Winter snow cover at Austre Okstindbreen is influenced strongly by patterns of atmospheric circulation, and by air temperatures during precipitation. Differences of circulation over the North Atlantic and Scandinavia during the winters of 1988–89 and 1989–90 were reflected in the ionic and isotopic composition of snow that accumulated at the glacier. Early summer ablation did not remove, or smooth out, all the initial stratigraphic differences. In the first half of the 1988–89 winter, most air masses took a relatively short route between a marine source and Okstindan; late winter snowfalls were from air masses which had taken a longer continental route. The snow that accumulated in the first half of the 1989–90 winter was associated with air masses which had followed longer continental routes, and so brought higher concentrations of impurities from forests, lakes and crustal material. The ablation season began earlier in 1990 than in 1989, and summer winds and rain supplied more impurities to the snowpack surface.

The friction of pure ice against various materials was studied at the melting point by pulling plates of the materials of known roughness under a melting ice sample, which was loaded from above, and by maintaining a surrounding air temperature of +2°C (±1°C). Speed was varied over a wide range from 0.05 to 400 mm s−1.

Results for an aluminium sheet of roughness Ra = 0.84 μm, showed a maximum in friction coefficient of 0.04 at a speed of 16 mm s−1. Below this speed the friction coefficient dropped to 0.002 at 0.2 mm s −1 and results from different ice samples were very reproducible. Above 16 mm s−1, the friction coefficient initially dropped to about 0.002 at 100 mm s−1, and then increased again to 0.037 at 400 mm s−1. Results at speeds above 16 mm s−1 were much less reproducible than those at lower speeds. Results are given also for the friction of ice on Formica, acrylic, and copper plates.

The amount of meltwater produced during a test was measured by weighing an absorbent tissue before and after mopping-up the meltwater. The amount of meltwater was significantly more for aluminium than for Formica or acrylic, showing that the thermal conductivity of the slider was controlling the amount of meltwater. The amount was also a strong function of velocity.

An analysis is presented of stress and strain measurements made during an investigation of the characteristics of cracks formed in columnar-grain, type S2 fresh-water ice, during uniaxial, compressive loading at the nominal strain rates of 10−3, 10−4 and 10−5s−1, and temperatures of −5°, −10°, −20° and −30°C. The analysis shows that for this range of strain rate and temperature, ice behaves as an anelastic solid. Results are given for the time, grain-size and temperature dependence of the elastic modulus in the plane perpendicular to the long direction of the grains. They are shown to be in reasonable agreement with results of an earlier study of the anelastic behaviour of the same type of ice. It is suggested that the grain-size and temperature dependence of the elastic moduli of ice for this range of strain rate and temperature may be due, in part, to the dependence of the relaxation time on these variables.

Controlled tests are needed to find the coefficient of friction of snow as a function of speed. An error analysis shows how the test must be designed to give accurate answers. It seems necessary to use a remotely controlled, aerodynamical sled in place of a skier to get accurate results. Otherwise, two sets of tests are necessary, one to determine air drag versus speed and one to determine the frictional force versus speed, and even these tests would probably not give satisfactory results. The slope used for testing should be sleep for a quick acceleration and then uniform, but not flat, where the actual measurements are taken. A continuously reading speed sensor is needed, not discrete measuring points. Even with the underlying principles understood, there will still be many practical problems to be solved before accurate results can be obtained.

Aerial photography was obtained for the Beaufort Sea north of Tuktoyaktuk. The flight path covered two distinct ice zones over a 15.5 km transect extending perpendicular to the coast, yielding fifty-nine photographs at a scale of 1 : 2000. The process of ridge extraction was automated using a series of computer algorithms for image filtering, edge detection and edge linking. Examples from two different sections along the transect are chosen for presentation: (a) a heavily ridged area, and (b) an area with one dominant linear ridge feature that separates ice cover of different age. Two parameters used in the automated process, a minimum edge gradient and minimum number of connected pixels said to form a continuous ridge segment, influence the number, length and spatial pattern of extracted ridges. Direct one-to-one correlations between manually interpreted ridges from photographs and the algorithm extracted ridges from digital data are not always possible. However, results indicate that the automated ridge extraction procedure reliably characterizes the overall direction and density of the ice ridges. The distribution of the ice-ridge directions is estimated from circular (angular) histograms constructed directly from the digital data. Analysis of the Beaufort Sea transect reveals that the ice ridging is strongly anisotropic, with a principal direction parallel to the local coastline.

Experiments were performed on columnar saline ice prepared in the laboratory. Specifically, using a true multiaxial loading system, relatively large cubes (159 mm on edge) were proportionally loaded along three orthogonal directions; viz. perpendicular to (σ13 and σ22) and parallel to (σ33), the long axis of the columnar grains. The ice was strained at 10−2 s at −10°C where it behaved in a brittle mariner. Four sets of experiments were performed by setting the ratio σ22/σ11 to 0, 0.25, 0.5 or 1, and varying the ratio σ22/σ11 and σ22/σ11. Sections through the failure surface were then constructed. For loading along σ22 = 0, the confining stress did not significantly affect the maximum principal stress at failure. For loading along σ22 =0.25σ11, σ22 = 0.5 σ11 and σ22 = 0.5 σ11, the application of a moderate confining stress resulted in a large increase in failure stress. However, further increase in the level of the confining stress did not have a significant effect on the failure stress. The observations are presented in terms of a failure surface and are discussed in terms of the possible failure mechanisms.

Understanding the mechanical properties of saline ice is important for engineering design as well as for operations in polar regions. In order to gain understanding of the basic mechanisms of deformation and fracture, laboratory-grown columnar saline ice, representative of first-year sea ice, was tested in uniaxial compression under a variety of conditions of Strain rate (10−7 to 10−1 s−1), temper-aiure (−40°, −20°, −10° and −5°C) and orientation (loading vertically or horizontally: i.e. parallel or perpendicular to the growth direction). The range of strain rate spanned the ductile-to-brittle transition for every combination of temperature and specimen orientation. The results of over 250 tests are reported. Mechanical properties, failure mode and ice structure are analyzed with respect to the testing conditons. The results show that strength is dependent upon the ice structure, orientation, strain rate and temperature. During loading in the ductile regime the structure is altered (e.g. by recrystallization), whereas in the brittle regime the majority of the structural change is through cracking. The results are compared to results from the literature on both natural sea ice and laboratory-grown saline ice. Where possible, they are interpreted in terms of micromechanica] models.

An explosive detonation in snow produces high intensity shock waves that are rapidly attenuated by momentum spreading as the snow is compacted. Our experimental measurements and numerical calculations indicate that the maximum shock-wave attenuation in seasonal snow (250 kgm−3) is proportional to between x−1.6 and x−3 for plane waves and x−3 for spherical waves (x is the propagation distance). Outside the region of shock-compacted snow or in air over snow, stresses are transmitted as acoustic/seismic waves. Attenuation of these waves depends on snow permeability and the effective modulus of the ice frame and is proportional to about x−0.7 for plane waves in seasonal snow and to about x−1 for spherical waves in air over seasonal snow. Increasing the scaled detonation height of an explosive up to 2mkgf−1/3 above a snow cover increases the far field (scaled distances greater than about 8m kgf−1/3 snow surface pressures. Scaled detonation heights greater than about 2mkgf−1/3 have little additional effect.

The efforts to develop damage models for ice cannot be disconnected from a better knowledge of the undamaged ice behaviour. In this respect the transient behaviour of polycrystalline ice still needs to be investigated. The present paper is a contribution to the development of rheological models which can be used in varying load situations. The deformation processes which should be the foundation of the models are described. The models of Le Gac and Duval (1980) and of Sunder and Wu (1989a) are tested against two uniaxial compression tests on isotropic granular ice under varying load. They fail to describe both primary creep and the response to increments/decrements of the applied load. A new model, based on a decomposition of the viscoplastic strain into two components which account separately for kinematic and isotropic hardening, is shown to give better results.

Arctic and sub-Arctic snow is deposited on ground that can have significant microrelief due to tundra hummocks and tussocks. The microrelief, a substantial fraction of the total snow depth, causes basal layers of snow (usually depth hoar) to be discontinuous. In-situ measurements made at four locations in Alaska indicate lateral temperature gradients up to 60°C m −1 exist at the snow/ground interface due to the microtopography. For all sites, the winter average range of temperature along a 1.5 m transect at the interface varied from 4°C to greater than 7°C. Heat-flux transducers placed at the tops and bases of tussocks indicated that vertical heat flow was consistently 1.4 to 2.1 times higher at the top than the base. Results of a conductive model based on tussock height are consistent with these measurements.

The metamorphism of snow in the absence of a significant temperature gradient was investigated. The first part of the study involved analytical modeling of the exchange of mass between grains of differing surface curvature and the process of intergranular sintering. Physical models were developed to evaluate these two processes. For the first process, it was assumed that mass exchange took place primarily by vapor transport between neighboring grains. The principles of mass balance, momentum balance and energy balance were utilized to evaluate time and spatial variations in temperature, vapor velocity, vapor pressure and mass exchange between the two grains. For the second process, mass exchange was also assumed to be dominated by vapor flow from the grain surface to the neck surface. The same variables were solved for in this second process. Results obtained show that, as expected, the exchange rates between grains of different surface curvature depend upon the radii of curvature, pore size and temperature. The rate of sintering, as determined by the rate of vapor deposition on the neck is determined by temperature, grain curvature, and neck curvature. In addition to the physical modeling, an experimental program was undertaken to measure rates of metamorphism in specially prepared snow consisting of fine-grained spherical particles. This snow was made using specialized instrumentation developed in Japan. The mean grain size was 20 μm, which, while very small, allowed the observation of measurable changes in snow microstructure over short time spans. Test results showed that the grain size increased markedly with time and that the small grains were sacrificed as the large grains acquired mass from the smaller grains.

The snowfall series of Turin, northwest Italy, is one of the longest available for Europe, with daily observations starting in 1784 and continuous since 1788. The unpublished 207 years data set was carefully obtained from original manuscripts and filed on magnetic media. Mean yearly snowfall amount is 48.9 cm showing a high interannual variability (variation coefficient 79%), with about seven snow days from October through April; the maximum amount was measured in winter 1784–85 (233 cm), followed by 1808–9 with 163 cm. Maximum daily amount was on 4 December 1844 with 64 cm. During the whole period a negative trend is exhibited, increasing in the years following 1890. This pattern is confirmed by the Mann-Kendall test. The change derives from regional climate rather than expansion of the urban area. Return periods of yearly maximum snow loads are calculated in order to contribute to the definition of new values for structural design. A case study of heavy snowfall in January 1987 is examined.

Ionic and isotopic analyses of snow samples collected at four sites at the Norwegian glacier Austre Okstindbreen during two field seasons in 1991 showed that, before melting started, the snowpack was vertically inhomogeneous. Patterns of variation with depth of both ions and oxygen isotopes were maintained throughout the pre-melt period. Horizontal variations of ionic concentration were smaller than vertical ones. The stratigraphic pattern of ionic concentrations in the pack at lower altitudes reflected the influence of melting-refreezing processes, as well as original variations in the falling snow. The mean ionic content of the first set of samples collected at the lowest site was much lower than that at the others, indicating that ions had already been removed by meltwater. Much liquid water was present in the snowpack when drainage started, and ions were removed quickly with the first meltwater. During the melting phase, comparative rates of loss of ions resulting from differential movement through the pack were SO42− > Na+ > Cl−. At 1475m, only 13% of the winter accumulation melted between 6 June and 9 July, but at least 88% of the Na+, 89% of the Cl− and about 100% of the SO42− was lost. Initially, there was no altitudinal trend in the mean δ18O values of the snowpack. Warming of the pack was accompanied by a tendency towards isotopic homogenisation. At the three sites at which snow remained in July, considerable 18O enrichment had occurred since the middle of June.

Broadband measurements of dielectric properties of natural snow samples near or at 0°C are reported. Measurement quantities are: dielectric permittivity, loss factor and complex propagation factor for electromagnetic waves. X-band measurements were made in a cold room in the laboratory; measurements at low and intermediate frequencies were carried out both in the field (Stubai Alps, 3300 m; Hafelekar near Innsbruck, 2100 m) and in the cold room. Results show that in the different frequency ranges the relative effect on snow dielectric properties of the parameters: density, grain-size and shape, liquid water content, shape and distribution of liquid inclusions and content of impurities, varies significantly. In the low-frequency range the influence of grain-size and shape and snow density dominates; in the medium-frequency range liquid water content and density are the dominant parameters. In the microwave X-band the influence of the amount, shape and distribution of liquid inclusions and snow density is more important than that of the remaining parameters.

Field measurements were made of snow gliding on steep, smooth rock slabs. Supporting dala included snowpack properties, snow rock interface temperatures, air temperatures and precipitation. In this paper, the temporal and spatial dependence of gliding is discussed from two seasons of measurements. The results showed that the basic temporal and spatial characteristics repeated from year to year at the site. The relationship of the measurements to snow-gliding constitutive relations and applications is briefly discussed.

Water content, water distribution and variations with time of these quantities in the natural snow cover are important parameters for microwave remote-sensing studies, snow stability investigations and snow hydrology studies. The most promising method for snow wetness determination is the measurement of the dielectric constant at radio frequencies. Recent developments of electronic devices for long-term recording of snow wetness are reported. The measurement system consists of two parts: the tuning and display unit with the battery pack and the flat capacitive sensor. The system is controlled by a built-in low-power microcomputer, the operation frequency for the sensor is 20.00 MHz. Measurement data are displayed on an LCD and are also stored in a RAM; data transfer for a PC for further data processing is possible by a built-in V24 interface. Up to four individual sensors can be operated simultaneously. Field measurements of long-term variations in snow wetness during diurnal cycles and registrations of penetrating meltwater or rain-water waves with the formation of water shock fronts are presented.

A distributed snowmelt prediction model was developed for a mountain area. Topography of the study area was represented by a digital map. Cells On the map were divided into three surface-cover types; deciduous forest, evergreen forest and deforested area. Snowmelt rates for each cell were calculated by an energy balance method. Meteorological elements were estimated separately in each cell according to topographical characteristics and surface-cover type. Distributions of water equivalent of snow cover were estimated by the model. Snowmelt runoff in the watershed was also simulated by snowmelt rates calculated by the model. The model showed thai the snowmelt period and snowmelt runoff after timber harvests would be about two weeks earlier than under the forest-covered condition.

This paper presents a partial analysis of data from an extensive series of laboratory indentation tests. The tests were conducted using flat indentors pushing against sheets of fresh-water ice of thickness 65 to 115 mm. The aspect ratio ranged from 0.9 to 2.6 with indentor velocities of 10 to 80 mm s−1. Details of an ice failure mode known as “crushing with flaking” are studied by making use of measured force-displacement signals and high-speed photography. With these test conditions, ice failure is associated with a production of symmetrical flakes which emanate simultaneously up and down. The failure begins in the middle level of the ice sheet as a rapid expansion of the ice. The post-peak phase of the ice failure involves loss ol the ice material over the whole contact area. The amount of ice that is extruded after the occurrence of the peak force is characterized by a finite failure depth parameter. According to present data, this failure depth is around 70% of the total depth of crushing and flaking that occur during a cycle of loading and unloading.

Results are presented from an experiment concerning operational space-borne ice charting based on the Russian Ocean and Resource satellite systems. The surface truth consisted of routine operational data, helicopter-borne reconnaissance, and some ground measurements. Examples of the satellite imagery are given and identification of ice types is described. Cluster-analysis has been used for automatic image segmentation. The potential of these satellites in operational ice charting is discussed. A 160 m resolution optical scanner and a 2 km resolution radar are found to be very useful complements to the present routine system.

An experimental and analytical study has been carried out to investigate the melting characteristics of ice blocks immersed in quiescent saline water. A horizontal ice cylinder and both downward- and upward-facing inclined ice plates were used as the testing blocks. The experiments were carried out in 3.5% (by weight) saline water at ambient temperatures ranging from 1.8° to 25.0°C for all kinds of ice blocks. Ice plates were tested at inclination angles from 0° to 75°. For downward-facing ice plates, melting rates were determined analytically using the profile method.