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.

The pattern of horizontal strain rate in an ice sheet is discussed from a topological point of view. In a circularly symmetric ice sheet, the isotropic point for strain rate at its centre is degenerate and structurally unstable. On perturbation the degenerate point splits into two elementary isotropic points, each of which has the lemon pattern for the trajectories of principal strain rate. Contour maps of principal strain-rate values are presented which show the details of the splitting.

Researchers have analyzed various properties of drumlins within individual drumlin fields in order to provide evidence to help in identifying the processes involved in drumlin formation. One property which has been examined is the spatial distribution of drumlins within a field. Traditionally, in such endeavours the individual drumlins have been represented as points and their distribution examined using techniques of point-pattern analysis. We suggest that not only is such a representation inappropriate at this scale, it also introduces statistical bias which makes the results of such analyses questionable. Consequently, we propose an alternative approach which involves representing individual drumlins as areal phenomena and considering their pattern as a two-phase mosaic. The advantages of such an approach are discussed and it is illustrated by applying it to two different drumlin fields.

During the summer of 1983 a 2 kW array of solar voltaic panels was used to power a drill which collected two cores of 154 m and 163 m length to bedrock on the Quelccaya ice cap in Peru. The operation and performance of this array are discussed, considering the need for future requirements in remote pristine areas of the world.

A 198.8 m deep borehole was drilled through ice to subglacial bedrock in the northwestern marginal part of Princess Elizabeth Land, ~12 km south of Zhongshan Station, in January–February 2019. Three years later, in February 2022, the borehole temperature profile was measured, and the geothermal heat flow (GHF) was estimated using a 1-D time-dependent energy-balance equation. For a depth corresponding to the base of the ice sheet, the GHF was calculated as 72.6 ± 2.3 mW m−2 and temperature −4.53 ± 0.27°C. The regional averages estimated for this area based, generally, on tectonic setting vary from 55 to 66 mW m−2. A higher GHF is interpreted to originate mostly from the occurrence of metamorphic complexes intruded by heat-producing elements in the subglacial bedrock below the drill site.

Surface height changes above three previously undetected subglacial lakes in northeastern Greenland are documented using CryoSat, DEMs and ICESat-2. Between 7 February and 6 March 2012, the central ice region (22.6 km2) above the largest lake dropped by ~37 m followed by a further drop of 12 m in the following 29 days. This implies a subglacial water outflow, or jökulhlaup, of at least 1 km3 at rates of hundreds of cubic meters per second. A comparable outflow occurred again between 23 July and 15 September 2019, with smaller outflows in the fall of 2014 and 2016. In contrast, a second smaller subglacial lake at a higher elevation had two subglacial outbursts of ~0.3 km3 in 2012 and 2019 but the lake filling was gradual and not strongly seasonal or episodic. Water remained in both lakes after the outflows but this may not be the case for the third smallest and lowest subglacial lake. While there appears to be some hydrological link between the three lakes, the flux of water moving under the ice in this area appears to be larger than would be expected from local summer melt. However, the source of the excess water remains uncertain.

Equations are derived, using a total potential-energy formulation, which predict the wavelength of the dominant wave pattern of a flowing snow slab. Account is taken of the visco-elastic properties of an assumed surface layer of snow which overlays a distinct visco-elastic foundation layer of snow. The predicted wave pattern is recognized as a precursory mechanism which influences the characteristics of the sawtooth flank fracture pattern that may remain following a snow avalanche, particularly on broad, uniform slopes. The parameters that influence the wave pattern are determined by an order-of-magnitu de reduction of the terms in the governing differential equation for visco-elastic slab response.

The hypothesis that ice-sheet evolution is only controlled by the long-term non-Newtonian viscous behavior of ice has been challenged by observations indicating that effects like brittle failure, stick-slip sliding, tides and wave action may affect ice-sheet evolution on sub-daily timescales. Over these timescales, the quasi-static-creep approximation is no longer appropriate and elastic effects become important. Simulating elastic effects in ice-sheet models over relevant timescales, however, remains challenging. Here, we show that by including a visco-elastic rheology and reintroducing the oft neglected acceleration term back into the ice-sheet stress balance, we can create a visco-elastic system where the velocity is locally determined and information propagates at the elastic wave speed. Crucially, the elastic wave speed can be treated like an adjustable parameter and set to any value to reproduce a range of phenomena, provided the wave speed is large compared to the viscous velocity. We illustrate the system using three examples. The first two examples demonstrate that the system converges to the steady-state viscous and elastic limits. The third example examines ice-shelf rifting and iceberg calving. This final example hints at the utility of the visco-elastic formulation in treating both long-term evolution and short-term environmental effects.

A melting probe system has been gerveloped which can be lowered down to 400 m in an ice bore hole of 135-165 mm diameter. At the gersired gerpth, a section of the bore hole is isolated and evacuated. Afterwards several tons of ice are melted under vacuum with an electrical heater. The inclusions which are principally gaseous, may be collected both during or after the melting procedure. The application of this system is mainly in the field of dating polar ice by radio-active isotope analysis.

An interacting continua framework is adopted to model a dry snow park, which is viewed as a three-constituent mixture composed of an ice matrix whose pore space is occupied by water vapour and dry air. We focus on the response of a one-dimensional vertical snowpack to changes in pressure and temperature at its surface. The time-scale of the surface forcing is assumed to be much longer than the time-scale for thermal transfers and phase change to take place. The constituents are, therefore, in thermal equilibrium with a common temperature Τ which is governed by a single bulk-energy balance. In addition, each constituent satisfies a mass and momentum balance. The constitutive postulates and external prescriptions necessary to close the system of equations are discussed in detail. Non-dimensional variables are then introduced formally to draw out the major balances in the equations and construct a reduced system that accurately models the dominant features in the snowpack. It is shown how the effects of phase change enter the leading-order balance. An iterative procedure is constructed to solve the system. Illustrations for the case of a sinusoidal annual temperature gradient imposed at the surface are presented.

Numerical methods based on quadrilateral finite elements have been developed for calculating distributions of velocity and temperature in polar ice sheets in which horizontal gradients transverse to the flow direction are negligible. The calculation of the velocity field is based on a variational principle equivalent to the differential equations governing incompressible creeping flow. Glen’s flow law relating effective strain-rate ε̇ and shear stress τ by ε̇ = (τ/B)n is assumed, with the flow law parameter B varying from element to element depending on temperature and structure. As boundary conditions, stress may be specified on part of the boundary, in practice usually the upper free surface, and velocity on the rest. For calculation of the steady-state temperature distribution we use Galerkin’s method to develop an integral condition from the differential equations. The calculation includes all contributions from vertical and horizontal conduction and advection and from internal heat generation. Imposed boundary conditions are the temperature distribution on the upper surface and the heat flux elsewhere

For certain simple geometries, the flow calculation has been tested against the analytical solution of Nye (1957), and the temperature calculation against analytical solutions of Robin (1955) and Budd (1969), with excellent results.

The programs have been used to calculate velocity and temperature distributions in parts of the Barnes Ice Cap where extensive surface and bore-hole surveys provide information on actual values. The predicted velocities are in good agreement with measured velocities if the flow-law parameter B is assumed to decrease down-glacier from the divide to a point about 2 km above the equilibrium line, and then remain constant nearly to the margin. These variations are consistent with observed and inferred changes in fabric from fine ice with random c-axis orientations to coarser ice with single- or multiple-maximum fabrics. In the wedge of fine-grained deformed superimposed ice at the margin, B increases again.

Calculated and measured temperature distributions do not agree well if measured velocities and surface temperatures are used in the model. The measured temperature profiles apparently reflect a recent climatic warming which is not incorporated into the finite-element model. These profiles also appear to be adjusted to a vertical velocity distribution which is more consistent with that required for a steady-state profile than the present vertical velocity distribution.

All available mean annual accumulation data on the Greenland ice sheet (excluding the Thule peninsula) have been collected and analyzed using multiple regression techniques to develop equations capable of predicting mean annual accumulation. The analysis was carried out for north Greenland, south Greenland, and for the transition zone between the two major regions. The resulting equations show that mean annual accumulation can be predicted from the independent parameters latitude, longitude and elevation. The patterns of accumulation are shown in a series of isohyetal (contours of accumulation in terms of water) maps. The major feature shown is a well defined asymmetry in accumulation; a pronounced east-slope maximum in south Greenland and an equally pronounced west-slope maximum in north Greenland. Poleward of lat. 69° N., isohyets decrease in elevation to the north. Mean annual accumulation ranges from >90 g./cm.2 in south-east Greenland to <15 g./cm.2 in north-east Greenland. A brief discussion of mass balance estimates of the Greenland ice sheet and of the relevance of this study to them is included.

Eight different ice budgets for the Antarctic Ice Sheet are examined. Five of these budgets call for rates of increase of the ice which are in surprisingly good agreement considering the wide dispersion of individual components of the budgets. The observed rise in sea-level of the world’s oceans would appear to contradict the removal of water required to nourish the Antarctic Ice Sheet at the claimed rates. The thermal expansion of oceanic columns, caused by “climatic” warming of the oceans, has been invoked to resolve this contradiction but it appears that this is not large enough judging from the 30 yr. difference in water temperatures measured by the Meteor and the Crawford in two profiles across the tropical Atlantic Ocean.

Changes in iceberg calving fluxes and oceanographic conditions around Antarctica have likely influenced the spatial and temporal distribution of iceberg fresh water fluxes to the surrounding ocean basins. However, Antarctic iceberg melt rate estimates have been limited to very large icebergs in the open ocean. Here we use a remote-sensing approach to estimate iceberg melt rates from 2011 to 2022 for 15 study sites around Antarctica. Melt rates generally increase with iceberg draft and follow large-scale variations in ocean temperature: maximum melt rates for the western peninsula, western ice sheet, eastern ice sheet and eastern peninsula are ~50, ~40, ~5 and ~5 m a−1, respectively. Iceberg melt sensitivity to thermal forcing varies widely, with a best-estimate increase in melting of ~24 m a−1°C−1 and range from near-zero to ~100 m a−1°C−1. Variations in water shear likely contribute to the apparent spread in thermal forcing sensitivity across sites. Although the sensitivity of iceberg melt rates to water shear prevents the use of melt rates as a proxy to infer coastal water mass temperature variability, additional coastal iceberg melt observations will likely improve models of Southern Ocean fresh water fluxes and have potential for subglacial discharge plume mapping.

The results of 66 Schlumberger geoelectric soundings on first-year sea ice are analysed to obtain average values of d.c. electrical resistivity both parallel ρ1 and perpendicular ρp to the long brine cell direction. This analysis yields ρ1 = 104 Ω m, 80 Ω m, 45 Ω m, and ρp = 298 Ω m, 230 Ω m, 129 Ω m for brine volumes νb of 40‰, 67‰, and 82‰ respectively. The observed dependence of ρ1 on νb is used in conjunction with a mixing formula for the electrical resistivity of a two-phase heterogeneous system to arrive at values of “average” brine cell lengths l for relatively warm sea ice. This treatment yields l ≈ 1.7 cm for 40‰ ≤νb≤ 70‰ with a rapid extension of brine cell lengths for brine volumes above c. 70‰.

The accumulation of snow in terrain depressions was studied in an alpine basin in central Colorado. Snow fences and a jet roof were built up-wind of several natural catchments to see if such barriers could be used in combination with terrain features to produce snow fields that would persist until late summer. At three of the six test sites, fences increased snow depths appreciably and the snow fields persisted longer than usual. At the other test sites snow depths were increased close behind the fences but were decreased farther down-wind with no net increase in the amount of snow caught.