Twin glaciers collapsed in 2016 near Aru Co, western Tibet and caused extreme loss to human beings. In this study, we attempted to track the dynamics of glaciers in the region, for example the glacier area and mass changes in Aru Co for the period 1971–2016, which were determined using topographic maps and Landsat images and ASTER-derived DEMs (2011–16), the Shuttle Radar Terrain Mission DEM (2000) and topographic maps (1971). Our results showed that the glacier area of Aru Co decreased by −0.4 ± 4.1% during 1971–2016. The geodetic mass-balance results showed that the glaciers in Aru Co lost mass at a rate of −0.15 ± 0.30 m w.e. a−1 during 1971–99, while they gained mass at a rate of 0.33 ± 0.61 m w.e. a−1 for the period 1999–2016. The twin glaciers experienced a larger negative mass budget than the others in the region before 1999. This process produced large amounts of meltwater, followed by a sustained increase in the meltwater on the pressure melting point, possibly in response to a period of positive mass balance (1999–2016) and then, transferred to the glacier bed until the glaciers collapsed.

We investigate the impact of climate change on Gurenhekou glacier, southern Tibetan Plateau, which is representative of the tens of thousands of mountain glaciers in the region. We apply a three-dimensional, thermomechanically coupled full-Stokes model to simulate the evolution of the glacier. The steep and rugged bedrock geometry requires use of such a flow model. We parameterize the temperature and surface mass-balance (SMB) uncertainties using nearby automatic weather and meteorological stations, 6 year measured SMB data and an energy-balance model for a nearby glacier. Summer air temperature increased at 0.02 Ka−1 over the past 50 years, and the glacier has retreated at an average rate of 8.3 m a−1. Prognostic simulations suggest an accelerated annual average retreat rate of ~9.1 ma−1 along the central flowline for the next 25 years under continued steady warming. However, regional climate models suggest a marked increase in warming rate over Tibet during the 21st century, and this rate causes about a 0.9 ± 0.3% a−1 loss of glaciated area and 1.1 ± 0.6% a−1 shrinkage of glacier volume. These results, the rather high warming rates predicted and the small sizes of most Tibetan glaciers, suggest that significant numbers of glaciers will be lost in the region during the 21st century.

The spatial pattern and morphometry of bedforms and their relationship to sediment thickness have been analysed in the Marguerite Bay Palaeo-ice stream Trough, western Antarctic Peninsula. Over 17 000 glacial landforms were measured from geophysical datasets, and sediment thickness maps were generated from acoustic sub-bottom profiler data. These analyses reveal a complex bedform pattern characterised by considerable spatial diversity, influenced heavily by the underlying substrate. The variability in length and density of mega-scale lineations indicates an evolving bedform signature, whereby landforms are preserved at different stages of maturity. Lineation generation and attenuation is associated with regions of thick, soft till where deformation was likely to be the greatest. The distribution of soft till and the localised extent of grounding-zone wedges (GZWs) indicate a dynamic sedimentary system characterised by considerable spatio-temporal variability in sediment erosion, transport and deposition. Formation of GZWs on the outer shelf of Marguerite Trough, within the error range of the radiocarbon dates, requires large sediment fluxes (upwards of 1000 m3 a−1 (m grounding line width)−1), and a >1 m thick mobile till layer, or rapid basal sliding velocities (upwards of 6 km a−1).

Observations of surface motion and ice deformation from 2002–03 were used to infer mean stress fields in a cross-section of Black Rapids Glacier, Alaska, USA, over seasonal timescales. Basal shear stresses in a well-defined zone north of the center line (orographic left) were approximately 7% and 16% lower in spring and summer, respectively, than in winter. Correspondingly higher stresses were found near the margins. These changes in the basal shear stress distribution were sufficiently large to cause mean surface velocities to be 1.2 and 1.5 times larger in spring and summer than in winter. These results were inferred with a simple inverse finite-element flow model that can successfully reproduce bulk surface velocities and tiltmeter data. Stress redistribution between the well-defined zone and the margins may also occur over much shorter time periods as a result of rapidly changing basal conditions (ice–bed decoupling or enhanced till deformation), thereby causing large variations in surface velocity and strongly influencing the glacier’s net motion during summer.

Ernst Sorge, a member of Wegener’s Greenland Expedition 1930–31, discovered an important law on the densification of snow in high polar glaciers. It is here given a simple mathematical form and some of its implications are formulated and discussed. Apart from its significance to glaciology and snow mechanics, Sorge’s law should also be useful in the study of consolidation of accumulating fine-grained lacustrian and oceanic sediments.

The microwave emission from a model snow field, consisting of randomly spaced ice spheres which scatter independently, is calculated. Mie scattering and radiative transfer theory are applied in a manner similar to that used in calculating microwave and optical properties of clouds. The extinction coefficient is computed as a function of both microwave wavelength and ice-particle radius. Volume scattering by the individual ice particles in the snow field significantly decreases the computed emission for particle radii greater than a few hundredths of the microwave wavelength. Since the mean annual temperature and the accumulation rate of dry polar firn mainly determine the grain sizes upon which the microwave emission depends, these two parameters account for the main features of the 1.55 cm emission observed from Greenland and Antarctica with the Nimbus-5 scanning radiometer. For snow particle sizes normally encountered, most of the calculated radiation emanates from a layer on the order of 10 m in thickness at a wavelength of 2.8 cm, and less at shorter wavelengths. A marked increase in emission from wet versus dry snow is predicted, a result which is consistent with observations. The model results indicate that the characteristic grain sizes in the radiating layers, dry-firn accumulation rales, areas of summer melting, and physical temperatures, can be determined from multispectral microwave observations.

Due to increased demand for electric energy, which in Norway is produced almost entirely by hydro-electric power plants, extensive glacierized basins are now considered for future power production, However, glacier behaviour has a great impact on the annual run-off from these basins, and information about expected annual deviations from a “normal” discharge must be obtained from mass-balance studies on representative glaciers within the basin. For this reason such studies are presently performed at eight selected Norwegian glaciers; the costs involved are in the order of $3 000-$10 000 annually for each observed glacier.

The transient snow line can be identified easily on conventional air photographs and its height determined by direct comparisons with reliable topographie maps (with contour lines on glaciers). The resolution in ERTS images is sufficiently good to use the satellite data for a similar height determination of the transient snow line on glaciers—at least on the larger valley glaciers and, of course, on ice caps.

Due to an existing correlation between the height of the transient snow line (at the end of the melt season) and the annual specific net mass balance, it is possible to construct a diagram expressing this relationship, provided detailed mass-balance studies have been performed during a period of several years of different mass-balance conditions (ideally comprising both years of negative and of positive net balances). Determinations of the transient snow-line height based upon ERTS data, obtained at the end of the summer season, can then be used to determine the mass balance for those glaciers where the above-mentioned relationship is established. This would be a great advantage in cases where there is a request for information on the net balance only; no separate data on winter balance or summer balance will be obtained by this method.

Experiments have been performed to delineate the transient snow line on glaciers directly from ERTS digital data (CCT magnetic tape). The results indicate that last winter’s snow is characterized by grey-levels 41-48 (of 63 possible grey-scale levels) on MSS-7, whereas exposed glacier ice is represented by levels 13—20 in the same multi-spectral band. Snow and ice can also be separated on MSS-4, but the difference in grey-scale levels between the two materials is much smaller.

A real-time video camera probe was deployed in a hot-water drilled borehole through the Amery Ice Shelf, East Antarctica, where a total ice thickness of 480 m included at least 200 m of basal marine ice. Down-looking and side-looking digital video footage showed a striking transition from white bubbly meteoric ice above to dark marine ice below, but the transition was neither microscopically sharp nor flat, indicating the uneven nature (at centimetre scale) of the ice-shelf base upstream where the marine ice first started to accrete. Marine ice features were imaged including platelet structures, cell inclusions, entrained particles, and the interface with sea water at the base. The cells are assumed to be entrained sea water, and were present throughout the lower 100-150 m of the marine ice column, becoming larger and more prevalent as the lower surface was approached until, near the base, they became channels large enough that the camera field of view could not contain them. Platelets in the marine ice at depth appeared to be as large as 1-2 cm in diameter. Particles were visible in the borehole meltwater; probably marine and mineral particles liberated by the drill, but their distribution varied with depth.

Glacier mass balance and runoff are simulated from 1955 to 2014 for the catchment (46% glacier cover) containing Chhota Shigri Glacier (Western Himalaya) using gridded data from three regional climate models: (1) the Rossby Centre regional atmospheric climate model v.4 (RCA4); (2) the REgional atmosphere MOdel (REMO); and (3) the Weather Research and Forecasting Model (WRF). The input data are downscaled to the simulation grid (300 m) and calibrated with point measurements of temperature and precipitation. Additional input is daily potential global radiation calculated using a DEM at a resolution of 30 m. The mass-balance model calculates daily snow accumulation, melt and runoff. The model parameters are calibrated with available mass-balance measurements and results are validated with geodetic measurements, other mass-balance model results and run-off measurements. Simulated annual mass balances slightly decreased from −0.3 m w.e. a−1 (1955–99) to −0.6 m w.e. a−1 for 2000–14. For the same periods, mean runoff increased from 2.0 m3 s−1 (1955–99) to 2.4 m3 s−1 (2000–14) with glacier melt contributing about one-third to the runoff. Monthly runoff increases are greatest in July, due to both increased snow and glacier melt, whereas slightly decreased snowmelt in August and September was more than compensated by increased glacier melt.

We have tested the ability of a 1.12–1.76 GHz bandwidth airborne Frequency Modulation–Continuous Wave (FM-CW) radar with an effective pulse duration of 3 ns to penetrate temperate ice of the ablation zone of Black Rapids Glacier, central Alaska, U.S.A. We used high-gain horn antennas to suppress clutter, and tested over cold and nearly ideal surface conditions. Englacial horizons dipping to at least 60 m depth were found along three sections of one axial profile. More narrow-band (1.21–1.29 GHz), low-resolution (24 ns pulse duration) profiles from a fourth section detected events at about 100–150 m depth. Comparative profiles recorded with a 100 MHz short-pulse-type radar reproduce the horizons of two of the sections, and verify the penetration in all cases. All horizons are composed of diffractions. We interpret voids from the phase of the 100 MHz diffractions within one of the horizons. The diffraction nature of the horizons, the void interpretation and the proximity to a nearby and up-glacier pothole field lead us to conclude that the horizons within two of the sections are meandering drainage channels. A more complex, branching structure with near-surface horizons profiled within the third section much farther down-glacier may also be a complex drainage system fed by near-surface melting. The FM-CW signal-to-clutter-noise ratios of some of the targets predict that they could be detected at 200 m depth in the 1–2 GHz range. Significant performance improvements at maximum vertical resolution could be achieved with higher-gain antennas.

We present a novel automated processing method for obtaining layer dip from radio-echo sounding (RES) data. The method is robust, easily applicable and can be used to process large (several terabytes) ground and airborne RES datasets using modest computing resources. We give test results from the application of the method to two Antarctic datasets: the Fletcher Promontory ground-based radar dataset and the Wilkes Subglacial Basin airborne radar dataset. The automated RES processing (ARESP) method comprises the basic steps: (1) RES noise reduction; (2) radar layer identification; (3) isolation of individual ‘layer objects’; (4) measurement of orientation and other object properties; (5) elimination of noise in the orientation data; and (6) collation of the valid dip information. The apparent dip datasets produced by the method will aid glaciologists seeking to understand ice-flow dynamics in Greenland and Antarctica: ARESP could enable a shift from selective regional case studies to ice-sheet-scale studies.

Sediment production at a terrestrial section of the ice-sheet margin in West Greenland is dominated by debris released through the basal ice layer. The debris flux through the basal ice at the margin is estimated to be 12–45 m3 m−1 a−1. This is three orders of magnitude higher than that previously reported for East Antarctica, an order of magnitude higher than sites reported from in Norway, Iceland and Switzerland, but an order of magnitude lower than values previously reported from tidewater glaciers in Alaska and other high-rate environments such as surging glaciers. At our site, only negligible amounts of debris are released through englacial, supraglacial or subglacial sediment transfer. Glaciofluvial sediment production is highly localized, and long sections of the ice-sheet margin receive no sediment from glaciofluvial sources. These findings differ from those of studies at more temperate glacial settings where glaciofluvial routes are dominant and basal ice contributes only a minor percentage of the debris released at the margin. These data on debris flux through the terrestrial margin of an outlet glacier contribute to our limited knowledge of debris production from the Greenland ice sheet.

We investigate the dynamics of a small surge-type valley glacier as part of a study to characterize glacier response to climate in the Donjek Range, southwest Yukon, Canada. Pole displacements were measured using kinematic GPS techniques during three consecutive summer field seasons. Measured surface velocities range from <10 m a−1 over the lower 1500 m of the 5 km long glacier to a maximum of ∼25–35 m a−1 over the upper 3500 m. Basal velocities along an approximate flowline are reconstructed from the measured surface velocities using inverse methods. Control tests are used to validate the inversion scheme, and sensitivity tests are performed to evaluate the influence of the flow-law coefficient, shape factor and longitudinal averaging length. Inversion of the real data shows that basal motion accounts for 50–100% of the total surface motion along the flowline. Based on these results, and several other lines of evidence, we suggest this glacier may be undergoing a slow surge.

We conducted seismic refraction surveys in the upper ablation area of Storglaciären, a small valley glacier located in Swedish Lapland. We estimated seismic-wave attenuation using the spectral-ratio method on the energy travelling in the uppermost ice with an average temperature of approximately −1 °C. Attenuation values were derived between 100 and 300 Hz using the P-wave quality factor, QP, the inverse of the internal friction. By assuming constant attenuation along the seismic line we obtained mean QP = 6 ± 1. We also observed that QP varies from 8 ± 1 to 5 ± 1 from the near-offset to the far-offset region of the line, respectively. Since the wave propagates deeper at far offsets, this variation is interpreted by considering the temperature profile of the study area; far-offset arrivals sampled warmer and thus more-attenuative ice. Our estimates are considerably lower than those reported for field studies in polar ice (∼500–1700 at −28°C and 50–160 at −10°C) and, hence, are supportive of laboratory experiments that show attenuation increases with rising ice temperature. Our results provide new in situ estimates of QP for glacier ice and demonstrate a valuable method for future investigations in both alpine and polar ice.

A hanging glacier at the east face of Weisshorn, Switzerland, broke off in 2005. We were able to monitor and measure surface motion and icequake activity for 25 days up to 3 days prior to the break-off. The analysis of seismic waves generated by the glacier during the rupture maturation process revealed four types of precursory signals of the imminent catastrophic rupture: (1) an increase in seismic activity within the glacier; (2) a change in the size–frequency distribution of icequake energy; (3) a modification in the structure of the waiting-time distributions between two successive icequakes; and (4) a correlation between the seismic activity and the log-periodic oscillations of the surface velocities superimposed on the global acceleration of the glacier during the rupture maturation. Analysis of the seismic activity led us to identify two regimes: a stable phase with diffuse damage and an unstable and dangerous phase characterized by a hierarchical cascade of rupture instabilities where large icequakes are triggered.

This paper introduces the Instructed Glacier Model (IGM) – a model that simulates ice dynamics, mass balance and its coupling to predict the evolution of glaciers, icefields or ice sheets. The novelty of IGM is that it models the ice flow by a Convolutional Neural Network, which is trained from data generated with hybrid SIA + SSA or Stokes ice flow models. By doing so, the most computationally demanding model component is substituted by a cheap emulator. Once trained with representative data, we demonstrate that IGM permits to model mountain glaciers up to 1000 × faster than Stokes ones on Central Processing Units (CPU) with fidelity levels above 90% in terms of ice flow solutions leading to nearly identical transient thickness evolution. Switching to the GPU often permits additional significant speed-ups, especially when emulating Stokes dynamics or/and modelling at high spatial resolution. IGM is an open-source Python code which deals with two-dimensional (2-D) gridded input and output data. Together with a companion library of trained ice flow emulators, IGM permits user-friendly, highly efficient and mechanically state-of-the-art glacier and icefields simulations.

Freezing temperatures, desiccation and high levels of solar radiation make the surface of the Antarctic ice sheet one of Earth’s harshest habitats. However, our study in the Vestfold Hills area of East Antarctica shows that favourable conditions for microbial production become established just beneath the surface of blue-ice areas, which collectively cover about 2% of the ice-sheet periphery. Their translucent, wind-polished surface allows solar heating to create meltwater in a greenhouse-type environment at depths of up to 1 m. Melting is intensified around dark debris particles, or cryoconite, where we found microbiological activity to be greatest. Rates of photosynthesis (average 2060 ng C (g cryoconite)−1 d−1) were adapted to low light intensities (∼10% of surface irradiance values) and most likely dominated by cyanobacteria and Chloroplastida. A heterotrophic bacterial community was also found to be active within the cryoconite, although average bacterial growth rates (5.7 ng C (g cryoconite)−1 d−1) were far lower than average community respiration (1870 ng C (g cryoconite)−1 d−1). The majority of the respired carbon was most likely associated with the autotrophs and several protists. Therefore, blue-ice areas constitute oases for microbial life around the periphery of Earth’s coldest ice sheet.

We present a set of new volume scaling relationships specific to Svalbard glaciers, derived from a sample of 60 volume–area pairs. Glacier volumes are computed from ground-penetrating radar (GPR)-retrieved ice thickness measurements, which have been compiled from different sources for this study. The most precise scaling models, in terms of lowest cross-validation errors, are obtained using a multivariate approach where, in addition to glacier area, glacier length and elevation range are also used as predictors. Using this multivariate scaling approach, together with the Randolph Glacier Inventory V3.2 for Svalbard and Jan Mayen, we obtain a regional volume estimate of 6700 ± 835 km3, or 17 ± 2 mm of sea-level equivalent (SLE). This result lies in the mid- to low range of recently published estimates, which show values as varied as 13 and 24 mm SLE. We assess the sensitivity of the scaling exponents to glacier characteristics such as size, aspect ratio and average slope, and find that the volume of steep-slope and cirque-type glaciers is not very sensitive to changes in glacier area.

Compared with freshwater ice, whose physical properties are well known, sea iceis a relatively complex substance whose transition to a completely solid mixtureof pure ice and solid salts is completed only at extremely low temperaturesrarely encountered in nature. The physical properties of sea ice are thusstrongly dependent on salinity, temperature and time. Many of these propertiesare still not fully understood or accurately known, particularly those importantfor the understanding of a natural ice cover. The specific heat for example isan important term in the calculation of the heat energy content of a cover.However, Malmgren (1927), whose calculatedvalues of the specific heat of sea ice are in general use, neglected the directcontribution of the brine present in inclusions. Re-examination of thequestion of specific and latent heats of sea ice has led to distinguishingbetween the freezing and melting points and enabled significant observations inthis range. Similarly, because the thermal conductivity is a necessary parameterin the description of the thermal behaviour of ice. the sea-ice modelsuggested by Anderson (1958) has beenmodified and extended in the present work to the case of saline ice containingair bubbles. This enabled the completion of calculations of density andconductivity. In order to illustrate the theoretically calculated values.measurements were made on sea-ice samples to determine the specific heat,density and thermal conductivity.

Radio-echo sounding data are used to investigate bed roughness beneath the three enhanced-flow tributaries of Slessor Glacier, East Antarctica. Slow-moving inter-tributary areas are found to have rough beds, while the bed of the northernmost tributary is relatively smooth. A reconstruction of potential subglacial drainage routing indicates that water would be routed down this tributary, and investigations of basal topography following isostatic recovery reveal that the bed would have been below sea level in preglacial times, so marine sediments may have accumulated here. Together, these factors are further support for the dominance of basal motion in this tributary, reported elsewhere. Conversely, although the other two Slessor tributaries may have water routed beneath them, they would not have been below sea level before the growth of the ice sheet, so cannot be underlain by marine sediments. They are also found to be rough, and, within the range of uncertainties, it is likely that basal motion does not play a major role in the flow of these tributaries. Perhaps the most interesting area, however, is a deep trough where flow rates are currently low but the bed is as smooth as the northern Slessor trough. It is proposed that, although ice deformation currently dominates in this trough, basal motion may have occurred in the past, when the ice was thicker.