Glacial mass-balance reconstruction for a long-term time-scale requires knowledge of the relation between climate change and mass-balance fluctuations. A large number of mass-balance reconstructions since the beginning of the century are based on statistical relations between monthly meteorological data and mass balance. The question examined in this paper is: are these relationships reliable enough for long-term time-scale extrapolation? From the glacier de Sarennes long mass-balance observations series, we were surprised to discover large discrepancies between relations resulting from different time periods. The importance of the albedo in relation to ablation and mass balance is highlighted, and it is shown that it is impossible to ignore glacier-surface conditions in establishing the empirical relation between mass-balance fluctuations and climatic variation; to omit this parameter leads to incorrect results for mass-balance reconstruction in the past based on meteorological data.

Findelengletscher, Switzerland, advanced about 250 m between 1979 and 1985, and retreated thereafter. Subglacial water pressure, surface velocity and surface strain rate were determined at several sites. The measurements were made early in the melt seasons of 1980, 1982, 1985 and 1994 and in the autumn of 1983 and the winter of 1984. Changes of surface geometry were assessed from aerial photographs.

The estimated basal shear stress changed little between 1982 and 1994. Nevertheless, large changes in the relationship of subglacial water pressure and surface velocity were observed, which cannot be reconciled with the most commonly used sliding law unless it is modified substantially. Consideration of possible reasons indícales that a change in the subglacial drainage system occurred, probably involving a change in the degree of cavity interconnection. Isolated cavities damp the variations in sliding velocity that normally result from changes in water pressure, because the pressure in isolated cavities decreases as the sliding speed increases. In contrast, by transmitting water-pressure fluctuations to a larger area of the bed, interconnected cavities amplify the effect of water-pressure fluctuations on sliding speed. Thus, we suggest that an observed decrease in velocity (for a given water pressure) between 1982 and 1994 was a consequence of a decrease in the interconnectedness of the subglacial cavity system.

Landsat digital imagery was used to search the island archipelagos of Franz Josef Land, Severnaya Zemlya and Novaya Zemlya, Russian High Arctic, for the presence of looped moraines characteristic of past glacier surges. The imagery provides almost complete summer-time coverage of the 60 000 km2 of ice in these islands. very few surge-type glaciers are identified: none in Franz Josef Land, three in Novaya Zemlya and two on Severnaya Zemlya. This contrasts greatly with Svalbard (ice-covered area 36 600 km2), to the west, where 36% of glaciers and ice-cap drainage basins are inferred to surge. The strong climatic gradient across the Eurasian High Arctic, with decreasing temperature and moisture eastward, may provide a gross control on this pattern through colder glacier thermal structure, limiting basal drainage on the thinner ice masses in particular.

To study near-surface heat flow on the Antarctíc ice sheet, snow temperatures were measured at South Pole Station to a depth of 3 m at 15 min intervals during most of 1992. Solar heating and water-vapor transport were negligible during the 6 month Winter, as was inter-grain net thermal radiation, leaving conduction as the dominant heat-transport mechanism. The rate of temperature change at depth over 15 min intervals was smaller than that at the surface, by one order of magnitude at 20 cm depth and two orders of magnitude at 1 m depth. A finite-difference model, with conduction as the only heat-transfer mechanism and measured temperatures as the upper and lower boundary conditions, was applied to foursets of three thermistors each. The thermal conductivity was estimated as that which minimized the difference between modeled and measured 15 min changes in temperatures at the center thermistor. The thermal conductivity obtained at shallow depths (above 40 cm) was lower than that given by existing parameterizations based on density, probably because the snow grains were freshly deposited, cold and poorly bonded. A model using only vertical conduction explains on average 87% ofthe observed 15 min temperature changes at less than 60 cm depth and 92% below 60 cm. The difference between modeled andmeasured temperature changes decreased with depth. The discrepancies between model and observation correlated more strongly with the air-snow temperature difference than with the product of that difference with the square of the wind speed,suggesting that the residual errors are due more to non-vertical conduction and to sub-grid-scale variabilis of the conductivity than to windpumping. The residual heating rate not explained by the model of vertical conduction exceeds 0.2 W m−3 only in the top 60 cm of the near-surface snow.

Sixty-three ice cores were collected in the Bellingshausen and Amundsen Seas in August and September 1993 during a cruise of the R.V. Nathaniel B. Palmer. The structure and stable-isotopic composition (18O/16O) of the cores were investigated in order to understand the growth conditions and to identify the key growth processes, particularly the contribution of snow to sea-ice formation. The structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the Bellingshausen Sea in March 1992 are reassessed. Frazil ice and congelation ice contribute 44% and 26%, respectively, to the composition of both the winter and summer ice-core sets, evidence that the relatively calm conditions that favour congelation-ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil-ice growth and pancake-ice formation. Both frazil- and congelation-ice layers have an av erage thickness of 0.12 m in winter, evidence that congelation ice and pancake ice thicken primarily by dynamic processes. The thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover. Snow-ice layers have a mean thickness of 0.20 and 0.28 m in the winter and summer cores, respectively, and the contribution of snow ice to the winter (24%) and summer (16%) core sets exceeds most quantities that have been reported previously in other Antarctic pack-ice zones. The thickness and quantity of snow ice may be due to a combination of high snow-accumulation rates and snow loads, environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow/ice interface, and bottom melting losses being compensated by snow-ice formation. Layers of superimposed ice at the top of each of the summer cores make up 4.6% of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice. The accumulation of superimposed ice is evidence that melting in the snow cover on Antarctic sea-ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass.

The historical length variations in Unterer Grindelwaldgletscher have been simulated by coupling a numerical mass-balance model to a dynamic ice-flow model. As forcing functions, we used (partly reconstructed) local climatic records, which were transformed by the mass-balance model into a mass-balance history. The ice-flow model then computes the length variations that have occurred over the course of time.

In a model run from AD 1530 to the present, with both seasonal temperature and precipitation variations as forcing functions, the observed maximum length of the glacier around AD 1860 and the subsequent retreat are simulated. The observed AD 1600 maximum, however, does not show up in the simulation. This is probably due to an incorrect reconstruction of the mass balance for this period, as detailed climatic data are available only since 1865. The root-mean-square difference between the simulated and the observed front positions is 0.28 km. The simulated glacier geometry for 1987 fits the observed geometry for that year reasonably well.

Because of the success of the historical simulation, an attempt is made to predict future glacier retreat on the basis of two different greenhouse-gas scenarios. For a Business-as-Usual scenario, only 29% of the 1990 volume would remain in AD 2100.

Laboratory tests on sediment over-ridden by the last ice sheet in north-western Germany reveal very low ice-induced pre-consolidation and high palaeo-pore-water pressures. Sediment consolidation at the base of the glacier was largely controlled by hydraulic properties of the substratum. Generally low permeabilities of the bed caused sustained high pore-water pressure in over-ridden sediments close to the flotation point. This implies a serious possibility of hydraulic lifting of the ice sheet. It is believed that the reduced basal coupling limited the transformation of glacier shear stress on to the bed sediments, which is indicated by a lack of sedimentological evidence for widespread pervasive bed deformation. Ice motion was probably focused at the glacier sole by some combination of sliding and ploughing. However, isolated spots with deformation occur, so that the subglacial system in the study area can be characterized as a stable/deforming mosaic.

Two-dimensional, isothermal, non-stationary, cold-glacier dynamics are analysed by perturbation methods, when the ice creep is described by Glen’s flow law. This approach allows us in model the ice-divide dynamics separately from that of the glacier and to pose a simplified problem for the ice divide. To order of the glacier-aspect ratio, all unknown characteristics near the ice divide can be searched for in an infinite layer with parallel boundaries, whose thickness coincides with that found by the shallow-ice approximation. The problem for the ice divide is stationary and does not depend on the ice and glacier characteristics, such as a flow-law constant, ice thickness and accumulation rate. At the ice divide, the ice upper surface curvature is finite and the shallow-ice approximation is inadequate.

In bedlock covered by continental ice, the depth to electrically conductive saline waters enriched below permafrost can be defined by electromagnetic measurements. Thus, if the ice thickness is also measured we obtain estimates of permafrost thickness variations in the survey area. Moreover, using the relation between ice and permafrost thicknesses and approximations of the melting temperature of saline waters combined with the average annual temperature at the surface, we can estimate temperature variations within both the bedrock and the ice. These can further be used for estimating the temperature values at the ice base.

The method was developed for interpreting two geophysical field profiles measured on continental ice in western Dronning Maud Land, Antarctica. Gravity, magnetic and electromagnetic profiles were measured between the nunataks Basen and Plogen (≈22 km) and Basen and Fossilryggen (≈38km). In the Basen–Fossilryggen profile the electromagnetic soundings revealed good conductors in the bedrock beneath the ice. The significant correlation between the ice thickness and the depth of the conductor in the bedrock strongly suggests that the conductors are not sedimentary rock layers but rather saline groundwater in which salinity has been enhanced by permafrost processes. From the regression curve we can conclude that the temperature vs depth curve in the ice can be represented by a first-degree line and that the “warm” ice base of about −2° C is expected to occur at depths of about 650 m, the base of permafrost in outcropping bedrock being at about 1 km. The mean temperature gradients in the ice and in the bedrock can be estimated as being about 20°Ckm−1 and 13°C km−1 respectively.

In the Basen–Plogen profile, conductors were detected only in the beginning of the profile, where ice thickness was below 650m. In the main part of the profile where the ice thickness exceeds 650 m, no conductors were observed. In those areas our interpretation is that the icebase is “warm” and no saline waters enriched by permafrost are present.

Major processes controlling the existence of a large sub-continental glacier system were identified on the basis of glaciological, meteorological and isotopic analyses using expeditionary and long-term data. Observations were made on the southern Inylchek glacier located in the Pobeda-Khan Tengry massif, the largest sub-continental glacier system on the northern periphery of central Asia. More than 1200 glaciers with a total area of about 4320 km2 comprise the massif. Melt is for the most part caused by radiation and is most intensive during periods of anticyclonic weather with fohn development. The proportion of solar radiation input in relation to heat balance is more than 90%. Evaporation and condensation are negligible during most times and comprise 7% of heat expenditure. Accumulation was associated with cold cyclonic weather. Four ice-formation zones were identified, the upper boundary of liquid runoff is at 5200 m and the recryslallization zone is above 5900 m. The calculated net glacier mass is negative, −318 kg m−2 a−1, and indicates the degradation of modern Pobeda-Khan Tengry glaciers.

The frequency of avalanches at a given location is the primary variable for calculating the risk as input to zoning applications and decisions about avalanche-control options. In this paper, we present an in-depth study of avalanche frequency using an extensive data base of avalanche-occurrence records from Rogers’ Pass, British Columbia (43 avalanche paths; 24 years of records). This study, the first of its kind for high-frequency avalanche paths, yields the result that the frequency of avalanches may be described by a Poisson distribution. Study of the relationship between terrain variables and precipitation estimates shows that avalanche frequency is significantly correlated with path roughness, 30 year maximum water equivalent, east-west location from Rogers’ Pass summit, wind exposure and run-out zone elevation and inclination. With the length of avalanche-occurrence records and quality of the data, we believe our study is the most comprehensive in existence about avalanche frequency and its relation to terrain variables.

Electrical conductivity profiling allows definition of the hydrology of glacier boreholes occupied by contrasting water types. An inexpensive, robust conductivity profiling system is described that allows detailed description of borehole hydrostratigraphy with reasonable reproducibility. Field dato demonstrate the need to distinguish between bottom water in boreholes and basal water in drainage systems at the glacier bed.

Glaciological experiments have been carried out at Dôme du Goûter (4300 m a.s.l.), Mont Blanc, in order to understand the flow of firn/ice in this high-altitude Alpine glacierized area. Accumulation measurements from stakes show a very strong spatial variability and an unusual feature of mass-balance fluctuations for the Alps, i.e. the snow accumulation does not show any seasonal patterns. Measured vertical velocities which should match with long-term mean mass balance are consistent with observed accumulations. Therefore, the measurement of vertical velocities seems a good way of quickly obtaining reliable mean accumulation values for several decades in such a region.

A simple flow model can be used to determine the main flowlines of the glacier and to propose snow/ice age of core samples from the two boreholes drilled down tο the bedrock in June 1994. These results coincide with radioactivity measurements made to identify the well-known radioactive snow layers of 1963 and 1986. We can hope to obtain ice samples 55–60 years old about 20 or 30 m above the bedrock (110 m deep). Below, the deformation of the ice layers is loo great to be dated accurately.

In order to study, in situ, the rheology of a deforming subglacial till, various instruments were emplaced in till beneath Storglaciären, Sweden. Boreholes were used to gain access to the till beneath about 100 m of ice. Tiltmeters provided an estimate of the shear strain rate in the till. Two other instruments yielded measures of till strength. In addition, water pressures were recorded in boreholes and in the till, a computer-controlled distance meter provided an effectively continuous record of the surface velocity and data from frequent surveys of a stake network were used to estimate the mean basal drag, based on a force-balance calculation.

Tilt rates varied directly with effective pressure, so decreases in water pressure apparently increased the coupling between the glacier and the bed. Surface speed was either out of phase with tilt or varied independently of tilt. Thus, increases in speed were apparently a consequence either of longitudinal coupling or of reduced coupling between the glacier and the bed; they were not a result of till deformation! Till strength varied directly with effective pressure, which is consistent with it being a Mohr – Coulomb, or frictional material. The devices measuring till strength are presumed to have been pulled through the till at a speed that varied in phase with the surface speed but till strength did not vary systematically with surface speed. This implies that the residual strength of the till is insensitive to strain rate. Thus, the appropriate constitutive equation for till rheology may be of the form:

where k is a constant. This is consistent with experimental data reported in the geotechnical literature.

We have analyzed the flow of polythermal McCall Glacier in Arctic Alaska. Using measurements of surface velocity from the 1970s and 1990s, together with measurements of ice thickness and surface slope, we have investigated both the present flow and seasonal and long-term flow variations. Our analysis of the present flow reveals that (i) longitudinal stress coupling is important along the entire length of the glacier, and (ii) there is significant basal sliding beneath a 2 km long section of the lower glacier. This sliding exists year-round and it accounts for more than 70% of the total motion there. We have developed a numerical model which shows that such a sliding anomaly causes an asymmetric decrease in ice thickness. Accompanying this decrease in thickness is a decrease in surface slope at the center of the anomaly and an increase in slope up-glacier from it. Both effects are reflected in the observed surface profile of McCall Glacier.The longitudinal stress-coupling length of McCall Glacier is three times the ice thickness, almost twice that typical of temperate glaciers. This is a direct effect of lower strain rates, which themselves are associated with the smaller mass-balance gradients of Arctic and continental glaciers. Long-term variations in surface velocity between the 1970s and 1990s are explained solely by the effects of changes in glacier geometry on the deformational flow contribution. This means that long-term variations in the spatial patterns of longitudinal stresses and basal sliding must have been small. Seasonally, Velocities reach their annual minimum in spring and increase during the short summer nick season by up to 75% above mean winter values. However, the extra motion associated with the period of elevated velocities is only about 5% of the total annual motion. The speed-up is due to an increase in basal sliding. This implies that most of the glacier bed is at the melting point. The zone a affected by the melt-season speed-up extends well up-glacier of any moulins or other obvious sources for melt water at the bed.

A physics-based snow model has been calibrated using data collected at Halley Bay, Antarctica, during the International Geophysical Year. Variations in snow temperature and density are well-simulated using values for the model parameters within the range reported from other polar field experiments. The effect of uncertainty in the parameter values on the accuracy of the predictions is no greater than the effect of instrumental error in the input data. Thus, this model can be used with parameters determined a priori rather than by optimization. The model has been validated using an independent data set from Halley Bay and then used to estimate 10 m temperatures on the Antarctic Peninsula plateau over the last half-century.

Using analytical and numerical techniques, a two-dimensional (2-D) map-plane model and a 2-D flowline model are utilized to elucidate the horizontal and vertical ice deformation at the confluence of two glaciers. For a perfectly symmetrical confluence, the junction point of the two tributaries can be modeled as a no-slip/free-slip transition. A strongly localized surface depression develops around the junction point, accompanied by two broadly elevated zones positioned close to the margins of the tributaries facing the junction point. The confluence center line is subjected to horizontal longitudinal extension and a transverse compression. The compression generally exceeds the concomitant longitudinal extension in magnitude. Depth-integrated vertical strain rates along the center line are positive (extension), but the strain-rate variation with depth depends critically on the type of basal boundary conditions at the glacier bed. For a no-slip boundary condition, vertical strain rates change from positive at the surface to negative close to the base, whereas for a free-slip boundary condition (perfect sliding) vertical strain rates are positive throughout the depth. These theoretical results are compared with field measurements from Unteraargletscher, Bernese Alps, Switzerland.