The effect of pressurized subglacial water on the sliding process is examined by a parameter called the “bed separation index”. This index indicates the relative extent of cavity formation by combining the effects of variation of bed-normal stress across undulations (Kamb, 1970) and steady-state water pressure in a Röthlisberger conduit at the glacier bed. Data from three glaciers of widely varying size are used to test the correlation of the bed separation index with inferred sliding rates. For Columbia Glacier and Ice Stream B in West Antarctica it is shown that high water pressure enhances sliding. More complete data from the third test case. Variegated Glacier, are used to compare a number of possible formulations of a “sliding law”. A Weertman-type power law (exponent c. 3), modified for the effect of subglacial water pressure, appears to be most preferable. Other formulations, including the “lubrication factor” hypothesis used by Budd (1975) are tentatively rejected. Consideration of the temporal variations of the “bed separation index” indicate that, on short time scales of days and weeks, variations of water pressure can dominate the sliding process. A rapid order-of-magnitude increase in water discharge causes a hundredfold transient increase in the water pressure. A bi-modal hydraulic regime is revealed for water flow transverse to the direction of main ice flow. This behavior is in accord with the observation of a sudden acceleration of the ice due to increased sliding in early summer or following heavy rainstorms.

The theory of Nye and of Weertman of traveling waves on glaciers is extended to cover the situation where the presence of abundant basal water or increased basal water pressure produces increased sliding of a glacier over its bed. It is found that the ratio of traveling-wave velocity to surface velocity is independent of the amount of water or the basal water pressure. The theoretical value of this ratio, about 4 to 5, agrees with that found in field measurements (the most recent data are from Mer de Glace). It is concluded that field observations of traveling-wave velocities lend strong support to any glacier sliding theory in which the sliding velocity is proportional to the basal shear stress raised to about a second to fifth power and in which the sliding velocity is a function of either or both the amount of water at the bed of a glacier and the pressure within this water.

Results of systematic movement studies carried out by means of an automatic camera on Unteraargletscher since 1969 are discussed together with supplementary theodolite measurements made at shorter intervals and over a longer section of the glacier. In addition to the typical spring/early summer maximum of velocity known from other glaciers, an upward movement of up to 0.6 m has been recorded at the beginning of the melt season. It was followed, after a few fluctuations of the vertical velocity, by an equal but slower downward movement which continued at an almost constant rate for about three months. Possible explanations of the uplift are discussed, the most satisfactory explanation being water storage at the bed. The observations then suggest that this storage system is efficiently connected with the main subglacial drainage channels only during times of very high water pressure in the channels. Detailed measurements showed that the times of maximum horizontal velocity coincided with the times of maximum upward velocity rather than with the times when the elevation of the surveyed poles had reached a maximum. On the basis of the hypothesis of water storage at the bed this finding means that the sliding velocity is influenced mainly by the subglacial water pressure and the actual, transient stage of cavity development, while the amount of stored water is of lesser influence.

The ice velocity slowdown occurring at Lewis Glacier, Mount Kenya, during the twentieth century has continued beyond 1978. In an earlier paper, a surface velocity decrease approaching 50% was predicted between 1978 and 1985. Measurements to January 1982, halfway through the period, reveal trends generally in line with this forecast: a velocity reduction of order 20% has taken place. The mass flux decreased by at least 25%. Intra-annual variability in velocity pattern and magnitude is apparent; comparatively rapid values occur during the January–February dry season.

Field study of the bergschrund of a small avalanche-cone glacier at the base of Mt Chephren, in Banff National Park, has been carried out as part of a general exploratory study of glacier-head crevasses in the Canadian Rockies. The bergschrund consists of a wide, shallow, partly bedrock-floored gap, underneath which extends a nearly vertical Randkluft, and a small, offset, subsidiary crevasse (or crevasses). The following observations regarding the behavior of the bergschrund and ice adjacent to it are of particular interest: (1) topography of the subglacial bedrock is a control on the location of the main bergschrund and subsidiary crevasses, (2) the main bergschrund and subsidiary crevasse(s) are connected by subglacial gaps between bedrock and ice; the gaps are part of the “bergschrund system”, (3) snow/ice immediately down-glacier of the bergschrund system moves nearly vertically downward in response to rotational flow of the glacier, allowing the bergschrund components to keep the same location and size from year to year, (4) an independent accumulation, flow, and ablation system exists in the snow/ice up-glacier of the bergschrund system. (5) most of the void space in the bergschrund system is maintained through the winter, although the wide, shallow part of the main bergschrund fills up with snow, (6) some mass transfer of snow/ice occurs across the bergschrund system, (7) displacement across the bergschrund due to flow of the main glacier body results in significantly more snow being deposited each winter down-glacier of the bergschrund than up-glacier of it.

Isotropic points are structurally stable features of any complicated field of stress or strain-rate, and therefore will almost always be present on the surface of a glacier. A given isotropic point for strain-rate will belong to one of six different classes, depending on the pattern (lemon, star, or monstar) of principal directions and the contours (ellipses or hyperbolas) of constant principal strain-rate values in its neighbourhood. The central isotropic point on a glacier should theoretically have a monstar pattern, but the contours around it may sometimes be elliptic and sometimes hyperbolic. Nearby, but not coincident with it there will be an isotropic point for stress. This will also have a monstar pattern but, in contrast to the strain-rate point, the contours around it must be hyperbolic. Published examples are consistent with these conclusions. In addition to isotropic points for strain-rate a glacier surface will contain isolated points of pure shear; these also can be classified into six different types. Stable features of this kind give information about the essential structure of a tensor field and form useful points of comparison between observation and numerical simulation.

A theory advanced by Budd (1970) for ice-flow variation due to bed effects is improved and applied to the flow of the ice sheet leading to Byrd Station, Antarctica. Linear viscous rheology is used and a biharmonic equation for stress and strain-rate variation is solved. Basal boundary conditions include an undulating bottom topography and longitudinal variations in basal sliding and shear stress. Near Byrd Station it is found that variations in basal sliding and shear stress have more important direct effects than does the bed topography. This result is important to considerations on the stability of glacial flow. Distortions of internal layers are calculated and these closely match the distortions observed in the internal layers detected by the NSF-SPRI-TUD radar. The phase relationship between internal layer distortion and surface topography provides a positive test for the theory. The theory does not predict a spectral power maximum in surface topographic relief at a wavelength of three ice thicknesses. Such wavelengths however dominate and we speculate that this may be due to the dynamics of glacial erosion and deposition or with subglacial water motion.

Crevasses can be ignored in studying the dynamics of most glaciers because they are only about 20 m deep, a small fraction of ice thickness. In ice shelves, however, surface crevasses 20 m deep often reach sea-level and bottom crevasses can move upward to sea-level (Clough, 1974; Weertman, 1980). The ice shelf is fractured completely through if surface and basal crevasses meet (Barrett, 1975; Hughes, 1979). This is especially likely if surface melt water fills surface crevasses (Weertman, 1973; Pfeffer, 1982; Fastook and Schmidt, 1982). Fracture may therefore play an important role in the disintegration of ice shelves. Two fracture criteria which can be evaluated experimentally and applied to ice shelves, are presented. Fracture is then examined for the general strain field of an ice shelf and for local strain fields caused by shear rupture alongside ice streams entering the ice shelf, fatigue rupture along ice shelf grounding lines, and buckling up-stream from ice rises. The effect of these fracture patterns on the stability of Antarctic ice shelves and the West Antarctic ice sheet is then discussed.

Surface and airborne radar sounding data were used to identify and map fields of bottom crevasses on the Ross Ice Shelf. Two major concentrations of crevasses were found, one along the grid-eastern grounding line and another, made up of eight smaller sites, grid west of Crary Ice Rise. Based upon an analysis of bottom crevasse heights and locations, and of the strength of radar waves diffracted from the apex and bottom corners of the crevasses, we conclude that the crevasses are formed at discrete locations on the ice shelf. By comparing the locations of crevasse formation with ice thickness and bottom topography, we conclude that most of the crevasse sites are associated with ice rises. Hence we have postulated that six ice rises, in addition to Crary Ice Rise and Roosevelt Island, exist in the grid-western sector of the ice shelf. These “pinning points” may be important for interpreting the dynamics of the West Antarctic ice sheet.

Ten maps show where and when 90 000 km of airborne laser terrain profiles of Arctic sea ice have been obtained. The laser terrain profiling system is briefly described. The data reduction procedure is also briefly described.

Flexural–gravity waves in the 3 ms to 50 ms period range were recorded on floating layers of ice ranging from 6 cm to 52 cm in thickness. These inversely dispersive waves are analogous to Rayleigh waves propagating on a multi-layered structure. Therefore, flexural–gravity wave dispersion curves can be calculated by the well-known Haskell–Thompson method. This approach allows the effects of snow layers and stratification of the ice to be evaluated. In earlier methods of calculating flexural–gravity wave dispersion. the structure was restricted to a single homogeneous solid layer over a homogeneous fluid. The effect of a low-velocity snow layer is to reduce the short-period phase velocity, and to increase the velocity at long periods. Dispersion curves for ice layers with and without a snow cover cross at an intermediate period that increases as ice thickness increases. These effects are measurable in seismic experiments on frozen ponds and lakes.

The analysis of sea-ice cores from three summer field operations to the European Arctic is reported, and the ice properties are related to general conditions of ice distribution, thickness, and ridging in the experimental areas. The operations were in 1978 and 1979 to the Kong Oscars Fjord area of East Greenland (about lat. 72° N.) and in 1980 to the Barents Sea, Fram Strait, and the Arctic Ocean north of Svalbard and Zemlya Frantsa Iosifa on the Swedish Ymer-80 expedition. Salinity profiles show the effect on multi-year floes of a year’s additional confinement in a fjord, the effect of a month’s desalination (July to August) on first-year and multi-year ice, and the difference between first-year and multi-year ice at the end of the melt season. The average salinity as a function of ice thickness agrees reasonably well with the results of Cox and Weeks (1974). Temperature, density, pH, and ionic composition results are also reported, and the effect of brine volume on dielectric constant discussed.

The 210Pb(210Po) method has for the first time been successfully applied for dating cold alpine firn/ice cores. The mean accumulation rate on Grenzgletscher near Colle Gnifetti (Switzerland, altitude 4 450 m) is found to be 37 cm year−1 and 32 cm year−1 for the two ice cores drilled down to 32 m and 65 m in 1976 and 1977, respectively. The surface activity amounts to 4 dpm kg−1 ice. It is shown that a good agreement between the data of the two ice cores is reached with a model taking into account an effect of decreasing annual ice layers with depth. With this thin-out correction, the accumulation rate in the 1977 core increases to 39 cm year−1.

The possible use of index paths to assess avalanche potential in large avalanche samples was evaluated with probability theory on 56 uncontrolled avalanche paths in Colorado. Results showed the technique yields limited information of little diagnostic value because of low conditional probabilities of joint occurrence and high yearly variance. 90% of pairs tested had probabilities ≦0.20 for a six-year period. Implications for researchers and field personnel are discussed.

Between 16 and 19 June 1981 a large water pocket of volume 183 000 m3 burst from glacier de Tsidjiore Nouve. From hourly stream discharge and suspended sediment concentration observations a suspended sediment output of 1 674 × 103 kg was calculated. The transport of bed-load was estimated at 3 840 × 103 kg, hence a total quantity of around 5 500 × 103 kg of sediment were removed from the catchment, including the pro-glacial field, in the four days of the outburst.

The derivation of a constitutive law to describe large-scale sea-ice deformation commonly uses the so-called “flow rule”. This method introduces a mathematically imposed relationship between shear strength and dilatation which is not based on physical postulates. In this note a more general procedure is described which uses the Reiner–Rivlin equation as a starting point. The method is illustrated by deriving a particular constitutive law and applying it to a simple problem of sea ice blown against a shoreline.