Wide-angle seismic reflections from a glacier bed are sensitive to the presence of subglacial water and to the mechanical strength of the basal zone. The phase of a compressional to shear (P-SV) converted wave is particularly sensitive to the shear coupling between the glacier and its bed. Both shear (SV) and compressional (P) reflections from the bottom of Variegated Glacier were obtained before the 1982–83 surge event using explosive sources, and the phases of these reflections (relative to the source) were positive as expected for an ice/bedrock interface. During surge, P-wave reflections from the deepest part of the glacier bed were phase reversed, while somewhat shallower P-wave reflections were not. SV reflections were not clearly observed during surge and cannot be interpreted with confidence, even though the experiments were designed to detect them using three-component geophones. The unexpected P-wave phase reversal might be explained by a thin, mechanically weak or fluidized basal debris layer during surge which acts as a strong seismic absorber and suppresses multiple reflections within the layer. However, the required amount of seismic attentuation in the layer seems unreasonably large. An alternative explanation requiring ∼4–8 m or more of water or water-saturated debris (without strong attenuation) is implausible.

Is it justified to adopt a two-dimensional continuum model for the movement and large-scale deformation of pack ice? A preliminary study oi’ ERTS-1 photography shows that the details of the ice movement are readily measurable; the problem is not in the accuracy of the remote sensing but in the inherent graininess of the sea ice. There is a spatial variation of ice velocity on a scale of several hundreds of kilometres; smaller-scale variations are superimposed on this, but their amplitude is not enough to obscure the large-scale trend. A continuum model is applicable, but, because of the small-scale variations in the velocity of the sea ice itself, it is not meaningful to specify continuum strain-rates on a scale of, say, 100 km to more than a certain accuracy, If ERTS pictures are available during the AIDJEX main experiment they could provide the necessary strain and displacement measurements for comparison with the predictions of the AIDJEX model.

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.

An approximate analysis of (he processes of inciting and freezing of a drill hole, 500 m depth and 0.15 m m initial radius, through an ice shelf was made. Results are expressed in graphical form showing the time available for experimentation under the hole as a function of heating duration. It was also found that refreezing has a much slower rate than melting.

A model, relating spatial patterns of snow accumulation in the alpine belt of major mountain ranges to the angular relationship which exists among terrain features such as cirque basins, mean storm-path trajectories, and incident solar radiation, is presented together with a limited amount of relevant empirical data. It is suggested that an “orientation gradient” exists in both the temporal and spatial variation of accumulation and ablation in the alpine terrain, the importance of which varies as some function of the relative control exerted by wind redistribution of snow and of direct incident solar radiation on the accumulation and ablation processes. The data obtained to date suggest that the importance of the orientation gradient varies widely among the mountain ranges studied, being a good predictor of snow distribution patterns in the Front Range of the Colorado Rockies and the Snowy Range in southern Wyoming, both of which are relatively windswept, while in the much less windy Bridger Range, in south-western Montana, both orientation and elevation appear to contribute on an almost equal basis. An indirect method of estimating relative amounts of annual mass turnover, using eleven glaciers located in the Wind River of west central Wyoming, is presented.

Since its inception in 1975, the Northwest Avalanche Center (NWAC) has developed and produced micro- and mesoscale weather forecasts to support avalanche forecast and control needs for the Olympic and Cascades Mountains of Washington and Oregon, U.S.A. This paper describes NWAC’s array of data, observational results, and analytical techniques that make “avalanche weather” forecasting possible. In addition, NWAC’s operational program and the general terrain and climate of the area are described. A sample forecast is also included.

The ice movement on the Byrd Glacier, Antarctica, was measured as function of time, on the basis of aerial photography. The method of aero-levelling strip triangulation with a minimum of geodetic control was applied. The methods and procedures were verified over Laufen-Bauma test area.

The appearance of a diurnal hysteresis in snow albedo is a widely reported phenomenon. This note discusses the relative importance of two separate effects: surface morphosis and surface irregularities (sastrugi). It is concluded that surface morphosis is the more important effect of the two in the region of the marginal cryosphere. Surface irregularities probably are the dominant influence only on permanent cryospheric areas such as the Greenland and Antarctic plateaux.

The temperature dependence of the high-frequency conductivity of snow was studied for eight samples in the range — 10°C to — 80°C. The activation energies for granular snow varied from 0.60 eV at temperatures down to — 25°C to 0.24 eV at temperatures below — 25°C, and for dry snow from 0.42 eV to 0.18 eV in the same temperature ranges. Dry snow samples had higher conductivities and lower activation energies than granular icy samples throughout the complete temperature range.

Volume and surface conduction processes were operative. At the higher temperatures above — 25°C volume conduction was attributed to Bjerrum defect migration, while at lower temperatures Bjerrum conduction was replaced by ionic-defect conduction. Granular samples which had experienced melting and reflecting on the surface of the crystals have a structural change which decreased the ionic-defect density at the surface and lowered the sample conductivity.

Above — 25°C, the activation energies for granular icy snow were consistent with those for temperate glacier ice and for laboratory single and polycrystalline ice samples, but was not in agreement with those of either polar snow or ice. Below — 25°C, the activation energies for granular snow were consistent with those for temperate glacier ice, containing impurities, and for polar snow and ice. Fresh dry temperate snow-samples had lower activation energies than in situ polar snow.

Thermal convection in the Antarctic and Greenland ice sheets has been dismissed on the grounds that radio-echo stratigraphy is undisturbed for long distances. However, the undisturbed stratigraphy lies, for the most part, above the density inversion in polar ice sheets and therefore does not disprove convection. An echo-free zone is widespread below the density inversion, yet nobody has cited this as a strong indication that convection is indeed present at depth. A generalized Rayleigh criterion for thermal convection in elastic-viscoplastic polycrystalline solids heated from below is developed and applied to ice-sheet convection. An infinite Rayleigh number at the onset of primary creep decreases with time and becomes constant when secondary creep dominates, suggesting that any thermal buoyancy stress can initiate convection but convection cannot be sustained below a buoyancy stress of about 3 kPa. An analysis of the temperature profile down the Byrd Station core hole suggests that about 1000 m of ice below the density inversion will sustain convection. Creep along the Byrd Station strain network, radar sounding in East Antarctica, and seismic sounding in West Antarctica are examined for evidence of convective creep superimposed on advective creep. It is concluded that the evidence for convection is there, if we look for it with the intention of finding it.

A comprehensive set of ice-velocity and thickness data from traverses within the IAGP study area (bounded by long. 90°E. and 135°E., and north of lat. 80°S.) is compared with steady-state mass-flux calculations based on Scott Polar Research Institute (SPRI) map compilations.

The results of previous regional mass-budget estimates are reviewed and followed by a description of the new field measurements and the basis upon which a computer “grid–point” program is used to calculate balance fluxes.

A comparison of measured and balance fluxes indicates that the ice sheet in this region of East Antarctica is unlikely to be significantly out of balance.

The ratio of average column to surface velocity is discussed and calculated to be 0.89.

An analysis of the mean shear strain-rate (VS/Z), versus down-slope basal shear stress (τb = ρgᾱZ), suggests that power flow-law parameters of n = 3.21 and k = 0.023 bar−n m−1 are appropriate for the effective basal shear zone in this region of the Antarctic ice sheet.

Numerical methods based on quadrilateral finite elements have been developed for calculating distributions of velocity and temperature in polar ice sheets in which horizontal gradients transverse to the flow direction are negligible. The calculation of the velocity field is based on a variational principle equivalent to the differential equations governing incompressible creeping flow. Glen’s flow law relating effective strain-rate ε̇ and shear stress τ by ε̇ = (τ/B)n is assumed, with the flow law parameter B varying from element to element depending on temperature and structure. As boundary conditions, stress may be specified on part of the boundary, in practice usually the upper free surface, and velocity on the rest. For calculation of the steady-state temperature distribution we use Galerkin’s method to develop an integral condition from the differential equations. The calculation includes all contributions from vertical and horizontal conduction and advection and from internal heat generation. Imposed boundary conditions are the temperature distribution on the upper surface and the heat flux elsewhere

For certain simple geometries, the flow calculation has been tested against the analytical solution of Nye (1957), and the temperature calculation against analytical solutions of Robin (1955) and Budd (1969), with excellent results.

The programs have been used to calculate velocity and temperature distributions in parts of the Barnes Ice Cap where extensive surface and bore-hole surveys provide information on actual values. The predicted velocities are in good agreement with measured velocities if the flow-law parameter B is assumed to decrease down-glacier from the divide to a point about 2 km above the equilibrium line, and then remain constant nearly to the margin. These variations are consistent with observed and inferred changes in fabric from fine ice with random c-axis orientations to coarser ice with single- or multiple-maximum fabrics. In the wedge of fine-grained deformed superimposed ice at the margin, B increases again.

Calculated and measured temperature distributions do not agree well if measured velocities and surface temperatures are used in the model. The measured temperature profiles apparently reflect a recent climatic warming which is not incorporated into the finite-element model. These profiles also appear to be adjusted to a vertical velocity distribution which is more consistent with that required for a steady-state profile than the present vertical velocity distribution.

A stress-wave model is used to describe snow-slab failure under dynamic loading conditions. This model indicates that dilational waves and shear waves can interact with a thin, weak bedding layer underlying a snow slab causing dilatational and shear stresses in the layer. The magnitude and distribution of stresses in the layer are shown to depend strongly on the height of the loading source above the bedding plane, the difference in impedance between the slab and the loading source, the difference in impedance between the slab and its substratum, and the initial stress magnitude of the loading source. Failure occurs in the bedding layer when the generated stresses exceed the strength of the layer. This causes a loss of shear strength capacity at the bedding plane and a re-distribution of stress in the slab. If the shear capacity is reduced sufficiently the body-force loading of the slab will cause snow-slab failure.

Existence of a very thin layer of adsorbed water adjacent to particles embedded in ice allows relative motion between ice and particles even at sub-freezing temperatures if there are either applied stresses or macroscopic temperature gradients. Theoretical analysis of such motion involving a single sphere demonstrates that such motion is dominantly due either to “viscous” deformation in the ice or to mass transport in the liquid layer at temperatures below the nominal pressure melting-point, depending on the ratio of the sphere’s radius to a temperature-dependent “transition radius”. This result should also hold for motion of a cylinder (for which the creeping flow problem has no known analytical solution). Reviewing data on wire regelation at sub-freezing temperatures in the context of this analysis suggests that all “anomalous” data correspond to cases in which wire radii were greater than the transition radius, leading to dominance of ice-deformation effects. Ice motion past very small particles, on the other hand, is essentially accommodated entirely by mass transfer through the liquid layer. This result lends support to the “rigid-ice” model of frost heaving as proposed by R.D. Miller and co-workers, and permits approximate analysis of ice movement through a porous soil. In all cases involving relative motion between ice and particles at sub-freezing temperatures, the existence of macroscopic temperature gradients plays an important role.

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.

Inclinometry with embedded probes is analyzed with a Stokes model of a solid body floating in a fluid with much smaller viscosity for a two-dimensional flow field. The assumption that such a probe behaves like a Lagrangian unit vector is only justified for probes embedded in a Newtonian fluid with lengths at least four times their width. A fluid with Glen-type rheology results in a slightly smaller rotation rate of the probe compared to Newtonian fluids.

The results of 66 Schlumberger geoelectric soundings on first-year sea ice are analysed to obtain average values of d.c. electrical resistivity both parallel ρ1 and perpendicular ρp to the long brine cell direction. This analysis yields ρ1 = 104 Ω m, 80 Ω m, 45 Ω m, and ρp = 298 Ω m, 230 Ω m, 129 Ω m for brine volumes νb of 40‰, 67‰, and 82‰ respectively. The observed dependence of ρ1 on νb is used in conjunction with a mixing formula for the electrical resistivity of a two-phase heterogeneous system to arrive at values of “average” brine cell lengths l for relatively warm sea ice. This treatment yields l ≈ 1.7 cm for 40‰ ≤νb≤ 70‰ with a rapid extension of brine cell lengths for brine volumes above c. 70‰.

Ice originating near the inland ice divide of the ice sheet can reappear as marginal ice at the surface near the ice terminal in the ablation area. We have analyzed δ18O values and ion concentrations of the Skallen, Skarvsnes and Hamna terminal ice sections, located along the estuary line in the Sôya drainage basin, East Antarctica. The data suggest that the upper part of the Skallen terminal ice section could have originated from inland precipitation on the Shirase drainage basin during marine isotope stage (MIS) 5e, while the upper part of Skarvsnes and Hamna terminal ice sections could have originated from inland precipitation on the Sôya drainage basin. We calculate past elevation maps for the Antarctic ice sheet using the three-dimensional model, SICOPOLIS. This model suggests that the upstream portion of the Sôya drainage basin during the glacial period (MIS 2, 3 or 4) was located to the northeast of its present location. A flow history is proposed wherein ice from the inland Shirase drainage area flowed over the present ice-divide line from the Shirase to the Sôya drainage basin during the glacial period. The ice in the Sôya drainage basin then flowed to the marginal part of the sheet after the ice divide had assumed its present position.