The mass balance and sensitivity of calculated mass balance to uncertainties in the data and in the model for the variation of ice velocity with depth are addressed, using data from the EGIG transect and from the OSU transect in south Greenland (Drew and Whillans, 1984). The calculation uses a non-steady continuity model with allowances for three-dimensional flow and horizontal velocity variation with depth. Depth variation in horizontal velocity is obtained, using the constitutive relation for ice with calculated temperature profiles and with full allowance for longitudinal stresses and enhancement of flow due to ice anistrophy and texture. Separate calculations are made for different thickening or thinning rates, until a match between observed and calculated surface velocities is obtained.

For the EGIG transect, our mass-balance results are in the range reported by Mälzer and Seckel (1975) and Bindschadler (1984). Results for the OSU transect, just south of the Arctic Circle on the south dome, are also reported.

Of particular interest is the sensitivity study, which is designed to determine which aspects of the data and flow behavior are most critical to the calculations. Data that are comparatively well-constrained are flow-line definition, surface velocity and thickness. The flow lines and lateral spreading are obtained from satellite radar altimetry (Zwally and others, 1983) and checked against velocity data along the OSU profile. Thicknesses are from aerial radar sounding (Overgaard, personal communication). Surface velocities along the EGIG transect are corrected in a manner similar to that suggested by Robin (1983, figure 2.17b) and possible errors are not critical. Along the OSU transect the surface velocities are well-determined by Doppler satellite tracking in short-arc translocation mode.

Accumulation rates are not well-determined and show substantial scatter for reasons that are not understood. Along the OSU transect, accumulation rates were obtained by augering for the nuclear bomb horizons. As reported earlier (Mock, 1967), the accumulation rates in this region show no clear pattern with elevation or slope. Similar, but less severe, problems exist in the EGIG area. The lack of a good model describing the geographic variation in accumulation rate results in calculated surface velocity uncertainties of 9% for the OSU and 6% for the EGIG transect.

The calculated results are comparatively insensitive to parameters affecting the temperature profile. This is because, in this model, the mean velocity is determined by continuity and temperature affects only the ratio of horizontal velocity at a given depth to the mean velocity for the entire profile.

Longitudinal stresses are included because they affect the viscosity through the effective shear stress. Neglecting this would lead to a 30% error in calculated surface velocity near the ice divide and about 6% away from the divide. Provided longitudinal stresses are included, uncertainties in these stresses are not critical.

Enhancement factors are, however, important. Most authors believe that ice fabric, texture, and impurity content can affect strain rates by 100% to 1200% (Shoji and Langway, 1984). As with the temperature profile, this problem does not affect calculated mean velocities, which are based on continuity, but it does affect the ratio of surface to mean velocity. Enhancement factors are more critical than temperature uncertainties and therefore failure to include depth-variable flow enhancement alters calculated surface velocities by 5 to 10%.

In summary, the mass balance along two transects has been investigated by comparing measured and calculated surface velocities. The most critical problems are (1) understanding the geographic distribution in accumulation rate and (2) correctly allowing for enhanced shearing due to structural variations with depth.

To confirm radio-echo layering due to changes in density variations and in specific conductivity in the amount of acid impurities, radio-echo sounding surveys with impulse radar technique were carried out. The continuous and strong internal layers of the snow covers were found to give good correlation with strong peaks of specific conductivity of melted samples from ice cores, rather than the differences in density fluctuations between depositional layers. Measured high conductivity due to acidity variations in ice cores may be correlated with recent volcanic eruptions in the northern hemisphere, and in the Scotia Arc and the South Sandwich Islands.

Two models simulating snow avalanches impacting retaining dams at oblique angles of incidence are presented.

First, a lumped-mass model applying the Voellmy-Perla equation is used to calculate the path of the centre-of-mass along the side of a retaining dam.

Secondly, a one-dimensional continuum model, applying depth-integrated equations of balance of mass and linear momentum, is expanded to take into account that real avalanche flows are three-dimensional. The centre-line of the avalanche path is determined by the flowing material as it progresses down the channelized avalanche path. The nonlinear constitutive equations comprise viscosity, visco-elasticity and plasticity.

Both models are calibrated by simulations of a registered avalanche following a strongly curved channel. The path and the run-up height of the avalanche on the natural deflecting dam with oblique angle of incidence as calculated by the two models, are compared with the observations made.

Reported are results of incorporating recent snow avalanche processes into hydrodynamic uniform flow equations, used to model motion of snow avalanches. Actual modifications include the relating of dissipative coefficients of the flow model to slab release depth, the representation of the material as a locking fluid, and the mini-segmentation of the avalanche path at low flow speeds in order to numerically accomodate viscous transition and avalanche cessation of motion. The purpose in looking at different formulations of the uniform flow hydrodynamic flow equations is to reduce the variation in the drag coefficients when the theory is applied to different avalanche paths, as compared to what has been previous experience. The model that reduced parameter variation the most was one in which the total drag force decreased in an intermediate velocity range, a mechanism that has had recent experimental verification.

Late Wisconsinan glacial sediments, exposed on Whidbey Island and Camano Island, Puget Sound (Washington State, USA), were deposited in a proglacial shallow marine/outwash environment during northward retreat of the Puget Lobe of the Cordilleran ice sheet. Sediments mainly comprise massive and cross-bedded sand and gravels, and rhythmically-bedded clay and silt/fine sand couplets, interbedded with diamictons that were deposited by a range of mass flows of different viscosities. Although sediment stratigraphy and ice advance–retreat patterns are well established for the Puget Lobe, brittle and ductile deformation structures within, and separating, these sediment units are less well understood. These structures record the nature of ice–bed interactions taking place in subglacial and proglacial environments. This study examines evidence for these processes and environments. Key deformation structures identified include open to overturned folds, normal and reverse faults, clastic dikes and hydrofractures and passive-loading structures. Evidence for coeval development of ductile and brittle deformation structures shows the close relationship between porewater changes, sediment rheology and sediment system responses to changes in strain caused by ice–bed interactions.

Mapping of areas exposed to avalanche hazard for the Norwegian Army was started by the Norwegian Geotechnical Institute in 1986. The background to this mapping is that large-scale military exercises are held annually in northern Norway, in terrain where there is a high danger of avalanche activity. Avalanche areas are divided into two zones: potential starting zones, and potential run-out zones. All potential avalanche areas are indicated on maps, and mapping is carried out by computer using a terrain model and digital maps. An interactive graphic work station is used to outline danger areas. Starting and run-out zones are identified by using terrain parameters which may be extracted from digital maps. The usual scale of the avalanche maps is 1 : 50 000, with 20 m contour intervals.

A fluid-dynamical model of powder-snow avalanches is developed which takes into account three-dimensional topography and can compute an avalanche’s running course. The model also predicts the variations of height, speed and concentration of snow particles in the avalanche, as well as the level of turbulence. Application of the model to the Maseguchi avalanche, which occurred in 1986 at Niigata, Japan, shows it can provide reasonable prediction of the running course, height and speed of an avalanche.

The concentration and size distribution of water insoluble microparticles were measured in 2 332 snow and firn samples from (a) two sites on the Antarctic Peninsula, (b) the Byrd station strain network, West Antarctica, (c) the Q-13 and base camp sites on the Ross Ice Shelf, and (d) the South Pole and Dome C sites in East Antarctica. These near-surface microparticle studies indicate that, while the number of particles per unit volume of sample remains fairly uniform from site to site, the annual particle accumulation is greatest at locations nearest the coast and decreases rapidly with distance inland. The relationship between particle accumulation and distance from the coast is analogous to a relationship between snow accumulation and distance from the coast. Ten times more particles are deposited annually at stations within 50 km of the coast than at the South Pole and Dome C sites. The size distribution data reveal that, with the possible exception of the Q-13 site, the particulates deposited in Antarctica are well-sorted, indicating little contribution from local sources.

A combination of image-based velocity mapping techniques and finite-element modeling has been used to study a part of the southern shear margin of Ice Stream D, Antarctica. The study area is a region over which the margin shows considerable development morphologically, where a new southern margin is forming in response to an abrupt increase in ice-stream width just upstream of the study area. A series of ice-speed profiles perpendicular to the margin was determined by semiautomated displacement measurements of small ice features in sequential Landsat TM images. Transverse speed gradients ∂u/∂y of these profiles were determined by calculating the slope of a high-order polynomial fit to the speed profiles. Maximum ice speed and ∂u/∂y increase dramatically as the margin develops in the downstream direction, from 420 to 670 mal,and from 0.02 to 0.16 a, respectively. Finite-element modeling of the upstream and downstream profiles suggests that a considerable change occurs in the stiffness of the ice in the marginal zone between the two profiles, and in the stiHness or amount of sliding in the basal layer underlying the margin. Ice in the downstream profile appears to have marginal zones of softer ice in which shear strain is concentrated and uniformly low resistance to deformation in the bed. For the upstream profile, modeling suggests that the ice is not softened near the margin and that the bed is stiffer near the margin. Model-based calculations suggest that the bed shear is responsible for 69% of the resistance to flow in the upstream margin area;this value is 51 % in the downstream area.

An energy-balance climate model designed for coupling to ice-sheet models is presented. Its independent variables are longitude, latitude and time of the year. The model is based on the vertically integrated equations of conservation of energy and humidity. It can predict the vertically averaged temperature. Since it includes a hydrological cycle, it can also diagnose the net fresh-water flux and hence the annual snow budget at the atmosphere–ice-sheet interface. To this end, the model does not require observed precipitation rates. The computational cost is reduced by using an analytically computed Fourier–Legendre representation of daily insolation. For a highly idealized test-case configuration, two simple sensitivity experiments are carried out.

The mechanisms of strong winds associated with snow clouds, and the relationship between strong winds and blowing/drifting snow, were investigated. A snowstorm occurred with a typical L-mode snow band which was generated and organized longitudinally during a continental cold-air outbreak over the Sea of Japan. Doppler radar observations revealed that the snow band consisted of small echo cells arranged along the direction of the snow band. When one of the echo cells passed, blowing/drifting snow was generated and intensified by a snow cloud-induced gust, and the horizontal visibility near the ground surface was significantly decreased. Doppler radar and radiosonde data showed that the gust was due to the cold air outflow (CAO) from the snow clouds. The leading edge of the CAO was about 9 km ahead of the center of the snow cloud and the depth of the CAO was about 600 m near the forward flank of the snow cloud. The CAO was caused by a downdraft at the center of the snow cloud, which was initiated at a height of about 1.3 km and with a velocity in excess of 1 ms−1. The observed CAO speed was explained by the theory of the gravity current.

A relatively simple, three-parameter model is used to simulate the annual precipitation (accumulation) distribution for the Greenland ice sheet and surrounding regions. The three parameters are (1) the flux of relative vorticity at the 500 mbar level (a measure of cyclonic activity), (2) atmospheric moisture content, and (3) surface terrain. The climatological (1946–79) precipitation distribution predicted by the model displays major features of the observed distribution derived from pit studies. However, the model suggests that, due to changes in storm tracks during this period of 33 a, accumulation distribution maps based on pit studies for varying periods of record may not be representative of a true mean for a uniform period of record. The model is then applied to reconstructed ice-age conditions. Compared to present conditions, accumulation reductions of 60¾ or more are indicated for much of the southern half of Greenland; only slight reductions are noted for northern Greenland.

Characteristic growth processes were investigated by measuring cross-sectional areas of ice crystals for four 30 m snow cores drilled in Mizuho Plateau, Antarctica. Considerable difference was found in the growth rate of crystals between a temperature-gradient layer above 6 m depth and an isothermal layer below 10 m depth: the growth rate in the temperature-gradient layer was much larger than that in the isothermal layer. In the isothermal layer, temperature dependence of the growth rate K was expressed by an equation K = K0 exp(−E/RT), where R and T are the gas constant and absolute temperature respectively. The apparent activation energy E is 44.7 kJ mol−1.

On the other hand, in the temperature-gradient layer, the apparent activation energy was as small as 12 kJ mol−1: the difference was explained as due to the temperature gradient. Using the temperature profiles in snow that have been estimated from the meteorological data from several stations, the growth rates in the temperature-gradient layer were calculated. The calculated temperature dependence of the growth rates, taking into consideration vertical flux of water vapor between ice particles caused by the temperature gradient, showed good agreement with measured results. It is concluded that the growth process in the layer above 6 m depth is mainly due to vapor transport under the vertical temperature gradient.

Snowdrift formation has been monitored in the eastern Spanish Pyrenees since 1992 at an experimental study plot at the La Molina ski resort between 2000 and 2400 m. Several instruments were installed to characterize the wind, quantify snow-mass flux, detect snowdnfting episodes and measure the evolution of a natural snowdrift.

This plot is situated within a natural snowdrift and is equipped with measuring instruments such as snow poles, three columns of snow collectors (prismatic boxes) facing the dominant winds and an anemographic station.

During the 4 years of data acquisition, the thickness of the snowdrift has been measured and the snow collectors checked once each week. An active interest has been taken in the relationship between snowdrift development and drifting snow during a wind episode.

The relationship observed between wind, drifting snow and the development of the snowdrift is presented The results show: (1) the amount of snow collected in the snow collectors is related to wind intensity and to the availability and the quality of drifting snow, and (2) wind intensity principally affects the relative location of maximum snowdrift growth rather than controlling the thickness of the snowdrift.

By comparing the evolution of the snowdrift with Tabler’s (1975) model, we observed that it fits with the topographic features of our study area for the three seasons shown.

A time series of satellite passive microwave observations by the Special Sensor Microwave/Imager (SSM/I) instrument, of the Antarctic marginal ice shelves, reveals sharp transitions in the radiometric brightness temperatures at 19 and 37 GHz. These transitions, sometimes occurring over the period of a single day, indicate the onset of surface melting of the ice. Monitoring the day of the onset of melting and the permanent re-freezing will be a measure of rising air temperatures as a result of global warming. The response from a stable ice shelf, the Ronne, where no appreciable melting occurs, is compared with observations from the marginal ice shelves on Antarctic Peninsula. It is observed that the spectral gradient (Tb19 - Tb37) varies as a function of time on a clear annual cycle. It is shown that variations in the spectral gradient arise due both to the temperature profile within the snow and the dielectric effects of a wet surface layer.

Drifting snow creates problems which have practical effects in France in two situations. The first situation is when the result of wind action on snow is to cause accumulation of this snow on mountains, leeward of crests, and consequently to create the potential hazard of avalanche. The second is when the result is to pile up snow in flat regions wherever there are obstacles such as road cuttings and vegetation. This paper focuses on the second type of problem, which affects large areas of central and north-eastern France. We explain how we have chosen our test site, which initial experiments we have conducted in order to assess the general geometrical features which a snow fence must possess in order to function most effectively in collecting snow, and how subsequently we have assessed the properties and costs of different fencing systems.

The equations of motion (continuity and momentum balance) for a dispersed, negatively buoyant particulate of snow entrained in a turbulent airflow contain apparent turbulent forces or turbulent particle buoyancies. These turbulent buoyancies arise from the constitutive assumption that the turbulent fluctuations of the snow phase velocity vector U’s, and the drift snow density ρ’s, are proportional to the deviatoric mean rate of deformation tensor for the airflow.

For an established, discretized airflow regime, the momentum balance equation for the snow phase can be solved by finite difference techniques for the snow particle velocity field. The snow phase continuity equation can then be solved for the drift snow density field.

The solutions for the snow phase equations of motion for a one dimensional airflow adjacent a solid surface show that the theory can reproduce an inertia! snow particle effect. The snow particle decelerates less rapidly than the airflow, resulting in the snow particle having a positive horizontal impact velocity at the solid surface, where air velocity goes to zero.

The solutions for the snow phase equations of motion for mixture flow and subsequent wind-aided snow accumulation on the immediate lee of a model mountain slope show that the theory can reproduce the geometries typical of wind-aided snow accumulation profiles, measured on the lee of mountain slopes.