Authors: Frolov A.D. , Gusev B.V.
Published: September 2017

The results of measurements of dielectric properties of frozen soils are analysed on the basis of modified theory of dielectrics. The relaxational character of frequency and temperature dependence is shown and the basic equations are derived. The characteristics of distribution of relaxation times and effective relaxation times as depending on the temperatures are discussed. The values of activation energy are estimated.
Simulation of Ice Flow using the Finite-Element Method
Authors: Nguyen T.Q. , Emery J.J.
Published: September 2017

A plane-strain, incremental, initial-strain finite-element analysis, incorporating creep laws appropriate for the ranges of stresses and temperature involved, is used to simulate typical ice-slope flow problems. The flow of a uniform ice slope, assuming the mass is intact and no basal sliding occurs, shows that differences in steady-state velocities can be by orders of magnitude for various creep laws. A non-uniform ice slope and a uniform slope behind a concrete wall are also considered. Time-independent developments of tensile crack and basal shear are investigated by introducing joint elements with appropriate stiffness properties at ice−rock interfaces and tension zones. Then, the simulation model is modified to account for both time-dependent basal sliding (surging) and tensile crack development. In one case, basal shear failure is considered imminent if the shear strain in a thin basal ice layer, that allows wide variation in sliding velocity, exceeds a critical value. For the other case, the basal ice layer is replaced by joint elements and the progressive shear-stress failure mechanism during flow is demonstrated.
Tensile Strength of Compressed Snow Formed on Roads
Authors: Nakamura T. , Nakamura H. , Higashiura M. , Abe O.
Published: September 2017

Tensile fracture strengths of fine-grained compressed high-density snow, of compressed and metamorphosed high-density snow-ice, of fine-grained naturally settled snow, and of snow-ice artificially made from the settled snow by freezing with absorbed water, were obtained at constant deformation speeds (constant strain-rates) in a temperature range of 264 to 270K. No remarkable temperature dependence of fracture stresses was observed in this temperature range. A critical deformation speed in a tensile test above which all the snow samples, except settled snow, fractured, was 4.2 × 10–7 m s–1. The fracture strength ρ (in N m–2) varied with snow density ρ (kg m–3) as σ = 2.5 × 104 × 1.004 6ρ. In a power-law relationship between strain-rate and maximum stress, ∝ σn, the constant n obtained was 5.3 for all the unfractured snow samples.
Snow and Ice Studies By Thematic Mapper and Multispectral Scanner Landsat Images
Authors: Orheim Olav , Lucchitta Baerbel K.
Published: September 2017

Digitally enhanced Landsat Thematic Mapper (TM) images of Antarctica reveal snow and ice features to a detail never seen before in satellite images. The six TM reflective spectral bands have a nominal spatial resolution of 30 m, compared to 80 m for the Multispectral Scanner (MSS). TM bands 2–4 are similar to the MSS bands. TM infra-red bands 5 and 7 discriminate better between clouds and snow than MSS or the lower TM bands. They also reveal snow features related to grain-size and possibly other snow properties. These features are not observed in the visible wavelengths. Large features such as flow lines show best in the MSS and lower TM bands. Their visibility is due to photometric effects on slopes. TM thermal band 6 has a resolution of 120 m. It shows ground radiation temperatures and may serve to detect liquid water and to discriminate between features having similar reflectivities in the other bands, such as blue ice.

Repeated Landsat images can be used for sophisticated glaciological studies. By comparing images from 1975 and 1985, flow rates averaging 0.72 km a−1, and mean longitudinal and transverse strains of respectively 1.3 × 10 −4 a −1 and 130 × 10−4 a−1 have been measured for Jutulstraumen, Dronning Maud Land.
Evolution of under Water Sides of Ice Shelves and Icebergs
Authors: Orheim Olav
Published: September 2017

A systematic programme of side-scan sonar and plumb- line soundings was carried out in the Weddell Sea area in 1985 to measure the under-water sides of ice shelves and icebergs. From these observations the following model is suggested for the evolution of the ice front:

(1)

Initial stage: fracturing of the ice shelves takes place along smooth, curvi-linear segments with vertical faces.

(2)

Formative stage: the freshly formed vertical face is eroded both by wave and swell action around the water line, by small calvings from the undercut, overhanging subaerial face, and by submarine melting. The melting has a minimum at 50–100 m depth, and increases with depth to a rate of around 10 m a−1 at 200 m, This is about twice the rate of erosion at the water line. The variation in melting with depth results from a combination of summer melting by near-surface water, and year-round melting by water masses that are increasingly warmer than the pressure melting-point with depth.

(3)

Mature stage: this stage is reached after a few years of exposure. The backward erosion of the face leads to a shape with a prominent under-water “nose” with a maximum projection to more than 50 m at 50–100 m depth. The ramp above this slopes upwards to meet the vertical wall about 5 m below the water line. The ice below the nose is melted back beyond the above-water face. There is no net buoyancy and ice shelves at this mature stage are generally not up-warped at the front.
Mapping of Amery Ice Shelf, Antarctica, Surface Features by Satellite Altimetry
Authors: Partington K.C. , Cudlip W. , McIntyre N.F. , King-Hele S.
Published: September 2017

Ice shelves are important regions to observe because they are likely to be sensitive indicators of climatic change. The satellite-borne radar altimetry is highly suited to ice-shelf monitoring; experience with Seasat, which flew in 1978, has demonstrated that a height-measurement precision of the order of 1 m can be obtained over ice surfaces (Brooks and Others 1983).

We identify subtle changes in altimeter wave forms associated with crevassed zones and the grounding line. Normal retracking procedures are shown to be inadequate in detecting such changes, and so methods which provide sensitive indication of the presence of these features in the sampled areas are devised. By ranging to the first return in the echo, the grounding line is identified, and by differencing this measurement with the half-peak power range, a measure of surface roughness is obtained which can be used to detect crevassed zones.

Detection of crevassed shear zones allows delimitation of distinct zones of flow in the ice shelf which can be monitored by future altimeter missions. Monitoring of the grounding-line position can provide sensitive indication of mass-balance conditions over the grounded part of the drainage basin.
Possibilities and Limits of Synthetic Aperture Radar for Snow and Glacier Surveying
Authors: Rott H. , Mätzler C.
Published: September 2017

The physical background for the interpretation of microwave measurements on snow and ice is summarized. The angular and spectral behaviour of backscattering is shown for various snow types based on measurements carried out in the Swiss Alps. The information content of SAR images in regard to snow and glacier applications is discussed, and examples are shown for Seasat SAR and airborne SAR images. The preliminary specifications are given for an optimum SAR system for snow and glacier monitoring. The main advantage of SAR is due to its weather independence; for special applications the SAR information on the physical state of snow and ice may be of interest. Future SAR sensors can become important components in a snow and glacier monitoring system, but in order to fulfil all tasks, high-resolution optical sensors and improved passive microwave sensors will also be required.
Bottom Topography and Internal Layers in East Dronning Maud Land, East Antarctica, from 179 MHz Radio Echo-Sounding
Authors: Yoshida Minoru , Yamashita Kazunobu , Mae Shinji
Published: September 2017

Extensive echo-sounding was carried out in east Dronning Maud Land during the 1984 field season. A 179 MHz radar with separate transmitting and receiving antennae was used and the echoes were recorded by a digital system to detect minute reflections. The results gave cross-sections of the ice sheet along traverse routes from lat. 69 °S. to 75°S, Detailed observations on the ground at Mizuho station showed that there was elliptical polarization in the internally reflected echoes when two antennae, kept in parallel with each other, were rotated horizontally. The internal echoes were most clearly distinguished when the antenna azimuth was oriented perpendicular to the flow line of the ice sheet. The internal echoes with a high reflection coefficient were detected at depths of 500–700 m and 1000–1500 m at Mizuho station. Since a distinct internal echo at a depth of 500 m coincides with a 5 cm thick volcanic ash-laden ice layer found in the 700 m ice core taken near the observation site, these echoes may correspond to the acidic ice layers formed by past volcanic events in east Dronning Maud Land.
Radar and Seismic Ice-Thickness Measurements Compared on Sub Polar Glaciers in Svalbard (Abstract)
Authors: Drewry D.J.
Published: September 2017

A comparison has been made of 46 radar-determined ice thicknesses and those resulting from seismic sounding on Bakaninbreen, Skobreen, and Paulabreen in central Spitsbergen. Significant differences were recorded between the two techniques, with 50% of the comparisons exceeding 15 m. Systematic differences between the three glaciers were also observed: on Paulabreen the seismic ice depths are consistently deeper than those determined by radio echo- sounding, whilst the opposite is true on Skobreen.

Instrumental errors from the radar (SPRI 60 MHz unit) and seismic equipment (ABEM Terraloc) are considered small or insignificant. Factors affecting the respective propagation velocities may be responsible for differences in mean thickness particularly in the case of seismic waves, although the changes are obtained from the first returns. One hypothesis to explain the differences on Paulabreen, and to a lesser degree on Bakaninbreen, is that these glaciers are underlain by a seismic low-velocity layer due to the presence of moraine or till. Unfortunately, equipment problems in the field prevented the digital logging of the seismic data and the analogue records are not of sufficient quality for detailed analyses to reveal the possible presence of a till horizon and its seismic velocities. However, observations at the snout of Paulabreen show considerable thicknesses of basal till. With a “P”-wave velocity in such a layer close to or less than that of ice acoustic returns would possibly come from the till–bedrock interface, whereas radar returns would be from the region of the ice–till boundary.

For the seismic ice depths that are shallower than the radar soundings on Skobreen an alternative explanation is required. The valley occupied by the glacier is considerably narrower than in the case of the other two glaciers. According to one detailed radio echo-sounding cross-profile, the line of the combined seismic and radar sounding was displaced to one side of the centre and deepest part of the glacier. This would result in early seismic returns from the nearest facets of the valley side rather than the subjacent bed. The radio waves, however, undergo a focussing effect in the ice, giving rise to a considerably smaller footprint. The difference in slant length between the general area of the bed viewed by the radar and that returning seismic energy is approximately +15–20 m at the location of the cross-profile. This value is of the order of the differences between the two systems and could therefore account for the observed disparity here and at the other locations.
Delineation of Glacier Drainage Basins on Western Vatnajokull
Authors: Björnsson Helgi
Published: September 2017

Three ice-drainage basins on western Vatnajökull have been delineated with the aid of the first available, accurate ice-surface maps. These basins drain ice towards the major river systems: Tungnaá, Sylgja, and Kaldakvísl, There seems to be an important difference in the location of ice-drainage basins and melt water-drainage basins for the rivers Tungnaá and Sylgja. This is due to the influence of the bedrock topography on the flow of basal water.