The sliding law is defined as a basal boundary condition for the large-scale bulk ice flow, relating the tangential traction τb, overburden pressure pb, and tangential velocity ub on a smoothed-out mean bed contour. This effective bed is a lower boundary viewed on the scale of the bulk ice flow and is not the physical ice/rock or sediment interface. The sliding relation reflects on the same scale the complex motion taking place in the neighbourhood of the physical interface. The isothermal steady-state ice-sheet analysis of Morland and Johnson (1980, 1982) is applied to known surface profiles from the Greenland ice sheet and Devon Island ice cap, with their corresponding mass-balance distributions, to determine τb, pb, and ub for each case. These basal estimates are used in turn to construct, using least-squares correlation, polynomial representations for an overburden dependence λ(pb) in the adopted form of sliding law τb ═ λ(pb)ub1/m with m ≥ 1.

The two different data sets determine functions λ(pb) of very different magnitudes, reflecting very different basal conditions. A universal sliding law must therefore contain more general dependence on basal conditions, but the two relations determined appear to describe the two extremes. Hence use of both relations in turn to determine profiles compatible with given mass-balance distributions can be expected to yield extremes of the possible profiles, and further to show the sensitivity of profile form to variation of the sliding relation. The theory is designed as a basis for reconstruction of former ice sheets and their dynamics which are related to the two fundamental determinants of surface mass balance and basal boundary condition.

A model of a non-linearly viscous ice sheet is used to investigate the influence of net mass-balance pattern, basal boundary condition, and subglacial topography on the size and shape of ice sheets. The aim is to enable geological evidence of the extent of former ice sheets to be used as indicators of palaeoclimate. A series of curves are presented showing the relationships between ice-sheet span, net mass balance, and equilibrium-line altitude (ELA) for zero and complete isostatic compensation. These are applicable to a very wide range of basal boundary conditions. The way in which they can be used to reconstruct net mass-balance gradients for former ice sheets is demonstrated. Changes in the basal boundary condition only have a strong influence on glacier span when they occur in the terminal zone. Ice-sheet expansion and contraction is not merely accompanied by changes in snow-line elevation, but also by changes in the net mass-balance gradient. The combinations of these required to cause ice-sheet expansion and contraction are analysed. A non-linearly viscous model for ice suggests that ice-sheet volume changes may not be a simple function of their change in areal extent.

Glaciological data collected from Taylor Glacier have been used to assess aspects of the dynamics and thermal regime of the glacier. Mass-balance studies suggest that the glacier is in near equilibrium. The thermal condition of the basal ice over much of the ablation area was calculated from estimates of the geothermal heat influx and measurements of near-surface ice temperatures, ice velocities, and ice thickness. It was found that, in as much as 50% of the lower ablation area, the basal ice may be melting.

Glaciological estimates of the ice supply to George VI Ice Shelf are obtained by integrating the accumulation over the catchment. The basal melt (or possible shelf thickening) rates for the ice shelf are calculated by balancing the accumulation with calving and melting. We calculate an average equilibrium melt rate for the ice shelf of 2 m a −1. If the ice shelf is in mass balance it alone provides 53 km3a −1 melt from its base compared to a total for Antarctica of only 320 km3a −1.

The mean oxygen isotope composition of recent accumulation on the catchment is determined by using accumulation and isotope data, supplemented by temperature measurements and a close empirical relationship between isotope ratio and temperature. The catchment has a mean isotope ratio of −20.8‰ relative to SMOW.

Oceanographic work has previously shown that the sea-water under the ice shelf at the north of George VI Sound is Warm Deep Water modified by melting ice. The melting ice has an isotope ratio of −20.3‰. The good agreement in isotope ratios suggest that the melting ice is from the catchment and because the basal ice of George VI Ice Shelf represents accumulation over the last few millennia the implication is that there has been no systematic change in the isotope composition of the accumulation during this period. This implies no secular change in either the elevation or the climatic temperature of this part of the ice sheet.

Two holes were drilled to depths greater than 300m in the Antarctic ice sheet, near Cape Folger on the Law Dome. The holes underwent considerable closure below 250m with localized strain-rates as high as 1 to 1.5×10−6 s−1. The closure observed in holes was non-uniform and occurred in zones 0.5 to 3 m wide. These Zones parallel the flow plane in the ice mass and are associated with a distinct domainal structure. High-closure zones are characterized by interlocking and irregular-shaped ice grains with many sub-horizontal c-axes and only occasional c-axis clusters at a high angle to the flow plane. Low-closure zones contain tabular grains with the long dimension parallel to the flow plane, abundant deformation features and a predominance of c-axes oriented at a high angle to the flow plane. The relationship between closure rate and c-axis fabric is attributed to marked plastic flow by intracrystalline slip on the basal plane to produce higher closure in areas where there is a greater variation in c-axis orientation. This deformation is attributable to overburden pressure and hence is related to depth, and is independent of shear within the main body of the ice mass.

Recent theoretical studies of glacier hydrology have assumed that subglacial conduits are completely filled with water under steady-state conditions. This, however, is not necessarily the case. Where discharges are larger than a few tens of liters per second and the down-glacier slope of the bed is more than a few degrees, the potential energy released by water descending this slope may be capable of melting the walls of a subglacial conduit many times faster than the conduit can close by plastic flow of the ice. As a result, the pressure in such tunnels may normally be atmospheric, or possibly even at the triple-point pressure if there is no open connection to the glacier surface. Simple calculations suggest that such pressures in subglacial conduits may be more common than heretofore anticipated.

The positions of such “open” conduits may be unstable to small perturbations in discharge or ice velocity. This is because the mechanical energy available in excess of that needed to balance closure can instead offset the general flow of the ice. Conduits can thus trend diagonally across the direction of ice flow. If an increase in the angle which such a conduit makes with the ice flow direction also results in an increase in slope of the conduit, more mechanical energy will become available, resulting in a positive feedback process.

Subglacial channels at atmospheric pressure may influence the origin and morphology of certain glacial landforms, such as eskers and “plastically-molded” features.

The relationship between synoptic-scale atmospheric circulation and glacier mass balance in the Cordillera of south-western Canada is investigated. Objective synoptic typing techniques are applied to glaciometeorological data from Peyto Glacier, Alberta, and Sentinel Glacier, British Columbia, and to climatological data from nearby weather stations. Two scales of 500 mbar synoptic weather maps are analyzed and compared. One is smaller with high-wavenumber patterns, the other is larger with more general patterns.

The results demonstrate that the mass balance of Peyto and Sentinel Glaciers are related to the 500 mbar patterns. Synoptic types with cyclonic curvature favor glacier accumulation, while anticyclonic types inhibit build-up of the regional snow-pack. Ablation is suppressed by synoptic types associated with cloudy days and/or low temperatures, and is enhanced by types associated with warm, sunny days. Furthermore, findings suggest that both the accumulation and ablation of Sentinel Glacier are controlled by small-scale, high-wavenumber synoptic patterns. Conversely, Peyto Glacier accumulation is more closely associated with large-scale patterns, suggesting that high-frequency mid-tropospheric oscillations embedded within the slow-moving baroclinic zones associated with long-wave disturbances may be dampened by the rough topography of the Canadian Cordillera. Ablation is predicted poorly by both scales at Peyto.

A simple equation is derived relating the net mass-balance and hypsometric curves of a steady-state valley glacier. It is used to examine how valley shape is linked to disparate extents and responses of glaciers subjected to similar climatic conditions. Examples are given which show that area-based indices (e.g. AAR) for estimating the equilibrium line altitude (ELA) may be subject to a substantial built-in variance because they implicitly rely upon similarity of glacier shape and regimen over a region. If accurate topographic maps are available, the equation may be used to infer the regimen of modern glaciers in the form of a dimensionless ratio of net mass-balance gradients. Alternatively, if similar information is available concerning regional glacier regimen, disparate extents and responses may be collectively utilized to estimate values of ELA or to infer climatic influence, taking glacier hypsometry into account.

Climatic change occurs over a wide range of time scales. Each glacier responds in a unique fashion to this spectrum of climatic forcings. The response of the extent of the Lewis Glacier terminus to sinusoidal fluctuation in the net balance is calculated. The net balance versus elevation profile is separately translated along the orthogonal balance and elevation axes. Net balance amplitudes of 0.1 to 0.5 m a−1 of ice and 10 to 50 m elevation, respectively, and periods ranging from 20 to 1000 years are covered. The time lag between forcing and terminus response is dependent on applied period, reaching a maximum of about 30 years at 1000 years period, but is independent of applied amplitude. For the shorter applied periods the response amplitude increases rapidly with period but asymptotically approaches a maximum at periods above approximately 200 years; it is linearly dependent on applied amplitude. Consideration of the Lewis Glacier response taken in perspective with similar results for other alpine glaciers identifies general characteristics of the terminus response.

Wave action causes ablation in a narrow zone around an iceberg’s waterline, at up to 0.3 m per day, in water of −1°C with waves up to 0.4 m high. Subsequent subaerial calving of ice from iceberg sides takes place up to a similar rate. Submarine melting is an order of magnitude slower than wave action but acts over the largest part of an iceberg. Ablation rates derived theoretically or statistically elsewhere for comparable environmental conditions, are in reasonable agreement with those measured here. Drifting icebergs trail a plume of mixed, slightly cooled and diluted sea-water in their wake.

Model-generated ice-thickness fields for the period 1961–80 are examined in the context of summertime sea-ice predictability in the Beaufort Sea. The correspondence between the modeled and observed fluctuations of ice-covered area is found to be quite good. Lag correlation coefficients based on departures from 20 year “normals” of the ice thicknesses show that the ice anomalies are persistent throughout the August–May period. However, because the thickness anomalies undergo large fluctuations during July and August, only a small amount of summertime predictability can be derived from the thickness data. The findings are consistent with the observational results of Rogers (1978), who found that summertime temperatures and wind directions accounted for much of the variability of Beaufort Sea ice during August and September.

The interaction of Stokes’ edge waves with a developing near-shore ice zone is examined from two points of view. First, the effect of a well-fragmented ice suspension on the classical Stokes’ edge wave is discussed. Secondly, the possibility that ice-cusp formation (and, thereafter, ice mounds or volcanoes) can be initiated by edge waves is examined. Results indicate a negligible effect of a well-fragmented floating ice field on the Stokes’ dispersion equation for typical wave periods, but do indicate that the presence of a standing Stokes’ edge wave may lead to the initiation of ice-field cusps as ice formation occurs in the near-shore zone.

During December 1973 the initial smooth ice cover on the Chukchi Sea near Barrow, Alaska, broke away from the shore during a period of strong wind and was replaced by a cover of broken, rafted ice which remained for the rest of the winter. Cores pulled from this cover were examined visually, and the salinity and density of sections of the cores were measured. Temperatures at several depths in the ice were recorded continuously, and these are presented near the date when the temperature gradient changed sign. Despite large deviations probably due to the irregularity of the ice cover, thickness and salinity followed the patterns seen by other observers.

Shock-wave studies of ice under uniaxial strain conditions have been conducted at stress levels up to 3.6 GPa. A light-gas gun accelerated the flat-faced projectile used to impact the ice-containing targets. The ice samples were initially at ambient pressure and at temperatures of –10 ± 2° C. Gages were implaced at different distances in the ice along the path of the shock wave to measure particle velocity time histories inside the ice samples. The recorded time histories of particle velocity show a precursor wave with an average wave velocity of 3.7 km/s and an average particle velocity amplitude of 0.06 km/s. This wave is travelling at a wave velocity approximately 10% greater than longitudinal sound speed and is believed to originate because of the onset of melting of ice I.

The particle velocity data from these experiments were converted to stresses and volumes using Lagrangian gage analysis and the assumption of a simple non-steady wave. This conversion provides a complete compression cycle (which includes both loading and unloading paths) for comparison with static measurements. All experiments show the onset of melting at 0.15 to 0.2 GPa. Experiments with maximum stress states between 0.2 and 0.5 GPa yield results which suggest that a mixed phase of ice I and liquid water exists at these conditions. For maximum loading stresses between 0.6 and 1.7 GPa the experimental results suggest that the final state is predominately ice VI. In these experiments the specific volume upon compression is changed from 1.09 m3/Mg to approximately 0.76 m3/Mg, which represents compaction of approximately 30%. The unloading paths determined from these experiments indicate that ice VI remains in a “frozen” or metastable state during most of the unloading process. This hysteresis in the compression cycle gives rise to a large “loss” of shock-wave energy to the transformation process. At stress levels above 2.2 GPa, ice VII should be the stable form for water according to static compression measurements. Experimental data at 2.4 and 3.6 GPa suggest that ice VII may be formed but these results indicate a mixed phase of ice VI and ice VII rather than complete transformation to ice VII.

Clasts modified by glacial erosion are described from lodgement tills in front of the glacier Mýrdalsjökull, south Iceland. Many clasts show modification of their lower surfaces in the same way as their upper ones. However, the lower surfaces have a smoothed down-glacier face and a truncated up-glacier face, which is the opposite orientation to that of the upper surfaces. This so-called double stoss-lee form is interpreted as a response to basal transport over abrading materials, following deposition of the clast and succeeded by glacial erosion. It is suggested that clasts with a double stoss-lee form are a diagnostic criterion for subglacial deposition by lodgement. Furthermore, the distribution and orientation of clasts with a stoss-lee form was investigated on a ground-moraine surface. 17.3% of 2199 clasts with an a-axis diameter > 30 cm had a stoss-lee form. The proportion of clasts with their smoothed ends facing up-glacier within ± 22.5° of the ice-flow direction was 72.7%. Thus, the preferred stoss-side orientation is closely related to the ice movement and indicates the direction from which the ice came. Only 11.7% of boulders with a divergent stoss-side orientation are located in connection with annual moraines. It is suggested that such boulders have mainly been re-deposited beneath the ice and not at the ice front by minor advances of the glacier.

A new lightweight hand-operated coring auger for use in firn or ice is described. Extensive use of glass-epoxy composites contributes to a drill weight of approximately 1 kg/m in 20 m and 50 m configurations.

A procedure is described for testing ice in tension. It incorporates a one-piece lucite mold, two carpeted “Synthane” end-caps and a pair of yokes anti ball joints. Use of the procedure has resulted in a successful test rate greater than 80%.

We have developed a new technique for making thin sections and surface replicas of ice at temperatures well below 273 K. Cyanoacrylate glue forms a strong bond with ice and glass at 245 K, eliminating the need to fix the sample to the thin-section slide by melting and freezing. Surface replicas are made by melting away sample material once the glue has cured. Glue replicas are permanent and highly detailed, making them suitable for microstructural and textural studies at room temperature. Thin sections glued with cyanoacrylate glue are comparable in quality to melted-on sections. The ability to make thin sections without melting sample material is important in textural and microstructural studies of ice deformed at low temperatures because of annealing effects we have observed during conventional section making.

During the period 1966 to 1983 Milne Glacier advanced 4.25 km at a mean annual rate of 250 m a−1. Since surges commonly occur over a two or three year period the maximum rate of advance could have been greater than 2 km a−1. The glacier terminus has a number of features indicative of past surge behaviour. Of these, at least three looped moraines suggest surges of the main valley glacier and tributary glaciers. As Milne Glacier is a cold glacier, surges may possibly be thermally regulated Accumulation rates on the ice caps of northern Ellesmere Island are low hence a critical condition in the “reservoir area” will be only slowly attained. As a consequence the periodicity of surges in Milne Glacier and other High Arctic glaciers is expected to be high.