Any model of snow avalanches must be able to reproduce velocity profiles. This is a key problem in avalanche science because the profiles are the result of a multitude of snow/ice particle interactions that, in the fend, define the rheology of flowing snow. Recent measurements on real-scale avalanches show that the velocity profiles change from a highly sheared profile at the avalanche front to a plug-like profile at the avalanche tail, preventing the application of a single, simple rheology to the avalanche problem. In this paper, we model not only the velocity profiles but also the evolution of the velocity profiles, by taking into account the production and decay of the kinetic energy of the random motion of the snow granules. We find that the generation of this random energy depends on the distribution of viscous shearing within the avalanche. Conversely, the viscous shearing depends on the magnitude of the random energy and therefore its collisional dissipation. Thus, there is a self–consistency problem that must be resolved in order to predict the amount of random energy and therefore the velocity profiles. We solve this problem by stating equations that describe the production and decay of random energy in avalanches. An important guide to the form of these equations is that the generation of random energy is irreversible. We show that our approach successfully accounts for measured profiles in natural avalanches.

Stresses at the surface and at depth are calculated for a stretch of Byrd Glacier, Antarctica. The calculations are based on photogrammetrically determined velocities and elevations, and on radio-echo-determined ice thicknesses. The results are maps of drags from each valley wall, of normal forces laterally and longitudinally, and of basal drag. Special challenges in the calculation are the numerical gridding of velocity, ensuring that unreasonable short-wavelength features do not develop in the calculation, and inference of ice thickness where there are no data.

The results show important variations in basal drag. For the floating part, basal drag is near zero, as expected. Within the grounded part, longitudinal components of basal drag are very variable, reaching 300 kPa with a dominant wavelength of 13 km. Generally, these drag maxima correlate with maxima in driving stress. Usually the across-glacier component of basal drag is small. An important exception occurs in the center of the grounded part of the glacier where the flow shows major deviations from the axis of the valley.

Other results are that side drag is roughly constant at 250 kPa along both margins of the glacier, tension from the ice shelf is about 100 kPa, and tension in the grounded part cycles between 250 and 150 kPa. Calculated deep velocities are too large and this is attributed to deficiencies in the conventional isotropic flow law used.

We report on analysis of meteorological data for the period 27 May–20 August 2004, from two automatic weather stations on McCall Glacier, Alaska, USA, aimed at studying the relationship between climate and ablation. One station is located on a mountain ridge and the other in the ablation area where we also analyzed the energy balance. The weather station on the glacier measured an average temperature of 5.3°C (at 2 m height above surface) and wind speed of 3.1 m s−1 (at 3 m height). A sonic height ranger and ablation stakes indicate a specific mass balance of –1.94 ± 0.09 m w.e between 15 June and 20 August. The specific mass balance calculated from the surface energy balance, –2.06 ± 0.18 m w.e., is in close correspondence to this. The latter is the sum of 0.12 m w.e. of snowfall, 0.003 m w.e. of deposition and –2.18 m w.e. of melt. Net radiation contributes 74% of the melt energy. Compared to ablation measurements in the early 1970s, summer ablation was large. This increase is explained by a combination of a relatively higher net radiation, a lower albedo and larger turbulent heat fluxes that led to more energy being available for melting. No single meteorological variable can be isolated as being the principal reason for the high ablation, however. The lower ice albedo (0.19) is possibly due to ash deposits from forest fires.

In this study we present 19 new or re-analysed series of glacier-wide seasonal mass balance for the Swiss Alps based on direct measurements. The records partly start around 1920 and continue until today. Previously unpublished and unevaluated observations of point winter and annual balance are compiled from various sources and archives. These highly valuable datasets have not yet been consistently evaluated and were thus unavailable to the scientific community. Using distributed modelling for spatial interpolation and extrapolation and homogenization of the point measurements, we infer continuous series of area-averaged mass balance. The results are validated against independent decadal ice volume changes from photogrammetric surveys. Six of the new seasonal series cover 60 years and more and add a substantial amount of information on the variations of regional glacier mass change. This will strengthen the worldwide collection of glacier monitoring data, especially for the data-sparse period before the 1980s. We compare our results to existing long-term series and present an updated assessment of mass-balance variability and glacier sensitivity throughout the European Alps.

We examine the validity of two methods for estimating glacier equilibrium-line altitudes (ELAs) from topographic maps. The ELA determined by contour inflection (the kinematic ELA) and the mean elevation of the glacier correlate extremely well with the ELA determined from mass-balance data (observed ELA). However, the range in glacier elevations above sea level is much larger than the variation in ELA, making this correlation unhelpful. The data were normalized and a reasonable correlation (r2 = 0.59) was found between observed and kinematic ELA.The average of the normalized kinematic ELAs was consistently located down-glacier from the observed ELA, consistent with theory. The normalized mean elevation of the glacier exhibited no correlation and suggests that the toe–headwall altitude ratio is not a good approximation for the ELA. Kinematic waves had no effect on the position of the kinematic ELA. Therefore, topographic maps of glacier surfaces can be used to infer the position of the ELA and provide a method for estimating past ELAs from historic topographic maps.

By comparing modelled and averaged satellite altimeter return, it is demonstrated that time profiles of altimeter return can be used to provide important information on the surface properties of the ice sheets. Altimeter ice-sheet radar echoes from low altitudes and/or relatively low latitudes are, in general, dominated by surface scattering and, in Greenland, the area of surface-dominated return broadly coincides with the zone of summer melting. Seasonal variations in the echo wave-form shapes are negligible in all regions studied, with the possible exception of an area near the margin of the Greenland dry-snow zone. In general, the model explains well the observed variations in mean wave-form shape, but small discrepances between the model wave forms and the recorded wave forms indicate that sub-surface layers may be influencing the shape of the return. The possibility of deriving quantitative estimates of surface properties is explored by fitting model returns to averaged altimeter wave forms from the Wilkes Land plateau in Antarctica. Surface roughness can be measured unambiguously from the wave-form data, but estimations of other parameters, such as grain-size, snow density, and snow temperature are found to be ambiguous because different surface parameters have a similar influence on the shape of the return. Despite this, the derived estimates compare well with ground-based observations and suggest that the satellite altimeter may have an important role to play in providing information on the surface properties of the ice sheets.

We investigate variations in the surface area of glaciers in Sagarmatha national park, Nepal, during the second half of the 20th century through comparison of a map applicable to the late 1950s with the official map of Nepal in the early 1990s. The comparison reveals a slight overall decrease in glacier area (by 4.9%, from 403.9 to 384.6 km2), a result which, though potentially subject to errors arising from cartographic interpretation, is in line with the area reductions found by other studies of Asian glaciers. We find that the areas of some individual glaciers, the largest situated at higher altitudes, increased during the study period. This was most apparent for the glaciers oriented to the south, with the increase occurring mainly in the glacier accumulation zones while the fronts tended to recede. Meanwhile, the smaller glaciers, situated lower and on steep basins, experienced a reduction. For the smaller glaciers, the sections most affected by change were the accumulation zones, and these glaciers showed a tendency for the front to advance. In this region there is a lack of climate data for high altitudes. Nevertheless, observations from stations situated around the park suggest that, alongside temperature variations which are often considered the primary factor eliciting glacier response, changes in precipitation play a significant role.

Many slab avalanches can be attributed to shear failure in a weak, thin basal layer at the slab base. A reasonable starting point for evaluation of the conditions prior to fracture is, therefore, an investigation of shear failure in thin samples of snow. This paper gives the experimental procedure and data on measurements of shear stress versus displacement for thin samples of snow under plane strain and approximately simple shear conditions. The data are given under varying conditions of strain-rate, normal stress, density and snow type. The results show that the samples exhibited strain-softening provided they were sheared faster than they gained strength by settlement under the chosen conditions. If snow fails at the base of a slab in the way in which it fails in the laboratory, then a mechanism is provided whereby tensile stresses would be produced in the slab and whereby the corresponding maximum principal stresses would be rotated toward a direction parallel to the slope, thereby promoting avalanche release.

Rutford Ice Stream and Carlson Inlet are neighbouring glaciers in West Antarctica. Rutford Ice Stream flows at speeds greater than 350 m a−1, whereas Carlson Inlet, which has some similar dimensions and supports a similar driving stress, flows 10–50 times slower. We discuss a range of observations concerning Carlson Inlet, and conclude that there is good indirect evidence that it is a relict ice stream, which ceased streaming more than 240 years BP, but sufficiently recently that its surface morphology, basal water content and basal morphology still retain characteristics produced by streaming. An analysis of expected subglacial drainage pathways indicates that Carlson Inlet is not streaming because it is currently starved of subglacial water, which is currently directed beneath Rutford Ice Stream. This current state of water piracy by Rutford Ice Stream is, however, sensitive to minor thickness changes on the ice streams; a ∼120 m (<4%) thickening of Rutford Ice Stream would divert almost all the subglacial water in the system towards Carlson Inlet and could reactivate its flow. The result highlights the importance of subglacial drainage in controlling ice-stream evolution and the requirement for ice-sheet models to couple ice flow with subglacial drainage.

Permeability and meltwater flow have been studied in sea ice in the Siberian and central Arctic during the summers of 1995 and 1996. A bail-test technique has been adapted to allow for measurements of in situ permeability, found to range between 10−11 and 10−8 m2. Permeability varied by about a factor of 2 between 1995 (above-normal melt rates) and 1996 (below-normal melt rates). Release of fluorescent tracers (fluorescein, rhodamine) furthermore allowed the derivation of flow velocities and assessment of the relevant driving forces. Hydraulic gradients in rough ice and wind stress in ponded ice were found to be particularly important, driving meltwater over distances of several meters per day. The mid- to late-summer ice was found to be permeable enough to completely divert meltwater from the surface into the ice interior. It is shown, however, that lower permeabilities of the upper ice layers as well as refreezing of meltwater, particularly during the early melt season, foster the development of surface melt ponds.

We investigate the mechanics of ice-stream shear margins based on the assumption that the underlying bed behaves plastically. Sliding is assumed to occur if a prescribed, locally defined yield stress is attained, while no sliding is assumed possible if basal shear stress is lower than the yield stress. Mathematically, the ice-flow problem takes the form of a contact problem, in which the zones of sliding are part of the solution and cannot be prescribed arbitrarily. Simplistic assumptions about the location of till failure, or about mechanical conditions at the bed, predict stress singularities at the margins which lead to corresponding singularities in the basal melt rate. The ice-flow problem is solved using a complex variable method, and an associated quasi-static thermal problem is also solved using a Green’s function. High stress concentrations, which coincide with high rates of strain heating, are found on the ice-stream side of the margins, where basal melting is also greatest. Our results further indicate that a temperate zone may form over time above the bed in the margins. These findings differ from earlier studies based on different sliding laws, suggesting a high sensitivity of margin behaviour to basal conditions.

West Antarctic ice streams show pronounced flow variability in their downstream reaches, with changes stranding formerly fast-flowing ice and redirecting discharge. A simple model, in which the temperature gradient in basal ice provides control of fast sliding in the downstream reach, can explain this behavior. Downstream thinning steepens the temperature gradient near the bed, increasing upward heat flow and the tendency toward basal freezing. The basal temperature gradient is steepest and the tendency toward basal freezing the strongest in ice that has experienced the most rapid downstream thinning, that is, the fastest-flowing ice. The most ‘successful’ rapid outflows are regions where basal water from elsewhere is likely to be consumed. Freezing here leads to episodic slow-downs and redirections of flow, the history of which appears in satellite imagery as ice rises, distorted streaklines, and margin jumps created when discharge migrates to areas with more favorable basal conditions. One compelling consequence of this process is that it makes catastrophic collapse less likely; if discharge currents are forced to slow when they become too fast (thin), then there may be an upper bound on the retreat rate and discharge flux of the West Antarctic ice sheet (WAIS) ice-stream system under the present climate.

We investigate the elevation and mass-balance response of tributary glaciers following the loss of the Larsen A and B ice shelves, Antarctic Peninsula (in 1995 and 2002 respectively). Our study uses MODIS imagery to track ice extent, and ASTER and SPOT5 digital elevation models (DEMs) plus ATM and ICESat laser altimetry to track elevation changes, spanning the period 2001–09. The measured Larsen B tributary glaciers (Hektoria, Green, Evans, Punchbowl, Jorum and Crane) lost up to 160 m in elevation during 2001–06, and thinning continued into 2009. Elevation changes were small for the more southerly Flask and Leppard Glaciers, which are still constrained by a Larsen B ice shelf remnant. In the northern embayment, continued thinning of >3 m a−1 on Drygalski Glacier, 14 years after the Larsen A ice shelf disintegrated, suggests that mass losses for the exposed Larsen B tributaries will continue for years into the future. Grounded ice volume losses exceed 13 km3 for Crane Glacier and 30 km3 for the Hektoria–Green–Evans glaciers. The combined mean loss rate for 2001–06 is at least 11.2 Gt a−1. Our values differ significantly from published mass-budget-based estimates for these embayments, but are a reasonable fraction of GRACE-derived rates for the region (∼40 Gt a−1).

The values of the Voellmy friction parameters of 735 historical avalanches that have occurred along 26 paths in the Chamonix valley, France, since 1958 are back-analyzed with a depth-averaged hydraulic model, including sub-models for erosion, entrainment and deposition. For each path, the longitudinal and crosswise topographic profiles were derived from a high-resolution digital elevation model acquired by laser scanning. The initial snow depth and snow cohesion, as well as various physical properties of snow, were computed from numerical simulations of the detailed snowpack model Crocus fed by the SAFRAN meteorological analysis. For each event, the full ranges of the two friction parameters were scanned and the pairs of friction parameters for which the run-out altitude is found close enough to the observed one (with an uncertainty of ±5 m) were retained. Statistical class analysis was used to investigate the correlation between the obtained friction coefficients and the snow physical properties. No evident trend with the snow parameters was found for the inertial friction coefficient. For the static friction coefficient, an increasing trend with temperature and density was observed, as well as a decreasing trend with liquid water content and initial snow depth. Although modeling assumptions and limitations regarding data and the calibration procedure should be kept in mind, these trends are worth noting, allowing avalanche simulations to be refined to take into account prevailing weather and snow conditions.

During 2000–07, five giant icebergs (B15A, B15J, B15K, C16 and C25) adrift in the southwestern Ross Sea, Antarctica, were instrumented with global positioning system (GPS) receivers and other instruments to monitor their behavior in the near-coastal environment. The measurements show that collision processes can strongly influence iceberg behavior and delay their progress in drifting to the open ocean. Collisions appear to have been a dominant control on the movement of B15A, the largest of the icebergs, during the 4-year period it gyrated within the limited confines of Ross Island, the fixed Ross Ice Shelf and grounded C16. Iceberg interactions in the near-coastal regime are largely driven by ocean tidal effects which determine the magnitude of forces generated during collision and break-up events. Estimates of forces derived from the observed drift trajectories during the iceberg-collisioninduced calving of iceberg C19 from the Ross Ice Shelf, during the iceberg-induced break-off of the tip of the Drygalski Ice Tongue and the break-up of B15A provide a crude estimate of the stress scale involved in iceberg calving. Considering the total area the vertical face of new rifts created in the calving or break-up process, and not accounting for local stress amplification near rift tips, this estimated stress scale is 104 Pa.

Present-day mass loss from the West Antarctic ice sheet is centred on the Amundsen Sea Embayment (ASE), primarily through ice streams, including Pine Island, Thwaites and Smith glaciers. To understand the differences in response of these ice streams, we ran a perturbed parameter ensemble, using a vertically-integrated ice flow model with adaptive mesh refinement. We generated 71 sets of three physical parameters (basal traction coefficient, ice viscosity stiffening factor and sub-shelf melt rate), which we used to simulate the ASE for 50 years. We also explored the effects of different bed geometries and basal sliding laws. The mean rate of sea-level rise across the ensemble of simulations is comparable with current observed rates for the ASE. We found evidence that grounding line dynamics are sensitive to features in the bed geometry: simulations using BedMap2 geometry resulted in a higher rate of sea-level rise than simulations using a rougher geometry, created using mass conservation. Modelled grounding-line retreat of all the three ice streams was sensitive to viscosity and basal traction, while the melt rate was more important in Pine Island and Smith glaciers, which flow through more confined ice shelves than Thwaites, which has a relatively unconfined shelf.

In glacial environments particle-size analysis of moraines provides insights into clast origin, transport history, depositional mechanism and processes of reworking. Traditional methods for grain-size classification are labour-intensive, physically intrusive and are limited to patch-scale (1 m2) observation. We develop emerging, high-resolution ground- and unmanned aerial vehicle-based ‘Structure-from-Motion’ (UAV-SfM) photogrammetry to recover grain-size information across a moraine surface in the Heritage Range, Antarctica. SfM data products were benchmarked against equivalent datasets acquired using terrestrial laser scanning, and were found to be accurate to within 1.7 and 50 mm for patch- and site-scale modelling, respectively. Grain-size distributions were obtained through digital grain classification, or ‘photo-sieving’, of patch-scale SfM orthoimagery. Photo-sieved distributions were accurate to <2 mm compared to control distributions derived from dry-sieving. A relationship between patch-scale median grain size and the standard deviation of local surface elevations was applied to a site-scale UAV-SfM model to facilitate upscaling and the production of a spatially continuous map of the median grain size across a 0.3 km2 area of moraine. This highly automated workflow for site-scale sedimentological characterization eliminates much of the subjectivity associated with traditional methods and forms a sound basis for subsequent glaciological process interpretation and analysis.

Subglacial hydrology plays a key role in many glaciological processes, including ice dynamics via the modulation of basal sliding. Owing to the lack of an overarching theory, however, a variety of model approximations exist to represent the subglacial drainage system. The Subglacial Hydrology Model Intercomparison Project (SHMIP) provides a set of synthetic experiments to compare existing and future models. We present the results from 13 participating models with a focus on effective pressure and discharge. For many applications (e.g. steady states and annual variations, low input scenarios) a simple model, such as an inefficient-system-only model, a flowline or lumped model, or a porous-layer model provides results comparable to those of more complex models. However, when studying short term (e.g. diurnal) variations of the water pressure, the use of a two-dimensional model incorporating physical representations of both efficient and inefficient drainage systems yields results that are significantly different from those of simpler models and should be preferentially applied. The results also emphasise the role of water storage in the response of water pressure to transient recharge. Finally, we find that the localisation of moulins has a limited impact except in regions of sparse moulin density.

Knowledge of iceberg calving is important for understanding instabilities of tidewater glaciers and ice sheets. Since 1995 the terminus of LeConte Glacier, Alaska, U.S.A., has retreated about 2 km and the glacier has thinned approximately 120 m at its 1999 terminus position. Our focus is short-term (hours to weeks) variability of the frequency and magnitude of calving events and calving flux. Both photogrammetric and visual observations are employed in a temporal analysis over a several-week period. We combined these data with measurements of ice speed, tide level, surface water input and water-storage estimates in an attempt to better understand the calving process. Contrary to results obtained over longer time-scales on other glaciers, our results show no correlation between ice speed and the frequency of calving. However, calving events do not appear to occur randomly; often they are a response to measurable changes in other parameters within the terminus region. Caclving can often be attributed to buoyancy perturbations and possibly flexure of the nearly floating terminus. Given the multiple possibilities for buoyancy perturbations, we have found no simple relationship between any specific forcing parameter and calving at short time-scales.