We have used micrometeorological data collected at Hailey Research Station, Antarctica, to estimate monthly totals of snow sublimation. Direct sublimation from the snow surface is calculated using bulk-transfer formulae, while the sublimation of blowing snow is estimated using a model for suspended-particle number density and individual particle sublimation rates. During the winter months, sublimation losses are negligible, but between November and March sublimation removes around 25% of the snowfall. Surface sublimation and sublimation of blowing snow make roughly equal contributions to this total. Estimates of sublimation using micrometeorological data agree well with estimates made from daily snow-stake measurements.

Bakaninbreen, Svalbard, was in the late phase of a prolonged surge during 1995–96. In order to investigate the nature of the basal mechanical and hydraulic regime, sets of tilt sensors equipped with pore-pressure sensors were installed into the basal till layer. Water-pressure transducers were also installed in the boreholes above the ice–till interface. During 1995, the measured mean strain rate in the till was 0.44 a−1 up-glacier of the surge front, while down-glacier the rate was 0.04 a−1. Our interpretation indicates that deformation was the dominant component of basal motion. Strain rates fluctuated strongly, and periods of both positive (down-glacier) and negative (up-glacier) strain occurred. No consistent relationship was apparent between effective pressure and strain rate within the basal till layer. The viscosity of the basal sediments ranged from 1.3 × 1012 to 3.4 × 1012 Pa s. Such high values suggest that the till layer beneath Bakaninbreen may be partially frozen. Analysis of simultaneous measurements of pore-water and borehole water pressure suggests the hydraulic diffusivity of the till layer ranges from 1.2 to 5.0 × 10−6 m2 s−1, and the hydraulic conductivity from 3.2 × 10−7 to 7.7 × 10−8 m s−1.

Bakaninbreen in Svalbard and Trapridge Glacier in Yukon Territory, Canada, are two prominent examples of surging glaciers which are thought to be controlled by their thermal regime. Both glaciers have developed large bulges which have propagated forward as travelling wave fronts, and which are thought to divide relatively stagnant downstream cold-based ice from faster-moving warm-based upstream ice. Additionally, both glaciers are underlain by a wet, metres thick layer of deforming till. We develop a simple model for the cyclic surging behaviour of these glaciers, which interrelates the motion of the ice and till through a description of the subglacial hydrology. We find that oscillations (surges) can occur if the subglacial hydrological transmissivity is sufficiently low and the till layer is sufficiently thin, and we suggest that these oscillations are associated with the development and propagation of a travelling wave front down the glacier. We therefore interpret the travelling wave fronts on both Trapridge Glacier and Bakaninbreen as manifestations of surges. In addition, we find that the violence of the surge in the model is associated with the resistance to ice flow offered by undulations in the bed, and the efficiency with which occasional hydrological events can release water accumulated at the glacier sole.

This research investigates snow stability on the eastern side of a small mountain range in southwest Montana, U.S.A., on one mid-season day and one late-season day during the 1996/97 winter. Although previous research has addressed snow stability at smaller spatial scales, this is the first field-based study to investigate snow stability (as measured by stability tests) over a mountain range in order to better understand its spatial distribution and the implications for predicting dry-slab avalanches. Using helicopter access, six two-person sampling teams collected data from over 70 sites on each of the two sampling days. Variables for terrain, snowpack, snow strength and snow stability were generated from the field data, and analyzed using descriptive statistics, correlation analysis and multiple regression. Results from the first sampling day show stability is only weakly linked to terrain, snowpack and snow-strength variables due to consistently stormy weather conditions leading up to that day. The second field day’s results demonstrate a stronger relationship between stability and the other variables due to more variable weather conditions that ranged from periods of sunshine to storms. On both days stability decreased on high-elevation, northerly-facing slopes. The data-structure complexity provides insights into the difficulties faced by both scientists and conventional avalanche forecasters in predicting snow avalanches.

The surface motion of Haut Glacier d’Arolla, Switzerland, was monitored at a high spatial and temporal resolution. Data are analyzed to calculate surface velocities, surface strain rates and the components of the glacier force budget before, during and after an early melt season speed-up or “spring event”. We investigate the extent to which variations in glacier motion can be attributed to hydrologically induced local forcing or to non-local forcing transmitted via horizontal stress gradients. Enhanced glacier motion is dependent on a change in the spatial distribution of areas of high drag across the glacier.

In this paper a detailed record of major ions from a 20 m deep firn core from Amundsenisen, western Dronning Maud Land, Antarctica, is presented. The core was drilled at 75° S, 2° E (2900 m a.s.l.) during austral summer 1991/92. The following ions were measured at 3 cm resolution: Na+, Mg2+, Ca2+, Cl−, NO3−, S042− and CH3SO3H (MSA). The core was dated back to 1865 using a combination of chemical records and volcanic reference horizons. The volcanic eruptions identified in this core are Mount Ngauruhoe, New Zealand (1974–75), Mount Agung, Indonesia (1963), Azul, Argentina (1932), and a broad peak that corresponds in time toTarawera, New Zealand (1886), Falcon Island, South Shetlands, Southern Ocean (1885), and Krakatau, Indonesia (1883). There are no trends in any of the ion records, but the annual to decadal changes are large. The mean concentrations of the measured ions are in agreement with those from other high-altitude cores from the Antarctic plateau. At this core site there may be a correspondence between peaks in the MSA record and major El Niño–Southern Oscillation events.

Snowmelt regions on Greenland ice are mapped daily with the SeaWinds wideswath Ku-band (13.4 GHz) scatterometer on the QuikSCAT satellite. The approach exploits the high temporal resolution of SeaWinds/QuikSCAT data for the melt mapping using diurnal backscatter change independent of the absolute calibration. The results reveal several pronounced melting and refreezing events, and effects of topography are evident in the melt patterns. The spatial resolution is sufficient to identify melt features on the Sukker-toppen Iskappe west of the main ice sheet. An anomalous warming event, caused by down-ward mixing of warm air, is detected in late September 1999 over the west flank of the southern Greenland ice sheet. Time-series images of melt regions are presented over the period from summer to the fall freeze-up. The satellite observations are verified with in situ measurements from the Greenland Climate Network stations.

Glaciar Chacaltaya is an easily accessible glacier located close to La Paz, Bolivia. Since 1991, information has been collected about the evolution of this glacier since the Little Ice Age, with a focus on the last six decades. The data considered in this study are monthly mass-balance measurements, yearly mappings of the surface topography and a map of the glacier bed given by ground-penetrating radar survey. A drastic shrinkage of ice has been observed since the early 1980s, with a mean deficit about 1 m a−1 w.e. From 1992 to 1998, the glacier lost 40% of its average thickness and two-thirds of its total volume, and the surface area was reduced by >40%. With a mean estimated equilibrium-line altitude lying above its upper reach, the glacier has been continuously exposed to a dominant ablation on the whole surface area. If the recent climatic conditions continue, a complete extinction of this glacier in the next 15 years can be expected. Glaciar Chacaltaya is representative of the glaciers of the Bolivian eastern cordilleras, 80% of which are small glaciers (<0.5 km2). A probable extinction of these glaciers in the near future could seriously affect the hydrological regime and the water resources of the high-elevation basins.

Measurements of strain rate are used to describe the stress distribution at the lateral margin of an active West Antarctic ice stream. The goal is to describe the way in which drag at the sides operates to control the motion of this ice stream. The problem is inherently complex, but with some approximations a mainly analytic solution is obtained. Allowing for spatially varying ice strength shows that the shear strain rate decreases over a larger distance from the ice stream than for ice of uniform strength. The simplest explanation using the results of field measurements is that the upper 40% of the ice stream is able to support lateral stress. For the slow-moving interstream ridge, rather more of the thickness is strong. The lateral shear stress from the ice stream is transferred to a basal zone about 3 km wide where basal drag reaches 60 kPa. This basal zone controls the speed of the ice stream.

Oxygen isotopic and soluble ionic measurements made on snow-pit (2 m depth) and firn-core (12.4 m depth) samples recovered from the accumulation zone (5100 m) of Inilchek glacier (43° N, 79° E) provide information on recent (1992–98) climatic and environmental conditions in the central Tien Shan region of central Asia. The combined 14.4 m snow-pit/firn-core profile lies within the firn zone, and contains only one observed melt feature (10 m temperature = −12°C). Although some post-depositional attenuation of the sub-seasonal δ18O record is possible, annual cycles are apparent throughout the isotope profile. We therefore use the preserved δ18O record to establish a depth/age scale for the core. Mean δ18O values for the entire core and for summer periods are consistent with δ18O/temperature observations, and suggest the δ18O record provides a means to reconstruct past changes in summer surface temperature at the site. Major-ion (Na+, K+, Mg2+, Ca2+, NH4+, Cl−, NO3−, SO42−) data from the core demonstrate the dominant influence of dust deposition on the soluble chemistry at the site, and indicate significant interannual variability in atmospheric-dust loading during the 1990s. Anthropogenic impacts on NH4+ concentrations are observed at the site, and suggest a summer increase in atmospheric NH4+ that may be related to regional agricultural (nitrogen-rich fertilizer use) activities.

During El Niño–Southern Oscillation (ENSO) warm events, outer tropics glaciers usually experience a deficit of precipitation, an increase of air temperature and a strongly negative mass balance. At Glaciar Zongo, Bolivia, this was particularly striking during the vigorous 1997/98 El Niño event, one of the strongest of the century, and which resulted in an annual depth of runoff two-thirds higher than normal. We compare the energy balance on the glacier between two contrasting cycles, 1996/97 (La Niña year) and 1997/98 (El Niño year). Due to a 1.3°C increase of annual mean air temperature, the sensible-heat flux slightly increases from 6.1 to 9.8 W m−2 During the El Niño year, sublimation is reduced, leaving more energy for melting (LE = −18.1 W m−2 in 1996/97 and LE = −11.6 W m−2 in 1997/98). The main factor responsible for the dramatic increase in melting is the net all-wave radiation, which is three times higher in 1997/98 than in 1996/97 (48.7 and 15.8 W m−2, respectively). This sharp increase of net all-wave radiation is related to the decrease of albedo due to the precipitation deficit.

In the low latitudes there is an absence of major thermal seasonality, yet there are three different climate regimes related to global circulation patterns and their seasonal oscillation: the humid inner tropics, the dry subtropics and, intermediate between these two, the outer tropics. For the respective glacier regimes the vertical profiles of specific mass balance (VBPs) are modeled considering vertical gradients of accumulation, air temperature and albedo, the duration of the ablation period and a factor for the ratio between melting and sublimation. The model is first calibrated with data from Hintereisferner, Austrian Alps, and is then applied to tropical conditions. The simulated VBP matches well the measured profiles from Irian jaya and Mount Kenya. Due to lack of field evidence, the subtropical VBP cannot be verified directly. However, application of the respective model versions separately to the humid and dry seasons of the outer-tropical Glaciar Uruashraju, Cordillera Blanca, Peru, provides reasonable results. Glaciers in the humid inner tropics are considered to be most sensitive to variations in air temperature, while dry subtropical glaciers are most sensitive to changes in air humidity. The two seasons of the outer tropics have to be viewed from these different perspectives.

Sequential satellite imagery and modeling are used to investigate crevasse patterns at the head of Ice Stream B tributary B1b. The crevasses, informally called the “chromosomes”, form at the upstream limit to B1b’s northern shear margin and chaotic crevasse zone. We find that the onset to crevasse formation, and by inference the onset to streaming flow, has migrated upstream over time at a mean rate of 230(16) m a−1. A possible cause for that migration is changes in net basal friction due to changes in basal water production rate and storage.

We present the snow-accumulation distribution over Austfonna, Nordaustlandet, Svalbard, based on 29 shallow ice cores that were retrieved from this ice cap during 1998 and 1999. Mean annual net accumulation is deduced from radioactive layers resulting from the 1954–74 atmospheric nuclear tests (maximum in 1963) and the Chernobyl accident (1986). The Chernobyl layer was located in 19 ice cores in the accumulation area, and the nuclear test layer was located in two deeper ice cores. In addition, the spatial variation of the depth of winter 1998/99 snowpack was mapped using snow probing, ground-penetrating radar methods and pit studies. The altitudinal gradient of the mean annual net mass balance and the altitude of the mean equilibrium line are determined along five transects ending at the top of the ice cap. The mean annual net mass balance and the equilibrium-line altitudes show a high degree of asymmetry between the western and eastern parts of Austfonna, in accordance with the distribution of winter accumulation. Large interannual variations of the accumulation exist. However, the study of the mean annual net mass balance shows no trend for two different time periods, 1963–86 and 1986 to the date of the drillings (1998/99).

This paper addresses the causes of the prevailing meteorological conditions observed over an Antarctic blue-ice area and their effect on the surface mass balance. Over blue-ice areas, net accumulation is zero and ablation occurs mainly through sublimation. Sublimation rates are much higher than over adjacent snowfields. The meteorological conditions favourable for high sublimation rates (warm, dry and gusty) are due to the specific orographic setting of this blue-ice area, with usually a steep upwind mountainous slope causing strong adiabatic heating. Diabatic warming due to radiation, and entrainment of warm air from aloft into the boundary layer augment the warming. The prevailing warm, dry conditions explain roughly 50% of the difference in sublimation, and the different characteristics of blue ice (mainly its lower albedo) the other 50%. Most of the annual sublimation (∼70%) takes place during the short summer (mainly in daytime), with winter ablation being restricted to occasional warm, dry föhn-like events. The additional moisture is effectively removed by entrainment and horizontal advection, which are maximum over the blue-ice area. Low-frequency turbulent motions induced by the upwind mountains enhance the vertical turbulent transports. Strong gusts and high peak wind speeds over blue-ice areas cause high potential snowdrift transports, which can easily remove the total precipitation, thereby maintaining zero accumulation.

An analysis of motion in the terminus region of LeConte Glacier, Alaska, U.S.A., delineates mechanisms that are important to tidewater glacier stability. This glacier is undergoing rapid retreat. Since 1995 it has retreated 2 km and thinned >125 m at the present location of the terminus. Ice velocities in this region are quite high; at the terminus they exceed 27 m d−1. Our analysis reveals that fluctuations in speed and surface elevation are forced by ocean tides, surface melt and precipitation. The nearterminus ice speed is 180° out of phase with the tide, such that high tide corresponds to low speed. Smaller, melt-forced diurnal variations in speed are present throughout the lowermost 7 km. Speed-ups in excess of 10% of the mean often occur after rainstorms as a result of increased basal water pressure and storage, but the relation is not simple. The velocity does not vary over the spring and summer seasons.

In most models of the flow of glaciers on till beds, it has been assumed that till behaves as a viscoplastic fluid, despite contradictory evidence from laboratory studies. In accord with this assumption, displacement profiles measured in subglacial till have been fitted with viscoplastic models by estimating the stress distribution. Here we present a model that illustrates how observed displacement profiles can result from till deformation resisted solely by Coulomb friction. Motion in the till bed is assumed to be driven by brief departures from static equilibrium caused by fluctuations in effective normal stress. These fluctuations result from chains of particles that support intergranular forces that are higher than average and that form and fail at various depths in the bed during shearing. Newton’s second law is used to calculate displacements along slip planes and the depth to which deformation extends in the bed. Consequent displacement profiles are convex upward, similar to those measured by Boulton and colleagues at Breidamerkurjökull, Iceland. The model results, when considered together with the long-term and widespread empirical support for Coulomb models in soils engineering, indicate that efforts to fit viscoplastic flow models to till displacement profiles may be misguided.

Causes of ice-sheet layering at ice depths greater than about 900 mina transect between Dome C and the Transantarctic Mountains are examined using 60 MHz radar data, collected in the 1970s by the U.K.–U.S.–Danish collaboration. Normally, a dual-frequency technique is required for accurate determination of internal reflection mechanisms. However, by extracting the depth-related features of 60 MHz radar profiles and comparing them with the dual-frequency data collected by the Japanese Antarctic Research Expedition, we have identified a simple method to estimate internal reflection mechanisms. Two zones can be distinguished: (1) the CA zone, where change in electrical conductivity due to variation in acidity is the major cause of internal reflection, and (2) the PCOF zone, where change in dielectric permittivity due to crystal-orientation fabrics is the major cause of internal reflections. Our analysis shows that the radar data reveal the development of PCOF zones in regions where large amounts of ice shearing are expected. This analysis shows how a similar interpretation of the full radar-data archive may reveal information on internal reflection mechanisms across a large part of the East Antarctic ice sheet.