An existing thermodynamic ice-growth model (Semtner, 1976) has been tested for its ability to predict the growth of fast ice in McMurdo Sound, Antarctica. Significant discrepancies between observed and predicted ice thicknesses were found to occur, primarily due to the presence of sub-ice platelets and the formation of a snow-ice layer. Although these ice-growth processes are not well enough understood to permit rigorous physical modelling, it is shown that fairly simple modifications to the model greatly improve the accuracy of the thickness predictions, and serve to highlight the importance of these processes in the Antarctic fast-ice environment. Surface flooding and snow-ice formation are assumed to occur immediately upon the establishment of a positive hydrostatic water level, and a surface temperature in excess of a critical value, above which interconnecting channels in the ice matrix permit the flow of water to the surface. The presence of the sub-ice platelet layer is assumed to increase columnar ice growth at a rate proportional to the volume fraction of ice in the platelet layer, a simple technique but one that permits estimates of platelet-enhanced growth without detailed knowledge of oceanographic conditions. The resulting model predictions are in close agreement with measurements of fast-ice growth and decay in McMurdo Sound; however, data suitable for testing the model over a complete range of conditions and over multi-year cycles are not available at the present time.

A comprehensive survey of the Larsen Ice Shelf has been conducted using precise orbit and retracked Seasat radar-altimeter data with editing of erroneous values resulting from intrumental artefacts. Contour maps of elevation and radar back-scatter (with absolute accuracies of 1 m and 2 dB, respectively) have been produced and it has also been possible to map rifts, grounding points, rough terrain, and about 30% of the ice shelf’s seaward margin. Ice thicknesses derived from these elevation data show broad agreement with those derived from previous airborne radio-echo surveys. The maps of parameters measured by Seasat represent a very substantial improvement over those previously available. They thus provide a reference against which comparison may be made with a view to detecting substantial climatic changes. This is of particular interest since, as the most northerly major ice shelf in Antarctica, the Larsen Ice Shelf may be more sensitive than others to global climatic trends.

The hydrographs of two jökulhlaups resulting from the sudden drainage of an ice-dammed lake in West Greenland in 1984 and 1987 are compared. The first flood had a similar peak discharge to the second but drained only two-thirds of the total volume of the 1987 event which amounted to 32–36 × 106 m3 in 36 h. Calculations based on the lake refill time suggest that it drains every 2–3 years, but that peak flows may be variable from flood to flood. The timing of the jökulhlaups in relation to the melt season may reflect variations of water pressure within the subglacial drainage networks, and changes in the configuration of these networks and the positions of crevasses on an annual basis.

The shift of the equilibrium-line altitude by climatic perturbations of air temperature δTa, absolute humidity δρv, cloudiness δw and annual accumulation 6c in West Greenland (EGIG profile) is analyzed by heat-balance modelling. The perturbations δTa = +1 K, δρv = +0.25 g m−3, δc = +50 kg m−2 result in a shift of the equilibrium-line altitude of 87.5, 9.8, and −24.3 m, respectively, while perturbations in cloudiness are negligible. The most important influence originates from changing air temperature, as air temperature affects daily heat-flux density of melt and duration of the ablation period. In regimes with negative values of the gradient of annual accumulation, the shift of the equilibrium line is enhanced.

Long-term records (10–30 years of measurements) of North American glaciers are compared using Lliboutry’s simplified linear model. This model separates the mass balance into two additive terms, one dependent on the location of the glacier and the other on time. The time-dependent term provides a common signal for the variations of different glaciers. Principal-component analysis indicates that these similarities amount to between 65 and 70% of the total variance for glaciers up to about 500 km apart. Within this distance, similar variations of mass balance and, therefore the same yearly climatic variations, can be observed.

Ice salinity and 18O/16O ratios were measured on 12 ice cores drilled from thick, multi-year land-fast sea ice (MLSI) off the north coast of Ellesmere Island, Canada. Fresh, brackish, and sea ice were identified in the ice cores using the 18O/16O ratios. Two cases are considered: case 1, which assumes that no isotopic fractionation occurs on freezing; and, case 2, which assumes that a maximum isotopic fractionation factor (a) of 1.003 applies. The amount of each ice type is variable among the cores, but overall the 12 cores comprise 29.6% brackish ice, 70.0% sea ice, and 0.4% fresh ice in case 1, and 42.3% brackish ice, 57.3% sea ice, and 0.4% fresh ice in case 2. The data suggest that time-dependent brackish sea-water stratification below the ice is quite common and is often associated with the inverted bottom topography. However, the stratification is not always confined to small, areally limited under-ice melt pools in inverted depressions, and neither is it a summer-only phenomenon. Brackish ice growth apparently occurs in a brackish water layer that in some instances underlies the ice sheet year-round. For both case 1 and case 2 the salinity distribution in brackish ice is positively skewed, with 50% of salinity values occurring in the range 0–0.49‰. Sea-ice salinity values are more evenly distributed. In case 1, brackish ice has mean salinity and mean δ18O values of 0.66 and –19.9‰, respectively, compared to mean values of 1.88 and –6.5‰ for the sea ice. In case 2, brackish ice has mean salinity and mean S18O values of 0.75 and –18.1% compared to mean values of 2.03 and –5.2‰ for the sea ice. The salinity of brackish ice and sea ice, ice-growth mechanisms, and the inclusion of brine in the sub-structure are discussed briefly.

From observations on the sub-polar glaciers of Phillips Inlet, north-west Ellesmere Island, neither complex basal thermal regimes nor internal thrusting need be invoked to explain all types of debris distribution in the basal ice of sub-polar glaciers. Debris is present in the terminal ice cliffs as: (1) debris-poor folia expressing internal flow patterns; (2) debris-rich bands of various thickness; and (3) augens or clots. Debris-rich bands and augens are concentrated predominantly in the basal ice, contain a wide range of grain-sizes, cut across debris-poor folia, rarely extend >1 m laterally, and are irregularly spaced.

Observations on patterns of entrainment and contemporary processes at ice margins, together with clast-shape analyses, suggest that the recycling and re-incorporation of fluvial/deltaic sediment, aprons, and pro-glacially thrusted blocks at the ice face are an alternative process of debris entrainment to basal plucking and large-scale freeze-on at the base of the glacier. The most active processes observed at the glacier margins are fluvial, and the origins of some debris-rich bands and augens are linked to thermal-erosional niches and abandoned meanders in the base of the glacier cliff face. Because the large-scale accumulation of ice-cored debris at glacier snouts represents periods of increased run-off and snout recession (specifically during the early Holocene), basal and englacial debris concentrations resulting from glacial over-riding and re-incorporation have great palaeoclimatic significance.

Water in polycrystalline ice at its melting point forms a system of veins at the three-grain junctions. The veins join together at nodes, which are the four-grain junctions. The shape of a node, a tetrahedron with non-spherical faces and open corners, is determined completely by the dihedral angle for water in contact with a grain boundary. Using the observed value for this angle, namely 33.6°, the paper computes the tetrahedral shape. This is a surface-tension problem with initially unknown boundaries. The result shows that the ratio of vein volume to node volume is R = 0.072 l/d, where l is the average length of a vein between two nodes, and d is the vein diameter measured between edges. For example, in a specimen of ice grown from the melt in the laboratory R was 18.

A mathematical model is proposed which gives operational criteria for the construction of artificial, floating ice platforms by water flooding and spraying. The model is based on the one-dimensional heat conduction equation. It gives the change in time of the internal temperature field of the ice layer as it responds to changes in the external conditions. The influence of the atmospheric conditions, including wind speed, air temperature, and cloud cover, on the thermal changes in the ice layer have been considered, both for flooding and for spraying. The importance of the water-delivery conditions, the mass flux of the supplied water, and the degree of droplet cooling during spraying, have also been investigated. The rate of ice growth has been examined for repetitive spraying and flooding, and the quantitative advantage of spraying has been demonstrated.

The temperature field is derived for a sinusoidally varying surface temperature with varying solar radiation penetration. The growth rates of snow crystals are calculated to explain the rapidly growing layers of faceted crystals (i.e. depth hoar) that form just below the surface at high altitudes and in polar snow. The solutions also show that a layer of wet snow can exist just below the surface even on days when the surface temperature remains sub-freezing.

The study is based on an observation program since 1974, including the continuous monitoring of net balance during 1978–86. The 8 year vertical net-balance profile, characterized by negative values throughout and an increase of absolute amounts from the higher towards the lower elevations, defines the recent climatic forcing.

A model is developed with a spatial resolution by 100 m wide bands, relating glacier morphology, ice flow, and mass economy, using as input ice thickness, surface slope, width of height contours, area of 100 m wide bands, volume flux, and net balance as a function of elevation. In 1 year time steps, the model calculates the changes in ice thickness and surface topography commensurate with the difference between net balance and longitudinal divergence of volume flux, and then the corresponding changes in surface slope, contour width, area of 100 m wide bands, volume flux, and net balance corresponding to the new surface elevations. This information serves as input for the next time step.

The model was applied to the intervals 1974–78, 1978–82, and 1982–86, as training periods, to explore the diagnostics of ice flow and mass economy, and to ascertain the model performance in treating long-term evolution in glacier behavior. The experiments yielded a reasonable agreement between calculated and observed changes in ice thickness, velocity, and volume flux, over the three aforementioned 4 year periods of field monitoring. Two sets of prediction experiments beyond 1986 were then undertaken. The first used as input the observed 1978–86 vertical net-balance profile (a), and thus simulated the future evolution of the glacier given continuation of the recent climatic forcing. In the second set of experiments, the 1978–86 net-balance values were doubled to yield a more extreme net-balance profile (b), representing climatic conditions considerably more adverse to the maintenance of the glacier.

Predictions are presented for the epochs 1990, 1994, 1998, and 2000. Given continuation of the recent climatic conditions (profile a), the following changes are anticipated from 1986 to the year 2000: a shrinkage of the volume from 4 to 1 x 106 m3; an area decrease from 25 to 17 χ 104 m2; a shortening of the glacier from 990 to less than 800 m; a slow-down of fastest ice flow from 2.5 to less than 1ma−1; a decrease of the maximum volume flux from 13 to less than 3 χ 103 m3 a−1; and substantial up-glacier displacements of the velocity and volume-flux maxima. Under more extreme negative net-balance conditions (profile b), the decay would be so greatly accelerated that Lewis Glacier may completely disappear well before the end of the millennium. This prospect is inherent in a possible change from recent climatic conditions.

A joint dynamical system comprising both an eroding glacier and an eroded bed is considered to describe the formation of cirques and stepped longitudinal profiles of trough valleys. A glacier is modelled as a layer of a very viscous incompressible fluid flowing down an inclined bed. The rate of erosion is assumed to be determined by the basal shear stress. The dynamics of small longitudinal perturbations are studied. The analysis shows that the perturbations propagate up the glacier bed with velocities that are different for the perturbations of different spatial scales. As a result, a perturbation of a specific spatial scale stands out against the others and develops into the morphological forms considered here.

The late Pleistocene Big Timber glacier of west-central Montana was used as the test case for a model which calculates the mass balance of a paleoglacier using glacial flow theory. Application of Glen’s flow law to a detailed reconstruction of the glacier provided an estimate of the component of mass flux due to internal deformation. Assuming basal slip to be zero where mass flux due to deformation was a maximum, the mass flux at the equilibrium-line altitude (ELA) an ablation gradient of 3.0 ± 0.6 mm/m, and an accumulation gradient of 1.0 ± 0.2 mm/m were determined. Application of the continuity model above and below the ELA generated a second estimate of mass flux at discrete points along the glacier. The difference between deformation flux and continuity flux yields a first approximation of slip, which is highly variable along the glacier. Since the mass-balance gradients are climatically controlled, this model provides information on the paleoclimatic setting of the glacier. The low gradients indicate that, during the last glacial maximum, the east side of the central Rocky Mountains experienced a cold, dry environment much like that of modern-day glaciers in the Brooks Range of Alaska.

A substantial data set of digitally recorded radio echo-sounding data was collected over 44 ice masses in Spitsbergen and the ice caps on Nordaustlandet, Svalbard. These data have allowed quantitative analysis of bed and internal power-reflection coefficients. Substantial regional differences were observed and have been correlated with the presence of water and/or moraine at the bed and with the bulk thermal regime of the ice mass. Values of bed power-reflection coefficient varied between −40 ± 5 and −8 ± 6 dB. It is suggested that the ice caps in north-east Spitsbergen (possessing among the lowest reflection coefficients observed) are frozen to their beds as is much of Austfonna (in Nordaustlandet), and that such values imply the likelihood of a layer of debris-rich ice above the bedrock. It is proposed that significant quantities of water are present at the ice/bed interface of many of the glaciers in north-west Spitsbergen. Further, it is believed that two geological divides were detected. A number of extraordinary internal reflecting horizons are also discussed.

A numerical model has been developed to simulate energy and mass evolution of snow cover at a given location, as a function of meteorological conditions: precipitation, air temperature, humidity, wind velocity, and incoming short-wave and long-wave radiation.

This model, named CROCUS, was first tested on a well-instrumented field during a whole winter, showing its ability to simulate the important phenomena affecting the evolution of the snow layers: high temperature gradients, wetting, compaction, and melting-freezing cycles. A second test was conducted at two locations in the French network used for operational avalanche forecasting. Though the weather observations are made there only twice daily, the snow profiles calculated by the model were very close to those obtained once a week by a pit observation. CROCUS proved itself sufficient to be considered now as a useful objective tool for operational avalanche forecasting.

A numerical simulation of the Ross Ice Shelf, Antarctica, in which discharge from Ice Streams A-E is changed suddenly between extreme states, is used to investigate ice-shelf thickness and flow anomalies generated by ice-stream transience. At one extreme, ice-stream discharge rates specified as model boundary conditions are balanced individually with snow accumulation in the ice-stream catchment areas. At the other, discharge rates are fixed at current observed values which widely depart from mass balance. The simulated ice-shelf evolution between initial and final steady states suggests that ice-thickness and velocity fields adjust to new ice-stream conditions over a relatively short time span (approximately 500 years). In contrast, transitory geometrics of medial moraines and relict-crevasse bands persist over a longer time span (up to 2000 years). Contortions of medial moraines and relict-crevasse bands thus may provide a useful long-term history of past ice-stream activity. The past stoppage of Ice Stream C, for example, should be evident today in some medial moraine trajectories even if the stoppage occurred over 1000 years ago. Ice-shelf thickness fluctuations induced by ice-stream activity are generally restricted to the neighborhood of the grounding line. These fluctuations may constitute a trigger for ice-rise formation near ice-stream outlets.

Experiments have established that the fracture toughness of fresh-water, bubbly ice is not affected by the presence of salt water.

More than 100 simultaneously measured profiles of wind speed and temperature were analyzed to determine the aerodynamic and thermal roughness lengths of glacier ice. The results proved to be extremely sensitive to measurement height, which is difficult to define precisely on the hummocky terrain of a glacier. Therefore, aerodynamic roughness lengths were estimated from the microtopography of the surface, yielding 2.46 mm for ice, and 5.5 mm for snow. Despite the indeterminate nature of the profile analysis, it did support the view that the thermal roughness length must decrease as the roughness Reynolds number increases, a relationship which has been modelled in the literature. Good agreement between bulk-transfer estimates and eddy-correlation measurements of fhe sensible heat-flux density on melting ice and snow was obtained by combining the aerodynamic roughness length with a suitable model for thermal roughness length.

A polarization-sensitive aperture-synthesis experiment has been carried out using radio-echo data from Storglaciären, Sweden. Echoes were recorded in each of three antenna configurations over an array of sites on the glacier surface. The echo information was transferred to a mainframe computer and manipulated in order to reveal any major individual targets present. Within a 100 m cube, six major targets were identified, each with its own echoing characteristics. Echo strengths indicate that the targets are probably cavities containing water. It cannot be determined whether they are isolated or parts of a continuous system.

The first known occurrence of outburst flooding at Ape Lake, British Columbia, was in October 1984 following the formation of a subglacial tunnel in an ice dam created by Fyles Glacier. Following tunnel closure, the lake refilled in 150 d and then a second outburst flood occurred in August 1986. During both events, 55% of the Apc Lake volume or 46 × 106 m3 was released in less than 24 h into the 50 km long, ungauged Noeick River, producing an average discharge of 540 m3 s−1. Channel and flood-plain erosion, damage to access roads, bridges, a logging camp, and an airstrip were related to the peak or maximum instantaneous discharge. In the absence of direct measurements, and to facilitate planning for future flood events, several independent methods were employed to estimate peak discharge. A modified version of the Clague-Mathews formula and the slope-area method yield consistent estimates which approach 1600 m3 s−1 near the ice-dam outlet. Attenuation of the flood peak in Noeick River is as high as 25% in the upper 12 km due to channel and flood-plain storage. Results using Clarke’s (1982) physical-based model suggest lower discharges and may be related to the irregular morphology of Ape Lake. Since Fyles Glacier is in continuous retreat, drainage around the margin of the ice dam which began in the summer of 1987 is expected to continue and no further outburst floods are anticipated.