We synthesize previously published remote-sensing observations, radar data and model output to obtain a ~1000 year ice flow history for the Siple Coast ice-stream system in West Antarctica to investigate the timing and magnitude of changes in mass flux. The synthesized history shows significant short-term variability in ice-stream shear margin and grounding line position due to internal variability of the coupled system. The chronology highlights the interplay between adjacent ice streams, which implies that the behavior of any individual ice stream should not be examined in isolation. Furthermore, individual events cannot be fully interpreted without an understanding of the broad-scale, long-term variability in the ice sheet. In the context of this millennium-scale history, we interpret the relatively recent stagnation of Kamb Ice Stream (KIS) as just one stage in the thermodynamic cycle of an ice stream in this region. The changes in mass balance that result from the KIS stagnation may thus be viewed as century-scale 'noise' relative to the longer-term trend. Understanding and characterizing this noise is a necessary step before accurate model-based predictions of ice-sheet mass balance for the next century can be made.

Crystal-orientation fabric (COF) has a large influence on ice-sheet flow. Earlier radar studies have shown that COF-based birefringence occurs within ice sheets. Radio-wave scattering in polar ice results from changing physical properties of permittivity and conductivity that arise from differing values of density, acidity and COF. We present an improved mathematical model that can handle all these phenomena together. We use this matrix-based model to study the two-way propagation of depolarized radio waves that scatter at both isotropic and anisotropic boundaries. Based on numerical simulations, we demonstrate how COF affects the radar signals in terms of radar polarization and frequency. We then compare the simulated features with VHF radar data obtained at two contrasting inland sites in East Antarctica, where COF is known from ice-core studies. These two sites are Dome Fuji, located near a dome summit, and Mizuho, located in a converging ice-flow region. Data at Dome Fuji are dominated by typical features resulting from birefringence. In contrast, both birefringence and anisotropic scattering affect the radar data at Mizuho. We argue that radar methods can be used to determine principal axes and strength of birefringence in the ice sheets.

The instability of hanging glaciers and more generally of avalanching glaciers is discussed on the basis of observations performed on several glaciers located in the European Alps. A classification of avalanching glaciers is proposed, which allows a primary appreciation of the danger inherent in these glaciers. On the basis of field observations and results of numerical simulations of crevassing, the fracture processes which lead to major icefalls, as well as their recurrence, are analyzed. A method for predicting the time of failure is then discussed. The disaggregation of the unstable ice masses usually observed prior to large icefalls is investigated and its implications for the forecasting of icefalls analyzed.

Limitations of access have long restricted exploration and investigation of the cavities beneath ice shelves to a small number of drillholes. Studies of sea-ice underwater morphology are limited largely to scientific utilization of submarines. Remotely operated vehicles, tethered to a mother ship by umbilical cable, have been deployed to investigate tidewater-glacier and ice-shelf margins, but their range is often restricted. The development of free-flying autonomous underwater vehicles (AUVs) with ranges of tens to hundreds of kilometres enables extensive missions to take place beneath sea ice and floating ice shelves. Autosub2 is a 3600 kg, 6.7 m long AUV, with a 1600 m operating depth and range of 400 km, based on the earlier Autosub1 which had a 500 m depth limit. A single direct-drive d.c. motor and five-bladed propeller produce speeds of 1–2 m s−1. Rear-mounted rudder and stern-plane control yaw, pitch and depth. The vehicle has three sections. The front and rear sections are free-flooding, built around aluminium extrusion space-frames covered with glass-fibre reinforced plastic panels. The central section has a set of carbon-fibre reinforced plastic pressure vessels. Four tubes contain batteries powering the vehicle. The other three house vehicle-control systems and sensors. The rear section houses subsystems for navigation, control actuation and propulsion and scientific sensors (e.g. digital camera, upward-looking 300 kHz acoustic Doppler current profiler, 200 kHz multibeam receiver). The front section contains forward-looking collision sensor, emergency abort, the homing systems, Argos satellite data and location transmitters and flashing lights for relocation as well as science sensors (e.g. twin conductivity–temperature–depth instruments, multibeam transmitter, sub-bottom profiler, AquaLab water sampler). Payload restrictions mean that a subset of scientific instruments is actually in place on any given dive. The scientific instruments carried on Autosub are described and examples of observational data collected from each sensor in Arctic or Antarctic waters are given (e.g. of roughness at the underside of floating ice shelves and sea ice).

Glacier response to climate can be characterized by a single time-scale when the glacier changes sufficiently slowly. Then the derivative of volume with respect to area defines a thickness scale similar to that of Jóhannesson and others, and the time-scale follows from it. Our version of the time-scale is different from theirs because it explicitly includes the effect of surface elevation on mass-balance rate, which can cause a major increase in the time-scale or even lead to unstable response. The time constant has a dual role, controlling both the rate and magnitude of response to a given climate change. Data from South Cascade Glacier, Washington, U.S.A., illustrate the ideas, some of the difficulty in obtaining accurate values for the thickness and time-scales, and the susceptibility of all response models to potentially large errors.

Since the mid-19th century, most glaciers have been losing area and volume. This loss of area has not been homogeneous in time and space, and direct observations are sparse, making regional and global estimates of glacier change difficult. This paper focuses on developing a single index for monitoring glacier change, one that would be particularly useful for remote-sensing applications. We combine the results of direct glacier mass-balance observations B, total glacier area S and accumulation area Sc derived from maps or remotely sensed images. Using the accumulation–area ratio (AAR = Sc/S), we note the differences between observed AAR, time-averaged 〈AAR〉 and the equilibrium state AAR0, as determined by its value at B = 0 from a regression of B(AAR). We suggest that αd = (〈AAR〉 – AAR0)/AAR0 quantifies the difference between the currently observed state of glaciers and their equilibrium state and measures the delay in the dynamic response of S relative to the climatic response of Sc. Using all available observations for the period 1961–2004, αd ≈ −65% for tropical glaciers, which implies their rapid shrinkage as S continues to decrease and ‘catch up’ with Sc. During the same period, mid-latitude and polar glaciers show less negative values of αd. Of 86 glaciers from all latitudes and regions, only 11 show positive αd at any time between 1961 and 2004. Averaged over 1961–2004, αd is −15.1 ± 2.2%, and 〈B〉 is −360 ± 42 mm a−1 w.e. Values for AAR0 range between about 40% and 80%, but the bulk of the equilibrium values are between 50% and 60%. The average AAR0 is 57.9 ± 0.9% and has remained stable over time (the equilibrium AAR has not changed with climate). Overall, the observed negative αd suggests a committed retreat of glaciers and their continuing contribution to sea level even if global temperature is held constant.

We present estimates of internal shear rates of real-scale avalanches that are based on velocity measurements. Optical velocity sensors installed on the instrument pylon at the Swiss Vallée de la Sionne test site are used to measure flow velocities at different flow heights of three large dry and wet snow avalanches. Possible sources of error in the correlation analysis of the time-lagged reflectivity signals measured by optical sensors are identified for real-size avalanches. These include spurious velocities due to noise and elongated peaks. An appropriate choice of the correlation length is essential for obtaining good velocity estimates. Placing restrictions on the maximum possible accelerations in the flow improves the analysis of the measured data. Coherent signals are found only in the dense flowing cores. We observe the evolution of shear rates at different depths between the front and tail of the flowing avalanche. At the front, large shear rates are found throughout the depth; at the tail, plug flows overriding highly sheared layers near the bottom of the flow are observed. The measured velocities change strongly with height above the ground and fluctuations around the measured mean velocity can be identified. We find that the dense flows are laminar, undergoing a transition from supercritical to subcritical flow behaviour from the head to the tail. Furthermore, we provide real-scale experimental evidence that the mean shear rate and the magnitude of velocity fluctuations increase with the mean discharge.

Radio-echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale. Radar signals of 320–370 MHz penetrate ice at sub-freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water. Radar signals of 5–20 MHz, on the other hand, see through both the cold and the temperate ice down to the glacier bed. Radio-echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in Svalbard: Kongsvegen, Uvérsbreen, Midre Lovénbreen and Austre Brøggerbreen. In the ablation area of Kongsvegen, a cold surface layer (50–160 m thick) was underlain by a warm basal layer which is advected from the temperate accumulation area. The surface ablation of this cold layer may be compensated by freezing at its lower cold-temperate interface. This requires that the free water content in the ice at the freezing interface is about 1 % of the volume. The cold surface layer is thicker beneath medial moraines and where cold-based hanging glaciers enter the main ice stream. On Uvérsbreen the thermal regime was similar to that of Kongsvegen. A temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between Kongsvegen and Uvérsbreen where meltwater accumulates during the summer (near the subglacial lake Setevatnet, 250 m a.s.l.). Lovénbreen w as frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer (up to 50 m thick) was fed by temperate ice from two cirques. On Austre Brøggerbreen, a temperate basal layer was not detected by radio-echo soundings but the basal ice was observed to be at the melting point in two boreholes.

Annual-layer thickness data, spanning AD 1534–2001, from an ice core from East Rongbuk Col on Qomolangma (Mount Everest, Himalaya) yield an age–depth profile that deviates systematically from a constant accumulation-rate analytical model. The profile clearly shows that the mean accumulation rate has changed every 50–100 years. A numerical model was developed to determine the magnitude of these multi-decadal-scale rates. The model was used to obtain a time series of annual accumulation. The mean annual accumulation rate decreased from ∼0.8 m ice equivalent in the 1500s to ∼0.3 m in the mid-1800s. From ∼1880 to ∼1970 the rate increased. However, it has decreased since ∼1970. Comparison with six other records from the Himalaya and the Tibetan Plateau shows that the changes in accumulation in East Rongbuk Col are broadly consistent with a regional pattern over much of the Plateau. This suggests that there may be an overarching mechanism controlling precipitation and mass balance over this area. However, a record from Dasuopu, only 125 km northwest of Qomolangma and 700 m higher than East Rongbuk Col, shows a maximum in accumulation during the 1800s, a time during which the East Rongbuk Col and Tibetan Plateau ice-core and tree-ring records show a minimum. This asynchroneity may be due to altitudinal or seasonal differences in monsoon versus westerly moisture sources or complex mountain meteorology.

Ice cliffs have been identified as a reason for higher ablation rates on debris-covered glaciers than are implied by the insulation effects of the debris. This study aims to improve our understanding of cliff backwasting, and the role of radiative fluxes in particular. An energy-balance model is forced with new data gathered in May and October 2013 on Lirung Glacier, Nepalese Himalaya. Observations show substantial variability in melt between cliffs, between locations on any cliff and between seasons. Using a high-resolution digital elevation model we calculate longwave fluxes incident to the cliff from surrounding terrain and include the effect of local shading on shortwave radiation. This is an advance over previous studies, that made simplified assumptions on cliff geometry and radiative fluxes. Measured melt rates varied between 3.25 and 8.6 cm d−1 in May and 0.18 and 1.34 cm d−1 in October. Model results reproduce the strong variability in space and time, suggesting considerable differences in radiative fluxes over one cliff. In October the model fails to reproduce stake readings, probably due to the lack of a refreezing component. Disregarding local topography can lead to overestimation of melt at the point scale by up to ∼9%.

Water in polycrystalline ice at its melting point forms a system of veins at the three-grain junctions. The veins join together at nodes, which are the four-grain junctions. The shape of a node, a tetrahedron with non-spherical faces and open corners, is determined completely by the dihedral angle for water in contact with a grain boundary. Using the observed value for this angle, namely 33.6°, the paper computes the tetrahedral shape. This is a surface-tension problem with initially unknown boundaries. The result shows that the ratio of vein volume to node volume is R = 0.072 l/d, where l is the average length of a vein between two nodes, and d is the vein diameter measured between edges. For example, in a specimen of ice grown from the melt in the laboratory R was 18.

Since 1 October 1995, an automatic weather station has been operated on the tongue of Morteratschgletscher, Switzerland. The station stands freely on the ice, and sinks with the melting glacier surface. It is located at 2100 m a.s.l., and measures air temperature, wind speed and direction, incoming and reflected solar radiation, pressure and snow temperature. A sonic ranger, mounted to stakes drilled into the ice, measures surface height from which melt rates and snow accumulation can be derived. In this paper the data for the period 1 October 1995 to 30 September 1998 are used to evaluate the surface energy balance. The turbulent energy fluxes are calculated with the bulk method. The turbulent exchange coefficient Ch is used as a control parameter. With Ch = 0.00127 the calculated melt equals the observed melt, which is 17.70 m w.e. over the 3 years. When averaged over the time when melting occurs (i.e. 35% of the time), the mean surface heat flux equals 191 W m−2. Net shortwave radiation contributes 177 W m−2, net longwave radiation −25 W m−2, the sensible-heat flux 31 W m−2 and the latent-heat flux 8 W m−2.

We use European Space Agency Envisat data to present the first observational evidence that a Northern Hemisphere tsunami triggered Antarctic ice-shelf calving more than 13 000 km away. The Honshu tsunami of 11 March 2011 traversed the Pacific Ocean in <18 hours where it impinged on the Sulzberger Ice Shelf, resulting in the calving of 125 km2 of ice from a shelf front that had previously been stable for >46 years. This event further illustrates the growing evidence of ocean-wave impact on Antarctic calving and emphasizes the teleconnection between the Antarctic ice sheet and events as far away as the Northern Hemisphere.

During summer 2011, seismic activity in the ablation zone of the western Greenland ice sheet (GrIS) was monitored using a network of three-component seismometers. The seismic record includes a large variety of icequakes and seismic tremors that demonstrate a clear correlation with subglacial water flow. We verified the existence of well-known shallow icequakes (related to surface crevasse formation), deep icequakes (located at 100–160 m depth) and narrow-banded short-term seismic tremors (tens of seconds in duration). In addition, we present previously unreported long-term tremors lasting several hours. Using attenuation of the measured tremor amplitude, we locate the epicentre of this long-term tremor to a large moulin within our study area. Between 3 and 11 Hz, our continuous seismic record is dominated by this ‘moulin tremor’ and shows strong correlation with the water level of the generating moulin. We argue that monitoring of icequake and glacial tremor sources bears high potential for investigating glacier hydraulics and dynamics, and is thus an ideal supplement to traditional glaciological measurements.

The available methods for dating of ice cores are based on radioactive decay, ice-flow calculations, or stratigraphic observations. The two former categories are broadly outlined, and special emphasis is given to stratigraphic methods. Reference horizons are established back to A.D. 1783, in the form of elevated electrical conductivities due to fallout of soluble volcanic debris. Seasonal variations in the concentrations of insoluble microparticles and/or stable isotopes are measured over the entire 400 m lengths of three ice cores, recovered by Greenland Ice Sheet Program (GISP). The resulting absolute time scales are probably accurate within a few years per thousand. Techniques are outlined for re-establishing the approximate, original shape of heavy-isotope profiles that have been more or less smoothed by diffusion in firn and ice. Annual-layer thickness measurements on 24 increments down to 1130 m depth in the Camp Century ice core determine a flow pattern, consistent with that suggested by Dansgaard and Johnsen (1969), and a Camp Century time scale with an estimated uncertainty better than 3% back to 10000 years B.P.

The spatial distribution of accumulation across Siple Dome, West Antarctica, is determined from analysis of the shapes of internal layers detected by radio-echo sounding (RES) measurements. A range of assumed accumulation patterns is used in an ice-flow model to calculate a set of internal layer patterns. Inverse techniques are used to determine which assumed accumulation pattern produces a calculated internal layer pattern that best matches the shape of internal layers from RES measurements. All of the observed internal layer shapes at Siple Dome can be matched using a spatially asymmetric accumulation pattern which has been steady over time. Relative to the divide, the best-fitting accumulation pattern predicts 40% less accumulation 30 km from the divide on the south flank of Siple Dome and 15–40% more accumulation 30 km from the divide on the north flank. The data also allow the possibility for a small time variation of the pattern north of the divide. The mismatch between the calculated and the observed layer shapes is slightly reduced when the accumulation rate north of the divide is higher in the past (> 5kyr BP) than at present. Sensitivity tests show that the predicted change in the spatial accumulation pattern required to cause the slight Siple Dome divide migration (inferred from previous studies) would be detectable in the internal layer pattern if it persisted for > 2 kyr. Our analysis reveals no evidence that such a change has occurred, and the possible change in accumulation distribution allowed by the data is in the opposite sense. Therefore, it is unlikely that the Siple Dome divide migration has been caused by a temporal change in the spatial pattern of accumulation. This conclusion suggests the migration may be caused by elevation changes in Ice Streams C and D at the boundaries of Siple Dome.

The glaciers in the Melville Bay region of northwest Greenland have shown a mean retreat since the earliest observations at the beginning of the 20th century. The largest, Steenstrup Gletscher, has retreated ∼20 km, partly during the period of atmospheric cooling 1940–80. Melville Bay air-temperature observations starting in 1981 indicate a regional change of +0.20°C a−1. This exceeds the warming on the east coast of Greenland, confirming the west coast to be a region of relatively large change, also in a global perspective. The largest temperature increase is observed in the winter months (0.3–0.4°C a−1). Results from a 4 year (2004–08) net ablation record obtained by an automatic weather station (AWS) near the calving front of Steenstrup Gletscher show an ablation rate that is relatively low for a low-elevation position on the Greenland ice sheet (2.4 m ice equivalent per year). A first-order estimate from positive degree-day totals suggests that net ablation has roughly doubled since the 1980s. A surface energy and mass-balance model is applied to the Steenstrup AWS data to quantify the energy flux contributions to surface melt. Solar radiation is the main source for melt energy, but, due to shortwave radiation penetration into the ice, only one-third of the melt takes place at the glacier surface; nearly two-thirds occurs within the upper ice layers.

The surface mass balance (SMB) at Dome Fuji, East Antarctica, was estimated using 36 bamboo stakes (grid of 6 × 6, placed at 20 m intervals) from 1995 to 2006. The heights of the stake tops from the snow surface were measured at 0.5 cm resolution twice monthly in 1995, 1996, 1997 and 2003, and once a year for the rest of the study period. To account for snow settling, the average snow density at the stake base during the measurements was used for converting the stake-height data to SMB. The annual SMB from 1995 to 2006 at Dome Fuji was 27.3 ± 1.5 kg m−2 a−1. This result agrees well with the annual SMB from AD 1260 to 1993 (26.4 kg m−2 a−1) estimated from volcanic signals in the Dome Fuji ice core. Over the period 1995–2006, there were 37 (8.6% of the measurements) negative or zero annual SMB results. Variation in the multi-year averages of annual SMB decreased with the square root of the number of observation years, and 10 years of observations of a single stake allowed the estimation of annual SMB at ±10% accuracy. The frequency distributions of annual and monthly SMB were examined. The findings clarify the complex behavior of the annual and monthly SMB at Dome Fuji, which will be common phenomena in areas of low snow accumulation of the interior of the Antarctic ice sheet.

We present an analysis of temporal trends in ∼55 000 avalanches recorded between 1946 and 2010 in the French Alps and two north/south subregions. First, Bayesian hierarchical modelling is used to isolate low-, intermediate- and high-frequency trends in the mean avalanche occurrence and runout altitude per year/winter. Variables are then combined to investigate their correlation and the recent evolution of large avalanches. Comparisons are also made to climatic and flow regime covariates. The results are important for risk assessment, and the development of new high-altitude climate proxies. At the entire French Alps scale, a major change-point exists in ∼1978 at the heart of a 10 year period of high occurrences and low runout altitudes corresponding to colder and snowier winters. The differences between this change-point and the beginning/end of the study period are 0.1 avalanche occurrences per winter and per path and 55 m in runout altitude. Trends before/after are well correlated, leading to enhanced minimal altitudes for large avalanches at this time. A marked upslope retreat (80 m for the 10 year return period runout altitude) accompanied by a 12% decrease in the proportion of powder snow avalanches has occurred since then, interrupted from about 2000. The snow-depth and temperature control on these patterns seems significant (R = 0.4–0.6), but is stronger at high frequencies for occurrences, and at lower frequencies for runout altitudes. Occurrences between the northern and southern French Alps are partially coupled (R∼0.4, higher at low frequencies). In the north, the main change-point was an earlier shift in ∼1977, and winter snow depth seems to be the main control parameter. In the south, the main change-point occurred later, ∼1979–84, was more gradual, and trends are more strongly correlated with winter temperature.

The deformation of the ground surface that is produced by frost heave has motivated almost a century of concerted laboratory, field and theoretical studies. Well before the development of equipment capable of resolving the microscopic films that support liquid transport towards growing ice lenses, early investigators predicted their occurrence and noted their importance. Idealized experiments continue to prompt theoretical advances that have been combined to develop predictive models for the macroscopic frost-heave characteristics that are seen in the field. This contribution highlights steps on the road to our current understanding of the physical interactions that control how ice forms in unconsolidated porous media.