An ice sheet with fixed boundary conditions may have two steady configurations, as shown by a new one-dimensional model including the physics and continuity of ice, water, and deforming subglacial till. In one steady state, a steep surface slope causes rapid internal ice shearing but forces basal water through subglacial aquifers, suppressing basal velocity; in the other steady state, a gentle surface slope causes only slow ice shearing but allows water to lubricate the ice-bed interface and cause rapid basal velocities. Small climatic forcing may cause large ice-sheet response during a switch between steady states.

The dynamic state of the West Antarctic ice sheet has been termed the grand problem of glaciology. An attempt is presented to assess it by simulating the observed ice thickness and ice velocities along a cross-section from ice stream B (Ross Sea) to Pine Island Glacier (Pine Island Bay) with a numerical model developed from the one described by Budd and McInnes (1978). A kinematic analysis with topographical and regime data from various sources shows the mass fluxes observed near the grounding line of the Ross Ice Shelf to be of the order expected for steady-state balance. Deformation of the ice accounts for only a small fraction of the observed flow there. Simulations (to be described in detail elsewhere) with the Budd/McInnes surging mechanism can approximate the existing ice thickness as a post-surge feature but fail to reproduce the high balance velocities. Both these velocities and the existing ice-thickness profile are simulated successfully as a state of steady sliding, with parameterizations involving the ice thickness above that corresponding to buoyancy and realistically assumed longitudinal strain-rates. A range of results is presented to illustrate the sensitivity of the simulation to changes in various parameters.

Dependence of Kinosita’s hardness R of wet snow on its dry density ρd and free water content W was obtained in the following form where a, b and c are constants. When wet snow was qualitatively classified into two types, I (coarse-grained granular) and II (new and fine-grained compact) and the constants were determined separately for each type, the correlation coefficients of the above relation were high except between In R and W for snow I. For further investigation of the effect of W on R, a dry snow sample was prepared and R was measured before and after water addition. Aging effect on R was also investigated.

A numerical study has been carried out on the flow of ice in the transition zone between an ice sheet and an ice shelf. The study was motivated by the need for global ice-sheet-ice-shelf modelling to determine the characteristics of the transition zone. The problem is dealt with from an academic viewpoint, and the study especially focuses on two-dimensional vertical sharp transition zones. Stokes equations are solved using a finite-element method. Conclusions include: (1) in ice-sheet-ice-shelf modelling, each of the two components can be computed separately then linked by a jump-boundary condition [or the horizontal velocity; (2) as shown by studies on the response of an ice shelf to tidal forcing, the surface elevation/thickness ratio passes through the hydrostatic equilibrium value.

Ice pile-up and ride-up are common occurrences along beaches in the sub-Arctic and Arctic. An understanding of the factors which lead to pile-up is important for design of a defensive strategy to prevent damage to coastal installations.

Since ice action on a sloping beach is complex, an experimental model study was undertaken to determine the factors which promote ice pile-up. The factors varied in this study were the freeboard, slope, and roughness of the beach. One experiment was performed to observe the effectiveness of a shore defense structure against ice ride-up.

In Honshu Island, Japan, tremendous amounts of snow falls over a vast area facing the Sea of Japan. The depth of deposited snow sometimes exceeds 2 m, even in urban areas. The weight of snow on roofs can damage conventional wooden houses. It is of great importance, therefore, to monitor and control roof snow loads.

A model system has been developed for controlling snow on roofs. A precipitation detector capable of differentiating between solid and liquid precipitation and a water gauge for detecting the meltwater from a roof are combined to estimate the roof snow load. When the calculated load exceeds a critical value, an electric heater on the roof is energized to melt a portion of the snow. The whole system is controlled by a personal computer. The system was tested for about a month in 1990 with satisfactory results.

We use a two-dimensional flowline model to study the flow of the Gregoriev ice cap, Tien Shan, central Asia. The model takes into account the transverse change of glacier width, data on the measured thickness of the glacier, the surface velocity at the glacier front, and mass-balance measurements in 1987 and 1988. The calculated ice velocity varies from 0 to 3 ma−1 along the glacier flowline. The velocity maximum is shifted from the lowest part towards the middle part of the ice cap for the time interval considered (1980–2050) in the study. The derived changes of the glacier show the degradation and decrease of glacier extent on the south slope of Terskey Ala Tau, Tien Shan. Seasonal variations of temperature in the subsurface layer result in oscillations of stresses and velocities that are due to seasonal changes of viscosity. The consequent stresses can exceed the compressive/tensile strength that would produce crevasses.

Broadband measurements of dielectric properties of natural snow samples near or at 0°C are reported. Measurement quantities are: dielectric permittivity, loss factor and complex propagation factor for electromagnetic waves. X-band measurements were made in a cold room in the laboratory; measurements at low and intermediate frequencies were carried out both in the field (Stubai Alps, 3300 m; Hafelekar near Innsbruck, 2100 m) and in the cold room. Results show that in the different frequency ranges the relative effect on snow dielectric properties of the parameters: density, grain-size and shape, liquid water content, shape and distribution of liquid inclusions and content of impurities, varies significantly. In the low-frequency range the influence of grain-size and shape and snow density dominates; in the medium-frequency range liquid water content and density are the dominant parameters. In the microwave X-band the influence of the amount, shape and distribution of liquid inclusions and snow density is more important than that of the remaining parameters.

Frontal ablation, the combination of submarine melting and iceberg calving, changes the geometry of a glacier's terminus, influencing glacier dynamics, the fate of upwelling plumes and the distribution of submarine meltwater input into the ocean. Directly observing frontal ablation and terminus morphology below the waterline is difficult, however, limiting our understanding of these coupled ice–ocean processes. To investigate the evolution of a tidewater glacier's submarine terminus, we combine 3-D multibeam point clouds of the subsurface ice face at LeConte Glacier, Alaska, with concurrent observations of environmental conditions during three field campaigns between 2016 and 2018. We observe terminus morphology that was predominately overcut (52% in August 2016, 63% in May 2017 and 74% in September 2018), accompanied by high multibeam sonar-derived melt rates (4.84 m d−1 in 2016, 1.13 m d−1 in 2017 and 1.85 m d−1 in 2018). We find that periods of high subglacial discharge lead to localized undercut discharge outlets, but adjacent to these outlets the terminus maintains significantly overcut geometry, with an ice ramp that protrudes 75 m into the fjord in 2017 and 125 m in 2018. Our data challenge the assumption that tidewater glacier termini are largely undercut during periods of high submarine melting.

Russian satellite imagery of the polar regions has recently become available to western scientists through Sojuzkarta. The KFA-1000 photographic camera is of particular interest to glaciologists due to its high resolution (a nominal 5 m). Digitized photographic products from this instrument are compared with digital data from Landsat and SPOT series satellites for a partly glacierized area of northwest Spitsbergen. Comparison of KFA-1000 data with detailed maps of man-made structures at the settlement of Ny Ålesund demonstrates that the resolution of the photographic imagery is about 3 m, but scanner resolution limited our digital data to about 6 m. Significantly less detail can be resolved on Landsat TM imagery and Landsat MSS data fail to resolve any of the structures. KFA-1000 data are compared with Landsat TM and MSS images and SPOT HRV multispectral imagery for several tidewater glaciers in Spitsbergen. KFA-1000 imagery is of a significantly higher geometric resolution than the other sensors, allowing the clear identification of individual crevasses and other ice surface features. KFA-1000 scenes from 1985 and 1988 are used to measure ice marginal fluctuations for several northwest Spitsbergen glaciers, and the onset of a surge can also be identified. This imagery has a 60% overlap between scenes and the heighting accuracy of the stereoscopic data is calculated at 45 m. Radiometric analysis of KFA-1000 data is restricted to relative brightness values, since no absolute calibration is available. The photographic products appear speckled, and the range and standard deviation of normalized pixel brightness values over snow is greater than for equivalent Landsat TM data. The very high spatial resolution of the KFA-1000 camera is its principal attraction for glaciologists.

Reorientation of individual crystal-glide planes as isotropic surface ice is deformed during its passage to depth in an ice sheet, lattice rotation, creates a fabric and associated anisotropy. A simple macroscopic description is that these material glide planes are rotated towards planes normal to an axis of compression, and away from planes normal to an axis of extension, inducing an instantaneous orthotropic viscous response with reflexional symmetries in the planes orthogonal to the current principal stretch axes. An orthotropic viscous law is presented for the strain rate expressed in terms of the deviatoric stress, the deformation, and three structure tensors based on the principal stretch axes. This anisotropic relation is expressed in terms of a single fabric response function in addition to the isotropic ice viscosity. The predicted responses in uniaxial compression and simple shear are determined. While the uniaxial response yields an explicit relation between the axial strain rate and stress, it is found that the shear response is governed by three, complicated, coupled relations between the shear strain rate and three deviatoricstress components. The new result derived here is the solution of this system: an explicit relation between the shear strain rate and shear stress. Correlation of these relations with idealized uniaxial and shear responses is then used to determine the required fabric function in the model law.

Based on studies in the Antarctic Oceans, the contribution of the snow cover to sea-ice growth has become of major interest. Snow can result in upward ice growth in contrast with ordinary downward congelation growth at the bottom. A sea-ice study was conducted to verify the upward ice growth found in a previous study and to investigate the relation between sea-ice growth and radar backscattering signature. Sea-ice samples collected at four points in Lützow-Holm Bay, Antarctica, from 1998 to 2003 are analyzed. Analyses of snow-/ice-gauge measurements, snow depth and ice structure reveal an extremely large amount of upward ice growth of up to 1.0 m during one full year compared with a slight amount of downward growth. The upward growth was caused mostly by snow ice and to a lesser extent by superimposed ice. The salinity profile remained unchanged, although the ice survived the summer melt season. Characteristics of superimposed ice such as salinity, δ18O values and structure were obliterated during the summer, implying complete melting or dissolution of the superimposed layer. The ERS-2 backscatter showed a remarkable annual variation: It had a minimum value in midsummer and increased abruptly to a maximum value in late summer, then decreasing gradually in wintertime. The relation of the backscatter coefficient to the growth and properties of the snow cover and sea ice are discussed.

The continentality index is a good measure of the nature of the climate in a region, as it reflects not only the temperature but also the large-scale circulation. It correlates well with glacier mass-balance parameters. The climate along the west–east transect slightly north of the Arctic Circle across the Scandinavian Caledonides is governed by the prevailing westerlies; however, during winter the eastern part of the Caledonides is influenced by weather systems from the southeast. The differences in continentality meant by temperature and precipitation have a major impact on the response times of glaciers. The climatic change in this area has been dominated by increased summer mean temperatures (1910–20) and increased maritime influence since the 1980s. The slower-reacting glaciers on the Swedish side of the mountains are still adapting to the temperature increase at the beginning of the 20th century, and the increase in maritime influence gradually becomes less important towards the west. Thus, differences in the behaviour of glacier fronts along the west–east transect mirror differences in continentality.

A global coupled atmosphere-ocean-ice model is used to examine the interdependence among several components of the hydrologic cycle in the Arctic Ocean, including river discharge, sea-ice cover, and the flow of sea ice through Fram Strait. Since the ocean model has a free surface, fresh-water inflow from rivers is added directly to the ocean. The timing of the peak spring river flow depends on snowmelt runoff and its subsequent routing through the river system. Thermodynamic sea ice is included, and a new sea-iee advection scheme is described. The model’s river discharge affects salinity at the mouth of large rivers. The effect of the river discharge on sea-ice cover is not clear, either locally or at the basin scale. There is significant inter-annual variability of ice flow through Fram Strait, but the model’s flow is about half of that observed. The anomalous ice flow through Fram Strait is most highly correlated with the meridional wind stress. Potential implications for the “great salinity” anomaly are discussed.

In the 1870s and 1880s, after a long period of cold conditions, most of the glaciers of Svartisen ended near their maximum Neoglacial limit. Subsequent changes, although principally a response to the climatic controls of mass balance, have been influenced by glacier geometry, including area/altitude relations and aspect, and by glacier dynamics. Calving has played a principal role in the decrease of size of two of the larger glaciers, Austerdalsisen and Flatisen, both of which became unstable once the grounded distal sections of their tongues lost contact with their beds. Mass balance variations reflect climatic controls of the length of the accumulation and ablation seasons, as well as changes of summer temperature. The mass balance record of Engabreen, a maritime outlet of the Vestre Svartisen ice cap, monitored since 1970 by the Norwegian Water Resources and Energy Administration, is not representative of the area as a whole: the more continental glaciers of Østre Svartisen are likely to experience negative net balances when that of Engabreen is slightly or moderately positive. However, the pattern of year-to-year changes of net balance is similar, not only for the Svartisen area as a whole, but also for a larger area.

The mechanical configuration of cavities associated with clasts is discussed, and how this affects the water pressure underneath the clast. The range of permissible water pressure is determined by flow parallel to the bed rather than by flow towards the bed. The actual pressure is controlled by hydraulic connections to areas away from the clast. The degree of cavitation provides an additional degree of freedom which adjusts to ensure that horizontal and vertical forces respect the Coulomb friction condition.

The detection of small changes in concentration or thickness in the Arctic or Antarctic ice cover is an important topic in the current global-climate-change debate. Change detection using satellite data alone requires rigorous error analysis for their derived ice products, including inter-satellite validation for long time series. All models of physical processes are only approximations, and the best models of complicated physical processes have errors and uncertainties. A promising approach is data assimilation, combining model, in situ data and satellite remote-sensing data. Sea-ice monitoring from satellite, ice-model estimates, and the potential benefit of combining the two are discussed in some detail. In a case-study we demonstrate how the sea-ice backscatter for the Beaufort Sea region was derived using a backscattering model in combination with an ice model. We conclude that, for data assimilation, the first steps include the use of simple models, moving, with success at this level, to progressively more complex models. We also recommend reconfiguring the current remote-sensing data to include precise time tags with each pixel. For example, the current Special Sensor Microwave Imager data might be reissued in a time-tagged orbital (or gridded) format as opposed to the currently available daily averaged gridded data. Finally, error statistics and quality-control information also need to be readily available in a form useful for assimilation. The effectiveness of data-assimilation techniques is directly linked to the availability of data error statistics.

A hot-water drill developed during the past 2 years at Alfred-Wegener- Institut was used to penetrate Ekströmisen several times near the German wintering-over base, Neumayer (70°39´S, 08° 15´W). The drilling operation was very successful and the initial large diameter (≥ 35 cm) allowed easy access to the ocean. One hole was used to install an ultrasonic echo-sounder which recorded the ablation at the ice-shelf bottom continuously. Another hole was destined for emplacement of a thermistor string throughout the 237 m thick ice shelf for ice-temperature measurements. Several CTD profiles in the 175 m deep water column and the analysis of water samples provided valuable data for the understanding of ice-shelf-ocean interactions.

The Woore Moraine, situated within the Cheshire Plain, is one of the largest glacial landforms in Britain. However, its key characteristics, internal structure and glaciological significance are poorly understood due to limited exposure of its key geological features. This paper focuses on the results of a suite of complementary geophysical techniques (ground-penetrating radar, electrical resistivity tomography and seismic refraction) that were used to image the interior structure of the moraine and help determine its origin. Geophysical imaging reveals a two-layer moraine structure comprising a thin and heterogeneous carapace of intercalated sediments overlying a core of subglacial clay-rich diamicton and proglacial sands deformed by a series of fore- and back-thrusts. These features indicate that the moraine is glaciotectonic in origin, involving initial compression of proglacial sediments against a bedrock obstruction and subsequent modification due to overriding.

The impact of April sea-ice thickness (SIT) initialization on the predictability of September sea-ice extent (SIE) is investigated based on a series of perfect model ensemble experiments using the MIROC5.2 climate model. Ensembles with April SIT initialization can accurately predict the September SIE for greater lead times than in cases without the initialization – up to 2 years ahead. The persistence of SIT correctly initialized in April contributes to the skilful prediction of SIE in the first September. On the other hand, errors in the initialization of SIT in April cause errors in the predicted sea-ice concentration and thickness in the Pacific sector from July to September and consequently influence the predictive skill with respect to SIE in September. The present study suggests that initialization of the April SIT in the Pacific sector significantly improves the accuracy of the September SIE forecasts by decreasing the errors in sea-ice fields from July to September.