We develop theoretically a description of a possible subglacial drainage mechanism for glaciers and ice sheets moving over saturated, deformable till. The model is based on the plausible assumption that flow of water in a thin film at the ice-till interface is unstable to the formation of a channelized drainage system, and is restricted to the case in which meltwater cannot escape through the till to an underlying aquifer. In describing the physics of such channelized drainage, we have generalized and extended Röthlisberger’s model of channels cut into basal ice to include “canals” cut into the till, paying particular attention to the role of sediment properties and the mechanics of sediment transport. We show that sediment-floored Röthlisberger (R) channels can exist for high effective pressures, and wide, shallow, ice-roofed canals cut into the till for low effective pressures. Canals should form a distributed, non-arborescent system, unlike R channels. For steep slopes typical of alpine glaciers, both drainage systems can exist, but with the water pressure lower in the R channels than in the canals; the canal drainage should therefore be unstable in the presence of channels. For small slopes typical of ice sheets, only canals can exist and we therefore predict that, if channelized meltwater flow occurs under ice sheets moving over deformable till, it takes the form of shallow, distributed canals at low effective pressure, similar to that measured at Ice Stream B in West Antarctica. Geologic evidence derived from land forms and deposits left by the Pleistocene ice sheets in North America and Europe is also consistent with predictions of the model.

The first field experiment in the 5 year seasonal Sea Ice Monitoring Site (SIMS) program was conducted in Resolute Passage, Canadian Eastern Arctic, between 15 May and 8 June 1990. This period signals the early melt season of sea ice in that region. A standard array of ice and snow measurements was collected on a daily basis from first-year and multi-year ice to monitor temporal evolution. Measurements included ice salinity, ice temperature and ice-surface roughness, snow salinity, snow temperature, snow density and snow depth. The complex dielectric constant of sea ice was computed from these measurements. Rapid desalination of first-year ice was noticed in the surface layer. Towards the end of the experiment period, salinities of the snow-hoar layer were higher than those of the ice-surface layer. Variation in air temperature is replicated by ice-surface temperature but not by the salinity or dielectric properties. No temporal variation in permittivity and dielectric loss was observed for first-year ice, but a slight increase in both parameters was observed for multi-year ice. As a result, a slight decrease in the microwave-penetration depth was observed for multi-year ice. Physical properties of ice and snow were compared against results obtained from other experiments conducted in different ice-formation regions in the late winter and in the early melt season.

The limitations of current and immediate future single-frequency, single-polarization, space-borne SARs for winter sea-ice mapping are quantitatively examined, and improvements are suggested by combining frequencies and polarizations. Ice-type maps are generated using multi-channel, air-borne SAR observations of winter sea ice in the Beaufort Sea to identify six ice conditions: (1) multi-year sea ice; (2) compressed first-year ice; (3) first-year rubble and ridges; (4) first-year rough ice; (5) first-year smooth ice; and (6) first-year thin ice. At a single polarization, C- (λ = 5.6 cm) and L- (λ = 24 cm) band frequencies yield a classification accuracy of 67 and 71%, because C-band confuses multi-year ice and compressed, rough, thick first-year ice surrounding multi-year ice floes, and L-band confuses multi-year ice and deformed first-year ice. Combining C- and L-band improves classification accuracy by 20%. Adding a second polarization at one frequency only improves classification accuracy by 10–14% and separates thin ice and calm open water. Under similar winter-ice conditions, ERS-1 (Cvv) and Radarsat (CHH) would overestimate the multi-year ice fraction by 15% but correctly map the spatial variability of ice thickness; J-ERS-1 (LHH) would perform poorly;and J-ERS-1 combined with ERS-1 or Radarsat would yield reliable estimates of the old, thick, first-year and thin-ice fractions, and of the spatial distribution of ridges. With two polarizations, future single-frequency space-borne SARs could improve our current capability to discriminate thinner ice types.

An examination of both experiments and computer models of polycrystalline ice undergoing a simple shear suggests that there is good agreement. The model has correctly reproduced the deformational and microstructural features caused by glide on (0001) in the ice aggregates. This success is particularly prominent for those ice grains with a lattice orientation suitable for hard or easy glide or kinking, and where there is a sub-horizontal с axis and a larger grain-size. A limitation may be that the model cannot explicitly simulate recrystallization and grain-boundary migration, which are two other important processes operating jointly with glide in experimentally deformed ice. However, through the use of the models, it is possible to show how kinematic factors can control the processes of recrystallization. The localization of recrystallization in the polycrystalline ice aggregate is determined by the stress and strain variations between neighbouring grains.

Shallow cores to about 17 m depth were recovered at nine sites distributed on a 150 km × 150 km survey grid centered Summit in central Greenland. Measurements of the stable oxygen-isotope ratio and the gross β activity as a function of depth enable annual summer horizons to be identified and dated. From these data, average accumulation rates were computed with an uncertainty of about 5–8%. The contours of constant accumulation rate in the region suggest a primary moisture flux from the southwest of the grid. Similarly, contours of the average oxygen-isotope ratio are consistent with the progressive isotopic depletion of a precipitating air mass moving from the southwest, and automatic weather-station data indicate that the moisture flux tends to be largest from the southwest quadrant. The annual variation in the total accumulation over the grid shows no persistent trend over the interval 1964–87 common to all cores.

Distance measurements using an automated electronic distance-measurement system in the north cirque of Storglaciären, Sweden, during the summer of 1989, revealed a diurnal variation in glacier speed. Amplitude and timing of the diurnal cycle correlate well with the timing and intensity of the diurnal temperature cycle, indicating that speed responds to variations in daily melt with a lag of approximately 4 h. One 2 d period of non-diurnal velocity variations corresponded with a large rainfall event. Finite-element modeling suggests that these velocity variations must be closely related to water inputs in the cirque rather than to longitudinal coupling with lower parts of the glacier.

Observations of pulsating flow conditions in a supraglacier meltwater channel on Harlech Gletscher, East Greenland, are reported. Waves of water with turbulent wave fronts and smooth recessive limbs were observed passing downstream at regular intervals of 6-7 s. Peak channel discharge was estimated at 0.5-1.0 m3 s−1, in between which discharge was zero. It is suggested that the phenomenon as observed was due to the formation of roll waves in response to channel morphology and prevalent discharge conditions. Measurements of channel morphology are given together with calculations of critical flow conditions, supporting the hypothesis of roll waves in a natural ice channel. A brief introduction to roll waves and the theory regarding their formation is included.

Microscopic observation of air-hydrate crystals was carried out using 34 deep ice-core samples retrieved at Vostok Station, Antarctica. Samples were obtained from depths between 1050 and 2542 m, which correspond to Wisconsin/Sangamon/Illinoian ice. It was found that the volume and number of air-hydrate varied with the climatic changes. The volume concentration of air-hydrate in the interglacial ice was about 30% larger than that in the glacial ice. In the interglacial ice, the number concentration of air-hydrate was about a half and the mean volume of air-hydrate was nearly three times larger than that in the glacial-age ice. The air-hydrate crystals were found to grow in the ice sheet, about 6.7 × 10−12 cm3 year-1, in compensation for the disappearance of smaller ones. The volume concentration of air-hydrate was related to the total gas content by a geometrical equation with a proportional parameter α. The mean value of α below 1250 m, where no air bubbles were found, was about 0.79. This coincided with an experimentally determined value of the crystalline site occupancy of the air-hydrate in a 1500 m core obtained at Dye 3, Greenland (Hondoh and others, 1990). In the depth profile of calculated α for many samples, α in the interglacial ice was about 30% smaller than that in the glacial-age ice.

Global fall-out from atmospheric testing of thermonuclear weapons produced horizon markers corresponding to the initiation of testing in 1953 and the maximum fall-out in 1963. The radioactive isotope 137Cs associated with these events has a half-life of 30.2 years. Therefore, with the appropriate radiation detectors, this fall-out can be used as a long-term temporal indicator in glaciers and snowpack. A prototype γ-ray detector system was successfully tested and was used to make in-situ measurements of the 137Cs marker in a borehole at Summit, Greenland. The system consisted of a 7.6 cm by 7.6 cm NaI(Tl) scintillation crystal/photomultiplier detector, commercial pre-amplifier, amplifier and power supplies, and a microcomputer-based pulse-height analyzer. The measurements were made in boreholes of 25.4 cm and 12.7 cm diameter to depths of 22 m. Based on the results reported here, the γ-ray detection technique promises to be a powerful way to locate quickly horizon markers in the field.

The traditional method of calculating glacier outflows by measuring velocities and areas is difficult, inaccurate and sometimes dangerous in fast mountain streams. The salt-dilution method offers a more accurate alternative but, until now, its use has been restricted because of the difficulty of mixing chemical solutions and measuring chemical concentrations in the field. A computer program has been written which uses a laptop microcomputer to control measurements of stream conductivity and which quickly computes the stream flow directly in the field. The development of this method is described and examples are presented of the application of the method for glaciers in the Rocky Mountains and the Coast Mountains of Canada.

Mechanical conditions at the base of Trapridge Glacier, Yukon Territory, were investigated using a “ploughmeter”. We describe the physical characteristics and the theory of this new instrument as well as its operation. Observational results reveal variations in ploughmeter response that might be attributed to spatial variability in subglacial processes or spatial variation in sediment granulometry. Quantitative analysis of the interaction of the ploughmeter with the basal layer yields estimates of rheological parameters. If the sediment is assumed to behave as a Newtonian viscous fluid, the estimated effective viscosity is 3.0 × 109 −3.1 × 1010Pas; if it is assumed to behave as an ideal plastic solid, the estimated yield strength is 48–57 kPa. In both cases, the estimated shear resistance of subglacial material is comparable to but somewhat less than that required to balance fully the applied basal shear stress.

This paper presents the distribution of average δD andδ18O values for the top 1 m of surface snow for a large area of Antarctica. The samples were collected on the 1990 International Trans-Antarctica Expedition which crossed the continent from the northern tip of the Antarctic Peninsula to Mirny Station. The empirical relationships between the isotopes, temperature and elevation are computed. The slopes of δD with respect to the surface temperature for the segments west (Patriot Hills-Vostok) and east of Vostok (Komsomolskaya-Mirny) are not significantly different to that observed between Dumont d’Urville and Dome C (Lorius and Merlivat, 1977) which are often used to interpret deep ice-core isotopic profiles. There is, however, a noticeable shift between the two regression lines with, for a given temperature, higher isotopic values west of Vostok. The deuterium excess values increase sharply at 3000 m.a.s.l. on the plateau, confirming the results of Petit and others (1991).

A stainless-steel platen, with a centrally located pressure sensor on the front face, has been used to crush mono-crystalline, bubble-free fresh-water ice samples. Two electrical conductors, located on the face of the pressure sensor, were connected to a bridge circuit so that the presence of liquid between the two conductors could be detected and its thickness measured. Video records of the ice/ steel contact zone during crushing were obtained by mounting samples on a thick Plexiglas plate which permitted viewing through the specimen to the ice/steel interface. Total load and pressure records exhibited a sawtooth pattern due to the compliance of the ice and the testing apparatus, and spalling of ice from the contact zone. When the region of contact was in the vicinity of the pressure transducer, liquid was detected and peaks occurred in the liquid sensor output when load drops occurred. Contact between the platen and the ice consisted of low pressure zones of highly damaged crushed and/or refrozen ice, opaque in appearance, and transparent, high-pressure regions of relatively undamaged ice. Upper limits for the liquid-layer thickness on the high-pressure undamaged ice were ~3 µm on the ascending sides of the sawteeth in the load records and ~ 21 µ on the sharp descending sides.

A finite-element method solution of the continuity equation is used to investigate complex features of the Younger Dryas period. By comparing results of the model with field evidence, we conclude that the climatic event responsible for the Younger Dryas stillstand was probably short (less than 500 years). The assumption of a general sliding condition for elevations below 100 m, with an enhanced sliding zone through the center of the Baltic and Gulf of Bothnia, yields broad agreement for marginal positions in Sweden and Finland during a simulated termination. A stillstand near the Younger Dryas moraine position is attained with a climatic equilibrium-line altitude (ELA) depression of 600 m for a time period of 500 years. Agreement of simulated behavior with observed behavior is less consistent in the more maritime western Sweden and western Norway.

Single crystals and bicrystals of water ice have been adiabatically pressurized to produce, and clearly illustrate, two types of internal melt figures: (1) dendritic figures that grow from nucleation imperfections on the specimen’s surface, or from air bubbles at grain boundaries, into the ice as pressure is elevated; and (2) compression melt fractures, flat liquid-filled disks, that nucleate at imperfections in the crystal and grow with the application of pressure eventually to sprout dendritic fingers at the periphery. The transparency of the ice permitted visualization of the growth and behavior of the figures, and this could be an important tool in understanding the role of phase transformations in deep-focus earthquakes. Correlation between figure size and pressure is noted for the first time.

Structural analyses of ice collected from the bare ice surface in the region of the Sør-Rondane Mountains were carried out. Crystal-orientation fabrics and the disposition of surface cracks were investigated to determine the stress/strain configuration in the ice sheet near the mountains. Single-maximum fabric patterns with the axis of the maximum roughly perpendicular to the flow line on the horizontal plane were observed. It was deduced from the observations that the ice exhibits a fabric pattern indicating that the ice sheet is subjected to vertical shear strain between the ice flow and the nunataks.

Tracer experiments, and water-level observations made while drilling 47 boreholes in an overdeepened section of Storglaciären, have demonstrated that nearly all of the water passing through this part of the glacier moves in englacial conduits. Much of the viscous energy dissipated by subglacial water flowing up an adverse bed slope out of such an overdeepening may be needed to warm the water to keep it at the pressure-melting point. If the adverse slope is sufficiently steep, freezing may occur within the conduits. The possibility for enlargement of conduits by melting is thus limited and water pressures become high. We infer that this, combined with possible blocking of conduits by freezing, forces the water to seek englacial pathways.

The frequency with which englacial conduits are encountered during drilling suggests that there are several hundred of them in any given cross-section of the glacier. Consequently, each must carry a small fraction of the total discharge, say ∼ 10−3 m3 s−1. Tracer experiments suggest that flow rates in these conduits are < 10− m s−1, so conduit cross-sectional areas must be ∼10−2 m2, a size that is consistent with video observations in boreholes. The observed mean hydraulic gradient through the overdeepening is ∼0.04. If the conduits were of uniform cross-sectional area, the roughness implied by these figures would be unreasonably high and water pressures in them would be lower than observed. Thus, we hypothesize that conduits are locally constricted to only a small fraction of their average cross-sectional area.

The aim of the present research is to evaluate changes in the glacierized area, glacier-water resources and glacial run-off during the last 25–30 years. The prevailing process of degradation has resulted in a 16% diminution of the glacierized area in Gissaro-Alai and 11% in the Pamirs. The ratio between the advancing, stationary and retreating glaciers in the Gissaro-Alai mountains is 1:5:17, and the one in the Pamirs is 1:1:4. Moraine-covering of the glaciers has increased from 8 to 11 % in the Gissaro-Alai and from 6 to 11 % in the Pamirs. Ice-volume diminution of glaciers in the Gissaro-Alai is 17% and in the Pamirs it is 12%. The mean long-term annual volume of total glacial melting, glacial run-off and variation coefficients of these values in the river basins of the Pamirs and the Gissaro-Alai are described as functions of the altitudes of glacier termini, equilibrium lines and a new parameter, which characterizes the influence of the glacierized area distribution according to altitude on run-off. The data presented here indicate changes in mean annual volumes of glacier water yield in the river basins of the Pamirs and the Gissaro-Alai mountains, related to glaciation evolution in 1957–80.

To determine the factors controlling natural levels of thermoluminescence (NTL) of fluvioglacially transported suspended sediment, samples were taken at hourly intervals from a meltwater stream emanating from Sólheimajökull in southern Iceland. The NTL of the samples were measured and compared with fluctuations in suspended-sediment load and in flow depth of the stream. It was found that the ratio of the 325°C and the 375°C regions of the NTL spectrum was more closely related to sediment load and flow depth than were the individual regions themselves. Analysis of the patterns suggests that NTL fluctuations are related to changes over time in the sources of sediment entrained by the stream. It is inferred that these changes relate to diurnal temperature cycles plus precipitation events. Such fluctuations raise doubts as to the validity of bulk sampling procedures in TL dating of Quaternary fluvioglacial sediments.

A finite-element solution of the time-dependent mass-continuity equation for column-averaged ice-sheet flow and sliding is applied to the Antarctic ice sheet. First, a calibration of the model to the steady-state present ice-sheet configuration is presented. With fitted values of the parameters describing the regions of sliding, the degree of bed coupling and the ice hardness, a change in the mean annual sea-level temperature is used to simulate variation of the climatic conditions over Antarctica for both warming and cooling of the climate. Paradoxically, a climate warming of up to 9 deg leads to an increase in ice volume, while cooling leads to decreasing ice volume as long as the present margins of Antarctica are maintained. Some extreme simulations of the Antarctic ice sheet for “maximum over-riding” and “minimum warm climate” are shown for situations where the present bed conditions are altered. Finally, a time-dependent simulation shows the response of the ice-sheet system to cyclical variations in the simulated climate, demonstrating the lag of the ice-sheet response to be approximately 2700 years.