Two models that estimate glacier ablation from simple meteorological observations are described. Both the energy-balance and bulk-aerodynamic approaches are used to determine the bulk-exchange coefficient for transfer of sensible- and latent-heat energy to the melting ice surface from 17 summer days of measurement on Ivory Glacier, New Zealand. The behaviour of the coefficient is examined over progressively increasing time intervals and as a function of wind speed and gradient, and of atmospheric stability. The models are verified with 36 d of independent data from a different summer on the same glacier. The more accurate short-term estimates of ablation are obtained using the energy-balance approach with empirically but independently derived values of the exchange coefficient.

During the decade prior to its 1982–83 surge, Variegated Glacier experienced progressive changes in geometry and velocity. It thickened in the upper 60% and thinned in the lower 40% of its 20 km length. Thickness changes were up to 20%. Annual velocity increased by up to 500%, reaching a maximum of 0.7 m d−1 in the year before surge onset. Amplitude of seasonal variation in velocity increased up to 0.3 m d−1 by 1978, but did not increase markedly after that. The changes in velocity were larger than predicted from changes in deformation rate caused by changes in shear stress and depth. This anomalous velocity was especially large after 1978 in the zone of thickening on the upper glacier. If it is assumed to arise from basal sliding, the inferred pattern of sliding shows qualitative features consistent with a direct effect from basal shear stress and an inverse effect from effective normal stress. A drop in effective normal stress in a zone of decreasing surface slope up-glacier from the largest thickness increase may have been significant in the initiation of surge motion in 1982.

Measurements of snow properties across and down snow slopes have been used to calculate a safety margin — the difference between the basal shear strength and the applied static stress. Areas of basal deficit exist when the applied shear stress exceeds the basal shear strength (the safety margin is negative), and basal areas are pinned when the safety margin is positive. As the size of deficit increases, stresses within the overlying slab also increase, and these may be sufficient to cause an avalanche.

Measurements made on five slopes (four of which had avalanched) were characterized by considerable spatial variability, and the safety margin has been treated as a random function which varies over the slope. Statistical models of Vanmarcke (1977[a], 1983) have been applied to determine the most likely size of deficit required for avalanching (95% confidence). In one case, an avalanche occurred when the length of deficit was only 2.9 m, and in the other cases the length was always less than 7 m. This size of deficit is small compared with the total area of many avalanche slopes which suggests that avalanches initiate from small zones of deficit, and makes it difficult to locate a deficit with just a few tests.

The optimum sampling interval and number of tests required to yield an adequate estimate of the statistical parameters of the safety margin are also discussed.

The 2037 m deep bore hole at Dye 3 in south Greenland was surveyed in 1981, 1983, 1985, and 1986. The directional surveys show the ice flow is planar with a surface velocity of 12.2m/year at an azimuth of 060°, which agrees with surface velocity measured by navigation satellites. Measurements of hole diameter and inclination are highly correlated with dust content in the ice. The temperature measurements show strong convection in the hole fluid with a cell height of about 20 m and an amplitude of 0.1 K. The calculated mean in-situ ice density is 921.3 ± 1.5kg/m3. Due to ice deformation, the lowest 4 m of the hole were not accessible in 1985 and the lowest 180 m were not accessible in 1986.

Among the various artificial radioactive markers (mainly from atmospheric nuclear tests), the contamination from the Chernobyl accident has been found at five sampling sites on Northern Hemisphere glaciers. Total beta-activity measurements reveal a very high radio-active level. However, due to the short time of its occurrence, the temporal resolution of this event in the snow layers can be generally quite low and positive results require careful sampling. The size of the signal also depends on the trajectory of the contaminant cloud, the amount of precipitation, and the surface conditions during deposition.

The annual mass of snow moved by avalanches was observed at 45 avalanche paths over a period of 19 years by measuring the volume and density of each individual avalanche. Several other methods to estimate the total annual avalanche mass were applied but they were found less efficient owing to inaccuracy and difficulties in timing.

For the data set, the yield ratio, i.e. the percentage of snow removed annually by avalanches, had a mean value of 11.2% and a 30 year maximum of 30.9%. The yield ratio varied strongly among avalanche paths and yearly, and could not be explained satisfactorily. The exposure to wind, inclination of the avalanche track, control by artillery, and the winter weather can all have an influence on the value of the parameter.

The temporal variability of avalanche yield is erratic but weather patterns frequently associated with high or low yield ratios could be identified. High values are usually associated with large avalanches triggered by major weather events in the late part of the winter.

The annual balance has been measured for ten North Cascade glaciers in 1983–84, 1984–85, 1985–86, and 1986–87 (1984, 1985, 1986, and 1987). Based on these data, an annual balance prediction method was designed and tested. Comparison of measured versus predicted annual balances indicates an accuracy of ±0.22–0.30 m. The method is based on annual measurement of the accumulation area ratio (AAR), and determination of the perennially constant activity index and area-altitude distribution on each glacier. The accumulation area ratio is determined from aerial and ground photographs at the end of the ablation season. The activity index is identified from observation of the rise of the snow line with time, compared to measured snow depths above the snow line. The AAR-activity index method was used to calculate the annual balance of 47 North Cascade glaciers in 1984, 1985, 1986, and 1987. The mean balance during the 4 year period was —0.33 m.

From the mass-balance records, it is apparent that North Cascade glaciers can be divided into six climatic sensitivity groups. Each glacier type responds differently to specific climatic conditions. The mass-balance variation for glaciers of the same type is small.

Since 1977, warmer, drier climatic conditions have prevailed in the North Cascades, resulting in the retreat of 42 of the 47 glaciers examined.

Run-off data for two basins in south Greenland, one of which contains glaciers, are compared with precipitation at a nearby weather station and with ablation measured in the glacier basin. Seasonal variations of run-off for the two basins are broadly similar while run-off from the glacier basin has smaller year-to-year variations. A simple statistical model shows that this is the result of a negative correlation between ablation and precipitation, which has the effect of reducing run-off variations in basins with a moderate amount of glacier cover although run-off variations may become large again for highly glacierized basins. The model also predicts an increasing run-off with ablation correlation and a decreasing run-off with precipitation correlation as the amount of glacier cover increases. Although there are still too few data sets from other parts of Greenland for final conclusions, there are indications that the present findings may be applicable to other Greenland basins.

An internally consistent data set of geometry and flow variables for the lower part of Columbia Glacier, south-central Alaska, is derived entirely from vertical aerial photography. The principle of mass conservation is imposed on the data in the form of a centered finite-difference approximation of the continuity equation. It is applied on a 120-node section of a square grid covering the 15 km long, high-velocity stretch ending at the grounded, heavily calving terminus of this large glacier.

Photography was obtained 22 times between June 1977 and September 1981. Surface altitudes on the dates of the flights and the displacement vectors between pairs of flights were determined photogrammetrically. Natural features on the glacier surface were sufficiently prominent and enduring to be followed from the date of one flight to the next.

Because both the altitude points and displacement vectors were irregularly positioned spatially, interpolation was necessary to get values on the grid nodes. The points had already been subjected to the method of optimum interpolation to get surface altitudes on the grid nodes. The displacement vectors are subjected here to a constrained–interpolation method to get velocity vectors at the grid nodes that are consistent, through the continuity equation, with the other variables.

The other variables needed to achieve closure of the variable set are bed topography and mass-balance distribution. The latter was taken to be a separate linear function of altitude for each time interval. Values for bed altitudes at 120 nodes and two coefficients of each 21 balance functions were inferred as the 162 model parameters in a non-linear minimization problem having 4305 observed velocity components as its data.

During the 1984 and 1985 melt seasons, flow velocities and dispersive characteristics of the englacial and subglacial hydraulic system on Storglaciären, a small valley glacier in northern Sweden, were studied with the use of dye-trace tests. Similar tests conducted on one of the two principal pro-glacial streams provided a basis for comparison of the combined englacial-subglacial system with the pro-glacial one. Velocities in the two systems were broadly comparable after compensating for the effect of slope differences. However, velocities in the glacial conduits increased almost linearly with discharge. Analysis suggests that this can be explained by an increase in water pressure in the conduits, combined with a decrease in effective sinuosity, as discharge increases. Dispersivity (the ratio of the dispersion coefficient to the water velocity) in the glacial system is high early in the season but decreases progressively during July. This is believed to reflect a change from an extensively braided to a more integrated drainage system. Dispersivity is only slightly lower in the pro-glacial streams than in the late-season glacial conduits, suggesting similar degrees of braiding. However, retardation of dye due to temporary storage is greater in the glacial conduits. This suggests that the glacial streams have a larger number of stable eddies in which dye can be trapped for extended periods of time.

On 4 July 1986, dye was injected at a point slightly above the equilibrium line on Storglaciären, a small valley glacier in northern Sweden. Just below the equilibrium line, the glacier bed is over-deepened. The dye re-appeared in a stream at the glacier terminus over the next 35 d. This stream normally carries relatively little sediment, in constrast to the situation in another nearby stream that also emerges from the glacier. This suggests that the dye traveled in englacial rather than subglacial conduits. Tracer tests utilizing salt in bore holes in the overdeepening support this interpretation, as the bore holes were draining well above the bed. The dye appeared during three distinct events, suggesting that it became divided into at least three separate parcels shortly after injection. This probably occurred in the crevassed area in the vicinity of the injection point.

The englacial location of the drainage may be explained by the fact that, in order to remain at the pressure melting-point, water in subglacial conduits coming out of the overdeepening may have had to warm up faster than would be possible by viscous heating alone. Such conduits would thus tend to freeze closed.

The relationship between the intensity of snow acoustic emission impulses and snow-cover stability is revealed by measuring the physical and mechanical properties of the snow cover in the starting zones of avalanches. This relationship is fundamental to the remote identification of an avalanche-hazard period.

In order to estimate the mechanical properties of a snow layer, a method of applying a rigid penetrometer equipped with a piezo-electric accelerometer is used. The viscosity coefficients of snow under destruction and the specific energy of destruction are determined. The overall effect of different elements of destruction is assessed using both structural investigations and acoustic methods (acoustic emissions).

A description of the reduction of two-dimensional equilibrium equations to one-dimensional form via the Kantorovich method is given. An appropriate interpolation function is obtained by relating basal shear stress to sliding velocity and integrating the constitutive model through the depth of ice. An example is presented which demonstrates the ability of the numerical model to effect solutions which are in good agreement with those obtained via full two-dimensional finite-element models; however, at a small fraction of computational and data input efforts. The technique described for the reduction of the equilibrium equations can also be used to convert three-dimensional stress equilibrium to two-dimensional form.

The initial conditions needed for formation of moulins are crevasses and a supply of melt water. Water pouring into a crevasse may fill it until it overflows at the lowest point, which is normally near the margin. However, as the crevasse deepens, it intersects englacial channels through which the water can drain. These channels may be finger-tip tributaries in a dendritic system such as that described by Shreve (1972) and observed by Raymond and Harrison (1975). When the crevasse closes, heat in the melt water keeps the connection open and a moulin is formed. The englacial channel enlarges rapidly by melting, utilizing mechanical energy released by the descending water.

Descents into moulins, and mapping of structures exposed at the surface after many years of melting, demonstrate that the drainage channels leading down from the bottoms of the moulins have inclinations of 0–45° from the vertical. These channels trend in the direction of the original crevasse but appear to be deeper than the expected depth of the crevasse. They have not, even at depths of 50–60 m, become normal to the equipotential planes described by Shreve.

Inexpensive add-on boards are currently available that enable personal computers to be used as digital image-processing systems. The capabilities of one such system are illustrated by two specific cases examining the surface characterization of a sea-ice cover and the statistical description of sea-ice structure. The unit discussed digitizes video input into a 512 × 512 array of pixels, assigning each a gray shade from 0 to 255. A key feature of the system is that the primitive commands of the board can be accessed through higher-level programming languages. This allows users to customize easily the system for their own needs.