We present a detailed, complete glacier inventory for Alaska and neighboring Canada using multi-sensor satellite data from 2000 to 2011. For each glacier, we derive outlines and 51 variables, including center-line lengths, outline types and debris cover. We find 86 723 km2 of glacier area (27 109 glaciers >0.025 km2), ∼12% of the global glacierized area outside ice sheets. Of this area 12.0% is drained by 39 marine-terminating glaciers (74 km of tidewater margin), and 19.3% by 148 lake- and river-terminating glaciers (420 km of lake-/river margin). The overall debris cover is 11%, with considerable differences among regions, ranging from 1.4% in the Kenai Mountains to 28% in the Central Alaska Range. Comparison of outlines from different sources on >2500 km2 of glacierized area yields a total area difference of ∼10%, emphasizing the difficulties in accurately delineating debris-covered glaciers. Assuming fully correlated (systematic) errors, uncertainties in area reach 6% for all Alaska glaciers, but further analysis is needed to explore adequate error correlation scales. Preliminary analysis of the glacier database yields a new set of well-constrained area/length scaling parameters and shows good agreement between our area–altitude distributions and previously established synthetic hypsometries. The new glacier database will be valuable to further explore relations between glacier variables and glacier behavior.

A field investigation of iceberg drift pattern and drift speed was conducted in September 2011 in Baffin Bay, northwest Greenland. Ten icebergs were equipped with GPS transponders during a field campaign. Above-waterline dimensions (length, width and height) of the icebergs were measured using a GPS/pressure altimeter and geometrically rectified digital photographs taken during the field campaign. Iceberg lengths, masses and drafts ranged from 95 to 450 m, 330 000 to 17 000 000 t and 70 to 260 m, respectively. The drift patterns and speeds were determined on the basis of GPS positions logged continuously at 1 hour intervals. The drift patterns differed significantly from iceberg to iceberg. The GPS signal was lost on six of the icebergs within the first 23 days of logging. Three transponders were transferring data for more than 5 months until the battery ran out of power. One transponder was sending data until summer 2012. The measured maximum drift speed was 68 cm s−1 (2.4 km h−1), and the mean drift speed for all ten icebergs was 10 cm s−1 (0.4 km h−1). Relations between iceberg size and drift speed were investigated, showing that icebergs with large surface areas moved at the highest speeds, which occurred particularly during strong wind conditions.

Radio-glaciological parameters from the Moore’s Bay region of the Ross Ice Shelf, Antarctica, have been measured. The thickness of the ice shelf in Moore’s Bay was measured from reflection times of radio-frequency pulses propagating vertically through the shelf and reflecting from the ocean, and is found to be 576 ± 8 m. Introducing a baseline of 543 ± 7m between radio transmitter and receiver allowed the computation of the basal reflection coefficient, R, separately from englacial loss. The depth-averaged attenuation length of the ice column, 〈L〉 is shown to depend linearly on frequency. The best fit (95% confidence level) is 〈L(ν)〉= (460±20) − (180±40)ν m (20 dB km−1), for the frequencies ν = [0.100–0.850] GHz, assuming no reflection loss. The mean electric-field reflection coefficient is (1.7 dB reflection loss) across [0.100–0.850] GHz, and is used to correct the attenuation length. Finally, the reflected power rotated into the orthogonal antenna polarization is <5% below 0.400 GHz, compatible with air propagation. The results imply that Moore’s Bay serves as an appropriate medium for the ARIANNA high-energy neutrino detector.

Runoff estimation in high-altitude glacierized basins is an important issue on the Tibetan Plateau. To investigate glacier mass balance, runoff and water balance in the Qugaqie basin and Zhadang sub-basin in the southern Tibetan Plateau, two glacier models and three snow models were integrated into the spatially distributed hydrological model JAMS/J2K. The results showed that the temperature index method simulated glacier runoff better than the degree-day factor method. The simulated glacier melt volume in the Qugaqie basin in 2006, 2007 and 2008 contributed 58%, 50% and 41%, respectively, to its total runoff. In the Zhadang basin, the glacier melt volume contributed 78% and 66% to its runoff during 2007 and 2008, respectively. Compared with the observation results, the simulated glacier mass balance showed similar variations with slightly higher values, indicating an underestimation of glacier melt volume. The water balance simulation in the upstream areas (705–874 mm) was comparable to that in the downstream areas (1051–1502 mm) and generally lower than the observed results. In both basins, the glacier mass-balance simulation was relatively accurate in the melt season compared to the other seasons.

Effects of damage on elastic properties were studied in columnar-grained specimens of freshwater and saline ice, subjected, at −10°C, to varying levels of inelastic strain. The ice was compressed uniaxially at constant strain rates up to 0.20 strain, which caused localized recrystallization and imparted damage in the form of non-propagating cracks. Damage was quantified in terms of dimensionless crack density, which, along with recrystallized area fraction, was determined from thin sections. The change in porosity due to stress-induced cracks served as another indicator of damage. Elastic properties were derived using P-wave and S-wave ultrasonic transmission velocities measured in across-column directions through the damaged ice, either parallel (x1) or perpendicular (x2) to the initial loading direction. In general, as damage increased with greater strain, the ice became more compliant and (particularly freshwater ice) more anisotropic. Furthermore, with increasing strain rate, the magnitude of these effects and crack density tended to increase, in contrast to the recrystallized area fraction, which tended to decrease. We observed compliance to correspond closely with porosity and with dimensionless crack density, for strains up to 0.10. At greater levels of strain these correspondences became less clear due, in part, to the different character of the damage.

In this study, we analyze a large dataset of seismic signals, recorded by station TROLL in Dronning Maud Land, Antarctica. The signals, recorded in April–December 2012, came from sources near the edge of the ice shelves, at distances of 230–500 km from TROLL. The sources, which moved westward with time, could be associated with four large, tabular icebergs, drifting between 15° E and 8° W. Combining the seismological data with information from satellite remote sensing, we find that one-third of the signals can be attributed to individual icebergs. The trajectories of three of the associated icebergs are known through iceberg-tracking databases, whereas the fourth, a fragment of one of the other three, is untracked, and only scarce information is available from satellite imagery. The observed seismic signals exhibit a wide variety of frequency characteristics, from unstructured episodes to occurrences of iceberg harmonic tremor. Although we are not able to determine the exact cause of the signals, we classify them into five classes on a phenomenological basis. This study demonstrates the potential of regional seismic networks for iceberg monitoring as supplementary resources to information obtained with remote-sensing technologies.

A model subglacial drainage system, coupled to an ice-dammed reservoir that receives a time-varying meltwater input, is described and analysed. In numerical experiments an ice-marginal lake drains through a subglacial channel, producing periodic floods, and fills with meltwater at a rate dependent on air temperature, which varies seasonally with a peak value of Tm. The analysis reveals regions of Tm parameter space corresponding to ‘mode locking’, where flood repeat time is independent of Tm; resonance, where decreasing Tm counter-intuitively increases flood size; and chaotic dynamics, where flood cycles are sensitive to initial conditions, never repeat and exhibit phase-space mixing. Bifurcations associated with abrupt changes in flood size and timing within the year separate these regions. This is the first time these complex dynamics have been displayed by a glaciohydraulic model and these findings have implications for our understanding of ice-marginal lakes, moulins and subglacial lakes.

We have constrained the value for thermal diffusivity of near-surface snow and firn at Summit Station, Greenland, using a Fourier-type analysis applied to hourly temperature measurements collected from eight thermistors in a closed-off, air-filled borehole between May 2004 and July 2008. An implicit, finite-difference method suggests that a bulk diffusivity of ∼25 ± 3m2 a−1 is the most reasonable for representing macroscale heat transport in the top 30 m of firn and snow. This value represents an average diffusivity and, in a conduction-only model, generates temperature series whose phase shifts with depth most closely match those of the Summit borehole data (rms difference between measurements and model output is ∼6 days). This bulk value, derived numerically and corroborated analytically, is useful over large tracts of the Greenland ice sheet where density and microstructure are unknown.

Most glaciological studies in Argentina have focused on the large outlet glaciers of the Southern Patagonia Icefield (SPI); the numerous smaller neighboring glaciers have received significantly less attention. We present an inventory of 248 medium- to small-size glaciers (0.01–25 km2) adjacent to the northeast margin of the SPI, describe their change over the period 1979–2005 and assess local and regional climatic variations in an attempt to explain the observed glacier changes. Based on an ASTER mosaic from 20 February 2005 and the ASTER Global Digital Elevation Model, we identified a total glacier area of 187.2 ± 7.4 km2 between 600 and 2870 m a.s.l. Glaciers are largely debris-free and are concentrated in the western, more humid sector adjacent to the SPI. Using a 20 March 1979 US military intelligence Hexagon KH-9 satellite photograph, we measured a total areal reduction of ∼33.7 km2 (15.2%) between 1979 and 2005. Ablation season temperatures from the study area have followed a regional warming trend that could partly explain the observed glacier shrinkage. Annual precipitation estimates show a gradual decrease between 1979 and 2002 that may also have contributed to the ice mass loss.

Spatial evolution of supraglacial debris cover on mountain glaciers is a largely unmonitored and poorly understood phenomenon that directly affects glacier melt. Supraglacial debris cover for 93 glaciers in the Karakoram, northern Pakistan, was mapped from Landsat imagery acquired in 1977, 1998, 2009 and 2014. Surge-type glaciers occupy 41% of the study area and were considered separately. The time series of debris-covered surface area change shows a mean value of zero or near-zero change for both surging and non-surging glaciers. An increase in debris-covered area is often associated with negative regional mass balances. We extend this logic to suggest that the stable regional mass balances in the Karakoram explain the zero or near-zero change in debris-covered area. This coupling of trends combined with our 37 year time series of data suggests the Karakoram anomaly extends further back in time than previously known.

The observable microstructures in ice are the result of many dynamic and competing processes. These processes are influenced by climate variables in the firn. Layers deposited in different climate regimes may show variations in fabric which can persist deep into the ice sheet; fabric may ‘remember’ these past climate regimes. We model the evolution of fabric variations below the firn–ice transition and show that the addition of shear to compressive-stress regimes preserves the modeled fabric variations longer than compression-only regimes, because shear drives a positive feedback between crystal rotation and deformation. Even without shear, the modeled ice retains memory of the fabric variation for 200 ka in typical polar ice-sheet conditions. Our model shows that temperature affects how long the fabric variation is preserved, but only affects the strain-integrated fabric evolution profile when comparing results straddling the thermal-activation-energy threshold (∼−10°C). Even at high temperatures, migration recrystallization does not eliminate the modeled fabric’s memory under most conditions. High levels of nearest-neighbor interactions will, however, eliminate the modeled fabric’s memory more quickly than low levels of nearest-neighbor interactions. Ultimately, our model predicts that fabrics will retain memory of past climatic variations when subject to a wide variety of conditions found in polar ice sheets.

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.

Snow avalanches are gravity-driven flows consisting of hard snow/ice particles. Depending on the snow quality, particularly temperature, avalanches exhibit different flow regimes, varying from dense flowing avalanches to highly disperse, mixed flowing-powder avalanches. In this paper we investigate how particle interactions lead to streamwise density variations, and therefore an understanding of why avalanches exhibit different flow types. A basic feature of our model is to distinguish between the velocity of the avalanche in the mean, downslope direction and the velocity fluctuations around the mean, associated with random particle movements. The mechanical energy associated with the velocity fluctuations is not entirely kinetic, as particle movements in the slope-perpendicular direction are inhibited by the hard boundary at the bottom giving rise to a change in flow height and therefore change in flow density. However, this volume expansion cannot occur without raising the center of mass of the particle ensemble, i.e. an acceleration, which, in turn, exerts a pressure on the bottom, the so-called dispersive pressure. As soon as the volume no longer expands, the dispersive pressure vanishes and the pressure returns to the hydrostatic pressure. Different streamwise density distributions, and therefore different avalanche flow regimes, are possible.

Arctic snow depth data products from four years (2009–12) of Operation IceBridge (OIB) surveys are examined. In our analysis, we found spurious spikes in the snow depth distributions of both the multi-year and seasonal ice covers. These spikes are artifacts that stem from the incorrect identification of side lobes and main lobes of the impulse response of the snow radar as returns from the air–snow interface. The current OIB snow depth retrieval algorithm does not explicitly account for the presence of these side lobes and main lobes. As a result, overall accuracy of snow depth returns and related statistics is negatively affected. Although the range locations of these side lobes are predictable for each radar installation, they vary with individual airborne campaigns. Comparisons with limited in situ snow surveys show significant differences of >20 cm between OIB and in situ snow surveys. These artifacts affect OIB ice thickness estimates because they rely on estimates of sea-ice freeboard, which are calculated as the differences between coincident snow freeboard from lidar elevations and the retrieved snow depth estimates discussed here. Since these products are widely distributed to the scientific community, our results suggest that earlier geophysical studies based on these products may need to be re-examined.

Melt layers are clear indicators of extreme summer warmth on polar ice caps. The visual identification of refrozen meltwater as clear bubble-free layers cannot be used to study some past warm periods, because, in deeper ice, bubbles are lost to clathrate formation. We present here a reliable method to detect melt events, based on the analysis of Kr/Ar and Xe/Ar ratios in ice cores, and apply it to the detection of melt in clathrate ice from the Eemian at NEEM, Greenland. Additionally, melt layers in ice cores can compromise the integrity of the gas record by dissolving soluble gases, or by altering gas transport in the firn, which affects the gas chronology. We find that the easily visible 1 mm thick bubble-free layers in the WAIS Divide ice core do not contain sufficient melt to alter the gas composition in the core, and do not cause artifacts or discontinuities in the gas chronology. The presence of these layers during winter, and the absence of anomalies in soluble gases, suggests that these layers can be formed by processes other than refreezing of meltwater. Consequently, the absence of bubbles in thin crusts is not in itself proof of a melt event.

Tibetan glaciers experience spatially heterogeneous changes, which call for further investigation of the mechanisms responsible from an energy and mass perspective. In this study, 2 year parallel observations (August 2010–July 2012) at 5665 m a.s.l. on Zhadang glacier (a subcontinental glacier) and 5202 m a.s.l. on Parlung No. 4 glacier (a maritime glacier) were used to reveal the drivers of surface energy and mass balance at these sites. Glacio-meteorological data show that air temperature and specific humidity were 1.7°C and 0.5 g kg−1 lower on Zhadang glacier than on Parlung No. 4 glacier. The mass accumulation occurred primarily before the Indian summer monsoon onset on Parlung No. 4 glacier and after its onset on Zhadang glacier. Point net mass loss was 2.5 times larger on Parlung No. 4 glacier than on Zhadang glacier, mainly due to the difference in melt energy. Overall, the physical mechanisms controlling the mass and energy difference can be attributed to both the feedback role of surface albedo through different snow accumulation characteristics and longwave radiation emission of the atmosphere due to different meteorological backgrounds. Finally, a review of the few studies dealing with energy balance on the Tibetan glaciers describes the possible spatial characteristics requiring further investigation in the future on larger spatial and temporal scales.