An index of regional snow-pack stability based on occurrences of natural slab avalanches was developed using a statistical distribution and a sequential testing procedure. The study interprets avalanche information on 185 paths in the Colorado Front Range. Results show general agreement with operational hazard estimates; test results have real-time evaluation potential.

The formation of frazil in water of different salinities and initial supercoolings was studied in the laboratory. Experiments were conducted both on genuine and artificial sea-waters. From analysing the experimental results, it was found that the production rate of frazil is highly sensitive to the initial supercooling of the water and will increase over three orders of magnitude as the initial supercooling increases from zero to 2° C. By properly non-dimensionalizing the parameters, it was found that the normalized concentration of frazil in water is principally a function of the normalized time. For the rate of production of frazil, however, it was found that the normalized rate of frazil production, besides being a function of the normalized time, is also affected by the salinity and the initial supercooling of the water. Different frazil crystals formed in water of different salinities and initial supercoolings are thought to be the reason for the different curves of frazil production rate. The normalization of parameters requires the determination of some characteristic parameters which were found to be well-defined functions of initial supercooling and salinity.

Two flood waves from the terminus of Peyto Glacier occurred as a result of very high precipitation in early July 1983 and a landslide which exposed a large section of ice-cored moraine. The flood waves induced erosion, and subsequent melt, of the moraine and deposited an estimated 6000 m3 of gravel in the valley. The majority of the deposition occurred in an area approximately 200 m × 20 m to depths of 3 m at the site of the National Hydrology Research Institute gauging station 1 km from the glacier terminus. The initial flood washed away most of the equipment from the site and the gravel deposition totally destroyed the rest of the installation. These events appear to be unique in the period that hydrological records have been maintained for Peyto Creek.

The ice-flow properties at great depths have a strong impact on the depth–age relationship of the strata in the Greenland ice sheet. Previous attempts to calculate this relationship have used Glen′s flow law with a temperature-dependent flow-law parameter. The data from the bore-hole-tilting at Dye 3, south Greenland, make it possible to calculate the flow-law parameter versus depth. The flow-law parameter shows a big change at the Holocene/Pleistocene transition with a mean flow enhancement factor of 3 for the ice deposited during the last glaciation. This high enhancement factor is believed to be due to high concentrations of dust and other impurities and small ice-crystal size in the Pleistocene ice. The derived flow-law parameter and the up-stream basal topography are used in a two-dimensional, multi-layer, first-order perturbation model to calculate the surface undulations and strain-rates. The results compare favourably with the observations. The results depend strongly on the flow-law parameter profile, which can therefore be estimated in other areas by perturbation-model calculations along flow lines, if the surface and base topographies are known.

A comparison of data from aircraft altimetry, Landsat imagery, and radia echo-sounding has shown characteristic surface topographies associated with sheet and stream flow. The transition between the two is abrupt and occurs at a step in the subglacial topography. This marks the onset of basal sliding and high velocities caused by subglacial water; it results in crevassed amphitheatre-like basins round the head of outlet glaciers. It is also the zone of maximum driving stress beyond which values decline rapidly as velocities increase. This abrupt transition appears to be topographically controlled since basal temperatures are at the pressure-melting point well inland of the change in regime. The Marie Byrd Land ice streams exhibit qualitative differences from other ice-sheet outlets, however; the change to lower driving stresses is much more gradual and occurs several hundred kilometres inland. Such ice streams have particularly low surface slopes and appear in form and flow regime to resemble confined ice shelves rather than grounded ice. The repeated association of the transition to rapid sliding with a distinct subglacial feature implies a stabilizing effect on discharge through outlet glaciers. Acceleration of the ice is pinned to a subglacial step and propagation of high velocities inland of this feature seems improbable. Rapid ice flow through subglacial trenches may also ensure a relatively permanent trough through accentuation of the feature by erosion. This is concentrated towards the heads of outlet glaciers up-stream of the region where significant basal decoupling occurs. This may be a mechanism for the overdeepening of fjords at their inland ends and the development of very steep fjord headwalls.

Spatial and temporal observations of electrical conductivity during the summers of 1978 and 1981 on the pro-glacial stream sytem of glacier de Tsidjiore Nouve, Valais, Switzerland, are described. Three space–time scales of electrical conductivity variations are considered: single-site, hourly monitoring for a two-month period; multiple-site sampling over 12 h periods using a 1 h sampling interval, and multiple-site sampling over monthly periods using a 24 h and 48 h sampling interval. Detailed analysis of the information from the three scales shows that the sampling strategies employed can reliably be used to investigate space–time patterns in the data. The results demonstrate that there are diurnal cycles in both electrical conductivity and discharge which are slightly different in form and which are out of phase with one another at the same site. Simultaneous multiple-site sampling of electrical conductivity shows that the tributary streams draining the glacier snout exhibit complementary shifts in electrical conductivity between ablation seasons, between days, and within days. The significance of these complementary shifts in tributary electrical conductivity are discussed in the light of possible source areas, storage, and routing fluctuations of melt water draining from the glacier.

An algorithm is developed for adjusting glacier surface-velocity vectors, given on the nodes of a square grid, so that they obey a central-difference approximation of the continuity equation. Also required on the grid nodes are the glacier thickness, the ratio of the surface-velocity to the average velocity in the column, and the difference between the mass balance and the thickness change. All these other variables are assumed to be known exactly, and only the surface-velocity field is adjusted. The result is optimum in the sense that the magnitude of the adjustment is minimized. Either the relative or the absolute adjustment can be minimized, depending on how weights are specified. No restriction is placed on the shape of the solution region, and no boundary condition is required. The algorithm is not iterative. The algorithm first forms a parallel flow field that satisfies the continuity equation, and then uses a stream function to add a divergenceless field to it. The stream function that leads to the minimum velocity adjustment is obtained as four independent, interlacing solutions covering the solution region. For each of the four, a well-conditioned, sparse-matrix system of simultaneous linear equations is solved. A compact, sub-optimum, well-behaved iterative procedure is also developed for transforming part of the velocity adjustment into an adjustment of the thickness field.

Most non-linear fluids for which the appropriate measurements have been made exhibit non-zero and unequal normal stress differences in shearing flows. Power-law models such as Glen’s law cannot represent this phenomenon. The simplest constitutive equation that does embody normal stress effects defines the second-order fluid. An exact analytical solution for biaxial creep of such a fluid is fit to data from four tests on polycrystalline ice. The model gives an excellent representation of both primary and secondary creep. The fits provide values for the three material constants. These coefficients indicate positive first and second normal stress differences. One consequence is the prediction that a steady open-channel flow will exhibit a longitudinal free-surface depression of up to several meters for sufficiently thick ice on steep slopes. In addition, the compressive principal stress at the channel margin is decreased and the tensile principal stress is increased in magnitude over those predicted by models without normal stresses. The normal stresses thus favor the formation of crevasses. Furthermore, the angle these crevasses form with the channel margin is decreased.

A variety of frost-crystal forms found growing from the vapor in ice caves and tunnels in the Antarctic are described and illustrated. Complex layered structures found within large, skeletal crystals are ascribed to the action of the temperature gradient. Some novel c-axis growth forms and a rare type of bicrystal growth – accelerated growth in a particular direction along a particular grain boundary – are also shown.

Factors which control the audibility within and outside deposited snow are described and applied to explain the preferential detection of sound by persons buried under avalanche debris as compared to persons on the overlying snow surface. Strong attenuation of acoustic waves in snow and the small acoustic impedance differences between snow and air are responsible for the strong absorption and transmission-loss characteristics that are observed for snow. The absorption and transmission-loss characteristics are independent of the direction of propagation of acoustic signals through the snow. The preferential detection of sound by a person buried under snow can be explained by the relatively higher level of background acoustic noise that exists for persons above the snow surface as compared to an avalanche burial victim. This noise masks sound transmitted to persons on the snow surface, causing a reduction of hearing senstitivity as compared to the burial victim. Additionally, the listening concentration of a buried individual is generally greater than for persons working on the snow surface, increasing their subjective awareness of sound.

In the north-western Himalaya, the distribution of modem glaciers and snowlines in the Ladakh and Zanskar Ranges adjacent to the Indus River valley suggests comparable climatic conditions prevail in the two ranges. Similarly, the positions of terminal moraines and reconstructed equilibrium-line altitudes (ELAs) indicate equivalent magnitudes of Neoglacial and Late Glacial advances in both ranges. However, the terminal positions and reconstructed ELAs from the late Pleistocene maximum advances are at least 400 m lower in the Ladakh Range than in the nearby Zanskar Range. These differences do not appear to reflect either climatic or tectonic controls. Rather, they are caused by an unusual bedrock configuration in the Zanskar Range, where vertical strata of indurated sandstones and conglomerates, and narrow steep-walled canyons cut through them, created a bulwark that effectively precluded significant down-valley advance. Without recognition of this physical impedance to glacial advance, uncritical reconstructions would greatly overestimate the altitude of the ELA in the Zanskar Range.

Evolution of sedimentological characteristics for traction debris is investigated along a transport path down-glacier from a subglacial point source at the northern rim of the ice cap MỲrdalsjökull, Iceland. Losses and gains from this path are discussed. Close to mature characteristics as to particle size, shape, roundness, and fabric are developed after only short basal transport, about 500 m, while further transport only results in minor changes. This development is interpreted as the result of selective subglacial lodgement of large particles and/or particles with longitudinal α-axis orientation, while particles of median size and/or oblique orientation tend to stay in basal transport. Implications for basal sliding and subglacial sedimentation patterns are discussed.

The crystal character of the ice core within frost blisters supports the hypothesis that groundwater injection into residual zones of the active layer followed by rapid freezing is the primary growth mechanism for these features. The ice core is characterized by an upper zone of relatively small randomly arranged equigranular ice crystals which change with increasing depth to columnar anhedral crystals, commonly exceeding 200 mm in length, and with crystal diameters ranging between 25 and 35 mm. Petrofabric analyses show that the c-axis orientations are normal to crystal elongations, with crystal growth along the basal plane in an a-axis direction. These observations eliminate ice segregation as a possible growth mechanism, thereby distinguishing seasonal frost mounds from palsas.

This paper discusses dielectric properties of snow according to various dielectric models and compares them with experimental results. The complex permittivity of wet snow is assumed to consist of two parts, being the sum of the permittivity of dry snow (a mixture of ice and air) and the excess permittivity due to liquid water (resulting from the dielectric mixture of water and air). In particular the effect of liquid water is considered. Exponential models and structure-dependent models based on mixture theories by Taylor and Tinga and others are applied. It is shown that the assumption that water inclusions have the form of either randomly oriented discs or needles, or of spheres do, not get empirical confirmation but the inclusions are preferably prolate ellipsoids (ellipticity 0.16) or oblate ellipsoids (ellipticity 0.12), dry snow being a dielectric mixture of randomly oriented disc-shaped ice particles and air.

Fracture-toughness testing of both fresh-water and sea ice has used specimen geometries designed for metals. These designs are too large and difficult to manufacture for testing material cored from a glacier. This paper presents an alternative specimen, a radially cracked ring fractured by internal pressure. Tests using this specimen on the Bersærkerbræ, a valley glacier in the Stauning Alper, north-east Greenland, gave a mean fracture toughness of 58 . This is half the value typically obtained by other workers in laboratory tests. The results are compared with other data and the reasons for the disagreement discussed.

Earlier work by Nye (1965), who obtained numerical solutions for axial independent flow of a non-linear Glen material in channels of rectangular, elliptic, and parabolic cross-sections with a null-slip basal condition, is extended by using an inverse technique. Exact analytical solutions are obtained for flow in irregular-shaped channels (subject to symmetry restrictions) for both a Newtonian and an n = 3 Glen material. The cross-sections are regulated by multi-parameters. Solutions are obtained for two types of channel: (a) those whose side walls meet the free ice surface vertically, and (b) periodic channel arrays whose basal profiles do not intersect the free ice surface, i.e. overfilled channels. Solutions for the second type have not been presented previously. The solutions for the n = 3 Glen material employ a small parameter which limits the geometry variation to perturbations on semicircular or uniform-depth channels. Basal slip conditions can be incorporated although results are not presented here.

Widespread wet-snow avalanches were observed on the southern boundary of Glacier National Park, Montana, in February 1979. Severe tilting, scarring, and breakage of trees were observed along a transverse trim-line of one path, 70 m from a wet-snow deposit. Tree-ring data were used to establish the date of occurrence, and the nature of damage was used to characterize the avalanche event. The event probably included a previously unrecognized dry-snow avalanche and associated wind blast. Such events present different problems for natural-hazard planning. The nature of vegetative damage along the margins of avalanche paths is shown to be a useful indicator of the characteristics of past unobserved avalanche events.

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.

At the beginning of spring snowmelt in an upland stream in Scotland a three-fold increase in total dissolved load occurs. This is shown to be the most significant of the acute events occurring during the year.

A simple mathematical expression for the density distribution of dry snow is described in this note. It compares very well with observations.