An extensive series of tests has been conducted on a Roating ice sheet on a deep, fresh-water lake. A variety of vehicles were driven a long an instrumented test track at a wide range of speeds, producing several characteristic patterns of ice and water response that have been recorded and analysed in detail. Tests were repeated at different stages of ice growth to accommodate changes in physical conditions. The use of a vibration transducer and a new type of deflectometer has permilled the study of many primary and secondary effects. As vehicle speed is increased, the ice and water pass through four characteristic modes of response, culminating in a wave effect at the higher speeds. It has been shown that the ice and water waves travel consistently at the speed of the vehicle. This factor has been used to modify a simple ice-wave theory, which then predicts a linear variation of wave frequency with vehicle speed that can be expressed in a universal form for deep -water conditions. The experimental measurements of frequency confirm this universal variation. The observed secondary effects include air-coupled Rexural oscillations, hydrodynamic Auctuations and systematic variations in ice fracture intensity with vehicle speed. This last effect leads to the proposition of a new criterion of vehicle safety.

Accurate forecasting of water run-off from snow covers and glaciers is increasingly important because of the increasing competition for scarce water resources. The trend toward conceptual computerized models of hydrologic system, require extensive knowledge of the physical aspects of those systems. Unlike river and stream network>, the hydrological characteristics of snow coven and glaciers are highly variable with time and cannot be easily defined. After reviewing the physical aspects of water flow through snow covers and glaciers, it is concluded that snow covers and glaciers are predictable hydrological systems once the melt metamorphism of the snow is complete and the englacial conduits have been established. However, much additional information about snow and ice masses must be generated before general forecasting techniques can be established for all situations.

Some observations which pertain to the interaction of ice and lake water in a high alpine environment and which were made in recent years in connection with hydroelectric projects and flood protection work are presented. In 1966, when the thin flat snout of Griesgletscher (Walliser Alpen) became submerged during the first filling of a newly constructed reservoir, waves of only very small amplitude were generated by the calving of a bout 150000 m3 of ice because most of the energy was dissipated by local turbulence. Far more spectacular waves have been experienced near steep ice cliffs in connection with work for flood control. For the design of an air bubbler system, air and water temperatures were measured in winter 1974–75 at Grimselsee, one of the largest reservoirs in the Bernese Alps. These measurements showed that the warmest water at the bottom of the lake was drained away during winter for the production of electricity. A strong temperature invenion forms in the air a bove the water behind the dam, as the lake level is lowered by several tens of metres.

In a two-dimensional model of an ice mass breaking off from a cliff, stresses and velocities are calculated numerically according to Glen's flow law. A tensile crack opens in the zone of maximum tensile principal stress σ1 and propagates to a depth where σ1, iɜ, zero. Ice flow then produces an overhang of the partly detached ice mass. Consequently, the stress σ1 below the tip of the crack becomes tensile again and the crack propagates for another small distance. This process goes on until the centre of gravity of the detaching ice mass has moved past the supporting edge of the bedrock. Velocities v of the ice mass calculated for different stages of the process are plotted as a function of time t. The plotted points lie in the vicinity of a curve given by

(1)

where vc, tA B and D are constants. The same type of function has been found for velocities measured at an ice mass breaking off the Grubengletscher.

The waste containers should be retrievable for a few centuries until further research has solved all problems and 90Sr and 137Cs have decayed to less than 0.1%. Safe and fairly cheap retrievability can be guaranteed without container mooring. The paper presents an example: The high-level waste of the whole world for the next 30 years could be put in to 3 × 107 spherical containers with 0.2 m radius and disposed of in an area with 15 km radius and a depth range of 20–100 m under the surface of either the Antarctic or the Green land ice sheet. The deposit does not affect the stability of the sheet. Even the most upsetting natural ice-sheet instabilities and/or climatic changes could not cause radioactive contamination.

The physical requirements for proposed frazil-ice nucleation theories are reviewed in the light of recent observations on frazil-ice formation. It is concluded that spontaneous heterogeneous nucleation in a thin supercooled surface layer of water is not a viable mechanism for frazil-ice nucleation. Efforts to observe crystal multiplication by border ice have not been successful. The mass-exchange mechanism proposed by Osterkamp and others (1974) has been generalized to include splashing, wind spray, bubble bursting, evaporation, and material that originates at a distance from the stream (e.g. snow, frost, ice particles, cold organic material, and cold soil particles). It is shown that these mass-exchange processes can account for frazil-ice nucleation under a wide range of physical and meteorological conditions. It is suggested that secondary nucleation may be responsible for large frazil-ice concentrations in streams and rivers.

A sub-sea permafrost drilling program was conducted near Prudhoe Bay, Alaska. Sub-sea permafrost was found at all offshore drill sites and was characterized as being ice bonded or unbonded. The unbonded sub-sea permafrost occurred in a thin layer at the sea bed; the near-shore thickness of this layer appears to be controlled by the bathymetry. The mean annual sea-bed temperatures were about —3.4°C at 203 m offshore, — 1.1°C at 481 m offshore and —0.7°C at 3370 m offshore. The thermal diffusivity was about 21 m2 a-1 for unbonded sandy gravel with silt. The sub-sea permafrost soils were sandy gravel with some silt overlain by a thin layer of silty sand which increased in thickness from a few meters near shore to about 14 m at 3370 m offshore. A few small ice lenses were found in a hole 195 m offshore but no massive ice was observed. Pore-water salt concentrations at the sea bed were 3-4 times that of normal sea-water where ice was frozen to the sea bed and 1–2 times that of normal sea-water otherwise. Preliminary laboratory experiments showed that the saturated hydraulic conductivity of the unbonded sub-sea permafrost was about 10–6–10–7 m s–1. The permeability of the subterranean permafrost was zero.

The first part of the paper is devoted to a historical review of applied glaciology problems in the French Alps since the last century (cog railway to the top of Mont Blanc, construction of mountain huts, preventive emptying of sub glacial water pockets under Tete Rousse glacier, etc.). The second part is devoted to the study of modern projects concerned with construction of cableway stations or cableway pylons on or near the glaciers, with the preparation of ski runs on glaciers during summer, with the different problems met during works to capture subglacial torrents for the needs of hydroelectric companies.

The design, construction and testing of a portable, constant strain-rate testing machine for determining the mechanical behavior of avalanche now is described. The machine is intended for use in determining the stress-strain-time behavior of low-density natural snow in the field. A technique for making direct measurements of strain in the snow sample is described and stress-strain curves are presented for strain-rates ranging from 0.5 to 5.0 × 10−5 s−1. The densities of the snow samples tested range from 186 to 335 kg m−3. Ultimate-strength data and relaxation curves are also presented.

An ice cover impinging on a long straight structure is assumed to be under a condition of plane strain. A technique is described for performing plane-strain compression tests, and results are presented for the strain-rate dependence of strength. The plane-strain compressive strength of ice having anisotropic structure (columnar-grained ice) is at least two and a half times the uniaxial compressive strength, whereas the plane-strain compressive strength of ice having an isotropic structure (granular-snow ice) is atmost 25% greater than the uniaxial case. The greater plane-strain compressive strength of columnar-grained ice, when the loading and confining directions are in the plane of the ice cover, can be attributed to its anisotropic structure, which leads to a different failure mechanism for the plane-strain case.

Floating ice sheets are loaded thermally as well as mechanically by winds, water currents, and at times by man-made structures. When floating ice sheets are to be used in engineering problems, all of the applied loads must be accounted for. Determining the forces that will cause an ice sheet to fail is difficult not only because of the various kinds of loads, but also because the properties of ice sheets (fresh and sea) are dependent upon many variables, and the properties vary through the thickness of the ice sheet.

Experimental and theoretical investigations have made it possible to define more exactly some features of ice formation on solid surfaces

Reduced-scale experiments were conducted in 1971 to study the forces experienced by conical structures during encounters with uniformly thick fields of ice. The tests were conducted in a model basin which was designed to test the behavior of ships and floating platforms in ice. A liquid nitrogen spray system was used to produce fields of high-salinity, fine-crystalline, ice which has the properties of elastic modulus and strength scaled down substantially below full-scale values.

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

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

Finally, it is concluded that current design practice of neglecting the effects of friction on a certain class of structures is likely to lead to conservative results. Future work necessary to better predict the actual margin of safety resulting from current design practice is identified.

We have attempted to develop a theoretical understanding of the field experience on the destruction of floating ice sheets by explosives, by performing small-scale laboratory explosions and developing a theory based on the elastic plate. Glass spheres 4.5 × 10¯2 m in diameter and c. 4 × 10¯4 m thick were immersed in water underneath a floating ice sheet c. 2 × 10¯2 m in thickness. The air pressure was raised till the sphere burst at pressures around 15 atmospheres. A high-speed camera (up to several thousand frames per second) recorded the details of the explosion: the growth of the gas bubble and the corresponding deformation and failure of the ice. We observed radial and circumferential cracks develop within 2 ms of the bursting of the sphere.

As a first step in the theoretical development, we have considered the response of an infinite elastic plate to impulsive pressure loading due to an underwater explosion. We have assumed potential, incompressible flow which is a valid approximation for the case of the above experiments and the analogous compressed-gas blasting in the field (Mellor and Kovacs, 1972). However the effects caused by the intense shock wave that is radiated by the detonation of a high explosive are thus not considered. We relate the maxima in the tensile stress with the crack pattern and the eventual damage, and have achieved qualitative agreement with the laboratory observations. The model does reproduce and clarify some aspects of the field data, in particular the role of the thickness (Mellor, unpublished); but it fails to relate the crater diameter to the weight of the explosive. It appears that at optimum blasting conditions with high explosives an incompressible-fluid, classical-plate-theory approach is inadequate.

With the present increase of commercial activity in the Arctic Ocean, there is a growing need for advanced engineering techniques and instrumentation. This paper discusses the application, design and testing of an acoustic ranging system used to measure the motion of sea ice at potential ice-platform drilling locations in the Canadian Arctic.

A “hydraulic" model of the motion of bed-type snow avalanches is developed, its qualitative particularities are discussed, and results of comparison of prediction and observations are presented. The proposed model allows calculation of the parameters of motion of snow avalanches possible for a given bed depending on the snow situation and other conditions. The characteristics concerned are the distribution of velocities averaged over the cross-section of the flow and the thickness of snow in an avalanche at every instant of its motion.

The class of avalanches considered is that in which a compact snow flow moves along a distinct avalanche bed consisting of an accumulation region, a bed, and an avalanche cone. It is proposed to model the avalanche bed with a certain inclined and curved channel of given width and shape of cross-section. The characteristics of the model channel are defined on the basis of a topographic map of the corresponding avalanche bed. The motion of avalanche snow is modelled by the flow of an incompressible “liquid" subjected to the action of gravity, internal resistance, and external friction. Destruction and capture of undisturbed snow by an avalanche from the slope is accounted for by introducing into the equations of motion distributed sources of mass the intensity of which depends on the sought characteristics of the problem and which is defined while solving the problem.

On the basis of simple physical considerations connected with the finite shear stress in the snow, it is shown that for sufficiently large avalanches the specific friction force becomes inversely proportional to the thickness of the flow. The proposed mechanism of friction explains the abnormally high mobility of catastrophically large avalanches.

The adopted model possesses a number of properties agreeing qualitatively with the observational data for avalanches. Computer solutions have the form of rather prolonged flows with the shape of the front part typical for avalanches and with characteristic wave formations in the flow which sometimes result in pulsating regimes of motion. The report concludes with results of comparison of predicted and observed characteristics of motions of avalanches for some real avalanche beds demonstrating possibilities of the proposed model.

A numerical model is developed for calculating the rate and total amount of ice accretion under atmospheric conditions. The principal application of the numerical approach is to aircraft icing and more specifically, helicopter icing problems. These problems are best solved using numerical techniques because of three factors: (1) the dependence of the ice accretion rate on the amount of ice previously deposited, (2) the existence of two different ice growth regimes, the “dry" and “wet" growth regimes, determined by the surface temperature of the accreting surface, and (3) variable velocities (e.g. along rotor blades) which affect the rate of capture of swept-out water droplets and the amount of heat generated by the flow on the accreting surface. These three factors cause feedback in the two governing equations for determining the mass rate of ice accumulation.

The first of these equations is for the mass rate of water captured, and the second equation is for the heat balance of the accreting interface. For the numerical calculation, the object, such as a helicopter rotor blade, is broken down into elements of constant velocity, and for each time step the resulting ice thickness is used to recompute new cross-sectional and surface areas which are then used as input to the next time step. Changes in the cross-sectional and surface areas caused by ice build-up affect both the mass rate (directly through the cross-section and indirectly through a change in collection efficiency) and the heat balance (directly through the cross-sectional and surface areas and indirectly through changes in the collection efficiency and Reynolds number). An additional instability in the ice growth rate develops when the transition between wet and dry growth occurs, enhancing the feed-back that already exists between the mass rate of ice accumulation and the thickness previously deposited. Numerical icing simulations using various helicopter configurations and the icing conditions they typically encounter are presented.