We present a model for the determination of a sliding law in the presence of subglacial cavitation. This law determines the basal stress at a clean ice‒bedrock interface in terms of the velocity and effective pressure. The method is based on an exact solution of the Nye—Kamb (linearly viscous) sliding problem with cavities, and uses ideas of Lliboutry (1979) to construct, via renormalization methods, an approximate law for general bedrock form. We show that, for a bedrock whose spectrum has a power‒law behaviour, one obtains a sliding law which gives the basal shear stress proportional to a power of the velocity, and to a power of the effective pressure.

The effect of subglacial cavitation on the drainage system is examined, using recent ideas of Kamb. For sufficiently high velocities, drainage through a Röthlisberger tunnel system is unstable, and drainage takes place through the linked system of cavities. This leads to a reduction of the effective pressure, and by taking account of this, one can rewrite the sliding law in terms of stress and velocity only.

This sliding law can be multi‒valued, and it is suggested that this underlies the dynamic phenomenon of surges.

McTigue and others (1985) identified a possible problem in the type of constitutive equation usually used for modeling the creep behaviour of polycrystalline ice. They pointed out that Glen’s flow law necessarily excludes the consideration of normal stress effects, which are of great significance in other disciplines that consider non-Newtonian fluids. Using the second-order fluid (with material parameters evaluated from laboratory data) as a tentative model for ice, they reached the conclusion that normal stress effects may be discernible in natural glacier flow. But, as noted by McTigue and others, the second-order fluid “fails to represent the non-linear rate dependence of ice in shear”; therefore it is in fact not a suitable constitutive model for glacier ice in shearing flow. In this note, parallel to what McTigue and others did for the second-order fluid, we present a similar analysis for (I) the modified second-order fluid and (II) the power-law fluid of grade 2, both of which are constitutive models recently proposed by Man as a tentative generalization of Glen’s flow law. Both models (I) and (II) can represent normal stress effects, and both agree with Glen’s flow law in the prediction of the depth profile of velocity in the steady laminar flow of glaciers. For ease of comparison, the same creep data of McTigue and others are used in quantifying the material parameters in these two models. Both models (I) and (II) predict far less pronounced normal stress effects in glaciers than those estimated by McTigue and others (whose data analysis in fact suffered from inconsistencies and over-parameterization).

This paper presents and discusses the results of constant deformation-rate tests on laboratory-prepared polycrystalline ice. Strain-rates ranged from 10−7 to 10−1s−1, grain–size ranged from 1.5 to 5.8 mm, and the test temperature was −5°C.

At strain-rates between 10−7 and 10−3 s−1, the stress-strain-rate relationship followed a power law with an exponent of n = 4.3 calculated without regard to grain-size. However, a reversal in the grain-size effect was observed: below a transition point near 4 × 10−6 s−1 the peak stress increased with increasing grain-size, while above the transition point the peak stress decreased with increasing grain-size. This latter trend persisted to the highest strain-rates observed. At strain-rates above 10−3 s−1 the peak stress became independent of strain-rate.

The unusual trends exhibited at the lower strain-rates are attributed to the influence of the grain-size on the balance of the operative deformation mechanisms. Dynamic recrystallization appears to intervene in the case of the finer-grained material and serves to lower the peak stress. At comparable strain-rates, however, the large-grained material still experiences internal micro-fracturing, and thin sections reveal extensive deformation in the grain-boundary regions that is quite unlike the appearance of the strain-induced boundary migration characteristic of the fine-grained material.

The flow of a glacier along a channel of constant longitudinal curvature is analyzed using analytical and finite-element methods. Channels of various cross–sectional shape are investigated, ranging from a simple rectangular form with zero shear traction along the bed to realistic profiles taken from Blue Glacier, Washington. Terms in the equilibrium and rate-of-deformation equations which are inversely dependent on radius and a body force which varies transversely across the glacier introduce several characteristic features into the stress and velocity fields of the curving glacier. The stress center line is shifted toward the inside of the bend, causing an asymmetric crevasse pattern and non‒zero stress magnitude at the surface on the geometric center line of the channel. The stress field is dependent on the stress exponent in the flow law and is non-linear across the surface. The surface–velocity pattern shows a “tilting” of the usual high‒order parabolic form, being skewed toward the inside of the bend. There is a shift in the velocity maximum from the deepest part of the channel. All of these curvature‒induced features are dependent on the radius of curvature, actual channel geometry, and stress exponent in the flow law. Model results show excellent agreement with the velocity and crevasse patterns on the curving Blue Glacier.

Victoria Lower Glacier is a complex structure of ice from two distinct sources (Schultz Glacier to the north and a local névé of Victoria Lower Glacier) that join at a broad median shear zone. Evidence from the margins suggest that both are currently retreating. Algae in a block of frozen stratified sediment from within the ice of the terminal margin has a radiocarbon age of 20 200 ± 2400 year BP (NZ 6531 A), indicating that the glacier has advanced since that time. Superposition of ice levels of Ross Sea I glaciation on a radio echo–sounding profile of bedrock beneath the glacier indicates that it is unlikely that Ross Sea I ice entered the valley. The radiocarbon date supports this finding.

“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.

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 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.

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.

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.

The ice-thickness profiling performance of a helicopter-mounted short-pulse radar operating at approximate center frequencies of 600 and 900 MHz was assessed. The antenna packages were mounted 1.2 m off the skid of a small helicopter whose speed and altitude were varied from about 1.8 to 9 m/s and 3 to 12 m. Clutter from the helicopter offered minimal interference with the ice data. Data were acquired in Alaska over lakes (as a proving exercise) and two rivers, whose conditions varied from open water to over 1.5 m of solid ice with numerous frazil-ice formations. The most readily interpretable data were acquired when the ice or snow surface was smooth. Detailed surface investigations on the Tanana River revealed good correlations of echo delay with solid ice depth, but an insensitivity to frazil-ice depth due to its high water content. On the Yukon River, coinciding temporally coherent surface and bottom reflections were associated with solid ice and smooth surfaces. All cases of incoherent surface returns (scatter) occurred over ice rubble. Rough-surface scattering was always followed by the appearance of bottom scattering but, in many cases, including a hanging-wall formation of solid frazil ice, bottom scattering occurred beneath coherent, smooth-surface reflections. Areas of incoherent bottom scattering investigated by drilling revealed highly variable ice conditions, including frazil ice. The minimum ice thickness that could be resolved from the raw data was about 0.2 m with the 600 MHz antenna and less than 0.15 m with the 900 MHz antenna.

A spectacular surge occurred on Peters Glacier, Alaska, in 1986 and 1987. Several observations on the glacier were made during the course of its surge. These observations are compared with those on other surging glaciers and then interpreted in terms of the ideas on surge mechanisms and dynamics as originally postulated by Post (unpublished) and further developed during the surge of Variegated Glacier by Kamb and others (1985) and Raymond and Harrison (1986, in press). It is shown that the concepts of rapid basal motion due to high water pressure at the glacier bed and the initiation of a surge during the winter due to a pressurization of the limited supply of basal water are well supported by these observations on the surge of Peters Glacier. An extremely high suspended sediment load rich in very fine material was observed, which also supports ideas on basal processes expected during this type of surge.

One interesting (and puzzling) feature of this surge cycle is that the termination of the surge occurred in late winter 1987, when surface melt water was at a minimum. This is in direct contrast to the termination of the surge on Variegated Glacier, which occurred during the period of peak ablation.

Small perturbations in Antarctic environ-mental conditions can culminate in the demise of the Antarctic ice sheet’s western sector. This may have happened during the last interglacial period, and could recur within the next millennium due to atmospheric warming from trace gas and CO2 increases. In this study, we investigate the importance of sea-level, accumulation rate, and ice influx from the East Antarctic ice sheet in the re-establishment of the West Antarctic ice sheet from a thin cover using a time-dependent numerical ice-shelf model. Our results show that a precursor to the West Antarctic ice sheet can form within 3000 years. Sea-level lowering caused by ice-sheet development in the Northern Hemisphere has the greatest environmental influence. Under favorable conditions, ice grounding occurs over all parts of the West Antarctic ice sheet except up-stream of Thwaites Glacier and in the Ross Sea region.

Basic glaciological measurements from the James Ross Island ice cap are presented, including mean annual accumulation and firn temperature. In addition to the well-known radioactivity levels of January 1955 and 1965 in Antarctic snow, two new radioactivity levels corresponding to January 1969 and January 1974 are used in determining the accumulation values. The measurements reveal certain climatic features of this ice cap.

An investigation of the combined heat, ice, and water balances was carried out in the Marukh glacier basin (west Caucasus) in 1966–67 to 1976–77, according to the International Hydrological Decade programme. Averaged glacier mass balance for these 11 years appears to be −55 g cm−2 year−1 according to stake measurements, and −51 g cm−2 year−1 according to geodetic measurements. The variability of accumulation is estimated as Cv = 0.15 and of ablation as Cv = 0.11. Thus, the variation in accumulation governs the oscillations in glacier balance. The inner nourishment of the glacier was also taken into account. The glacier mass balance is closely related to the relation between the accumulation and ablation areas. The “transient” values of both figures during the whole period of ablation can be used for this relation. The forms of the accumulation and ablation fields are similar from year to year and from one 10 day period to another. The areas of the accumulation and ablation zones are very different from one year to another. On the contrary, the average specific balance for each zone changes very little. One can use these features for the construction of accumulation, ablation, and specific mass-balance maps from satellite imagery. Mean values for the mass-balance terms occur in the vicinity of the equilibrium line. They can be calculated by using the air temperatures. Deviations from the means in different areas of the glacier determine the typical fields of the mass-balance terms.

A stress–strain relation for dry snow in Greenland and Antarctica was derived. When this relation is integrated, it gives snow density as a function of time. For given surface density, temperature, and accumulation, the age of snow layers can be obtained as a function of depth in the snow-pack. Calculations compare well with observations. With some knowledge of the temperature range in the upper layer of the snow-pack, calculation for density versus depth can also be improved over the results where such temperature information was not used.