bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical and structural properties of weak snow layers measured in situ
Authors: Föhn Paul M. B. , Camponovo Christian , Krüsi Georges
Published: September 2017

Weak layers such as buried surface hoar or depth hoar frequently form the failure plane of slab avalanches. Therefore, the mechanical properties of such layers in relation to their snow structure have been investigated. Since it is difficult to transport samples containing a weak layer into cold rooms, the mechanical measurements have to be made in situ.

We investigate strain-rate dependency of shear strength by measuring concurrently strength, deformation and acceleration, using a digital force gauge attached to a 0.05 m2 shear frame to which an accelerometer and a displacement sensor are fixed. In doing so, a dynamic force comparable to a driving skier is applied. The measurements cover a strain-rate range 10-2 to 1 s-1. The samples fail in a brittle manner. The shear-strength values cover the range 0.2–2.8 kPa. The dataset is also used to approximate the coefficient G, the shear modulus, for different weak layers.

The snow structure has been analysed macroscopically in the field and for some layers representative snow samples have been extracted in order to prepare, in the cold laboratory, single-sided serial planes with cuts every 0.1 mm recorded by video. The analysis of these snow samples should have given the relation between some mechanical properties (strength, strain) and the structural properties. Due to basic problems in defining the connection between complex snow grains (e.g. surface hoar), we were unable to complete this part in due time. Only preliminary results on this aspect are presented here. Based on our long-term database, containing macroscopic structural and strength data of weak layers, a relationship between snow type and shear strength has been established.
A portable calorimeter for measuring liquid-water content of wet snow
Authors: Kawashima Katsuhisa , Endo Toru , Takeuchi Yukari
Published: September 2017

In order to facilitate the measurement of liquid-water content of snow in high mountains, a portable calorimeter named “Endo-type snow-water content meter” was developed. It is composed of a metal-coated container made of insulating materials and a lid of the container with a small-thermistor thermometer. Its strong points are its light weight, small size and easy fabrication with cheap materials. The total weight of the device is as light as 250 g, which is less than 10% of the snow-water content meter widely used in Japan (Akitaya-type snow-water content meter). The results of experiments have revealed that the device is capable of measuring the liquid-water content within 2 minutes with an accuracy of 2% by weight.
Differences in compaction behavior of three climate classes of snow
Authors: Sturm Matthew , Holmgren Jon
Published: September 2017

In a recent paper (Sturm and others, 1995), a global seasonal snow-cover classification system was developed with each class defined by snow properties like grain-size and type. Here, characteristic bulk density vs time curves are assigned to three classes using snow-course data from Alaskan and Canadian sites. Within each class, curves have similar slopes and intercepts but between classes they are different. The relationship between slope, intercept and snow rheology has been investigated using a finite-difference model in which snow layers are assumed to behave as viscous fluids. Using observed slopes, the density-dependent compactive viscosity of each class has been determined. These are consistent with published values. Results indicate that load and load history are less important to the compaction behavior than grain and bond characteristics, snow temperature and wetness. The study suggests that differences in compaction behavior arise primarily from differences in rheology, the result of climatically controlled differences in the character of the snow. This finding explains why regional snow densities have been successfully predicted from air temperature and wind speed alone, without considering snow depth.
New categories for the climatic division of snowy areas in Japan
Authors: Ishizaka Masaaki
Published: September 2017

New categories for the climatic division of snowy areas according to their snow-cover character in mid-winter are proposed. They are a wet-snow region, a dry-snow region, an intermediate snow region and a depth-hoar region. The wet-snow region is defined as the region in which every layer of deposited snow is wet due to percolation of snowmelt water throughout the winter. In contrast, areas in which the snow cover is dry, at least in the coldest period of the winter season, are classified into two categories, that is the dry-snow region and the depth-hoar region. In the latter region, the small snow depth and low air temperature induce development of depth hoar. The intermediate snow region was introduced to indicate an intermediate character between the dry-snow and wet-snow regions. From the climatic dataset calculated by the Japanese Meteorological Agency and from snow surveys, it has been found that in snowy areas, which have a climatic monthly mean temperature in January (Tjan) higher than 0.3°C, snow would be expected to be wet throughout the winter and, in areas that have Tjan, lower than −1.1°C, to be dry at least in the coldest period. Snow covers, where Tjan is between these two values, are expected to have intermediate characters. Therefore, these temperatures are supposed to be critical values among the wet, dry and intermediate snow regions. The criterion that separates the depth-hoar region from the dry-snow areas was found to be given by a climatic mean temperature gradient. This value lies between 10 and 12°Cm−1, which is derived by dividing the absolute value of the average of the climatic monthly mean air temperature, which is always below 0°C, by the average of the monthly maximum snow depth during January and February.
Determination of snow-covered area in different land covers in central Alaska, U.S.A., from aircraft data — April 1995
Authors: Hall Dorothy K. , Foster James L. , Chang Alfred T. C. , Benson Carl S. , Chien Janet Y. L.
Published: September 2017

During April 1995, a field and aircraft experiment was conducted in central Alaska in support of the Moderate Resolution Imaging Spectroradiometer (MODIS) snow-mapping project. The MODIS Airborne Simulator (MAS), a 50 channel spectroradiometer, was flown on board the NASA ER-2 aircraft. An objective of the mission was to determine the accuracy of mapping snow in different surface covers using an algorithm designed to map global snow cover after the launch of MODIS in 1998. The surface cover in this area of central Alaska is typically spruce, birch, aspen, mixed forest and muskeg. Integrated reflectance, Ri was calculated from the visible/near-infrared channels of the MAS sensor. The Ri was used to estimate different vegetation-cover densities because there is an inverse relationship between vegetation-cover density and albedo in snow-covered terrain. A vegetation-cover density map was constructed using MAS data acquired on 13 April 1995 over central Alaska. In the part of the scene that was mapped as having a vegetation-cover density of < 50%, the snow-mapping algorithm mapped 96.41% snow cover. These areas are generally composed of muskeg and mixed forests and include frozen lake. In the part of the scene that was estimated to have a vegetation-cover density of ≥50%, the snow-mapping algorithm mapped 71.23% snow cover. These areas are generally composed of dense coniferous or deciduous forests. Overall, the accuracy of the snow-mapping algorithm is > 87.41% for a 13 April MAS scene with a variety of surface covers (coniferous and deciduous and mixed forests, muskeg, tundra and frozen lake).
Measurements and numerical simulations of snow-particle saltation
Authors: Nishimura K. , Sugiura K. , Nemoto M. , Maeno N.
Published: September 2017

First, wind-tunnel experiments were carried out to measure the trajectories of saltating snow particles with varying friction velocity. Trajectories of saltating particles were recorded by a video system with a laser sheet and trajectory statistics, such as ejection and impact velocities and angles, were obtained for each particle. Parabolic trajectories are considerably elongated with an increase in the friction velocity; impact angle was approximately the same but ejection angle decreased with increasing friction velocity. Furthermore, it should be noted that the gradient of flux decay with height decreased with friction velocity. In the experiments, a snow-particle counter, which can sense not only the number of particles but also their diameters, was introduced. The flux distribution and the transport rate obtained as a function of the particle size gave a new insight into the relationship with the friction velocity.

Trajectories of saltating grains were computed, using the measurements of the initial ejection velocities, angles and the mean velocity profile of the air. The results agreed reasonably with our measurements. Using the measured probability distribution of the ejection velocities, an ensemble of trajectories was computed and thence the vertical profiles of stream-wise fluxes. The exponential decay of the flux on height was obtained in all cases and it supports the basic validity of the model, although agreement is less than expected.
The development of a rule-based spatial model of wind transport and deposition of snow
Authors: Purves R. S. , Barton J. S. , Mackaness W. A. , Sugden D. E.
Published: September 2017

This paper describes the early stages in the development and testing of a spatio-temporal rule-based model of snow transport by wind over complex terrain. The model uses a cell-based approach and takes into account a range of meteorological, snow-pack and topographic variables. Simple rules are used to determine movement of material from cell-to-cell within the model.

A geographic information system is utilized in modelling wind vectors and the influence of topography upon those vectors, and creating the resulting pattern of snow accumulation at a resolution of 50 m. These patterns of accumulation have been compared with empirical work in the field and, although field data were limited, a good qualitative correlation has been found; for example, modelled accumulations correlate with known areas of accumulation such as gullies and hollows.
Snowdrift modelling in a wind tunnel: vertical and horizontal variation of the snow flux
Authors: Naaim-Bouvet Florence , Naaim Mohamed
Published: September 2017

This paper deals with the influence of the vertical and horizontal variation of Aeolian snow flux on estimations of snow-storm duration and on snowdrift patterns simulated in a wind tunnel.

First of all, we shall review recent developments, including our own simulations, concerning the horizontal increase of mass flux until drifting-snow saturation has been reached.

Next, after a critical examination of various snowdrift-modelling criteria, we present the results of an experiment undertaken in our wind tunnel: We studied cross-section drill-area changes behind a small-scale snow fence as a function of time for different fetches but for the same mean wind speed at the beginning of the testing section. For each fetch, we carried out vertical profiles of sand particles using image processing and we studied the geometrical parameters of the drift. We conclude dial changes in the cross-section drift area depend on the ablation length and if particle saturation is not reached, the use of a storm-duration scale leads to Overevaluation of prototype storm duration. Moreover, we point out that drift pattern vary as a function of the concentration profiles.
Experimental mass-flux measurements: a comparison of different gauges with estimated theoretical data
Authors: Font D. , Mases M. , Vilaplana J.M.
Published: September 2017

In experimental snowdrifting mass-flux measurements many different instruments have been tested (Takeuchi, CEMAGREE Mases, etc.). Very often the results obtained are a function of the gauge used. However, in order to compare data from different instruments, orders of magnitude have to be similar.

Since 1992, snowdrifting has been studied at an experimental plot at La Molina ski resort (eastern Spanish Pyrenees). The alpine site, characterized by a plateau topography, is located at 2250 m.

In this paper, different gauges used to measure snowdrifting mass flux at this site are presented: one snow-collector column and two types of snow traps. Snow-collector columns (prismatic boxes) are permanent installations and are used to measure the mass-flux episode. Snow traps (Takeuchi, 1980: modified) are lighter and more mobile, and they are used for short experiments during a wind episode during which mass-flux data are obtained.

The three different gauges are compared and the rate of trapping efficiency is suggested from a comparison of the field data with estimated mass-flux data deduced from empirical formulae (Mellor and Fellers, 1986; Naaim-Bouvet and others, 1996). The mass-flux values obtained at the experimental site are lower than the estimated values.
Empirical model for snowdrift distribution in avalanche-starting zones
Authors: Mases M. , Buisson L. , Frey W. , Martí G.
Published: September 2017

Field data from Stillberg (Switzerland), provided by SFISAR, have been analysed in order to understand the spatial distribution of snow transported by wind in avalanche-starting zones. The results have been used to develop a new empirical model for snowdrift distribution. This model constitutes the “snow-wind module” of the knowledge-based computer system called ELSA.

The model is based on an empirical parameter called the wind or “aeolien” coefficient. It represents the relation between two snow heights at a given place: the snow accumulated at the end of a wind period (or wind episode) and the snow available for transport at the beginning of the wind period. The wind coefficient has been established using field data from the Stillberg site.
Density, velocity and friction measurements in a dry-snow avalanche
Authors: Dent J.D. , Burrell K.J. , Schmidt D. S. , Louge M.Y. , Adams E.E. , Jazbutis T.G.
Published: September 2017

A small avalanche path near the Bridger Bowl ski area in southwestern Montana has been instrumented to measure density, velocity and dynamic friction in a flowing avalanche. These measurements, made by an array of sensors mounted in the avalanche path, have been carried out for several dry-snow avalanches. Measurements of density were made using a capacitance probe that measures the dielectric constant of any material that passes in front of it. Through a calibration procedure, the dielectric constant of a given type of snow can be related to the density of that snow. Optical sensors were used to measure light reflected from the avalanche as it passed by the sensors. Signals from adjacent optical sensors were cross-correlated to determine velocity. Density and velocity measurements were made at several heights in the avalanche, with particular attention directed near the running surface. Results indicate that avalanche deformation is concentrated near the running surface where the snow density is found to be largest. Upward from the surface, the velocity gradient falls off greatly while the density also declines.

Finally, the dynamic-friction coefficient at the base of the avalanche was found by measuring shear and normal forces on a roughened 23 cm × 28 cm aluminum plate mounted parallel and flush with the avalanche running surface. The ratio of the shear force to normal force on the plate provides a measure of the dynamic-friction coefficient at the base of the avalanche.
Measurements of the velocity distribution in ping-pong-ball avalanches
Authors: Keller Stefan , Ito Yoichi , Nishimura Kouichi
Published: September 2017

Dense-flow avalanches may be simulated as granular flows. In this work, large-scale experiments on ping-pong-ball avalanches are investigated. In one situation, channeled flows with up to 6000 balls are produced. Another set-up is the open, three-dimensional flow over the landing track of a ski-jump field, using up to 300 000 ping-pong balls. The measurements focus on the internal velocity distribution, of the balls as well as of the air. A video camera positioned above the flow allows the measurement of the location and distance of a single ball, which finally leads to its velocity. Different profiles in the head and tail as well as other flow properties are obtained. With vertically placed lubes, in and above the flow, the open ends pointing towards the ground, the static pressure depression induced by the air flow is measured and leads to qualitative air-velocity profiles in and above the tail of the ping-pong-ball avalanches.
Measurement of snow-hardness distribution
Authors: Takeuchi Yukari , Nohguchi Yasuaki , Kawashima Katsuhisa , Izumi Kaoru
Published: September 2017

Disitributions of snow hardness minutely measured with a bandy-type digital load-gauge (push–pull gauge) are demonstrated. This push-pull gauge is of compact design and is useful for precise measurement of tension and compression loads. It can measure the maximum strength of a snowpack when it is destroyed by the attachment pushed horizontally into the side of the pit. Because it takes only a few seconds for one measurement, snow-hardness distribution can be measured at very small space intervals more quickly and with less effort than by using any previous hardness meter, such as a rammsonde, Canadian gauge, Kinosita-type hardness meter, and so on.

Snow-pit observations were made at Saiho, Sapporo and Minakami, Japan, in the winter seasons of 1996 and 1997. The snow hardness was measured with the push-pull gauge at regular intervals of 5 cm vertically and 10 cm horizontally. Some weak layers between harder layers could be detected with the push-pull gauge whereas they could not be using the rammsonde. The hardness of snow was observed to be almost uniform horizontally before snowmelt. Once meltwater infiltrated into the snowpack, its distribution became heterogeneous. It was revealed that the hardness of the fine-grained compacted snow layer with grain-sizes less than 0.5 mm showed a high correlation with the fourth power of the snow density.
Mathematical and physical modelling of powder-snow avalanches in Russia
Authors: Eglit M.E.
Published: September 2017

The paper describes mathematical and physical models for powder-snow avalanches developed by a group of researchers at Moscow State University.
Refinements to the stability index for skier-triggered dry-slab avalanches
Authors: Jamieson J.B. , Johnston C.D.
Published: September 2017

Stability indices for skier-triggering of slab avalanches are discussed in terms of an adjustment to the skier-induced stress to allow for ski penetration and an adjustment to shear strength (measured with a shear frame) to allow for normal load due to the slab overlying the weak layer. The proposed adjustment to shear strength depends on the microstructure of the weak layer. These adjustments are incorporated into a refinement of the previously established Swiss stability index for skier-triggering. The percentage of correct predictions for the Swiss and refined indices are evaluated using data from 115 weak layers on skier-tested avalanche slopes, 83 of which were classified as persistent weak layers of surface hoar, faceted crystals or depth hoar and 32 as non-persistent weak layers. The refined index reduces the number of incorrectly predicted slab avalanches for the persistent weak layers.
The Impact of surface perturbations on snow-slope stability
Authors: Conway H.
Published: September 2017

Measurements and observations by others indicate that a potential slab avalanche consists of a relatively cohesive slab of snow overlying a thin weak layer that coniains flaws where locally the shear stress from the overburden is not fully supported. Under favorable conditions, snow will shear strain-soften, which provides the basis for applying a slip-weakening model to examine the size of flaw needed to initiate sub-critical crack propagation along the weak layer. Using typical values for snow properties, the model predicts sub-critical crack growth can initiate from a relatively small flaw well before the shear stress from the overburden approaches the peak shear strength at tin-bed. The occurrence of small flaws or imperfections in the basal layer would explain field measurements which usually indicate that avalanching occurs before the applied shear stress exceeds the shear strength at the basal layer.

Widespread slab-avalanche activity often increases significantly soon after the onset of rain on new snow. Measurements of temperature and mechanical properties show that only the upper 0.15 m or less of the slab has been altered at the time of avalanching; alterations at the sliding layer have not yet been detected. Results from the slip-weakening model indicate that the rain-induced alterations would reduce the size of flaw needed to initiate sub-critical crack growth by 10–20%. The observations and model results show clearly the importance of the slab properties; it is evident that both the slab and the weak layer act together to control slope stability. A further implication is that the stability of freshly deposited snow is often close to critical, because a relatively small surface perturbation is often sufficient to cause avalanching. This is not surprising, because it is well known from field observations that new snow on slopes should be treated with caution.
Tentative investigations on surface hoar in mountain forests
Authors: Höller Peter
Published: September 2017

This paper deals with air temperature, net-radiation and relative-humidity measurements which we performed in Austria in different zones of mountain forests in recent years. Our aim using such measurements was to approximate the general conditions for the formation of surface-hoar layers in low-density forest stands near the timber line. These layers are a necessary condition for snow-slab release and avalanche formation.

Our investigations showed that the total radiation balance was negative but less negative in a forest with a close canopy (on clear nights about −30 to −40 W m−2) than within a small clearing (6 m by 6 m). Moreover, the total radiation balance within the forest clearing was almost the same as that in an open field. There we measured −60 to −80 W m−2 on clear nights. Approximations of surface temperature (ts) showed that ts was below the dewpoint (tE) in an open field but did not reach tE in the forest; moreover, ts was very close to tE within the forest clearing. Water-vapor flux was positive only in open terrain (i.e. condensation between 0.1 × 10−6 and 0.9 × 10−6 kg m−2 s −1 and evaporation occurred within the clearing and in the forest.
A field method for avalanche danger-level verification
Authors: Cagnati A. , Valt M. , Soratroi G. , Gavaldà J. , SelléS C. G.
Published: September 2017

Even though the danger-level verification indicated in a bulletin should be a priority aim of avalanche-forecast services, there are no easily applicable verification methods available today. The main difficulty lies in the fact that avalanche observation is no longer sufficient. Therefore, it is necessary to verify the actual condition of the snow-pack stability, particularly concerning low danger levels. This work introduces a procedure for “a posteriori” field verification of danger level, both in space and time (24–72 hours). The method is based on the following elements: avalanche-activity survey, observation of cross-country skiers’ activity, snow profiles and “Rutschblock” tests. These elements, relating both to time and the examination zone, are combined to provide an objective danger degree according to the European avalanche-danger scale. The method was used experimentally in the winter of 1993–94 in the Dolomites and subsequently, in the winter of 1995–96 in the Catalan Pyrenees. As far as 24 hour forecasts are concerned, the method has shown a forecast reliability of 93% in the Dolomites and 76% in the Catalan Pyrenees, while 48 hour forecasts have given values of 89% and 64%, respectively. The lower degree of forecast reliability in the Catalan Pyrenees is accounted for by the unusual weather conditions of winter 1995–96, which was very snowy and characterized by few foreseeable avalanche conditions. The practical application of the proposed verification method has given encouraging results, thus allowing experts to find the main errors in order to improve future forecasts. However, simpler survey procedures are necessary in order to operate on a regional scale. The method is suitable for further development relating to verification of both degree of danger and danger localization.
Modelling of the densification of polar firn: characterization of the snow–firn transition
Authors: Arnaud L. , Lipenkov V. , Barnola J. M , Gay M. , Duval P.
Published: September 2017

The transformation of dry snow to firn is described by the transition between densification by deformationless restacking and densification by power-law creep. The observed decrease with temperature of the density at the snow-firn transition seems to result from the competition between grain-boundary sliding and power-law creep. These two densification processess occur concurrently in snow, although there are probably micro-regions in which sliding alone occurs. Validation of a geometrical densification model developed for ceramics has been obtained from densification data from several Antarctic and Greenland sites and from the characterization of the structure of polar firn.
Modelling the change in structure and mechanical properties in dry-snow densification to ice
Authors: Golubev Vladimir N. , Frolov Anatoly D.
Published: September 2017

The regular packing of spheres or polyhedrons of various shapes linked by rigid bonds is presented and discussed as a model of snow structure. Basic structural parameters of this model are: the coordination number and introduced dimensionless factors of friability and rigidity. The snow densification is described as successive changes of these parameters. Use of the model allows us to relate the density increase from ~130 to ~320, ~550, ~700, ~820 and 917 kg m−3, while the coordination number of the structure increases accordingly from 3 (friable hexagonal) to 4 (tetrahedral), 6 (cubic), 8, 10, 12 (dense hexagonal). These structural changes are in good agreement with the critical densities established in experimental studies of snow densification and the physical properties of snow. It is shown that the model presented allows us to estimate the mechanical properties of ice-porous media: Young’s modulus, Poisson’s ratio and strength.
Elastic properties of snow-ice formations in their whole density range
Authors: Frolov Anatoly D. , Fedyukin Igor V.
Published: September 2017

The available experimental data on acoustic parameters and dynamic elastic moduli of dry coherent snow-ice formations in their whole density range are analysed and generalized in this paper. A set of critical densities at which there are sufficiently sharp changes in the laws of these property variations have been discovered and are discussed. The empirical equations describing the elastic-wave propagation velocities (Vp and Vs), acoustic resistivities and elastic moduli as functions of the porosity factor of the medium are obtained for five sub-ranges in the density range from light snow to massive ice.
Field observation and modelling of weak-layer evolution
Authors: Fierz Charles
Published: September 2017

For operational snow-cover simulations, an adequate modelling of the evolution of buried weak layers is of crucial importance. Therefore, the processes governing snow metamorphism within weak layers before and after burial must be known in detail. At the study site of the Swiss Federal Institute for Snow and Avalanche Research, 2540 ma.s.l., a 2 cm thick weak layer of column-grown cup-shaped crystals formed beneath a thin crust in mid-January 1996. Exposed to near-surface processes for about 4 weeks, the layer was buried on 8 February and persisted in the snowpack until mid-April. Numerous temperature profiles and characterizations of both the weak and the adjacent layers were performed in situ. Snow-grain samples, as well as larger snow blocks, were taken to the cold laboratory for further analysis of the texture. The shear strength of the buried weak layer was also investigated by means of shear-frame tests. The field observations and measurements are compared with model simulations of snow temperature and stratigraphy. The comparison shows potential and problems in the modelling of weak-layer evolution.
Comparison between experiment and computer modelling of plane-strain simple-shear ice deformation
Authors: Wilson C.J. L. , Zhang Y.
Published: September 2017

An examination of both experiments and computer models of polycrystalline ice undergoing a simple shear suggests that there is good agreement. The model has correctly reproduced the deformational and microstructural features caused by glide on (0001) in the ice aggregates. This success is particularly prominent for those ice grains with a lattice orientation suitable for hard or easy glide or kinking, and where there is a sub-horizontal с axis and a larger grain-size. A limitation may be that the model cannot explicitly simulate recrystallization and grain-boundary migration, which are two other important processes operating jointly with glide in experimentally deformed ice. However, through the use of the models, it is possible to show how kinematic factors can control the processes of recrystallization. The localization of recrystallization in the polycrystalline ice aggregate is determined by the stress and strain variations between neighbouring grains.
A glaciological model of the Younger Dryas event in Scandinavia
Authors: Fastook James L. , Holmlund Per
Published: September 2017

A finite-element method solution of the continuity equation is used to investigate complex features of the Younger Dryas period. By comparing results of the model with field evidence, we conclude that the climatic event responsible for the Younger Dryas stillstand was probably short (less than 500 years). The assumption of a general sliding condition for elevations below 100 m, with an enhanced sliding zone through the center of the Baltic and Gulf of Bothnia, yields broad agreement for marginal positions in Sweden and Finland during a simulated termination. A stillstand near the Younger Dryas moraine position is attained with a climatic equilibrium-line altitude (ELA) depression of 600 m for a time period of 500 years. Agreement of simulated behavior with observed behavior is less consistent in the more maritime western Sweden and western Norway.
Hydrology of a segment of a glacier situated in an overdeepening, Storglaciären, Sweden
Authors: Leb. Hooke Roger , Pohjola Veijo A.
Published: September 2017

Tracer experiments, and water-level observations made while drilling 47 boreholes in an overdeepened section of Storglaciären, have demonstrated that nearly all of the water passing through this part of the glacier moves in englacial conduits. Much of the viscous energy dissipated by subglacial water flowing up an adverse bed slope out of such an overdeepening may be needed to warm the water to keep it at the pressure-melting point. If the adverse slope is sufficiently steep, freezing may occur within the conduits. The possibility for enlargement of conduits by melting is thus limited and water pressures become high. We infer that this, combined with possible blocking of conduits by freezing, forces the water to seek englacial pathways.

The frequency with which englacial conduits are encountered during drilling suggests that there are several hundred of them in any given cross-section of the glacier. Consequently, each must carry a small fraction of the total discharge, say ∼ 10−3 m3 s−1. Tracer experiments suggest that flow rates in these conduits are < 10− m s−1, so conduit cross-sectional areas must be ∼10−2 m2, a size that is consistent with video observations in boreholes. The observed mean hydraulic gradient through the overdeepening is ∼0.04. If the conduits were of uniform cross-sectional area, the roughness implied by these figures would be unreasonably high and water pressures in them would be lower than observed. Thus, we hypothesize that conduits are locally constricted to only a small fraction of their average cross-sectional area.
Evolution of glaciation in the Pamiro-Alai mountains and its effect on river run-off
Authors: Konovalov V. G. , Shchetinnicov A.S.
Published: September 2017

The aim of the present research is to evaluate changes in the glacierized area, glacier-water resources and glacial run-off during the last 25–30 years. The prevailing process of degradation has resulted in a 16% diminution of the glacierized area in Gissaro-Alai and 11% in the Pamirs. The ratio between the advancing, stationary and retreating glaciers in the Gissaro-Alai mountains is 1:5:17, and the one in the Pamirs is 1:1:4. Moraine-covering of the glaciers has increased from 8 to 11 % in the Gissaro-Alai and from 6 to 11 % in the Pamirs. Ice-volume diminution of glaciers in the Gissaro-Alai is 17% and in the Pamirs it is 12%. The mean long-term annual volume of total glacial melting, glacial run-off and variation coefficients of these values in the river basins of the Pamirs and the Gissaro-Alai are described as functions of the altitudes of glacier termini, equilibrium lines and a new parameter, which characterizes the influence of the glacierized area distribution according to altitude on run-off. The data presented here indicate changes in mean annual volumes of glacier water yield in the river basins of the Pamirs and the Gissaro-Alai mountains, related to glaciation evolution in 1957–80.
Thermoluminescence in suspended sediment of glacier meltwater streams
Authors: Gemmell Alastair M.D
Published: September 2017

To determine the factors controlling natural levels of thermoluminescence (NTL) of fluvioglacially transported suspended sediment, samples were taken at hourly intervals from a meltwater stream emanating from Sólheimajökull in southern Iceland. The NTL of the samples were measured and compared with fluctuations in suspended-sediment load and in flow depth of the stream. It was found that the ratio of the 325°C and the 375°C regions of the NTL spectrum was more closely related to sediment load and flow depth than were the individual regions themselves. Analysis of the patterns suggests that NTL fluctuations are related to changes over time in the sources of sediment entrained by the stream. It is inferred that these changes relate to diurnal temperature cycles plus precipitation events. Such fluctuations raise doubts as to the validity of bulk sampling procedures in TL dating of Quaternary fluvioglacial sediments.
Historie retreat of Grand Pacific and Melbern Glaciers, Saint Elias Mountains, Canada: an analogue for decay of the Cordilleran ice sheet at the end of the Pleistocene?
Authors: Clague John J. , Evans S. G.
Published: September 2017

Grand Pacific and Melbern Glaciers, two of the largest valley glaciers in British Columbia, have decreased over 50% in volume in the last few hundred years (total ice loss = 250–300km3). Melbern Glacier has thinned 300–600 m and retreated 15 km during this period; about 7 km of this retreat occurred between the mid-1970s and 1987, accompanied by the formation of one of the largest presently existing, ice-dammed lakes on Earth. Grand Pacific Glacier, which terminates in Tarr Inlet at the British Columbia–Alaska boundary, retreated 24 km between 1879 and 1912. This rapid deglaciation has destabilized adjacent mountain slopes and produced spectacular ice-marginal land forms. The sediments and land forms produced by historic deglaciation in Melbern-Grand Pacific valley are comparable, both in style and scale, to those associated with the decay of the Cordilleran ice sheet at the end of the Pleistocene (c. 14–10 ka BP). Rates of historic and terminal Pleistocene deglaciation also may be comparable.
Is the Longitudinal Profile of Storglaciaren, Northern Sweden, in Balance with the Present Climate?
Authors: Holmlund Per
Published: September 2017

The main perturbation in the mass balance of Storglaciären during the twentieth century was caused by a sudden 1°C increase in the summer mean temperature around 1910. Later perturbations of the climate have been of minor importance in relation to the mass balance. Annual field surveys suggest that the mass budget on Storglaciären has been in near balance for the last 15 years. Because of this major step-like change, we can establish the validity of theoretical models giving response times for Storglaciären of the order of 50 years. According to these models, Storglaciären could by now have reached a profile in balance with the present climate. To study this problem, the emergence velocity was calculated and compared with the net balance. The result shows that the emergence velocity either balances or exceeds the net balance for the entire tongue except for the lowermost part, where it decreases to about half of the net balance. A slight further recession of the front position would thus be expected with today’s climate.

Calculated balance velocities also suggest that most of the present profile is close to a steady-state profile, if the mean annual sliding velocity is about 50% of the surface velocity. Lower sliding velocities would imply a thickening of the tongue and a thinning of the accumulation area during years of balanced mass budget.
Modelling Changes in Scattering Properties of the Dielectric and Young Snow-Covered Sea Ice at GHz Requencies
Authors: Drinkwater Mark R. , Crocker G.B.
Published: September 2017

Observations of the physical properties of the snow cover and underlying young fast ice in Resolute Passage, N.W.T., Canada, were made during the winter of 1982. Detailed measurements of snow density, and ice and snow temperatures, salinities, and brine volumes were made over a period of 46 d, beginning when the ice was 0.4 m thick and about 8 d old. The recorded values are used in a theoretical mixture model to predict the dielectric properties of the snow cover over the microwave frequency range. The results of this analysis are then used to investigate the effects of the snow properties on the radar back-scatter signatures of young sea ice. The results show that back-scatter is a function of the incidence angle and can change significantly over short periods of time during the early evolutionary phase of ice and snow-cover development. This has important consequences for the identification of young ice forms from Synthetic Aperture or Side Looking Airborne Radar images.
Fish Antifreeze Proteins and the Creep of Polycrystalline Ice
Authors: Glen John W. , Ives David J.
Published: September 2017

Creep curves obtained from the polycrystalline ice samples containing low concentrations of antifreeze glycopeptides (AFGPs) do not show the re-accelerating or tertiary creep that is found in pure ice samples. Previous work has shown that AFGPs inhibit grain-boundary migration in ice and the present results are consistent with this, as tertiary creep is associated with nucleation and growth of new ice grains.
Enhanced Radar Scattering From Water Inclusions In Ice
Authors: Bamber J.L.
Published: September 2017

It is believed that water-filled cavities on the scale of decimetres are present in a number of glaciers in Spitsbergen. The evidence for this hypothesis comes from airborne radio echo-sounding records collected by the Scott Polar Research Institute in 1983. The size of these cavities prevents the use of Rayleigh scattering theory and requires a more general analysis. Mie scattering theory is used to investigate the scattered power providing some unexpected results, the most significant of which is that for water bodies greater than approximately 0.25 m in radius the returned power from the volume illuminated is greater than that from a perfectly reflecting plane boundary.
Two-Dimensional Deformation Patterns in Sea Ice
Authors: Erlingsson Björn
Published: September 2017

The mechanical behaviour for the geometrical properties of two-dimensional deformation has been investigated. The Mohr formulation of failure, which is based on the concept of slip at the plane of weakness, is used in this study. It is shown that alteration of the shear stress τn at the plane of weakness requires self-similarity of features in deformation patterns. A general relationship between the angle of internal friction and the breaking angle of deformation patterns is derived. Using imagery data, this relationship is used to find the angle of internal friction from selected sea-ice deformation patterns. The value obtained for this angle is Φ = 15° ± 2° for deformation on a scale from 100 m to 100 km.
Early Discoverers XXXV: Descent of Glaciers: Some Early Speculations on Glacier Flow and Ice Physics
Authors: Walker J.C.F. , Waddington E.D.
Published: September 2017

Scheuchzer’s dilatation theory and Altmann’s rigid sliding theory were the first glacier-flow theories to receive serious scientific attention. When Agassiz began a research program at Unteraargletscher in 1839, he held several incorrect notions about glacier flow. Forbes understood the difficulties with the existing theories, and in the early 1840s he and Agassiz acquired motion, temperature, and structural data that were incompatible with the dilation and sliding theories but were suggestive of flow analogous to that of a viscous fluid. How an apparently brittle rigid solid like ice could flow became the central paradox requiring explanation. Some of the most able physicists of the mid-nineteenth century went through contortions in their largely misguided efforts to explain the viscous behaviour in terms of the known physics of rigid solids. Personality and speculation played a far larger part in their debates than we see in scientific discussions today.
The Mass Budget of the Lambert Glacier Drainage Basin, Antarctica
Authors: Allison Ian
Published: September 2017

Estimates have been made of the mass budget of the total drainage basin of Lambert Glacier. These show a small but significant positive state of balance for the interior basin (the accumulation area up-stream of the major ice streams), and strongly suggest a positive balance for the Lambert Glacier system (the region of major ice streams, between the Amery Ice Shelf and the interior basin). The total mass flux into the interior basin is estimated as 60 Gt a−1. Results are presented from a number of ice movement stations established between 1972 and 1974 around the perimeter of the southern Prince Charles Mountains. These results, together with ice thicknesses from radio echo-sounding in the area, give a total mass outflux through the 2 000 m contour of 30 Gt a−1, implying a budget excess of a further 30 Gt a−1 over the whole interior basin. Results from velocity and ice thickness measurements give a mass discharge through a section near the junction of Lambert Glacier and the Amery Ice Shelf of 11 Gt a−1. Losses within the Lambert Glacier system proper account for a further 7 Gt a−1 and an overall mass excess of 12 Gt a−1 is estimated for the Lambert Glacier system. This present positive state of balance contrasts with geomorphological evidence from the southern Prince Charles Mountains of a large drop in ice level in recent geological time, and the ice surface in the area may now be building up after a major recession.
On the Computation of Heat Transfer Coefficients from Energy-Balance Gradients on a Glacier
Authors: Kuhn Michael
Published: September 2017

The turbulent flux of sensible heat in the energy balance of a glacier surface is assumed to be proportional to the temperature difference between the glacier surface and the atmosphere at the same level but outside the thermal influence of the glacier. The factor of proportionality between them is first explained in terms of friction velocity, roughness height, and stability function of the logarithmic wind and temperature profile. It is then derived from climatological records and measurements of the energy balance and its altitudinal gradients at Hintereisferner. Examples of the energy-balance components and their change with altitude are given for the entire ablation season as well as for short periods. The heat transfer coefficients derived have a mean value of 1.7±0.2 MJ m−2 d−1 K−1 (40 ± 5 ly d−1 K−1).
Supraglacial Debris of G2 Glacier in Hidden Valley, Mukut Himal, Nepal
Authors: Nakawo M.
Published: September 2017

Field investigations of supraglacial debris were carried out during the monsoon season in 1974 on G2 glacier near Tukche Peak in Hidden Valley, Mukut Himal, Nepal. The thickness of the debris layer was observed to increase down-glacier. Laboratory analysis, however, showed a decrease in particle size in the same direction. This decrease is explained in terms of mixing of particles contained in glacier ice with the original debris as melting proceeds. A simple relation between debris mass and glacier flow is introduced to explain the observed results.
Is Vertical Shear in an Ice Shelf Negligible?
Authors: Sanderson T. J. O. , Doake C. S. M.
Published: September 2017

Vertical shear stress in ice shelves cannot be precisely zero, since the upper and lower surfaces are generally not parallel. By performing stress balance on a vertical column in an ice shelf we calculate what its magnitude must be. This is done for an unconfined glacier tongue and for a confined bay ice shelf; first, using the assumption of constant temperature and density with depth, and secondly, using realistic data and profiles for Erebus Glacier tongue and for the Amery ice shelf. Shear stresses increase almost linearly with depth and are proportional to surface slope. For Erebus Glacier tongue the shear stress is at most 5% of the magnitude of the direct stress deviators and its action through the ice shell should result in differential movement of 1.8 cm a−1 between the top and bottom of the ice shelf. For the Amery ice shelf, the shear stress is at most 0.4% of the magnitude of the direct stress deviators and this should lead to differential movement of 2.5 cm a−1 between the top and bottom of the ice shelf. Shear stresses are therefore generally negligible in comparison with direct stress deviators and can be ignored when considering the overall dynamics of ice shelves. Differential movement is unlikely to be detectable.
The Mechanics of Drumlin Formation with Particular Reference to the Change in Pore-Water Content of the Till
Authors: Menzies John
Published: September 2017

Most drumlins are composed of till that appears similar in all characteristics to non-drumlin till. Evidence, however, in the form of till layer sequences and from palaeomagnetic Koenigsberger ratios indicate that drumlin till may have a slightly higher pore-water content at the time of lodgement than nondrumlin till. In order that deposited till remains at the ice-glacier-bed interface to initiate drumlin formation, it must undergo rapid geotechnical changes whereby its pore-water content is dissipated thereby increasing the shear strength of the till. Two mechanisms of pore-water removal are possible. Firstly, pore water may be removed from localized patches within a mobile layer of till at the ice-glacier-bed interface, thus creating nuclei of higher-strength till around which deforming till may adhere. Secondly, removal of water initially from the thin water film at the base of a glacier may result in increased pressure melting of the ice leading to till melt-out and subsequent loss of pore water from the deposited till. The loss of water at the glacier bed may be either via permeable subglacial deposits or bedrock, or within subglacial depressions.
A System for Accurate Temperature Control of Small Fluid Baths
Authors: Morgan V. I.
Published: September 2017

A temperature controller is described which uses a thermistor sensor and electrical heating to maintain the temperature of a small bath of fluid to within a few millidegrees.