The environment conditions in the southern Beaufort Sea are described with special emphasis on pressure ridges and ice islands. Techniques for determining the geometric configurations and the physical and mechanical properties of sea-ice structures and ice islands are described. Profiles of pressure ridges were determined by surface surveys, drill-hole probes and side-looking sonar scanning. Multi-year pressure ridges with thicknesses up to 18 m and widths up to 110 m were examined in detail. The first-year ridge of 22 m thickness and 100 m width was studied. Results are given for several multi-year ridges and the first-year ridge. Information obtained from dives under the ice is also given. Corresponding data are given for grounded ice islands with particular attention being given to contact between the ice and sea bed. A 19 m thick ice-island fragment grounded in 13 m of water was one of several investigated. Measurements of temperature, salinity, tensile strength and compressive strength are given for ice taken from old pressure ridges and factors influencing the interpretation of test data are discussed. The data obtained in this study will be used in engineering design studies for off-shore structures for drilling and production of hydrocarbons from the Beaufort Sea area. Exploratory drilling in shallow water has already been carried out and off-shore drilling from drill ships is scheduled to commence in the study area during the open-water season of 1976.

This paper will be published in full in a future issue of Journal of Glaciology.

Snow melt water that is uniformly generated over the upper surface of the snow-pack does not percolate homogeneously through the snow. Consequently, the rate of arrival of melt water at a single collector at the lower surface does not give a true measure of the melt rate. The experiment described here measures the spatial variability of flow rate and the temporal variation of this two-dimensional pattern. Data are collected from an array of 64 sensors under control of a microprocessor. The microprocessor checks the consistency of the data, calculates the flow rate for each sensor and transfers the results to a recorder. These mean flow rates are calculated at regular intervals for the duration of the experiment. In this way the temporal and spatial variations of flow rate may be related to variations in meteorological conditions and the evolution of the structure snow-pack as the melting progresses.

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.

Our knowledge of ice avalanches is very limited in comparison to snow avalanches, for obvious reasons. Ice avalanches are restricted to remote areas with glaciers, whereas snow avalanches may occur in the middle of inhabited regions. Consequently, the economic importance of the two types of avalanches is quite different. Also the efforts and expenditure required to study them are different.

Two classes of ice avalanches may be discerned (with no sharp dividing line between them). A common form occurs on steep glacierized slopes below ice cliffs, from which ice breaks off at intervals. The avalanche debris remains on the glacier and can either be reincorporated or can form a regenerated glacier tongue. This is the type of ice avalanche primarily noticed by mountaineers because of the hazards involves, although little seems to have been done in the way of glaciological studies. A second class of ice avalanches consists of events more akin to landslides where a considerable portion of a glacier falls off a steep part of the bed and moves beyond the original position of the glacier onto ice-free ground, sometimes with disastrous effects. Through such glacier catastrophes, which are fortunately very scarce, more intensive glaciological studies have been initiated. The individual case histories serve best to illustrate the various problems related to ice avalanches.

The Altels avalanche of 11 September 1895, thoroughly documented by Heim (1896), can be regarded as a slab of ice sliding off a uniform inclined plane. It is remarkable for its size of 4.5 × 106 m3, its simple geometry at the origin, its equally simple trajectory involving a jump through the air, and the fact that in 1782 a similar avalanche had occurred. The slope of the bed at the origin was 30° to 32°, the mean ice thickness was 25 m (with a maximum of 40 m). No apparent signs had been noticed in the days preceding the catastrophe. The Altels avalanche provides one of the few sources of reliable empirical parameters in relation to ice stability and ice-avalanche dynamics.

The Allalingletscher avalanche of 30 August 1965 hitting the Mattmark construction site was of a very different origin. It occurred when about 106 m3 of ice broke off at the snout of the glacier during a surge-like active phase of a larger mass of some 3×106 m3. Since this event, it has been established that such active phases occur periodically at Allalin once every 1-3 years, alternating with quiescent periods. During the active phase, the fast motion sometimes starts in summer or autumn and comes to a halt in November or December. The active phase seems to depend on the presence of melt water and also on mass distribution. A direct effect of high water pressure in a communicating drainage system at the bed can be excluded, however. The surge-like motion appears to have been a prerequisite for the ice avalanche of 1965, but it does not give a sufficient explanation of the event, when one considers the frequent occurrence of active phases without a concurrent major ice avalanche at Allalin and elsewhere. It is conceivable that in 1965 a large dome-shaped cavity had formed below a particular rock knob and that the collapse of the dome then triggered the avalanche, but other forms of static instability at high speed of bed slip, developing because of a specific bed morphology and mass distribution, may equally be envisaged.

In the case of a hanging glacier on the Weisshorn, the village of Randa was severely damaged in 1819 by a very large avalanche approximately 13 x 106 m3 consisting mainly of snow but having been triggered by falling ice. This led to a detailed study in 1972/73 of a seemingly threatening situation. A volume of approximately 5 × 106 m3 of ice (firn) was accelerating in a characteristic way on a very steep slope of about 45°. Rough estimates showed that the acceleration was too large to be accounted for by frictional heating alone; a fracture mechanism had instead to be invoked to play the decisive role (besides possible recrystallization). A hyperbolic law has been found to fit best the data on change of velocity with time (Flotron, see the following abstract).

The Huascaran catastrophes of 1962 and 1970 have been some of the most disastrous events in glaciological history. In 1962 a true ice avalanche appears to have been the cause of a giant mudflow (Morales, 1966). For the first time in at least several hundred years a large volume, estimated at 2.5 to × 106 m3, broke off simultaneously over the full length of an ice cliff, 800 m long and 50 to 60 m high. It is an open question as to how this could happen. The mudflow was formed by mixing of the ice with rock and soil picked up along the course of the avalanche, bringing the total volume ot some 13 × 106 m3. In this process part of the ice was melted. The 1970 incident was not an ice avalanche proper, but rather a giant landslide caused by an earthquake, in which the ice played an important role in the form of a source of water causing lubrication and liquefaction.

The above examples constitute a diversity of problems which could be augmented further by additional cases. A certain order may nevertheless be brought to the subject of ice avalanches by looking at it from a practical point of view. The main objective is to look for means by which damage to property can be reduced and loss of life avoided.

The basic question is the one of stability of a large ice mass on a steep slope. The problem seems to be simple enough, but a closer inspection shows that the time scale and the unknown factors are such that laboratory results of, for example, strength are of no avail. On an empirical basis it can be noticed that temperate glaciers have become unstable on a slope of about 30°, while the limiting slope of cold glaciers is about 45°. The distribution and development of crevasses and, more generally, the flow pattern can help to delineate an acutely unstable ice mass. A special condition is the occurrence of a surge-like active phase which should be taken as an indication that part of the fast moving ice may slide off. There is a basic rule applicable to all types of ice avalanches, that if a particular one has occurred once it will happen again in a similar way; unfortunately our records do not extend sufficiently far back to allow us to depend on this rule very often.

The probable extent of the danger zone is of equal practical importance. Experience has shown that after an initial phase the ice becomes completely broken up so that snow-avalanche dynamics can be applied to estimate how far the debris will move, possibly with some modifications for large masses of landslide dimensions. The possibility that snow and loose rock and soil may be added along the path must be taken into account. Secondary effects must also be considered. Amongst these are an air blast, or the formation of destructive water waves in a lake or fjord, or the blockage of a river by a huge ice mass leading to a flood from an ice-dammed lake.

A warning by the glaciologist is hardly taken seriously unless it includes a forecast of the time of final rupture. At present the most promising approach for such a prediction is the almost perfect regularity by which certain large ice masses accelerate for a very long time prior to the instant when the avalanche starts to fall (see the Weisshorn case). The limitation of the forecasts lies as much in short-term irregularities as in the extreme difficulties of obtaining sufficiently accurate data without interruptions, and further in the lack of experience on the critical velocity that is reached immediately before final breakage. The physical explanation of the observed law is another question. Using a finite-element computational model for the analysis of stress and flow in a somewhat different case, Iken (1977) has shown that a stepwise crack extension alternating with phases of flow leads to the observed form of velocity–time relationship.

There are various possibilities in the way of preventive measures; none of them is completely satisfactory, however. The most certain consists in avoiding the danger zone altogether, a solution usually not acceptable to those involved. In view of the requirements necessary for withstanding an impact of exceptional magnitude, protective structures are generally not practical either. A stepwise elimination of the unstable ice mass by blasting could be considered, though the realization would be difficult and not without danger—not to speak of the legal problem encountered if the blasting should trigger the full-size avalanche. Consequently a certain calculated risk will occasionally have to be accepted whereby the dangers during an operation on the glacier and the extreme costs have to be weighed against the severity and small probability of a catastrophe. Viewed in proportion to other risks in everyday life (especially in road and air traffic, but also in relation to earthquakes), the dangers of ice avalanches should not be exaggerated.

Glaciological research can obviously contribute in a variety of ways to the solution of practical problems with ice avalanches, and there are ample opportunities for future studies. Of urgent need are more and better observations on almost every aspect of the problem, extending to phenomena hitherto not observed such as frequency and intensity of seismic signals. The inherent difficulty with the more interesting large-scale events is their scarcity, precluding proper experimentation. Advances in the theoretical treatment are also to be hoped for. There is also room for new ideas, for instance on how to prevent a particular ice mass from forming.

In 1972 the state of a hanging glacier on the Weisshorn gave cause for alarm, as part of it seemed to be accelerating and a repetition of an earlier avalanche of ice seemed possible (see Röthlisberger, previous abstract). For this reason movement surveys were undertaken. The various surveying methods applied on the Weisshorn are outlined and the accuracy of the measurements is given. By least-square analysis different types of curves have been fitted to the data for velocity versus time. The best fit obtained so-far has been with hyperbolae. The confidence of extrapolations from such curves is discussed in relation to forecasts. By evaluating repeated photographs taken by an automatic camera from a single position, using a stereo plotter, the flow pattern has been established at the surface, part of the front, and one of the lateral faces of the ice mass. Changes with time caused by the deformation of the ice mass, the formation of crevasses and the crumbling away of the ice at the edge have been observed.

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.

The retreat of glaciers since 1927 in Cordillera Blanca has produced dangerous lakes at the front of many glaciers. All the known data, most of them unpublished, are reviewed. The known aluviones are listed, and those of Chavin, Quebrada Los Cedros and Artesoncocha described in full. In these three cases a breach in the front moraine came from big ice falls into the lake. The protective devices made on the outlets are described, as well as the effects of the big earthquake on 31 May 1970. In the case of Laguna Parón, which keeps its level thanks to infiltrations, the fluctuations of the discharge of the springs as related to the level of the lake from 1955 to 1969 are reported. The projects for lowering the level of Laguna Parón and for emptying Safuna Alta are described. The latter partially emptied in fact by piping after the earthquake, allowing a final solution.

In front of Laguna Parón there is a huge moraine which turns through 90° in the middle of the valley and with a narrow covered glacier on the top. It has been studied by electrical exploration, and using the displacements of 43 marked boulders on the glacier. Assuming a uniform balance on the glacier tongue and semi-elliptical cross-sections, it has been possible to estimate this balance and the glacier thickness. A great amount of the measured velocity comes from the creep of the moraine itself, which seems to be a kind of rock glacier, probably without interstitial ice. It must have taken all the Holocene to be formed. During its complex history a pro-glacial lake must have formed at some time, the rupture of which explains the crooked form.

We explain how preliminary results concerning the internal constitution of the big push moraine at Safuna were obtained in 1967. Cross-sections which were obtained later through electrical and seismic exploration and arduous borings are given. Under the lake Safuna Alta there exists a layer of dead ice which is probably a remnant from an old glacier advance and over which the active glacier slides, but this dead ice does not extend into the push moraine. Since 1950 Safuna Alta has formed, the glacier tongue has lowered by 0.8 m per year on average, and the big push moraine has moved and settled.

The annual balance on the glacier tongue was measured in 1968. It increases by 3.9 m of ice per 100 m in altitude. The discharge of ice near the lake and the annual balance further up-valley allow an estimate of the mean annual balance in the accumulation zone (between 4 850 and 6 020 m) at 2.30 m of water per year. Until now no annual precipitation higher than 1 m/year had been measured in Cordillera Blanca, but this Cordillera includes many meso-climates.

Eight successive moraines are found at Safuna. They are tentatively correlated with the eight existing between Huaraz and Laguna Llaca. Clapperton’s “group 4" was not formed during the 20th, but during the 17th century. His “group 3" is not from A.D. 1750-1800, but is rather 5000 to 7000 years old, according to the offset of Cordillera Blanca great fault.

This contribution is published in full as three papers in Journal of Glaciology, Vol. 18, No. 79.

Frost heaving of soil is accompanied by a force which often causes severe damage to structures. It was suggested by Everett that this so-called “heaving force" can be attributed to the coexistence of ice and water in micropores among soil particles which characterize the soil type and can be computed thermodynamically. However, the actual heaving force changes in a complicated manner depending on various factors including freezing speed, constraining condition for a soil block, and, of course, soil type.

Measurements of heaving force were carried out on various soil samples (sand, sandy loam, sandy clay loam, and two kinds of clays) under various freezing conditions: freezing speed in a range from 0.10 cm/h to 0.35 cm/h, presence or absence of water supply, complete or loose axial constraint applied to a soil block. In each experiment, soil was packed in a cylindrical container with a diameter of 11 cm and a height of 10 cm. A disk was placed on top of the soil contained in the container to constrain the sample either rigidly (a complete axial constraint) or less rigidly through a spring (a loose axial constraint). Main results of the measurements were as follows:

• (1) Under complete axial constraint, the heaving force decreased with decrease in the freezing speed and with the increase in the size of soil particles (from 6 bars to 1 bar for clay; from 4 bars to 1 bar for sandy clay loam; from 4 bars to 0.8 bar for sandy loam; from 1.5 bars to 0.6 bar for sand).

• (2) Without the constraint, the heave amount was almost independent of the freezing speed when there was no water supply (8 mm for clay; 6.5 mm for sandy clay loam; 3.5 mm for sandy loam; 1 mm for sand).

• (3) The heaving force decreased very rapidly with the loosening of the axial constraint by weakening the spring.

The results indicate that it is practical to treat the heaving force phenomenologically as a kind of resistive force exerted by freezing soil on a container holding the soil. Because of a volumetric increase due to the transformation of water into ice at the freezing front, both unfrozen and frozen parts of the soil suffer some strain if the soil is somehow constrained by the container. The strains cause stresses which appear as the heaving force. A formula for the heaving force is given in which both the frozen and the unfrozen soil are treated as viscoelastic bodies.

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.

In order to measure the snow depth on a road, a new type of snow-depth meter based on trigonometry with an infrared beam source, beam reflection points on the snow surface and a detector of the reflected beam, was developed using a gallium-arsenide infrared-emission diode and a silicon infrared-detection dual diode. The prototype of this meter operated successfully from 1 February to 31 March 1975 at Nagaoka, Japan.

In the prototype, an infrared beam source, with 10 mW output power, and a detector were fixed 4 m above the ground facing each other at a distance of 5 m. These two photoelectric elements were set in small light-weight cases. Each has a small window (4 cm × 10 cm) to emit or receive the infrared beam. To avoid catching snow or rain in the windows, air was ejected through them. The visual field of the detector was 4.8° and the dip angle of its centre line was fixed at 45°. On the other hand the beam source emitted with 1.4° divergence and varied its dip angle from 90° to 20° with a period of 4 min in the vertical plane which contains the centre line of the visual field of the detector. This beam was reflected by the snow surface and received by the detector in its visual field. When the detection system of the meter detected the beam centre, the dip angle of the scanning beam was measured by a potentiometer connected mechanically to the infrared source scanner. Output voltages of the potentiometer indicated the measurement of snow depth within an accuracy of ±5 mm for the flat plate or snow surface from 0 to 1.5 m above the ground.

In addition, a phase-sensitive detection circuit with equivalent band-width of 0.4 Hz and driven by a synchronous signal of 1 kHz from the modulation circuit of the beam source was adopted in order to eliminate noise such as occurs due to sunshine, heavy snow-storms or traffic. As a result very reliable movements were obtained under conditions of heavy snowstorms with horizontal visibility less than 30 m at eye level in daytime.

A computer method for calculating the total melting from May to October has been developed both for a single glacier and for a glacial area. In the second case (which is the more interesting and important for hydrology and glaciology) it is necessary to calculate some characteristics of an “average" glacier of the region using morphometric characteristics included in the Catalogue of the U.S.S.R. glaciers. These are: glacier area; average area of moraine on the glacier; weighted average of heights of upper and lower ends of a glacier and weighted average of mean height of firn line. It is also necessary to obtain data on glacier area distribution by height, precipitation data, and data on air temperature and cloudiness at meteorological stations.

In addition to defining typical glacial regions within the limits of the glacial area considered and determination of the “average" glacier characteristics listed above, preparation of the computer programme includes (a) definition of precipitation dependence on orography height and calculation of appropriate parameters, (b) reduction (if necessary) of data obtained from the meteorological station nearest to glacial area to a more prolonged range, (c) calculation of a special balance index of accumulation and melting of seasonal precipitation which makes it possible to define maximum excess of seasonal snow line over the “average" glacier terminus in separate years, and (d) computation of total solar radiation occuring in clear days during May to October.

In the course of computation on computer the following operations are realized: (a) determination of an average value of total radiation arriving during months of May to October period given the real cloudiness conditions, (b) calculation of the height of the snow line on the glacier, (c) calculation of quantity and duration of solid atmospheric precipitation which melts between May and October on the glacier surface, (d) estimation of absorbed solar radiation taking account of the differing albedo of glacial surfaces situated above and below the seasonal snow line, (e) calculation of the total melting of glaciers belonging to the given mountain watershed.

Checking of the calculational method has been performed using data from Lednik Tsentralnyy Tuyuksu and Lednik Ayutor-2 where numerous ablation stakes were installed. Values of measured and calculated melting agree satisfactorily.

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 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.

The existing methods of predicting avalanche danger often do not meet users’ demands because of the empiric character of the insufficient volume of information used. In such forecasts the contribution of each individual parameter into the prognostic information is unknown, and this is very important when studying such an event as avalanche formation, which is conditioned by a complex interaction of numerous factors, including snow accumulation, the state of snow thickness, and the conditions of its development.

It is obvious that such problems can be successfully solved by statistical methods, and that explains the growing interest in numerical methods of avalanche forecasting. Problems of multi-dimensional observations arises in many scientific fields. The method suited for this problem is discriminant analysis, the purpose of which is to divide a multi-dimensional observation vector into predetermined classes.

This study considers the prognostic (diagnostic) problems of fresh-snow avalanches released during snowfall or in the two days after it has ceased. The theoretical basis is a complex of statistical methods: correlation and dispersion analysis, “sifting" for the choice of predictors’ informative groups, construction of linear parametric discriminant functions, predictions based on training sample, and verification of discriminant functions based on independent material.

The archive used in the study consisted of 500 avalanching cases and 1 300 non-avalanching ones. All situations were grouped according to geomorphological characteristics. Each situation is described by eight meteorological characteristics. The results of classification of snowfall situations into avalanching and non-avalanching ones are as follows: reliability of ρ is from 75% to 91%, H from 0.15 to 0.51; based on independent material the reliability of ρ is from 63% to 85%, H from 0.10 to 0.56.

This paper has been accepted in revised form for publication in a later issue of the Journal of Glaciology.

Icing on stationary structures is an increasingly serious problem as off-shore drilling operations in the sub-polar regions becomes more popular. Since this problem is less complicated than icing on a ship, an attempt was made to calculate accretion rate using existing data.

The rate of ice accumulation R can be calculated from R = CfCcF where F is the mass flux of the water drops and Cf and Cc are the proportions of spray frozen on the surface and coefficient of capture of drops, respectively. Cc can be close to unity for larger drops such as sea spray. Although many other factors may contribute, Cf seems to be a strong function of the air temperature.

Mass flux can be written as Vr3 dr where n(r) is the number of drops of radius r in unit volume, V is the wind velocity, ρ is the density of water; n(r) is a function of wind velocity and height of observation. For a stationary structure, the mass flux is primarily dependent upon the wind speed.

The ice accretion rate R, calculated using published data on the size distribution of sea spray and using a capture efficiency Cc of I agrees surprisingly well with the diagrams given by previous authors for icing on ships.