Glacier area changes on the Tibetan Plateau were studied in different drainage basins based on Landsat satellite images from three epochs: 263 in the mid-1970s, 150 in 1999–2002 and 148 in 2013/14. Three mosaics (M1976, M2001 and M2013) with minimal cloud and snow cover were constructed, and the uncertainty due to each epoch having a finite span was accounted for. Glacier outlines (TPG1976, TPG2001 and TPG2013) were digitized manually with guidance from the SRTM DEM v4.1 and Google Earth imagery. To achieve complete multi-temporal coverage in a reasonable time, only debris-free ice was delineated. Area mapping uncertainty was evaluated at three study sites, Mount Qomolangma (Everest), Mount Naimona'Nyi, Mount Geladandong, where the largest differences between present and earlier measurements were within ~±4%. Area differences with previous inventories ranged from −19.6% (TPG1976 minus the first Chinese Glacier Inventory) to −3.6% and −1.1% (TPG2013 and TPG2001, respectively minus the second Chinese Glacier Inventory), while the difference TPG2001 minus the GAMDAM Glacier Inventory was +10.4%. Glacier area on the plateau decreased from 44 366 ± 2827 km2 (1.7% of the study area) in the 1970s to 42 210 ± 1621 km2 in 2001 and 41 137 ± 1616 km2 in 2013. Shrinkage was faster in external drainage basins of the southeast than in the interior basins of the northwest, from a maximum of −0.43% a−1 (−1.60% a−1 during 1994–2013) in the Mekong catchment down to a minimum of −0.12% a−1 in the Tarim interior drainage.

In the framework of the European Project for Ice Coring in Antarctica (EPICA), a comprehensive glaciological pre-site survey has been carried out on Amundsenisen, Dronning Maud Land, East Antarctica, in the past decade. Within this survey, four intermediate-depth ice cores and 13 snow pits were analyzed for their ionic composition and interpreted with respect to the spatial and temporal variability of volcanic sulphate deposition. The comparison of the non-sea-salt (nss)-sulphate peaks that are related to the well-known eruptions of Pinatubo and Cerro Hudson in AD 1991 revealed sulphate depositions of comparable size (15.8±3.4 kg km–2) in 11 snow pits. There is a tendency to higher annual concentrations for smaller snow-accumulation rates. The combination of seasonal sodium and annually resolved nss-sulphate records allowed the establishment of a time-scale derived by annual-layer counting over the last 2000 years and thus a detailed chronology of annual volcanic sulphate deposition. Using a robust outlier detection algorithm, 49 volcanic eruptions were identified between AD 165 and 1997. The dating uncertainty is ±3 years between AD 1997 and 1601, around ±5 years between AD 1601 and 1257, and increasing to ±24 years at AD 165, improving the accuracy of the volcanic chronology during the penultimate millennium considerably.

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

The ApRES (autonomous phase-sensitive radio-echo sounder) instrument is a robust, lightweight and relatively inexpensive radar that has been designed to allow long-term, unattended monitoring of ice-shelf and ice-sheet thinning. We describe the instrument and demonstrate its capabilities and limitations by presenting results from three trial campaigns conducted in different Antarctic settings. Two campaigns were ice sheet-based – Pine Island Glacier and Dome C – and one was conducted on the Ross Ice Shelf. The ice-shelf site demonstrates the ability of the instrument to collect a time series of basal melt rates; the two grounded ice applications show the potential to recover profiles of vertical strain rate and also demonstrate some of the limitations of the present system.

We present results from cold-laboratory observations of changes in isotopic (δ18O and δD) content by sublimation in snow and ice samples under nearly isothermal conditions. The results show large increases in observed δ18O and δD in snow samples within several centimeters of the surface. They contradict the assumption of a non-changing isotopic content due to layer-by-layer transport mechanisms driven by sublimation/desublimation processes. The data also do not support the idea that isotopic changes of snow and firn are limited by the possibility that the ice matrix incorporates the atmospheric water vapor and that forced water-vapor diffusion in the pore space (wind pumping) is a requirement for isotopic content change. The observations show that sublimation from ice samples results in much lower increases in heavy-isotope content in the first several millimetres near the sublimating surface over the same time period, despite sublimation intensities similar to those of the snow samples. The results suggest that continuous phase transitions inside snow (recrystallization) are the process responsible for the isotopic content change because they are the primary mass-exchange mechanism between the snow mass and the surrounding environment. Modeling the isotopic content of the ice matrix therefore requires inclusion of a two-stage process: fractionation at the ice-matrix surface due to repetitive phase transitions, and fractionation due to preferable diffusion of light water isotopes in the pore space. For interpretation of the observed natural isotopic profiles in snow, the first process can be linked to the time a snow layer undergoes recrystallization, while the second process is related to the total ice/snow mass gain/loss determined by the external environmental conditions.

The dynamics of glacier motion are governed to a large extent by the properties of the basal interface. In this paper we address the interaction of a glacier with a layer of till at its bed in an attempt to test whether our physical understanding of till is sufficient to explain general features of the observed flow field and changes in geometry of Black Rapids Glacier, Alaska, U.S.A. We also investigate whether or not a till layer has a clear surface-observable signature in the dynamics of the glacier. Towards this end we use a finite-element ice-flow model with a Coulomb failure criterion within the basal till layer. We find that simple “till physics” can be used to describe decadal, seasonal and short-term (hours to days) velocity variations, and possibly uplift events. Mechanisms for each of these variations involve an increase in the extent of till at failure, a transfer of shear stress across the bed, and a consequent increase in ice deformation. “Effective shape factors” are calculated that permit a simple incorporation of this boundary condition into glacier response models. Our analyses, however, have not resulted in the identification of a clear and unique signature of a till layer in the surface dynamics of a glacier.

An approximation to the first-order momentum balance with consistent boundary conditions is derived using variational methods. Longitudinal and lateral stresses are treated as depth-independent, but vertical velocity gradients are accounted for both in the nonlinear viscosity and in the treatment of basal stress, allowing for flow over a frozen bed. A numerical scheme is presented that is significantly less computationally expensive than that of a fully three-dimensional (3-D) solver. The numerical solver is subjected to the ISMIP-HOM experiments and experiments involving nonlinear sliding laws, and results are compared with those of 3-D models. The agreement with first-order surface velocities is favorable down to length scales of 10 km for flow over a flat bed with periodic basal traction, and ∼40 km for flow over periodic basal topography.

During the snow-melt season of 1982, basal water pressure was recorded in 11 bore holes communicating with the subglacial drainage system. In most of these holes the water levels were at approximately the same depth (around 70 m below surface). The large variations of water pressure, such as diurnal variations, were usually similar at different locations and in phase. In two instances of exceptionally high water pressure, however, systematic phase shifts were observed; a wave of high pressure travelled down-glacier with a velocity of approximately 100 m/h.

The glacier-surface velocity was measured at four lines of stakes several times daily. The velocity variations correlated with variations in subglacial water pressure. The functional relationship of water pressure and velocity suggests that fluctuating bed separation was responsible for the velocity variations. The empirical functional relationship is compared to that of sliding over a perfectly lubricated sinusoidal bed. On the basis of the measured velocity-pressure relationship, this model predicts a reasonable value of bed roughness but too high a sliding velocity and unstable sliding at too low a water pressure. The main reason for this disagreement is probably the neglect of friction from debris in the sliding model.

The measured water pressure was considerably higher than that predicted by the theory of steady flow through straight cylindrical channels near the glacier bed. Possible reasons are considered. The very large disagreement between measured and predicted pressure suggests that no straight cylindrical channels may have existed.

X-ray diffraction photographs were taken of ice dendrites grown from water and from the vapour. In both cases [1120] was found to be the growth direction.

A method of growing cylindrical single crystals of any desired orientation has been devised. Some of these crystals were extended to several times their original length. Slip took place exclusively on the basal plane. Experiments designed to locate the glide direction gave inconclusive results and suggested that, in general, crystals near the melting point can glide in any direction.

Before deformation, ice crystals gave fairly sharp X-ray diffraction spots on Laue photographs. After deformation the spots are drawn out into streaks which later break up into rows of small spots. This indicates that bending of the crystals is followed by the formation of small crystallites of slightly differing orientations. Analogous effects are observed in metals.

We investigate the performance of five glacier melt models over a multi-decadal period in order to assess their ability to model future glacier response. The models range from a simple degree-day model, based solely on air temperature, to more-sophisticated models, including the full shortwave radiation balance. In addition to the empirical models, the performance of a physically based energy-balance (EB) model is examined. The melt models are coupled to an accumulation and a surface evolution model and applied in a distributed manner to Rhonegletscher, Switzerland, over the period 1929–2012 at hourly resolution. For calibration, seasonal mass-balance measurements (2006–12) are used. Decadal ice volume changes for six periods in the years 1929–2012 serve for model validation. Over the period 2006–12, there are almost no differences in performance between the models, except for EB, which is less consistent with observations, likely due to lack of meteorological in situ data. However, simulations over the long term (1929–2012) reveal that models which include a separate term for shortwave radiation agree best with the observed ice volume changes, indicating that their melt relationships are robust in time and thus suitable for long-term modelling, in contrast to more empirical approaches that are oversensitive to temperature fluctuations.

In order to account for the effects of debris cover in model scenarios of the response of glaciers to climate change and water resource planning, it is important to know the distribution and thickness of supraglacial debris and to monitor its change over time. Previous attempts to map surface debris thickness using thermal band remote sensing have relied upon time-specific empirical relationships between surface temperature and thickness, limiting their general applicability. In this paper, we develop a physically based model that utilizes Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) thermal band remotely sensed imagery and is based on a solution of the energy balance at the debris surface. The model is used to estimate debris thickness on Miage glacier, Italy, and is validated using field debris-thickness measurements and a previously published debris-thickness map. The temporal transferability of the model is demonstrated through successful application to a separate ASTER image from a different year using reanalysis meteorological input data. This model has the potential to be used for regional-scale supraglacial debris-thickness mapping and monitoring for debris up to at least 0.50 m thickness, but improved understanding of the spatial patterns of air temperature, aerodynamic roughness length and thermal properties across debris-covered glaciers is needed.

We used satellite-derived surface temperatures and time-lapse photography to infer temporal variations in the proglacial ice melange at Jakobshavn Isbræ, a large and rapidly retreating outlet glacier in Greenland. Freezing of the melange-covered fjord surface during winter is indicated by a decrease in fjord surface temperatures and is associated with (1) a decrease in ice melange mobility and (2) a drastic reduction in iceberg production. Vigorous calving resumes in spring, typically abruptly, following the steady up-fjord retreat of the sea-ice/ice-melange margin. An analysis of pixel displacement from time-lapse imagery demonstrates that melange motion increases prior to calving and subsequently decreases following several events. We find that secular changes in ice melange extent, character and persistence can influence iceberg calving, and therefore glacier dynamics over daily-to-monthly timescales, which, if sustained, will influence the mass balance of an ice sheet.

This study assesses the impact of a large 2010 calving event on the current and future stability of Petermann Glacier, Greenland, and ascertains the glacier’s interaction with different components of the climate and ocean system. We use a numerical ice-flow model that captures the major aspects of the glacier’s mass budget, the resistive forces controlling glacier flow, and includes dynamic calving. Satellite observations and model results show that the recent break-off of 25% of the floating tongue did not result in a significant glacier speed-up due to the low lateral resistance of this relatively wide and thin ice tongue. We demonstrate that seasonal speed-up at Petermann Glacier is mainly driven by meltwater lubrication rather than freeze-up conditions in the fjord. Results also show that sub-shelf ocean melt may have a profound effect on the future stability of Petermann Glacier, emphasizing the urgent need for more observations, and a better understanding of fjord temperature variability and circulation.

The specific surface area (SSA), defined as the surface area of ice per unit mass, is an important variable characterizing the complex microstructure of snow. Its application range covers the physical evolution of snow (metamorphism), photochemistry and optical and microwave remote sensing. This paper presents a new device, POSSSUM (Profiler Of Snow Specific Surface area Using SWIR reflectance Measurement), designed to allow the rapid acquisition of SSA profiles down to ∼20 m depth and with an effective vertical resolution of 10–20 mm. POSSSUM is based on the infrared (IR) reflectance technique: A laser diode operating at 1310 nm illuminates the snow at nadir incidence angle along the face of a drilled hole. The reflected radiance is measured at three zenith angles (20°, 40° and 60°) each for two azimuth angles (0° and 180°). A second laser operating at a shorter wavelength (635 nm), which is almost insensitive to SSA, allows the distance to the snow face to be estimated. The reflected IR radiance and the distance are combined to estimate bidirectional reflectances. These reflectances are converted into hemispherical reflectances and in turn into SSA using a theoretical formulation based on an asymptotic solution of the radiative transfer equation. The evaluation and validation of POSSSUM’s SSA measurements took place in spring 2009 in the French Alps. The new method was compared with the methane adsorption technique and DUFISSS, another well-validated instrument based on the IR technique. The overall measurement error is in the range 10–15%.

Avalanche deposits consist of rounded granules composed of aggregates of snow and ice particles. The size of the granules is related to vertical shear gradients within the flow; studying the granule-size distribution may be useful in understanding the flow and stopping of avalanches. We applied a sediment-size sampling method to measure snow granule-size distributions at different depositional environments on two dry and two wet avalanche deposits at three field sites. The granule-size distributions are approximately log-normal, similar to many natural sediment deposits. The median granule size in the wet and dry avalanches varies between 65 and 162 mm. Wet avalanches tend to produce more large granules than dry avalanches, indicating both smaller flow velocities and near-surface shear gradients. Granule size is similar in frontal lobes and levee deposits, suggesting that levee formation occurs independently of the size segregation at the avalanche front.

Despite their relatively small total ice volume, mid-latitude valley glaciers are expected to make a significant contribution to global sea-level rise over the next century due to the sensitivity of their mass-balance systems to small changes in climate. Here we use a degree-day model to reconstruct the past century of mass-balance variation at ‘Ka Roimata o Hine Hukatere’ Franz Josef Glacier, New Zealand, and to predict how mass balance may change over the next century. Analysis of the relationship between temperature, precipitation and mass balance indicates that temperature is a stronger control than precipitation on the mass balance of Franz Josef Glacier. The glacier’s mass balance, relative to its 1986 geometry, has decreased at a mean annual rate of 0.02m a–1 w.e. between 1894 and 2005. We compare this reduction to observations of terminus advance and retreat, of which Franz Josef Glacier has the best record in the Southern Hemisphere. For the years 2000–05 the relative mass balance ranged from –0.75 to +1.50m a–1 w.e., with 2000/01 the only year showing a negative mass balance. In a regionally downscaled Intergovernmental Panel on Climate Change mean warming scenario, the annual relative mass balance will continue to decrease at 0.02m a–1 w.e. through the next century.

Modes of debris entrainment and subsequent transfer in seven “normal” and five surge-type glaciers in Svalbard (76–79° N) are outlined in the context of the structural evolution of a glacier as the ice deforms during flow. Three main modes of entrainment and transfer are inferred from structural and sedimentological observations: (i) The incorporation of angular rockfall material within the stratified sequence of snow/firn/superimposed ice. This debris takes an englacial path through the glacier, becoming folded. At the margins and at the boundaries of flow units the stratified ice including debris is strongly folded, so that near the snout the debris emerges at the surface on the hinges and limbs of the folds, producing medial moraines which merge towards the snout. The resulting lines of debris are transmitted to the proglacial area in the form of regular trains of angular debris. (ii) Incorporation of debris of both supraglacial and basal character within longitudinal foliation. This is particularly evident at the surface of the glacier at the margins or at flow unit boundaries. It can be sometimes demonstrated that foliation is a product of strong folding, since it usually has an axial planar relationship with folded stratification. Foliation-parallel debris thus represents a more advanced stage of deformation than in (i). Although the presence of basal debris is problematic, it is proposed that this material is tightly folded ice derived from the bed in the manner of disharmonie folding. The readily deformed subglacial sediment or bedrock surface represents the plane of décollement. (iii) Thrusting, whereby debris-rich basal ice (including regelation ice) and subglacial sediments are uplifted into an englacial position, sometimes emerging at the ice surface. This material is much more variable in character than that derived from rockfalls, and reflects the substrate lithologies; diamicton with striated clasts and sandy gravels are the most common facies represented. Thrusting is a dynamic process, and in polythermal glaciers is probably linked mainly to the transition from sliding to frozen bed conditions. It is not therefore a solely ice-marginal or proglacial process.

Antarctica's ice shelves modulate the grounded ice flow, and weakening of ice shelves due to climate forcing will decrease their ‘buttressing’ effect, causing a response in the grounded ice. While the processes governing ice-shelf weakening are complex, uncertainties in the response of the grounded ice sheet are also difficult to assess. The Antarctic BUttressing Model Intercomparison Project (ABUMIP) compares ice-sheet model responses to decrease in buttressing by investigating the ‘end-member’ scenario of total and sustained loss of ice shelves. Although unrealistic, this scenario enables gauging the sensitivity of an ensemble of 15 ice-sheet models to a total loss of buttressing, hence exhibiting the full potential of marine ice-sheet instability. All models predict that this scenario leads to multi-metre (1–12 m) sea-level rise over 500 years from present day. West Antarctic ice sheet collapse alone leads to a 1.91–5.08 m sea-level rise due to the marine ice-sheet instability. Mass loss rates are a strong function of the sliding/friction law, with plastic laws cause a further destabilization of the Aurora and Wilkes Subglacial Basins, East Antarctica. Improvements to marine ice-sheet models have greatly reduced variability between modelled ice-sheet responses to extreme ice-shelf loss, e.g. compared to the SeaRISE assessments.

The Himalaya has some of the largest glacier concentrations outside the polar regions. Despite this, long-term measurements detecting the impact of global warming and changing precipitation patterns on glaciers are rare. The Nanga Parbat massif in northern Pakistan is an exception. The cartographer and glaciologist R. Finsterwalder investigated glacier dynamics of this mountain massif in the 1930s, and several other studies document changes since then. The aim of this study is to detect and analyse the changes of Raikot Glacier over the past seven decades. We use a multitemporal and multiscale approach, based on repeat terrestrial images, additional historical data and remotely sensed imagery (Corona, ASTER, Landsat, QuickBird). The multitemporal approach covers the period 1934–2007. While the analyses show a total glacier retreat of ~200 m in 73 years, this general trend was interrupted by a significant glacier advance between the 1950s and 1980s. Although down-wasting processes can be inferred from an increase in debris-covered area, a general trend of reduced glacier thickness does not appear significant over the whole observation period.