The net mass balance of four small cirque glaciers (0.7–1.4 km2) in the Torngat Mountains of northern Labrador was measured for 1981–84, allowing three complete mass-balance years to be calculated. The two largest glaciers experienced positive mass-balance conditions in 1982 while all the glaciers were negative in 1983. The temporal pattern relates directly to general climatic conditions, in particular winter snowfall. Spatial variations of mass balance on the glaciers are the result of several factors including altitude, extent of supraglacial debris cover, slope, proximity to side and backwalls of the enclosing cirque, and the height of the backwall above the ice surface. Abraham Glacier, the smallest studied and with consistently the largest negative mass balance (–1.28 m in 1983), re-advanced an average of 1.2 m each year between 1981 and 1984. Mean equilibrium-line altitude (ELA) for the four glaciers is 1050 m, varying substantially from one glacier to another (+240 to –140 m) and from year to year (+60 to –30 m).

Large ice masses contain a wealth of information regarding past climates and atmospheric chemistry. To interpret properly information from ice cores obtained from glaciers, a time-scale for the ice core must be established. A procedure based on the finite-element method, using velocity-pressure and stream-function formulations to establish particle paths and hence isochrones, is outlined. Examples are presented which demonstrate the ability of the procedure to predict particle paths and isochrones which can be used to determine the time-scale or to confirm dates established by other methods, of ice cores obtained from large ice masses.

A study is made of the sea-ice regime of the Ross Sea, Antarctica, using ESMR passive microwave data and supporting information. Inferences are made of the processes responsible for observed spatial and temporal sea-ice variations. Air flow appears to have a dominant influence on sea-ice distribution and movement, with oceanic circulation playing a more minor role. This is particularly so with coastal polynya development, where katabatic winds are important. It has been possible to identify broad areas of ice convergence and divergence by assimilating the rather limited oceanic and atmospheric information with observed sea-ice variations. In spite of some basic physical similarities of the Weddell and Ross Seas, it is apparent that the major differences in their sea-ice regimes are due to the differing roles of oceanic and atmospheric circulation in each area. The Antarctic Peninsula plays a key role in these differences. Suggestions for further research are also considered.

Mount Redoubt, a volcano located west of Cook Inlet in Alaska, erupted from 1966 to 1968. This eruptive cycle removed about 6 × 107 m3 of glacier ice from the upper part of Drift Glacier and decoupled it from the lower part during a sequence of jökulhlaups which originated in the Summit Crater and flooded Drift River. The same events blanketed the lower part of the glacier with sand and ash, reducing ice ablation. Normal snowfall, augmented by intense avalanching, regenerated the upper part of the glacier by 1976, 8 years after the eruptions. When the regenerated glacier connected with the rest of Drift Glacier, it triggered a kinematic wave of thickening ice accompanied by accelerating surface velocities in the lower part of the glacier. Surface velocities increased by an order of magnitude and were accompanied by thickening of 70 m or more. At the same time, parts of the upper glacier thinned 70 m. The glacier appears to be returning to its pre-eruption equilibrium condition.

Two isotropic points measured by Meier and others (1985) on Columbia Glacier, Alaska, are examined. The pattern classification of the upper one is on the borderline between monstar and lemon, and this is traced to the fact that the variation of strain-rate in the longitudinal direction is approximately equal to that in the transverse direction, contrary to the assumption made in Nye (1983). The conditions for the lower isotropic point to have the star pattern, as observed, are believed to be typical for a glacier that ends in an ice cliff, like this one, which calves icebergs. Where, as in this case, there is only a small transverse velocity, the isotropic points on a glacier must nearly coincide with stationary points for the speed, and these are almost always either maxima or saddles, alternating. The maxima correspond to lemon or monstar patterns, and the saddles to star patterns.

In order to determine the effect of basal debris drag as a component in a sliding law, it is necessary to know the basal debris concentration. Does, for example, this debris concentration exhibit uniformity, in an average sense, across a valley? What effect does a localized region of high quarryability have on basal debris concentration down-stream? The analysis presented here suggests that, for the case of sparse debris, debris concentration tends to be uniform over the entire bed. Consequently, the debris-drag term in a sliding law will also tend to be uniform.

In order to reach the above conclusions, it is necessary to consider debris balance, the balance of the quarrying, abrasion, and debris-flushing rates. This entails proposing and testing quarrying and flushing laws, since these laws have not been previously proposed. It is concluded that the quarrying, flushing, and erosion rates depend weakly on the sliding velocity. Furthermore, the abrasion rate is negligible compared to the quarrying rate. (This conclusion depends partially on the definition of abrasion.) The quarrying rate also depends on other factors such as the effective pressure_pressure-fluctuation mechanism; the cross-valley dependency of this mechanism is investigated. The flushing rate is found to depend on the ratio, N-channel area/bed area, and on average N-channel diameter.

A large valley, ideally suited for “selective linear erosion” by ice, extends from the Kreiger Mountains to Tanquary Fiord, north–central Ellesmere Island. During the last glaciation, the outlet glacier at the head of the valley advanced 18 km and was at least 250 m thick where it contacted the sea in the lower valley. Erosion of bedrock inside the last ice limit is recorded by an abraded diabase dike, and by crag–and–tail features developed in limestone. During deglaciation (7800 B.P.), melt–water streams along the ice margin incised a large alluvial fan that pre–dates the last glaciation. The fan shows little alteration by the over–riding ice and its final erosion by the melt–water streams incised, but did not remove, its original ice–wedge polygons.

The preservation of the fan indicates that the glacier was locally non–erosive and that it probably advanced across the fan by over–riding a protective frontal ice apron. Although it is commonly assumed that such alluvial fans occupying glaciated valleys are of post–glacial age, this need not be the case in permafrost terrain. In fact, at this site, there has been a net increment of alluvium versus glacial erosion or deposition spanning the last glacial cycle. The paper discusses the processes of erosion associated with sub–polar glaciers and questions whether erosion by them or more pervasive ice is responsible for such High Arctic valleys and fiords.

Two situations are studied in relation to the flow law of polar ice. In each case, models are used with a flow-law exponent of one, and with the more traditional exponent of three. The horizontal velocity profile at Devon Island, Arctic Canada, is better fitted by n = 1; for the vertical velocity profile, n = 3 gives a better fit, but both model profiles fall well within experimental error. For the Camp Century age–depth profile, only n = 1 gives an acceptable fit when temperature is allowed for. The large discrepancy between isothermal and non-isothermal models for n = 3 shows the importance of allowing for temperature in studies of ice-sheet properties.

The erosion rate of bedrock by glacier action is analyzed under conditions of constant-state radial convergent and divergent flow, assuming that the quarrying rate increases with increasing sliding velocity, and assuming a conventional power-function sliding law. Ice is modeled as a non-linear Glen material. Deviatoric stresses are computed but are shown to be negligible compared to the basal shear stress, provided that suitable restraints are placed on the ratio of channel radius of curvature to ice thickness. If the ice is sufficiently thick, radial divergent flow results in erosion rates which decrease in the down-stream direction This provides an explanation for the formation of the largest class of fjord thresholds which occur at channel widenings. In contrast, increased erosion rates are predicted at narrows which can explain the presence of deep troughs at gradual narrows. It is argued that the presence of pronounced thresholds in abrupt narrows can be explained by low quarryability or locally high roughness which reduces the sliding velocity. The origin of till overlying thresholds is explained as a natural consequence of a threshold being a position of relative stability for the terminus of a retreating tide-water glacier.

Conduit and regelation water are inferred to drain as ground water from up to 130 km2 of Columbia Icefield. Subglacial conduits appear to be generally occupied by free surface streams. Ground-water flow will allow exchange between the regelation film and conduits. Present-day discharge from beneath the accumulation zone carries little sediment, and past injections of sediment appear to correspond to ancient interglacials. Transport of sediment through cave passages may be analogous to transport through basal conduits.

The late Wisconsin Shelbyville till was deposited in southern Illinois c. 20 000–21 000 year B.P. and records the maximum southern advance of the Lake Michigan lobe of the Laurentide ice sheet. The yield strength calculated for a representative till debris flow found just south of the ice margin is 8 kPa (0.08 bar), and probably approximates yield strength of basal Shelbyville till. An ice-profile model assuming plastic behavior in basal till suggests the southern Lake Michigan lobe may have been unusually thin. Reconstructed Laurentide glacier profiles from the south-west and western Great Plains (South Dakota, Alberta, Minnesota, and Montana), and the MacKenzie Delta, N.W.T., are similar to those inferred for the southern Great Lakes area, and much thinner than those of most modern ice sheets. The Pleistocene Laurentide ice sheet may have been asymmetric: thicker in the east than in the west. Glaciers resting on weak sediments can move both by subglacial sediment deformation (creep) and sliding at the sediment–ice interface. Till rheology is complex; shearing of till by over-riding glaciers would increase porosity and further reduce yield strength.

A theoretical examination of salinity and porosity changes introduced in sea-ice samples by brine expulsion and gas entrapment caused by thermal cycling during shipping and storage shows that in extreme cases such effects can be significant, resulting in 15% reductions in porosity (n) More representative scenarios give porosity changes of less than 2% which, assuming that ice-property variations scale with n1/2, result in property variations of less than 1%.

We use a hybrid finite-element/finite-difference model of ice-shelf flow and heat transfer to investigate the effects of basal melting on the present observed flow of the Ross Ice Shelf, Two hypothetical basal melting scenarios are compared: (i) zero melting everywhere and (ii) melting sufficient to balance any large-scale patterns of ice-shelf thickening that would otherwise occur. As a result of the temperature-dependent flow law (which we idealize as having a constant activation energy of 120 kJ mol−1, a scaling coefficient of 1.3 N m−2 s1/3, and an exponent of 3), simulated ice-shelf velocities for the second scenario are reduced by up to 20% below those of the first. Our results support the hypothesis that melting patterns presently maintain ice thickness in steady state and conform to patterns of oceanic circulation presently thought to ventilate the sub-ice cavity. Differences between the simulated and observed velocities are too large in the extreme south-eastern quarter of the ice shelf to permit verification of either basal melting scenario. These differences highlight the need to improve model boundary conditions at points where ice streams feed the ice shelf and where the ice shelf meets stagnant grounded ice.

VLF surface-impedance measurements have been used in the past for sub-surface mapping. The application of this technique to glacial ice probing is discussed theoretically and results of measurements on Brewster Glacier, New Zealand, are presented. Results were fitted to a three-layer model and a section profile is given. Dramatic changes in the phase of the surface impedance were observed in the vicinity of crevasses. Results indicate that the technique has potential as a tool for quick, reliable, and non-invasive ice-thickness measurements.

Shipboard observations (in accordance with Norsk Polar-Institutt guidelines) from 6 years of Australian National Antarctic Research Expeditions (ANARE) voyages have provided data giving a detailed knowledge of iceberg sizes and concentrations in the Southern Ocean between long. 60° and 140° E. The resulting size–frequency distributions are examined in conjunction with a knowledge of water movement along known drift tracks in a selected study area (between lat. 59° and 64° S., and long. 90° and 120° E.) to determine iceberg-dissolution rates. The “median life” (before breaking) of icebergs less than 1000 m in horizontal dimension is estimated to be 0.2 a, which is significantly lower than was previously thought. The mean melt rate is estimated to be 0.12 m d–1, which agrees broadly with previous laboratory studies. The relative contributions of melt, calving, and breakage, plus the enhancement effect of roll-over, are examined in estimating the natural dissolution rate. Breakage appears to be the dominant mechanism for larger icebergs with melt and calving able to explain the disappearance of icebergs in the smallest categories only (within the mean “median-life” period). Examination of the historical records of Captain Cook indicates that iceberg concentrations, as well as the northerly extent in this region 200 years ago, were compatible with the present data.

The snow-pack on the Arctic Coastal Plain of Alaska has a well-developed depth-hoar layer which forms each year at the base of the snow-pack due to upward vapor transfer resulting from a temperature gradient in the snow-pack. The thickness of the depth-hoar layer tends to increase inland where greater temperature extremes (in particular, lower minimum temperatures) permit larger temperature gradients to develop within the snow-pack. Brightness temperature (TB) data were analyzed from October through May for four winters using the 37 GHz horizontally polarized Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR). By mid-winter each year, a decrease in TB of approximately 20K was found between coastal and inland sites on the Arctic Coastal Plain of Alaska. Modeling has indicated that a thicker depth-hoar layer in the inland sites could be responsible for the lower TBs. The large grain-sizes of the depth-hoar crystals scatter the upwelling radiation moreso than do smaller crystals, and greater scattering lowers the microwave TB. Using a two-layered radiative transfer model, the crystal diameter in the top layer was assumed to be 0.50 mm. The crystals in the depth-hoar layer may be 5–10 mm in diameter but the effective crystal diameter used in the radiative-transfer model is 1.40 mm. The crystal size used in the model had to be adjusted downward, relative to the actual crystal size, because the hollow, cup-shaped depth-hoar crystals are not as effective at scattering the microwave radiation as are spherical crystals that are assumed in the model. In the model, when the thickness of the depth-hoar layer was increased from 5 cm to 10 cm, a 21K decrease in TB resulted. This is comparable to the decrease in TB observed from coastal to inland sites in the study area.

The surface condition of the North Water was investigated during two winters (i.e. the three polynyas: Smith Sound polynya, Lady Ann Strait polynya, and Barrow Strait polynya). Since no detailed information was available on ice conditions and the extent of open water during winter, radiometric temperature measurements of the sea surface had to be taken along a flight line of 2650 km from an altitude of 300 m. From November to March 1978-79 and 1980-81, 14 remote-sensing flights were carried out. On the basis of the radiometric measurements, the following ice types were identified: ice-free, dark nilas, light nilas, grey ice, grey-white ice, and white ice. A comparison between the thermal and the visual ice classification (the latter being based on grey tones of the aerial images) showed a deviation of 3%. The analysis showed that in November, December, and January more than 50% of the Smith Sound polynya was covered by young ice, nilas, and ice-free, whereas in February and March white ice was dominant. Moreover, it was found that the two polynyas in Smith Sound and Lady Ann Strait were much smaller than previously believed. In Barrow Strait, a semi-permanent polynya was observed in the winter of 1980-81. The occurrence of polynyas in Barrow Strait seems to be connected with the location of the fast-ice edge. On the basis of the calculated ice-type distribution and heat-flux rates for different ice types, an energy loss of 178 W m-2 was found on the surface of the Smith Sound polynya due to open water and thin ice for the winter months November to March. Compared with other ice-covered sea surfaces in the Arctic, the heat release by the sea-water in the Smith Sound polynya is about 100 W m-2 larger.

Satellite images recorded in 1973, 1974, and 1985 of the Brunt Ice Shelf are compared. There are sufficient identifiable features moving with the ice shelf to show flow patterns over an area of ~10 000 km2. Velocities vary from 500 m a−1 in the west, near the Dawson-Lambton Ice Stream, to 1300 m a−1 in the east, within the Stancomb-Wills Ice Stream.

Medial moraines and lineations on the surface of composite glaciers enable the detection of structural and hydrological features. A study of the composite glacier Breidamerkurjökull, south Iceland, indicates relationships between subglacial waterways, ice structure in the junction area, and development of the glacier terminus. First, rivers are situated in or near medial moraines because melt water percolates to the bed and moves from there with the subglacial rivers mainly in the direction of ice flow. Secondly, the contact between two feeder glaciers sometimes forms an angle at the glacier terminus. Then the meltwater river escaping from the contact, generally in a radial direction (away from the glacier front), during the retreat will be transferred to the front of the first receding glacier. The drainage of the contact zone then changes from a radial to a tangential direction, destroying the terminal moraines of the recession stages.

Similar relations are found in relics of Pleistocene ice sheets, two examples of which are compared. The huge subglacial channel of the Münsterländer Kiessandzug-Esker below the ice sheet of the Saalian glaciation in the Münsterland, north-west Germany, was formed in the ice-flow direction. It therefore gives details of the morphology and of the great ice-dammed lake east of the Teutoburger Wald ridge. At the contact between the Norwegian and Baltic Sea glaciers, the terminus formed an angle during the maximum extent of the Weichselian glaciation in northern Jutland. During retreat, the Norwegian glacier receded first. The large melt-water river escaping from the contact between both glaciers had formed the huge Karup Sandur during the maximum, but now, during the recession, it changed to the front of the Norwegian ice, destroying the recession moraines there.

During the snow-melt season of 1982, basal water pressure was recorded in 11 bore holes communicating with the subglacial drainage system. In most of these holes the water levels were at approximately the same depth (around 70 m below surface). The large variations of water pressure, such as diurnal variations, were usually similar at different locations and in phase. In two instances of exceptionally high water pressure, however, systematic phase shifts were observed; a wave of high pressure travelled down-glacier with a velocity of approximately 100 m/h.

The glacier-surface velocity was measured at four lines of stakes several times daily. The velocity variations correlated with variations in subglacial water pressure. The functional relationship of water pressure and velocity suggests that fluctuating bed separation was responsible for the velocity variations. The empirical functional relationship is compared to that of sliding over a perfectly lubricated sinusoidal bed. On the basis of the measured velocity-pressure relationship, this model predicts a reasonable value of bed roughness but too high a sliding velocity and unstable sliding at too low a water pressure. The main reason for this disagreement is probably the neglect of friction from debris in the sliding model.

The measured water pressure was considerably higher than that predicted by the theory of steady flow through straight cylindrical channels near the glacier bed. Possible reasons are considered. The very large disagreement between measured and predicted pressure suggests that no straight cylindrical channels may have existed.