Recent mathematical models treat a natural snow-pack as a mixture body consisting of solid ice grains, liquid water, and a gas made up of air and water vapour. Such a model requires two independent constitutive equations for the two independent volume fractions. However, so far only one equation, a power law relating the liquid-water content to capillary pressure, has been suggested, by analogy with the so-called “characteristic” equation for liquid water in soils. Experimental data from drainage tests on snow columns may be used to determine the characteristic equation for snow for relatively high water contents. However, the experimental method is not valid when water exists in isolated inclusions in the snow, i.e. in the pendular regime. In this paper a theoretical method is used to derive two independent volume-fraction laws for snow in the pendular regime.

Snow-avalanche speeds, run-out distances, and the concepts from dense granular flows are combined in a model for prediction of speeds along the incline. Field measurements indicate that speeds and run-out distances are nearly independent of path steepness once a length is chosen to scale them. Application of granular-flow concepts explains these results. The most important feature of the model (and the speed data) is the steep gradient of speeds in the run-out zone. These results emphasize the need for high precision in run-out prediction when construction or defences are contemplated.

We present data on ice texture, salinity, and δ18O obtained from identical sections of ice cores during the Winter Weddell Sea Project 1986 on RV Polarstern from July through August 1986, in the longitude range between 5°W. and 7°E. We find no uniquely definable relationship between δ18O values and ice texture in a particular section. However, most of the snow ice as well as some sections of frazil ice are found to have negative δ18O concentrations. This is due to varying degrees of admixtures of meteoric ice (snow) and sea-water during formation of snow ice. In contrast to common assumptions, our results seem to indicate that a snow cover contributes positively to sea-ice growth rather than slowing down the overall growth rate. Based on a simple model, we have estimated the contributions of meteoric ice (mean of 3 ± 3%) and the combined meteoric ice/sea-water fraction (a minimum of 7 ± 6%) to the total ice thickness for the majority of the sampled floes. Although this is only a moderate contribution to the overall mass balance, in the absence of congelation growth it nevertheless enhances ice growth in general. This hypothesis is independently supported by our snow- and ice-thickness data (Wadhams and others, 1987), which demonstrate that the depression of the snow/ice interface below the water line (i.e. a negative freeboard) and the formation of snow ice is a common occurrence in the Weddell Sea. Therefore, we hypothesize that the major part of the observed apparent increase in ice thickness between our inbound and outbound tracks of WWSP’86 may not be derived from “regular”, thermodynamically driven congelation growth, but rather from the snow-ice component in floes of the Weddell Sea.

Since its inception in 1975, the Northwest Avalanche Center (NWAC) has developed and produced micro- and mesoscale weather forecasts to support avalanche forecast and control needs for the Olympic and Cascades Mountains of Washington and Oregon, U.S.A. This paper describes NWAC’s array of data, observational results, and analytical techniques that make “avalanche weather” forecasting possible. In addition, NWAC’s operational program and the general terrain and climate of the area are described. A sample forecast is also included.

Ice flow along the 20 km long strain network up-stream of the Dye 3 bore hole in Greenland is studied in detail. By solving the force-balance equations and using selected flow laws, stresses and strain-rates are calculated throughout the section of the ice sheet. The validity of the results is evaluated by comparison with the velocity profile derived from bore-hole-tilting measurements, and with observed surface strain-rates. A number of constitutive relations are tried and most predict a velocity profile at the bore-hole site that is in good agreement with that observed, if appropriate enhancement factors are used. However, there are major discrepancies between modelled and measured surface strain-rates. Use of Nye’s generalization of Glen’s flow law, or an anisotropic constitutive relation, requires unrealistically large along-flow variations in the enhancement factor. Inclusion of normal stress effects can lead to much better agreement, but it is possible that other processes, such as dynamic recrystallization or primary creep, should be included in the constitutive relation of polar ice.

Measured subglacial water pressures are frequently higher than theoretical values calculated by assuming that subglacial conduits are straight and either circular or semi-circular in shape. While this may be attributed to errors in the estimates of conduit roughness or ice viscosity, we suggest here an alternative explanation: namely, that the conduits are actually broad and low rather than semi-circular. Good agreement between measured and calculated pressures can be obtained by assuming that the cross-sectional shape of conduits resembles the space between the arc of a circle and its chord. The angle subtended by the arc, θ, is treated as an adjustable parameter. In four cases studied, θ ranged from 2° to 36°.

The glaciological investigations on Rhonegletscher were started in 1874. The mass-balance data measured during 1884/85–1908/09 and during 1979/80–1981/82 are presented. Two methods are used for estimating the mass changes. During 1882/83–1968/69, the cumulative specific net balance is −24 ± 6 m w.e. at the 90% confidence level by the regression model of annual mass balance, annual precipitation, and summer air temperature (the PT model), while the thickness change revealed by the maps is −23 ± 5 m w.e. The cumulative specific net balance during 1882/83–1986/87 is −26 ± 6 m w.e. at the 90% confidence level.

The study shows that Rhonegletscher generally experienced mass loss, especially during the periods from the late 1920s through the early 1960s with some short periods of positive balance. The glacier tongue retreated by 970 m during 1882–1986, that is, from 1780 ma.s.l. (1882) to 2130 ma.s.1. (1986). During 1882–1969, the ice-covered area decreased by 4.37 km2 and the volume by 4.71 × 108 m3.

The PT models of Rhonegletscher and other alpine glaciers suggest that the contribution of the temperature changes to the mass balance is of more importance than that of the precipitation changes. The great mass loss reflects the climatic warming after the end of the Little Ice Age, with the warmest period occurring around the 1940s in this region.

To date, the temperatures of 22 glaciers in China have been measured. It is suggested that the minimum temperature at the base of the active layer in the upper part of the ablation area (Tmin) be used as a characteristic temperature and compared with mean annual air temperature (Ta). The temperature distribution is discussed for various glaciers. Polar-type glaciers are characterized by low temperatures with Tmin < −10°C, Tmin close to Tv and a cold base in general; sub-polar-type glaciers with −10°C < Tmin < −1.0°C, Tmin higher than Tv and a melting base are usually located beneath the middle of the ablation area; and temperate-type glaciers with Tmin < −1.0°C, certainly higher than Ta and a sub-freezing near-surface layer in the ablation area all the year round, because the snow cover is thinner in winter.

Results of pollen analysis of a large firn sample from Dye 3, southern Greenland, are reported. The sample was divided into three sections: all dominated by pine, birch, and ragweed pollen. Pollen concentration for the entire sample is 15 pollen grains per litre and the annual pollen deposition rate has been estimated at approximately 0.73 grains cm−2 year−1 (7300 grains m−2 a−1). Although these values are slightly lower than expected, considering the relatively southern latitude of the site, they are within the range of values obtained from other Arctic ice caps.

A small ice-dammed lake near Søndre Strømfjord, West Greenland, drained suddenly during the night of 15–16 July 1988. This drainage was observed from within the lake basin near the tunnel mouth. The drainage had four main effects: the collapse of adjacent moraine ridges; the shearing of ice around the tunnel mouth; rapid incision of the lake bed; and the transport of sediment from the lake basin into the glacier. All of the above were confined to a period of 15–30 min following the exposure of a circular tunnel c. 6 m in diameter.

Coefficients of thermal linear expansion were determined for sea ice using a Michelson interferometer. Over a temperature range of −4 °to −15 °C, the coefficients varied from 45 ×10−6 to 54×10−6 °C−1 for ice with a salinity of 2 ppt, and from 33 ×10−6 to 53 ×10−6 °C−1 for ice with a salinity of 4 ppt. Initially, warming the sea ice resulted in coefficients that were the same as those for fresh-water ice, within the limits of experimental error. Subsequent sea-ice cooling resulted in coefficients that were initially lower than those for fresh-water ice, but that asymptotically approached the coefficient values for fresh-water ice at colder temperatures. On the second warming and cooling cycle, the coefficients of thermal linear expansion exhibited hysteresis and a decrease in magnitudes. We have also shown that Pettersson’s (1883) and Malmgren’s (1927) measurements of the thermal volume expansion of sea ice were the result of phase transitions that caused brine expulsion, when air-free sea ice was cooled, and internal porosity increases, when sea ice was warmed.

Our results indicate that Petterson’s (1883) and Malmgren’s (1927) measurements of the thermal volume expansion of sea ice are in error. Consequently, theoretical descriptions based on their results are incorrect (Anderson, 1960; Zubov and Savelyev (given in Doronin and Kheisin (1977)); Doronin and Kheisin, 1977). Our results for the initial sea-ice warming cycle do agree with Cox’s (1983) analysis.

Daily ice ablation on two outlet glaciers from the Greenland ice sheet, Nordbogletscher (1979–83) and Qamanârssûp sermia (1980–86), is related to air temperature by a linear regression equation. Analysis of this ablation-temperature equation with the help of a simple energy-balance model shows that sensible-heat flux has the greatest temperature response and accounts for about one-half of the temperature response of ablation. Net radiation accounts for about one-quarter of the temperature response of ablation, and latent-heat flux and errors account for the remainder. The temperature response of sensible-heat flux at QQamanârssûp sermia is greater than at Nordbogletscher mainly due to higher average wind speeds. The association of high winds with high temperatures during Föhn events further increases sensible-heat flux. The energy-balance model shows that ablation from a snow surface is only about half that from an ice surface at the same air temperature.

Airborne 60 MHz radio echo-sounding data were collected over 250 km of flight track from an ice cap (Kvitøyjøkulen) on Kvitøya in north-eastern Svalbard. These were combined with Landsat imagery to provide ice-surface and bed topographic information and inferences about the thermal and climatic conditions on the ice cap. Quantitative analysis of radio-echo strength measurements and the existence of offshore plumes of sediment-laden melt water indicate significant basal melting and a warmer thermal regime than would be expected from the geographical location of the ice cap. Analysis of the dielectric absorption of radio waves by the ice and data from a recently recovered ice core from a neighbouring ice cap (Austfonna) suggest considerable anthropogenic contamination of the precipitation falling on Kvitøya, most probably originating from Eurasia.

The lower 80 km of the fast-moving Jakobshavns Isbræ, West Greenland, is subject to significant melting during the summer season. The melt water drains into large supraglacial rivers which pour into moulins or feed into beautiful supraglacial lakes, some of which are observed to drain periodically. Except for a few streams that drain directly off the margins of the ice sheet within the drainage basin of this glacier, the fate of this melt water is unknown. However, a localized upwelling of highly turbid water is often observed during the melt season in the fjord adjacent Io the terminal cliff of the glacier, indicating that water from some source does move along the glacier bed.

As part of an investigation on the mechanisms of rapid flow on Jakobshavns Isbræ, measurements of surface velocity at several (∼25) locations along the ice stream at and below the equilibrium line were made in order to investigate the effects of this seasonally varying input of melt water on the speed of the glacier.

No significant seasonal variation in speed was found at any location. This indicates that, unlike many other sub-polar and temperate glaciers, surface melt-water production does not affect the motion of this glacier on a seasonal basis, and, thus, does not cause a significant temporal variation in basal sliding. This finding has important ramifications on the mechanisms of flow for this ice stream.

Data for daily ice ablation on two outlets from the Greenland ice sheet, Nordbogletscher (1979–83) and Qamanârssûp sermia (1980–86), are used to test a simple energy-balance model which calculates ablation from climate data. The mean errors of the model are only −1.1 and −1.3 mm water d−1 for Nordbogletscher (14 months) and Qamanârssûp sermia (21 months), respectively, with standard deviations of ±13.6 and ±18.9 mm water d−1 for calculating daily ablation. The larger error for Qamanârssûp sermia may be due to variations in ice albedo but the model also underestimates ablation during Föhn events.

According to the model, radiation accounts for about two-thirds of mean ablation for June-August at the two sites, while turbulent fluxes account for about one-third. The average ablation rate is higher at Qamanârssûp sermia than at Nordbogletscher because both sensible-heat flux and short-wave radiation are higher.

During the summers of 1987 and 1988, 15 dye-tracer tests from a total of eight injection points were conducted in the ablation area of Midtdalsbreen, a northern outlet of Hardangerjokulen, southern Norway. The spatial and temporal patterns of water discharge, shapes of the dye-return curves, through-flow velocities, dye-recovery rates, dispersivities, and velocity/discharge relationships suggest the existence of distinct catchments beneath the eastern and western halves of the glacier which are characterized by different types of drainage sytem. Experiments on the eastern side were associated with high melt-water discharges and produced short-lived and highly peaked dye-return curves, fast through-flow velocities, high dye-recovery rates, low dispersivity values which decreased through the melt season, and a velocity/discharge relationship with an exponent of 1.0. Experiments on the western side were associated with low melt-water discharges and produced flat, extended dye-return curves which often displayed secondary peaks, slow through-flow velocities, low dye-recovery rates, high dispersivity values which increased during the melt season, and a velocity/discharge relationship with an exponent of 0.6. Comparison of observed through-flow velocities with values calculated theoretically using various hypothetical drainage-system structures suggests that water flows in a major sinuous conduit beneath the eastern half of the glacier and in a system of linked cavities beneath the western half. A model for the seasonal evolution of the whole drainage network is postulated which has important implications for temporal variations in subglacial water pressures and glacier-sliding velocity.

Appropriate expressions describing the motion of powder-snow avalanches are derived. The model consists of four equations, i.e. the conservation equations of fluid mass, snow-particle mass, momentum of the cloud, and kinetic energy of the turbulence. Insofar as the density difference between the avalanche and the ambient air becomes rather large compared with the density of the ambient air, the Boussinesq approximation, which is typically used to analyze density currents, cannot be adopted in the present case. As opposed to previous models, the total buoyancy of a powder-snow avalanche is allowed to change freely via erosion from and deposition on to a static snow layer on a slope. In the model, the snow-particle entrainment rate from the slope is directly linked to the level of turbulence.

A discontinuous, large-scale powder-snow avalanche occurred on 26 January 1986 near Maseguchi, Niigata Prefecture, Japan. The avalanche appears to have had a dense core at its base. The present model is employed to simulate that part of the avalanche above any dense core. The depth of the layer of fresh snow is considered to be an important parameter in the model. The larger the depth of fresh snow, the larger is the concentration of snow attained in the avalanche, and the faster its speed. It is seen that the model provides a reasonable description of the powder-snow avalanche generated near Maseguchi. In particular, the model prediction that a powder-snow avalanche strong enough to reach Maseguchi requires a depth of fresh snow of at least 2 m is in agreement with the observed depth just before the event.