Radar-altimeter data from ERS-1 allow detailed topographic mapping of Antarctica to 82° S to be carried out, revealing several notable surface features. Among these is the large subglacial lake near Vostok which is mapped here in detail. The central part of the lake is found to have an exceptionally smooth surface with r.m.s. elevation variations of less than 0.2 m. A search for other large Antarctic lakes in the data is made based on the smoothness and low gradient of the surface. A number of other flat areas are identified with lake locations previously determined from radio-echo sounding observations. However, radar-altimeter observations show that a minimum lake size of 20 km is required for a surface above a lake to become flat. Numerous bowl-like features can be seen in the surface topography, and these may be associated with intermediate-sized subglacial lakes. It is determined that high spatial-resolution radar altimetery could be used to identify subglacial lakes greater than 10 km in lateral extent. Flat regions of the ice sheet are particularly useful as they may be used as height-reference surfaces to help fix the orbits of radar-altimeter satellites.

The mechanical response of snowpacks to penetrating liquid water was observed over two winter seasons in the central Cascade Mountains, Washington, U.S.A. Following the onset of rain, three evolutionary regimes of snow behavior were identified: immediate avalanching, delayed avalanching, and return to stability. Immediate avalanching occurred within minutes to an hour after the onset of rain and the time of release could be predicted with an accuracy of less than an hour from meteorological forecasts of the transition from snow to rain. These avalanches usually slid on surfaces substantially deeper than the level to which water or associated thermal effects had penetrated. The mechanism by which alteration of a thin skin of surface snow can cause deep slab failure has not been identified, but several possibilities involving a redistribution of stress are discussed. Delayed avalanches released several hours after rain started. The delay varied, depending on the rate of increasing stress associated with the additional precipitation, and on the time taken for water to penetrate and weaken a potential sliding layer. It is difficult to define accurately the evolving distribution of liquid water in snow which makes it difficult to predict accurately the time of avalanching. Depth profiles of the rate of snow settlement showed that a wave of increased strain rate propagated into the snow in response to penetrating water. This type of measurement could prove useful for predicting when snow stability is reaching a critical condition. Avalanche activity was rare after continuation of rain for 15 h or more. This return to stability occurred after drainage structures had evolved and penetrated the full depth of the snowpack. Established drain channels route water away from potential sliding surfaces and are also relatively strong structures within a snowpack.

Compaction experiments on porous samples of granular ice and ice/rock mixtures were conducted at low temperature, primarily to obtain rheological data useful in modeling the internal structure and evolution of icy satellites of the giant planets. The data may also be of interest for studying Earth’s glaciers and the Martian polar caps.

The samples tested were prepared from three types of ice: water, carbon dioxide and ammonia; three types of rock components were also used in the samples. The time-dependent compaction of samples a few centimeters in size was studied for a range of rock contents, pressures (2.2–17.7 MPa) and temperatures (140–261 K). An Equation (16), giving the compaction rate as a function of porosity, pressure, temperature and concentration of the rock component was fitted to the observed results. The presence of rock fragments strongly inhibits the compaction process.

A degree-day model developed for parameterizing melt rates on the Greenland ice sheet is adapted to the climatic conditions on glaciers in southern Norway. The model is calibrated by means of observed average mass-balance-elevation relationships (1963–90) for three glaciers in a west-east transect in southern Norway and 30 year normals (1961–90) of temperature and precipitation observed at nearby climate stations. The calibration gives a surprisingly small variation of the model parameters (degree-day factors for snow-and ice-melt, and precipitation-elevation gradient) from one glacier to another. The derived values of the parameters are used to estimate the change of the mass-balance-elevation relationship for different climatic scenarios. The study indicates that a low-lying glacier in the maritime, high-precipitation environment near the Atlantic coast is more sensitive to both temperature and precipitation changes than the high elevated glaciers in the dry, more continental climate farther away from the coast. However, all of the glaciers studied will lose mass in a warmer climate, unless the warming is accompanied by a dramatic increase in the precipitation of 25–40% deg−1 warming.

The Swiss rutschblock test provides practical information about the stability of snow slabs. However, its use by avalanche workers and ski guides is limited by the time required to perform the test and recommended minimum slope inclination (30°). The present study shows how time requirements can be reduced by cutting rutschblocks with cords or specialized saws — faster techniques that do not appear to affect the results. Comparing the rutschblock results with a stability index developed in Switzerland shows that the recommended minimum slope inclination can be reduced to 20°, provided a second person is present to observe the small block displacements associated with slope inclinations below 30°. Sets of rutschblocks on slopes that vary in inclination by 8° or more are used to determine the effect of slope inclination on rutschblock scores. Also, the frequency distributions of six large sets of repeated tests are used to estimate the precision of one or two tests on a uniform slope.

Over the last 15 years, satellite-altimeter data have been used to produce surface-elevation maps of the Greenland and Antarctic ice sheets with a 2 m accuracy. Analysis of Seasat and Geosat cross-over points showed that satellite altimeters can measure changes in the mass balance of the ice sheets. The retracking algorithm used to extract surface elevations from Seasat and Geosat return wave forms is based upon a modified form of the Brown surface-scattering model. Recent work has shown that altimeter wave forms over higher-altitude regions of the ice sheets are affected by sub-surface volume-scattering. Here, we develop a theoretical model for altimeter return wave forms over the ice sheets that is based on a combination of surface-and volume-scattering. By approximating the altimeter’s antenna pattern and transmitted pulse shape with Gaussian functions, we derive a closed-form analytical solution for the return-power volume-scattered from beneath the ice-sheet surface. We then combine the volume-scattering model with the Brown model and apply it to average wave forms from the Greenland and Antarctic ice sheets. The results show that the combined model accurately describes variations in altimeter wave-form shapes that are produced by differing contributions of surface-and volume-scattering to the received power. The combined model is then used to simulate return wave forms from a dual-frequency altimeter. The simulation shows that a two-frequency system can provide quantitative estimates of the absorption and scattering coefficients for near-surface snow.

Geosat-altimeter wave forms from the Greenland and Antarctic ice sheets are analyzed using an algorithm based upon a combined surface-and volume-scattering model. The results demonstrate that sub-surface volume-scattering occurs over major parts of the ice sheets. Quantitative estimates of geographic variations in the near-surface ice-sheet properties are derived by retracking individual altimeter wave forms. The derived surface properties correlate with elevation, latitude and microwave brightness-temperature data. Specifically, the extinction coefficient of snow obtained by this method varies from 0.48 to 0.13 m−1 over the latitudes from 65° to 72°N on the central part of the Greenland ice sheet and from 0.20 to 0.10 m−1 over a section of Wilkes Land in East Antarctica where the elevation increases from 2550 to 3150 m.

Analysis of passive-microwave data over East Antarctica shows that the brightness temperature increases with elevation as the extinction coefficient decreases. Larger snow grain-sizes occur at lower elevations of the ice sheet because of higher mean annual temperatures. The larger grain-sizes increase the extinction coefficient of snow and decrease the emitted energy (brightness temperature) from greater snow depths. The passive-microwave data are also used to determine the average number of melt d year−1 (1979–87) for the central part of the Greenland ice sheet. For latitudes from 65° to 68.5° N, the average number of melt days decreases from 3.5 to 0.25 d year, whereas no melt events are observed for latitudes above 69°N over the 8 year period. Snow subjected to alternate melting and freezing has enhanced grain-sizes compared to that of dry snow. This accounts for the larger values and larger spatial variations of ke on the Greenland ice sheet compared to East Antarctica, where surface temperatures are never high enough to cause surface melting.

This note describes an end-capping procedure used to prepare cylindrical ice-core samples for direct tension testing. The techniques developed build on work done by Cole and others (1985) and Lee (1986), and include a design modification to the loading train and a more reliable approach to establishing the fresh-water bond used to mount the end caps on the sample. Using these techniques, an 88% success rate was achieved in a recent series of uniaxial tension tests.