The relative importance of the principal elements of the thermal balance above snow during a period of melting has been evaluated using recent studies of the turbulent transfer in the boundary layer. Several anomalies in the profiles prove the continuing presence, near to the surface, of a thick layer of air apparently re-heated by the radiative flux. It is shown that the upper surface of this “exchange layer” ought to be considered as the new level for the origin of profiles, and taken as the exchange surface. The importance of nocturnal refreezing has been quantified. Excellent correlations have been found between mean air temperature and total energy balance; they have allowed the establishment of an approximate, non-linear expression for the effective daily ablation of snow as a function of mean air temperature. This relation gives satisfactory results at high and intermediate altitudes, in horizontal uncovered terrain. The measurements were made in the French Alps at 3550 m and in Spain at the latitude of Madrid à 1860 in.

Snow-cover settlement was measured in a dry, annual sub-alpine snow cover in the Colorado Rockies with settlement gages. Settlement viscosities were calculated from the change in gage heights over various periods during the winter and early spring, and the associated overburden over the gages as estimated from density measurements and precipitation records. When adjustments are made for local snow temperature, viscosities are in fair agreement with values found in the literature from similar snow covers, although considerable scatter for a given snow density is found in all sets compared. The viscosity for a given density does not appear to vary systematically with grain size.

Some flutes which occur on the surface of a series of glacio-fluvial sediments at the margin of Blomstrandbreen, north-west Spitsbergen, are described. A section in one has revealed a complex internal structure, in which originally horizontal beds have been folded into an anticline whose axis is normal to the ice margin, and whose structure is related to the morphology of the flute.

Comparison of the observed deformation with the theoretical distribution of stresses around the base of a subglacial tunnel shows that this deformation could have resulted from How under such a stress system. It is considered that these observations support the hypothesis that flutes are formed when unfrozen, water-soaked materials deform subglacially due to the pressure differences which exist in the vicinity of an ice tunnel formed in the lee of some rigid obstruction to ice flow.

A theory of icicle growth is presented. It is shown that icicles elongate as hollow tubes of ice with liquid water trapped inside the tip. A time-dependent computer model based on the theory shows that the growth of an icicle is a complicated process, which is very sensitive to the atmospheric conditions and water flux. The shape and weight of icicles predicted by the model agree well with laboratory data.

Radio echo-sounding surveys of Antarctica and Greenland have revealed extensive layering within the ice. Formulae for the effective reflection coefficient, when viewed by a pulsed radar, are derived for isolated or multiple randomly spaced layers. In the latter case the variation in dielectric constant with depth is described by a vertical autocorrelation function and a standard deviation. Some measurements of the reflection coefficient of layers, and the dielectric absorption of ice are given. The significance of the fading of layer echoes and the possible causes of variations in the dielectric constant are considered and some further investigations are suggested.

It is concluded that the echo strengths found in the Antarctic may be explained by multiple layering, and that the necessary fractional change in the dielectric constant may be as small as 10−4. It is suggested that this change in dielectric constant may be due to differences in orientation of anisotropic ice crystals.

A diagnostic, dynamic/thermodynamic ice-shelf model is applied to the George VI Ice Shelf, situated in the Bellinghausen Sea, Antarctica. The George VI Ice Shelf has a peculiar flow geometry which sets it apart from other ice shelves. Inflow occurs along the two longest, and almost parallel, sides, whereas outflow occurs on the two ice fronts that are relatively short and situated at opposite ends of the ice shelf. Two data sources were used to derive the ice thickness distribution: conventional radioecho sounding from the British Antarctic Survey was combined with thickness inferred from surface elevation obtained by the NASA GLAS satellite system assuming hydrostatic equilibrium. We simulate the present ice flow over the ice shelf that results from the ice thickness distribution, the inflow at the grounding line and the flow rate factor. The high spatial resolution of the ice thickness distribution leads to very detailed simulations. The flow field has some extraordinary elements (e.g. the stagnation point characteristics resulting from the unusual ice-shelf geometry).

Observations made of ice crystals growing on the surface of supercooled water show that they take the form of a composite structure, called surface needles, each of which consists of dendrites growing into the liquid, and of ribs growing in the liquid surface. Each needle is a single crystal. The precise form of the needle is determined by the orientation of the initial nucleus. If its optic axis is near normal to the surface, growth occurs rapidly in two dimensions and covers a much larger proportion of the surface than is covered by the narrow surface needles, so that ice forming this way appears to have its optic axis vertical. Hollow ice spikes observed on pools are shown to have been formed by the freezing of water forced from beneath the surface at the intersection of two or three surface needles, the shape of the spike depending on their orientation.

Scale-invariant phenomena are common in nature and fractals represent a suitable mathematical tool to describe them. Snow avalanche flow is made up of a mixture of grains and aggregates (granules) which can be broken or sintered together. The granular properties and interactions are important in understanding how avalanches flow. In this paper a fractal model for describing the grain-size distribution in the deposit of a snow avalanche is formulated by introducing the concept of aggregation probability. Although the model is two-dimensional, an extension to the three-dimensional case is proposed in the conclusions. The cumulative size distribution law is extrapolated from the model, and a physical discussion on fractal parameters is conducted. Finally, an experimental application to a real avalanche event is considered to confirm the predictions of the model and to present an extension to multifractality.

Temperature records from several randkluft sites at the margins and headwall of Boundary Glacier (lat. 52° 12′ N., long. 117° 12′ W.) in the Canadian Rocky Mountains are presented. These records indicate that during the ablation season a diurnal freeze-thaw air and rock-surface temperature regime occurs in a 2 m wide zone centred on the randkluft lip. Deeper in the randkluft, stable sub-zero conditions prevail whereas above the randkluft an above-freezing temperature regime prevails. The freeze-thaw temperature regime, observed freezing of melt water and rain water on randkluft rock surfaces, and copious in-situ loose weathering products on the headwall and marginal free faces suggest an active frost-shattering environment. Down-slope migration of the randkluft lip during the ablation season results in a migration of the freeze-thaw zone and thus a seasonal extension of the rock surface area exposed to the favorable weathering environment. Longer-term glacier fluctuations, with attendant thinning and thickening of the ice body, could result in large areas of marginal and headwall rock surfaces being exposed to the randkluft weathering environment over long periods of time. The data and observations from Boundary Glacier support an idea, suggested by Battle (1960), that open and shallow randklufts, rather than closed and deep bergschrunds, are a focus of weathering at glacier margins and thus a potential factor in cirque development.

During the 1976—77 season of the Ross Ice Shelf Geophysical and Glaciological Survey, a series of vertical electromagnetic sounding profiles of subsurface features was completed at station J-9. The survey comprised three five-kilometer north-west-south-east profiles separated by one kilometer and six two-kilometer north-east-south-west profiles, and was carried out on the surface using 35 MHz and 50 MHz radar systems. Folded-dipole antennae were used and oriented to detect reflectors both along and perpendicular to the profile path. This was done to facilitate the interpretation of the data, which indicated a complex system of bottom crevasses. Measurements of the positions, heights, and shapes of these crevasses showed at least two sets of crevasses varying in both strike and size. The larger crevasses, about 120 m high and oriented more or less normal to the flow direction, are probably associated with the movement of ice stream B across the grounding line between the West Antarctic ice sheet and the Ross Ice Shelf. A satisfactory explanation for the secondary set of crevasses, about 60 m high and forming an angle of 60° ±10° with the first set, has not yet been found.

Constant-load creep tests were performed at −10°C at various compressive stresses from 0.05 to 0.75 MPa on specimens taken every 10 m along a firn core extracted at Summit, Greenland in June 2017. The microstructures before and after creep testing were examined using both X-ray microtomography (micro-CT) and optical images from thin sections. An Andrade-like equation was used to describe the primary creep behavior and yielded the time exponent k of 0.17–0.76. The onset of secondary creep occurred at strains of ~0.5–3% but was sometimes not observed at all in shallow firn specimens and at stresses ⩽0.43 MPa even for strain up to 32%. For the 50–80 m firn crept at stresses ⩾0.55 MPa, secondary creep occurred at strains of 2.6 ± 0.28%, and the stress exponent, n, in Glen's law, was found to range from 4.1 to 4.6, similar to those observed for fully dense ice. Micro-CT observations of crept specimens showed that in most cases, the specific surface area, the total porosity and the structure model index decreased, while the structure thickness increased with increasing density. These microstructural characteristics are consistent with the densification of the firn. Optical images from thin sections showed that recrystallization occurred in some specimens that had undergone secondary creep.

The debris-rich ice from the bottom 6 m of the 82 m deep CAROLINE (Coastal Antarctic Record of Last Interglacial Natural Environment) ice core reaching bedrock, and from five 2 m long surface cores at Moraine Prudhomme in Terre Adélie (Antarctica) is described and compared to debris-laden ice from the core-drilling site DIO. Isotopic, total-gas content, CO2 concentration and SEM investigations of embedded particles, together with ice textures and fabrics, rule out “pressure-melting” regelation around bed obstacles or “freezing-on” as possible mechanisms for the debris entrainment at the ice-bedrock interface. It is suggested that the debris entrapment by purely mechanical means (e.g. shearing) is an efficient process in forming basal ice layers (BIL) at sub-freezing temperatures. This process might be dominant at the margin of the Antarctic ice sheet where no ice shelf exists and where a ramp terminus or a buttressing coastal relief induces compressive flow.

The ice-thickness profiling performance of a helicopter-mounted short-pulse radar operating at approximate center frequencies of 600 and 900 MHz was assessed. The antenna packages were mounted 1.2 m off the skid of a small helicopter whose speed and altitude were varied from about 1.8 to 9 m/s and 3 to 12 m. Clutter from the helicopter offered minimal interference with the ice data. Data were acquired in Alaska over lakes (as a proving exercise) and two rivers, whose conditions varied from open water to over 1.5 m of solid ice with numerous frazil-ice formations. The most readily interpretable data were acquired when the ice or snow surface was smooth. Detailed surface investigations on the Tanana River revealed good correlations of echo delay with solid ice depth, but an insensitivity to frazil-ice depth due to its high water content. On the Yukon River, coinciding temporally coherent surface and bottom reflections were associated with solid ice and smooth surfaces. All cases of incoherent surface returns (scatter) occurred over ice rubble. Rough-surface scattering was always followed by the appearance of bottom scattering but, in many cases, including a hanging-wall formation of solid frazil ice, bottom scattering occurred beneath coherent, smooth-surface reflections. Areas of incoherent bottom scattering investigated by drilling revealed highly variable ice conditions, including frazil ice. The minimum ice thickness that could be resolved from the raw data was about 0.2 m with the 600 MHz antenna and less than 0.15 m with the 900 MHz antenna.

Buried surface hoar and near-surface faceted crystals are known to lead to deadly avalanches. Over the course of three winter seasons a field investigation detailing the environmental conditions leading to the formation of these crystals was performed. Weather stations on north- and south-facing aspects were established. The weather data were accompanied by detailed daily observations and grain-scale photographs of the snow surface. During the three seasons, 35 surface hoar and 47 near-surface facets events were recorded. The mean weather conditions for the entire dataset (all three seasons and both stations) were compared to the nights when surface hoar formed. The comparison yielded five parameters that were statistically linked to the formation of surface hoar: incoming longwave radiation, snow surface temperature, wind velocity, relative humidity and the air/snow temperature difference. A similar comparison between the daytime mean values for all days with near-surface facet events revealed three parameters with statistically significant differences. Thus, these parameters (short- and longwave radiation and relative humidity) could be statistically linked to facet formation. This research also suggests that environmental conditions in the daytime hours before and after surface hoar formation are statistically similar to the conditions causing near-surface facet formation.

Field tests have been developed to measure the shear and tensile strengths of large volumes of snow. Basal shear strengths were measured across and down some slabs of snow, giving highly variable strengths. These measurements support the idea that the basal region of an avalanche may contain zones where the basal shear strength exceeded the gravitational shear stress (i.e. pinning areas) with weak zones between (deficit areas) where the shear strength was less than the gravitational shear stress. The slab tensile stresses induced by these deficit areas would become high if either the deficit length (down-slope) was large, or the deficit itself was large. Measurements of tensile strengths of slabs above weak layers, together with the down-slope gravitational stress of a snow slab, suggest that deficit lengths of only several metres are often sufficient to cause a local tensile failure. In some cases, this local failure may propagate across the remainder of the slope (depending on the pinning distribution) and cause an avalanche. We propose that the maximum local deficit, rather than the mean slope deficit of basal shear stress, and the maximum length of the local deficit, are the first important parameters to consider when evaluating slope stability in the field, since the magnitude of these factors determine the probability of a local tensile failure.

Ice shelves may develop either by continued thickening of sea ice that is held fast to the shore, or by the seaward extension of inland ice. For both processes, as well as for an understanding of ablation and of accumulation at the bottom surface of ice shelves, we need to understand melting and freezing processes in relation to salinity, temperature, and pressure. Consideration of these factors shows that basal melting beneath the thicker parts of ice shelves is much greater than is generally appreciated. This could be sufficient to bring the estimated mass balance of Antarctica into approximate equilibrium. It appears that most Antarctic ice shelves are dependent on the supply of inland ice for their continued existence. However the thick layer of sea ice beneath the Amery Ice Shelf is readily explained in terms of sub-ice water circulation.

Transport of heat and mass by water motion beneath ice shelves has the potential to change ice thicknesses by similar amounts to that caused by internal deformation of the ice shelf. Bottom freezing due to thermal conduction throughout the ice shelf is of minor importance.

While attention is drawn to the basic equations for flow of ice shelves, it is pointed out that they have yet to be applied satisfactorily to the problem of iceberg calving. This appears from field observations to be due primarily to creep failure of spreading ice shelves, possibly aided by impact from floating icebergs. Recent observations show the effectiveness and likely quantitative importance of this “big bang” theory of iceberg formation in Antarctica.

A brief discussion of the effects of climatic change on the disintegration of ice shelves is presented.

Under the potential to reconstruct the past climatic and atmospheric conditions from a deep ice core in the coastal Antarctic site (Styx Glacier), an 8.84 m long firn core (73°50.975′ S, 163°41.640′ E; 1623 m a.s.l.) was initially studied to propose a reliable age scale for the local estimation of snow accumulation rate. The seasonal variations of δ18O, methanesulfonic acid (MSA) and non-sea-salt sulfate (nssSO42–) were used for the firn core dating and revealed 25 annual peaks (from 1990 to 2014) with volcanic sulfate signal. The observed declining trend in annual accumulation rate with a mean value of 146 ± 60 kg m–2 a–1 is likely to be linked to the changes of sea-ice extent in the Ross Sea region. Moreover, the temporal variation of the annual mean δ18O, an annual flux of MSA and nssSO42– also likely to be under the influence of ice-covered and open water area. This study suggests a potential to recover past changes in an oceanic environment and will be useful for the interpretation of the long ice core drilled at the same site.

At places with an annual mean temperature lower than −20°C on the Greenland and Antarctic ice sheets, the temperature at a depth of 10 m is close to the annual mean at the surface and at the level of the meteorological shelter. With temperatures higher than about −35°C the size and sign of the différences vary. With lower temperatures the 10 m temperature becomes increasingly lower than the air temperature, at the coldest Antarctic station, “Plateau”, by nearly 4 deg.

White Glacier is a valley glacier at 79.5°N with an area of 38.7 km2. Its mass balance has been measured, over 32 years with a 3 year gap, by standard techniques using the stratigraphic system with a stake density of the order of one stake per km2. Errors in stake mass balance are about ±(200–250) mm, due largely to the local unrepresentativeness of measurements. Errors in the whole-glacier mass balance B are of the same order as single-slake errors. However, the lag-1 autocorrelation in the time series of B is effectively zero, so it consists of independent random samples, and the error in the long-term “balance normal” 〈B〉 is noticeably less. 〈B〉 is −100 ± 48 mm. The equilibrium-line altitude (ELA) averages 970 m. with a range of 470–1400 m. Mass balance is well correlated with ELA, but detailed modelling shows that the equilibrium line is undetectable on visible-band satellite images. A reduced network of a few stakes could give acceptable but less accurate estimates of the mass balance, as could estimates based on data from a weather station 120 km away. There is no evidence of a trend in the mass balance of White Glacier. To detect a climatologically plausible trend will require a ten-fold reduction of measurement error, a conclusion which may well apply to most estimates of mass balance based on similar stake densities.

We present a new algorithm for a fast iterative improvement of the shallow-ice approximation (SIA) for the modeling of glacier flow. Based on the traditional SIA scaling assumptions, the solution of the Stokes problem is found by an operator-splitting iterative technique. The SIA solution obtained in the first step is successively improved to obtain a higher-order approximation. Each iterative step has computational demands comparable to solving the SIA, which makes the algorithm substantially faster than other higher-order or full-Stokes solvers. The performance of the algorithm is tested on a model example taken from the ISMIP-HOM intercomparison project.