The characteristics of two full-depth slab avalanches that occurred in 1982 and 1984 at the same location on Meall Uaine in Glen Shee, Scotland, are described. Notable features include the relatively low altitude of the site (c. 670 m) compared to sites of other avalanches observed elsewhere in Scotland, the depth of snow involved (up to 4 m), a snow-pack similar to those recorded in the Cairngorm Mountains, and the entrainment, transport, and deposition of boulders and turf. The probability of the two avalanches occurring when they did was greater than 60%. It is suggested that further observations of full-depth slab avalanches might be obtained by identifying terrain similar to that of the site studied here.

“Whisky Glacier” on James Ross Island, Antarctic Peninsula, comprises a névé and clean ice trunk surrounded by an extensive area of debris-covered ice resembling a rock glacier. The debris-free trunk of the glacier abuts abruptly against the broad, totally debris-covered tongue at a number of concentric zones where debris-laden beds crop out at the surface in a manner similar to the “inner moraine” formations of many polar glaciers.

Ice structures and foliation suggest that “Whisky Glacier” is a polythermal glacier which is wet-based under the debris-free zone, and dry-based under the debris-covered zone. It is surmised that the glacier sole crosses the freezing front close to where the basal debris beds are upwarped towards the surface. Here, basal water is confined, and freezes to the under side of the glacier in thick beds of regelation ice which are uplifted to the surface along with the debris-laden beds. Ablation losses effectively cease beneath the blanket of debris covering the tongue.

The transition from wet-based to dry-based conditions at the glacier sole is a powerful mechanism for entraining debris into a glacier and, in the case of “Whisky Glacier”, for lifting debris to the surface. It is suggested that this may be a mechanism for forming some polar rock glaciers.

Our understanding of the basic physics underlying the properties of ice has dramatically changed during the last half century. At the beginning of this period it was known that the water molecules in ice were arranged with tetrahedral hydrogen bonding, and it had just been established that the hydrogens were not crystallographically arranged on these bonds; however, the way in which water molecules could re-orient was unknown and the implications of this for the mechanical properties and hence for glacier flow were unexplored. The suggestion of electrical point defects in ice, the L and D defects of Bjerrum and the ionic defects, pointed the way to an understanding first of the dielectric relaxation and electrical conductivity of ice and then to a possible interaction between these electrical properties and the movement of dislocations, and hence the plastic deformation of ice.

Menwhile, much work was done to study the behaviour of ice under various physical conditions and to establish more rigorous laws for many physical properties of single crystals of ice and of various forms of polycrystalline ice, and much work was done to find the crystallographic structures of the various phases of ice including those already known to exist at high pressures. The intriguing appearance of a cubic form of ice at low temperatures was also investigated together with vitreous ice formed at even lower temperatures.

Many of these properties are of great interest to meteorologists trying to understand cloud physics and the physics of thunderstorm electricity as well as to astronomers thinking about ice in space, comets, the icy satellites of the planets, or even on the planets themselves.

On 9 August 1982, the calving of a large ice mass, approximately 0.3 km x 1.5 km in size, from Jakobshavns Isbræ was filmed. The event, which took place as the tide was rising, is described by means of picture sequences from the ciné film. First, a large transverse crevasse opened in the glacier. The subsequently detached piece then split into large blocks which toppled forward one after the other in the direction of the fjord, so that finally large, clean ice slabs lay in front of the glacier terminus. The tilting ice blocks pushed the whole mass of fjord water, together with the ice debris which floated on it, in the direction of the sea. The tilting processes had terminated after approximately 8 min. Then a wave which had been reflected farther out in the fjord returned to the break-off zone, where it caused the formation of a large amount of ice debris and high jets of water.

Satellite imagery has substantially improved the quality of sea-ice observation over the last decades. Therefore, for a 25 year period, a statistical study based on the monthly Arctic sea-ice data and the monthly mean 700 mbar maps of the Northern Hemisphere was carried out to establish the relationships between sea-ice conditions and the general circulation of the atmosphere. It was found that sea-ice conditions have two opposing effects on the zonal circulation intensity, depending on the season. Heavier than normal ice in winter causes stronger than normal zonal circulation in the subsequent months, whereas heavier than normal ice in the summer-fall causes weaker zonal circulation in the subsequent months. Analyzing the two sectors, the Atlantic and Pacific ones separately, a negative correlation was found, which means a heavy ice year in the Atlantic Ocean is normally associated with a light one in the Pacific Ocean and vice versa.

Electrical resistivity measurements were made in a series of closely spaced holes drilled to the base of Storglaciären. Electrodes were lowered to the bottoms of the holes where they made contact with the substrate beneath the glacier. The measurements show that a layer of till, ~0.4–0.7 m thick, is present at the base of the glacier. The low resistivity of the layer indicates that it has a high water content, compared with tills of similar composition in the pro-glacial environment. A marked reduction in resistivity after a heavy rain storm demonstrates that the water content is sensitive to variations in water input at the surface.

The history of snow-cover research is divided into four distinct periods. Before 1900 there were systematic observations of snow but the tools were just being developed to begin serious research. From 1900 to 1936, many investigations were made because of the practical considerations of snow hydrology and snow avalanches. Individuals began the assessment of snow water equivalent for forecasting run-off and the observation of snow structure and texture. Quantitative and physical investigations quickened after government-sponsored laboratories were established in 1936, the same year as the founding of the International Glaciological Society. From 1936 through the 1960s, many detailed investigations were made into snow's physical properties and behavior. Professional societies organized national and regional meetings, and published the results of snow research. Many more laboratories became involved as knowledge about snow was developed and applied to run-off forecasting and avalanche defense. Snow research surged again during the 1970s with the establishment of a new generation of snow scientists using more advanced theory, computers, and instrumentation. As demands continue for solutions to snow problems with new emphasis on old themes, snow research generates knowledge about snow for a wide variety of applications.

Modes of formation and rates of collapse have been determined for kame terraces and a fan delta in the Adams Inlet area, Alaska. The hummocky and trenched surface of the kame terrace develops by mass-wasting processes caused by differential melting of buried ice. The dry channels in the collapsed part of the terrace are formed by melt water during stagnant-ice bursts. Measurements over a period of 17 years indicate that terrace back-wasting averages 4.3 m a−1. The fan delta is forming near sea-level by streams that derive part of their load from the kame terrace. The fan delta seaward of the retreating kame terrace is undergoing partial collapse to produce kettles ringed by concentric fractures. Vegetation, now as much as 5 m below high tide, suggests a fan-delta collapse rate of about 0.5 m a−1.

Many of the major advances in glaciology during the past 50 years have followed the development and application of new technology for viewing and measuring various characteristics of ice. Microscopes to study ice crystals, radars to probe the internal structure of large ice masses, mass spectrometers to analyze the atomic composition of ice cores, and satellite sensors to measure the global distribution of ice are some of the tools readily adapted by glaciologists. Today, new tools include microcomputers for automatic data logging, large-memory computers for data processing and numerical modeling, sensitive instruments for ice analysis, and satellite sensors for large-scale ice observations. In the future, continued advances in key technologies will help guide the evolution of science questions considered by glaciologists, expanding our view of ice, its fundamental properties, its interactions within the ice–ocean–land–atmosphere system, and its role in the evolution of our global environment.

The second 4 year phase of a long-term observation program on Lewis Glacier, Mount Kenya, was completed in March 1986. As for the 1978–82 interval, net-balance results at a stake network and repeated mapping of the ice-surface topography allowed assessment of the mass economy by both “glaciological” and “geodetic” methods.

The general findings from the 1978–82 observations are confirmed: the vertical flow component is directed downward in the upper glacier, and upward in the lower glacier; surface lowering and negative net balance increase down-glacier; ice flow mitigates surface lowering by the negative net balance in the lower glacier, but enhances it in the upper glacier. However, the major difference between the 1982–86 and 1978–82 periods is the progressive slow-down of ice flow. This entails a reduction of mass redistribution, in consequence of which the surface lowering becomes increasingly dependent on the in-situ net balance. It is expected that this circumstance will simplify any inference on future glacier behavior.

The problem of ice flow over threedimensional basal irregularities is studied by considering the steady motion of a fluid with a linear constitutive equation over sine-shaped basal undulations. The undisturbed flow is simple shear flow with constant depth. Using the ratio of the amplitude of the basal undulations to the ice thickness as perturbation parameter, equations to the first order for the velocity and pressure perturbations are set up and solved.

The study shows that when the widths of the basal undulations are larger than 2–3 times their lengths, the finite width of the undulations has only a minor influence on the flow, which to a good approximation may be considered two-dimensional. However, as the ratio between the longitudinal and the transverse wavelength L/W increases, the three-dimensional flow effects becomes substantial. If, for example, the ratio of L to W exceeds 3, surface amplitudes are reduced by more than one order of magnitude as compared to the two-dimensional case. The L/W ratio also influences the depth variation of the amplitudes of internal layers and the depth variation of perturbation velocities and strain-rates. With increasing L/W ratio, the changes of these quantities are concentrated in a near-bottom layer of decreasing thickness. Furthermore, it is shown, that the azimuth of the velocity vector may change by up to 10° between the surface and the base of the ice sheet, and that significant transverse flow may occur at depth without manifesting itself at the surface to any significant degree.

Temperature records from several randkluft sites at the margins and headwall of Boundary Glacier (lat. 52° 12′ N., long. 117° 12′ W.) in the Canadian Rocky Mountains are presented. These records indicate that during the ablation season a diurnal freeze-thaw air and rock-surface temperature regime occurs in a 2 m wide zone centred on the randkluft lip. Deeper in the randkluft, stable sub-zero conditions prevail whereas above the randkluft an above-freezing temperature regime prevails. The freeze-thaw temperature regime, observed freezing of melt water and rain water on randkluft rock surfaces, and copious in-situ loose weathering products on the headwall and marginal free faces suggest an active frost-shattering environment. Down-slope migration of the randkluft lip during the ablation season results in a migration of the freeze-thaw zone and thus a seasonal extension of the rock surface area exposed to the favorable weathering environment. Longer-term glacier fluctuations, with attendant thinning and thickening of the ice body, could result in large areas of marginal and headwall rock surfaces being exposed to the randkluft weathering environment over long periods of time. The data and observations from Boundary Glacier support an idea, suggested by Battle (1960), that open and shallow randklufts, rather than closed and deep bergschrunds, are a focus of weathering at glacier margins and thus a potential factor in cirque development.

Radio echo-sounding studies were used to detect water-filled cavities on Variegated Glacier, Alaska, during its surge in 1983. Cavity locations were determined by spatial surveys, and changes in cavity size and water content over a 5 week period were inferred from phase and amplitude changes in the echo wave form. Data were taken at both 4 and 8 MHz central frequencies of the impulse transmitter. These bi-frequency results, together with spectral analysis of the digitized wave forms, were used to provide additional information about the cavity dimensions. Cavity response is interpreted in terms of a simplified model of a thin layer of strong dielectric contrast. Computer simulations of radar pulses encountering such layers reproduce the main features of the data.

The literature reporting scientific and engineering investigations on ice has grown rapidly in the past 50 years, and increased by a factor of at least ten in the past 20 years. A review is presented of advances in engineering for ice problems during this period, including ice formation in rivers, lakes, and oceans; ice forces on structures; bearing capacity of ice covers; and atmospheric icing. The difficulties faced by engineers due to the unique physical and mechanical properties of ice and its normal thermal state are emphasized.

Evidence of a recent (1985) ice-cliff avalanche from an outlet lobe of a small plateau ice cap on north-west Ellesmere Island is discussed. Former avalanche events are evidenced by debris lying outside the 1985 avalanche material. Periodic activity seems to be linked to the build-up of melt water in the crevasses of the outlet lobe during the melt season. The exact magnitude and frequency of events are unknown. Some implications to geomorphology and the sedimentology of sub-polar glaciers are discussed.

A test series has been performed to investigate the influence of flaws or cracks in ice during an ice/structure interaction event. The tests were carried out by measuring the horizontal load on a 6 cm diamter vertical indentor which was being pushed through sheets of fresh-water ice containing flaws of various shapes, lengths, and densities. The results are analyzed and correlated in terms of an elementary damage theory. The tests show that flaws can have a significant influence on the load which an ice sheet can exert on a structure.

Snow-pack along the land-fast ice fringe off the north coast of Ellesmere Island was generally characterized by depth-hoar overlain by dense snow and wind slab. Mean snow depth in the study area was 0.54 m (1982-85) and the mean δ18O value of the snow-pack was -31.3˚/00. Isotope data were not obtained previously for this geographic region and, therefore, complement a previous study of δ18O variations in High Arctic snow (Koerner, 1979). The data are consistent with an Arctic Ocean moisture source. The δ18O profiles show seasonal variations, with winter snow being more depleted in 18O than fall and spring snow. However, the δ18O profiles are dominated by a trend to higher δ18O values with increasing depth. This is attributed to a decrease in δ18O values as condensation temperatures fall during the autumn-winter accumulation period. During this time, there is also a change from relatively open to almost complete ice cover in the Arctic Ocean. The change in evaporation conditions and consequent effect on δ values gives rise to a sharp discontinuity in the δ18O profiles and a bi-modal δ18O frequency distribution. The bi-modal distribution is reinforced by a secondary isotope fractionation that occurs during depth-hoar formation. This isotope effect leads to a wider δ18O range but does not significantly alter the mean δ18O value.

After the end of World War II glaciology entered a new golden age, which has yet to end. The quality of this golden age is comparable to the classic period of the nineteenth century. The International Glaciological Society has been the major catalyst, through its very active and co-operative international membership and its Journal of Glaciology in setting the modern major advances in the science of glacier and ice phenomena in motion and sustaining them.

This paper combines a study of the rock debris and δD/δ18O isotopic characteristics of basal ice sequences in three representative glaciers in South Georgia and concludes that the debris and ice has been entrained mainly by basal freezing. The size distribution of the rock debris is typical of crushing and abrasion, and reflects transport at the ice–rock interface. The δD/δ18O relationships show that clear ice associated with the debris has accreted through freezing. The white bubbly glacier ice has δD/δ18O relationships typical of precipitation which demonstrates an altitudinal effect between glaciers.

Inclinometry measurements in a 126 m bore hole slightly down-glacier from the crest of a riegel on Storglaciären showed what appears to be indisputable extrusion flow during the last 3 weeks of July 1984. The velocity at the bed was about five times that at the surface, and lay in a direction deviating 50–60° from that at the surface. The increase in velocity with depth began more than 50 m above the bed. In August and the first half of September the flow returned nearly to “normal” with only a slight tendency toward extrusion. The flow in July appeared to be related to a period of large diurnal water-pressure variation and cavity opening at the bed up-glacier from the riegel. Decoupling of the ice from the bed on the lowest parts of the riegel may have permitted the extrusion. The return to more “normal” conditions in August appears to have been related to a decrease in ice flux over the riegel and a widening of the zone of decoupling.