Knowledge of snow microstructure is relevant for modelling the physical properties of snow cover and for simulating the propagation of electromagnetic waves in remote-sensing applications. Characterization of the microstructure in field conditions is, however, a challenging task due to the complex, sintered and variable nature of natural snow cover. A traditional measure applied as a proxy of snow microstructure, which can also be determined in field conditions, is the visually estimated snow grain size. Developing techniques also allow measurement, for example, of the specific surface area (SSA) of snow, from which the optical-equivalent grain size can be derived. The physical snow model SNOWPACK simulates evolution of snow parameters from meteorological forcing data. In this study we compare an extensive experimental dataset of measurements of traditional grain size and SSA-derived optical grain size with SNOWPACK simulations of grain-size parameters. On average, a scaling factor of 1.2 is required to match traditional grain-size observations with the corresponding SNOWPACK simulation; a scaling factor of 2.1 was required for the optical equivalent grain size. Standard deviations of scaling factors for the winters of 2011/12 and 2012/13 were 0.36 and 0.42, respectively. The largest scaling factor was needed in early winter and under melting conditions.

Glacier response to climate forcing can be heterogeneous and complex, depending on glacier system characteristics. This article presents the decadal evolution of the Tsarmine Glacier (Swiss Alps), a very small and heavily debris-covered cirque glacier located in the Alpine periglacial belt. Archival aerial photogrammetry and autocorrelation of orthophotos were used to compute surface elevation, volume and geodetic mass changes, as well as horizontal displacement rates for several periods between 1967 and 2012. A GPR survey allowed us to investigate glacier thickness (15 m mean) and volume (4 × 106 m3) in 2015 and to anticipate its future evolution. Different dynamics occurred in recent decades because of the heterogeneous surface characteristics. The climate-sensitive upper debris-free zone contrasts with the progressively stagnant heavily debris-covered glacier tongue. Between 1967 and 2012, the glacier lost 1/3 of its initial volume (2 × 106 m3). The average mass balance stabilised at ~−0.3 m w.e. a−1 since 1999. Compared with other local glaciers, the Tsarmine Glacier shows a particular decadal behaviour both in time (divergence of mass balance since the 2000s) and space (inverted ablation pattern). This might be explained by the combined influence of debris cover, shadow, snow redistribution and permafrost conditions on this very small glacier.

We describe a high-precision method, now in use in our laboratory, for measuring the CO2 mixing ratio of ancient air trapped in polar ice cores. Occluded air in ice samples weighing ∼8–15 g is liberated by crushing with steel pins at −35°C and trapped at −263°C in a cryogenic cold trap. CO2 in the extracted air is analyzed using gas chromatography. Replicate measurements for several samples of high-quality ice from the Siple Dome and Taylor Dome Antarctic ice cores have pooled standard deviations of <0.9 ppm. This high-precision technique is directly applicable to high-temporal-resolution studies for detection of small CO2 variations, for example CO2 variations of a few parts per million on millennial to decadal scales.

The general properties of snow are described with a view to engineering applications of data. Following an introduction and a short note on the origins of snow, data are given for fall velocities of snow particles, and for mass flux and particle concentrations in falling snow and blowing snow. Notes on the structural properties of deposited snow cover grain size, grain bonds, bulk density, overburden pressure, and permeability. A section on impurities deals with stable and radioactive isotopes, chemical impurities, insoluble particles, living organisms, acidity, and gases. Mechanical properties are treated only selectively, and the reader is referred to another paper for comprehensive coverage. The selective treatment deals with stress waves and strain waves, compressibility, effects of volumetric strain on deviatoric strain, and specific energy for comminution. The section on thermal properties covers heat capacity, latent heat, conductivity, diffusivity, heat transfer by vapor diffusion, heat transfer and vapor transport with forced convection, and thermal strain. The section on electrical properties opens with a brief discussion on dielectric properties of ice, and proceeds to a summary of the dielectric properties of snow, including dielectric dispersion, permittivity, dielectric loss, and d.c. conductivity. There are also notes on the thermoelectric effect and on electrical charges in falling and blowing snow. The section on optical properties deals with transmission and attenuation of visible radiation, with spectral reflectance, and with long-wave emissivity. The review concludes with some comments on engineering problems that involve snow, and the requirements for research and development.

We evaluate the variability in basal friction for Kronebreen, Svalbard, a fast-flowing tidewater glacier. We invert 3 years (2013–15) of surface velocities at high temporal resolution (generally 11 days), to estimate the changing basal properties of the glacier. Our results suggest that sliding behaviour of Kronebreen within a year is primarily influenced by changes in water input patterns during the meltwater season and basal friction is highly variable from a year to another. At present, models usually employ parameterisations to encompass the complex physics of glacier sliding by mathematically simulate their net effect. For such ice masses with strong seasonal variations of surface melt, the spatio-temporal patterns of basal friction imply that it is neither possible nor appropriate to use a parameterisation for bed friction that is fixed in space and/or time, at least in a timescale of a few years. Basal sliding may not only be governed by local processes such as basal topography or summer melt, but also be mediated by factors that vary over a larger distance and over a longer time period such as subglacial hydrology organisation, ice-thickness changes or calving front geometry.

Results of laboratory uniaxial compression tests over the stress range 0.18–0.52 MPa and the strain range 0.5–8.6% at approximately –5 and –20°C are presented. Grain-size analysis and comparisons with annealing tests confirm that grain-growth reducing processes are active during deformation. Microstructural observations reveal that subgrain-rotation recrystallization and grain-shape changes due to strain-induced grain-boundary migration are the causes of the grain-growth deceleration. Further results from microstructural observations show that obstacle formation by dislocation walls and subgrain boundaries is the reason for isotropic hardening during creep. Subgrainboundary types that are likely to be relevant for studies on the activity of different dislocation types are described.

Lack of agreement between the deep portions of the Greenland Icecore Project (GRIP) and Greenland Ice Sheet Project II (GISP2) ice cores from central Greenland suggests that folds may disrupt annual layering, even near ice divides. We use a simple kinematic flow model to delineate regions where slope disturbances (“wrinkles”) introduced into the layering could overturn into recumbent folds, and where they would flatten, leaving the stratigraphic record intact. Wrinkles are likely to originate from flow disturbances caused internally by inhomogeneities and anisotropy in the ice rheological properties, rather than from residual surface structures (sastrugi), or from open folds associated with transient flow over bed topography. If wrinkles are preferentially created in anisotropic ice under divides, where the resolved shear stress in the easy-glide direction can be weak and variable, then the deep intact climate record at Dye 3 may result from its greater distance from the divide. Alternatively, the larger simple shear at Dye 3 may rapidly overturn wrinkles, so that they are not recognizable as folds. The ice-core record from Siple Dome may be intact over a greater fraction of its depth compared to the central Greenland records if its flat bedrock precludes fluctuations in the stress orientation near the divide.

This paper addresses the nature of incongruent dissolution of calcite in glacial settings using an experimental approach. Various CaCO3 samples were comminuted using two contrasting techniques (dry machine-milling, and hand-grinding of an ice-water mixture) and dissolved to calcite saturation in both high-pCO2 (10−2 atm) and low-pCO2 (10−3.5 = atmospheric) conditions. Ion yields of Ca, Mg and Sr were determined at the end of the experiments. Leachates displayed enhancement of Mg/Ca and Sr/Ca by a factor of 1.3–8.3 compared with bulk solid carbonate. Lower Mg/Ca and Sr/Ca ratios under higher-pCO2 conditions reflect the percentage dissolution of the carbonate, not the pCO2 per se. The experimental results imply that reported natural incongruent dissolution is readily reproducible in the laboratory and is primarily dependent on the water/rock ratio. Quantitative analysis of new and previous results suggests that the effect relates to the most reactive 0.15–0.25% of the sample, equating volumetrically to the outer few lattice layers, and it is interpreted as an anomalous leaching behaviour of calcite surfaces freshly exposed by crushing. This phenomenon could serve as an index of the relative efficiencies of fragmenting and dissolutional processes in glacial environments.

Sortebræ is a surge-type tidewater glacier complex draining southeastward from the Geikie Plateau, East Greenland. Sortebræ’s main flow unit surged around 1950 and again between 1992 and 1995. The 1990s surge affected the lower 50 km of Sortebræ over an area of approximately 335 km2. Over a period of <1 year the tidewater front advanced >5 km. Surge velocities in the order of kilometres per annum are about 100-fold the quiescent velocities. Multi-model photogrammetric analysis shows a thinning of the reservoir zone of up to 219 m and thickening of the receiving zone of up to 74 m. The surge transported approximately 18.6 km3 of ice down-glacier. The total calving volume as a result of the surge amounted to 11.7 km3, equivalent to a calving flux of 3.9–7.3 km3 a−1. The surge characteristics and environmental setting suggest that the surge mechanism involves a switch in the subglacial drainage. This surge of Sortebræ is more similar to the fast, short Alaskan-type surges than to the sluggish, long Svalbard-type surges.

New high-resolution velocity maps of the eastern St Elias Mountains, North America, are obtained from speckle tracking of winter 2011 and 2012 RADARSAT-2 image pairs. This includes the most complete velocity mapping to date of Hubbard Glacier, allowing for an upward revision of the Hubbard Glacier calving flux to 5.48 ± 1.16 km3 a−1. Combined with historical velocities from feature tracking of Landsat image pairs (1980s−2000s), and previously published results, these new velocity measurements allow for an evaluation of the interannual variability of motion at eight glaciers in this region, due to both long-term force-balance effects and surge dynamics. Multi-decadal velocities at the non-surge-type Kaskawulsh Glacier indicate little change along most of its length, except for the lowermost 10 km where deceleration has been pronounced since the late 1980s in a region that has undergone rapid recent thinning. Interannual variability of surge-type glaciers was high, with year-to-year velocity variations of up to several hundred m a−1. These glaciers were also characterized by distinct patterns of deceleration and/or acceleration along their length.

A record of accumulation and ablation from a network of 47 stakes at a coastal blue-ice area in Terre Adélie, Antarctica, is presented and analyzed. The record covers early 2004 to early 2006, from 25 field surveys including some in austral winter. The two years are very different, with a virtually null surface mass balance during the 2004 winter but large accumulation during the 2005 winter. A snow/ice energy- and mass-balance model is used to reproduce the accumulation and ablation record. A parameterization for snow erosion by wind is included. Input meteorology is from the European Centre for Medium-Range Weather Forecasts (ECMWF) analyses and forecasts, corrected using 1 year of local meteorological observations from an automatic weather station. Model results agree reasonably well with the observations. Wind erosion is the largest contributor to ablation, removing much of the precipitation. Sublimation and, to a lesser extent, melt/runoff together account for >60 cm w.e. of ablation in 2 years, mainly in summer. Although the record is short, it confirms high interannual variability and thus high sensitivity to meteorology and climate. Monitoring and understanding the mass balance of such coastal blue-ice areas may help monitor and detect climate change in the Antarctic coastal regions.

Periods of dramatically accelerated motion, in which the flow velocity increases suddenly from about 55 cm/d to a peak of 100–300cm/d and then decreases gradually over the course of a day, occurred repeatedly during June and July 1978–81 in Variegated Glacier (Alaska), a surging-type glacier that surged in 1982–83. These “mini-surges” appear to be related mechanistically to the main surge. The flow-velocity peak propagates down-glacier as a wave at a speed of about 0.3 km/h, over a reach of about 6 km in length. It is accompanied by a propagating pressure wave in the basal water system of the glacier, in which, after a preliminary drop, the pressure rises rapidly to a level greater than the ice-overburden pressure at the glacier bed, and then drops gradually over a period of 1–2 d, usually reaching a new low for the summer. The peak velocity is accompanied by a peak of high seismic activity due to widespread fresh crevassing. It is also accompanied by a rapid uplift of the glacier surface, amounting to 6–11 cm, which then relaxes over a period of 1–2 d. Maximum uplift rate coincides with the peak in flow velocity; the peak in accumulated uplift lags behind the velocity peak by 2 h. The uplift is mainly due to basal cavitation driven by the high basal water pressure, although the strain wave associated with the mini-surge motion can also contribute. Basal cavitation is probably responsible for the pulse of high turbidity that appears in the terminal outflow stream in association with each mini-surge. In the down-glacier reach, where the mini-surge waves are attenuating, the observed strain wave corresponds to what is expected for the propagating pulse in flow velocity, but in the reach of maximum mini-surge motion the strain wave has a form quite different, possibly related to special features in the mini-surge initiation process from that point up-stream. The flow acceleration in the mini-surges is due to enhanced basal sliding caused by the high basal water pressure and the consequent reduction of bed friction. A preliminary velocity increase shortly before the pressure wave arrives is caused by the forward shove that the main accelerated mass exerts on the ice ahead of it, and the resulting preliminary basal cavitation causes the drop in water pressure shortly before the pressure wave arrives. The mini-surge wave propagation is controlled by the propagation of the water-pressure wave in the basal water-conduit system. The propagation characteristics result from a longitudinal gradient (up-glacier increase) in hydraulic conductivity of the basal water system in response to the up-glacier increase of the basal water pressure in the mini-surge wave. The mini-surge waves are initiated in a succession of areas situated generally progressively up-glacier during the course of the summer season. In these areas, presumably, melt water that has accumulated in subglacial (?) reservoirs is released suddenly into the basal water system immediately below, generating a pressure rise that propagates down-stream from there. Relationships of the mini-surges to the main surge are seen in the role of high basal water pressure in causing the rapid glacier motion in both phenomena, in the pulse-propagation features of both, and in the high outflow turbidity associated with both. The mini-surges of Variegated Glacier have a strong resemblance to movement and uplift events observed in Unteraargletscher and Findelengletscher, Switzerland. This bears on the question whether the mini-surges are a particular characteristic of surge-type glaciers prior to surge.

We conducted a mass-balance study of debris-free Trambau Glacier in the Rolwaling region, Nepal Himalaya, which is accessible to 6000 m a.s.l., to better understand mass-balance processes and the effect of precipitation on these processes on high-elevation Himalayan glaciers. Continuous in situ meteorological and mass-balance observations that spanned the three melt seasons from May 2016 are reported. An energy- and mass-balance model is also applied to evaluate its performance and sensitivity to various climatic conditions. Glacier-wide mass balances ranging from −0.34 ± 0.38 m w.e. in 2016 to −0.82 ± 0.53 m w.e. in 2017/18 are obtained by combining the observations with model results for the areas above the highest stake. The estimated long-term glacier mass balance, which is reconstructed using the ERA-Interim data calibrated with in situ data, is −0.65 ± 0.39 m w.e. a−1 for the 1980–2018 period. A significant correlation with annual precipitation (r = 0.77, p < 0.001) is observed, whereas there is no discernible correlation with summer mean air temperature. The results indicate the continuous mass loss of Trambau Glacier over the last four decades, which contrasts with the neighbouring Mera Glacier in balance.

Surface melt on the coastal Antarctic ice sheet (AIS) determines the viability of its ice shelves and the stability of the grounded ice sheet, but very few in situ melt rate estimates exist to date. Here we present a benchmark dataset of in situ surface melt rates and energy balance from nine sites in the eastern Antarctic Peninsula (AP) and coastal Dronning Maud Land (DML), East Antarctica, seven of which are located on AIS ice shelves. Meteorological time series from eight automatic and one staffed weather station (Neumayer), ranging in length from 15 months to almost 24 years, serve as input for an energy-balance model to obtain consistent surface melt rates and energy-balance results. We find that surface melt rates exhibit large temporal, spatial and process variability. Intermittent summer melt in coastal DML is primarily driven by absorption of shortwave radiation, while non-summer melt events in the eastern AP occur during föhn events that force a large downward directed turbulent flux of sensible heat. We use the in situ surface melt rate dataset to evaluate melt rates from the regional atmospheric climate model RACMO2 and validate a melt product from the QuikSCAT satellite.

This paper introduces a new way to investigate in situ processes, the wireless multi-sensor probe, as part of an environmental sensor network. Instruments are housed within a ‘probe’ which can move freely and so behave like a clast. These were deployed in the ice and till at Briksdalsbreen, Norway. The sensors measure temperature, resistivity, case stress, tilt angle and water pressure and send their data to a base station on the glacier surface via radio links. These data are then forwarded by radio to a reference station with mains power 2.5 km away, from where they are sent to a web server in the UK. The system deployed during 2004/05 was very successful and a total of 859 probe days worth of data from the ice and till were collected, along with GPS, weather and diagnostic data about the system.

The subglacial chemical weathering environment is largely controlled by low temperatures and the presence of freshly comminuted minerals with a high surface area. These characteristics are believed to promote dissolution processes that give rise to low silica and high Ca2+ fluxes emanating from glacierized basins. We test an alternative hypothesis, that mineral precipitation reactions in the subglacial environment play an equally important role in controlling the water chemistry in glacierized basins. We analyze borehole and proglacial water chemistry from a subarctic polythermal glacier, complemented by mineral XRD analysis of suspended sediment, till and bedrock samples. In conjunction with a thermodynamic analysis of the water and mineral chemistry, we use reaction-path modelling to study the chemical enrichment of water through the glacier system. We find that the high pH of the subglacial environment is conducive to secondary mineral precipitation, and that it is not possible to balance the water chemistry using dissolution reactions alone. We show that low silica can be explained by standard weathering reactions without having to invoke mineral-leaching reactions. Our results suggest that subglacial weathering intensity may be significantly underestimated if the production of secondary minerals is not considered.

Deformation rates of single hexagonal crystals, deforming by glide on the basal plane, are described as a function of stress state and crystal orientation. These results are used to infer the deformation rate of crystal aggregates assuming that the stress distribution within the crystal aggregate is homogeneous. Analytical equations for the deformation rate of anisotropic ice aggregates are derived for vertically symmetric girdle fabric. This type of fabric is approximated by a uniform distribution of c-axis orientations between a cone angle and a smaller girdle angle relative to the symmetry axis. For simple shear stress acting on a single-maximum fabric there is a slight de-enhancement for cone angles of 60–90°. In uniaxial compression a maximum enhancement of ∼1.7 occurs at a cone angle of 57°. A pure shear stress state has similar features, with the additional complication that it causes a non-zero transverse strain rate, except for perfect vertical alignment of crystals and isotropic fabric. In combined states of stress the contribution of each stress component to the strain rate depends on fabric. A single enhancement factor is not adequate to describe the effects of anisotropy for complex stress states.

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.

This paper presents the changes in the thermal structure of the polythermal glacier Storglaciären, northern Sweden, over the 20 year period 1989-2009 derived by comparing maps of the depth of the englacial transition between cold ice (permanently frozen) and temperate ice (which contains water inclusions). The maps are based on interpreted ice-penetrating radar surveys from 1989, 2001 and 2009.

Complex thinning of the cold layer, first identified between 1989 and 2001, is still ongoing. A volume calculation shows that Storglaciären has lost one-third of its cold surface layer volume in 20 years, with a mean thinning rate of 0.80 ± 0.24 m a-1. We suggest that the thinning of the cold layer at Storglaciären is connected to the climatic warming experienced by sub-Arctic Scandinavia since the 1980s and we argue that repeated ice-penetrating radar surveys over the ablation area of polythermal glaciers offer a useful proxy for evaluating glacier responses to changes in climate.