Taylor Glacier hosts an active englacial hydrologic system that feeds Blood Falls, a supraglacial outflow of iron-rich subglacial brine at the terminus, despite mean annual air temperatures of −17°C and limited surface melt. Taylor Glacier is an outlet glacier of the East Antarctic ice sheet that terminates in Lake Bonney, McMurdo Dry Valleys. To image and map the brine feeding Blood Falls, we used radio echo sounding to delineate a subhorizontal zone of englacial brine upstream from Blood Falls and elongated in the ice flow direction. We estimate volumetric brine content in excess of 13% within 2 m of the central axis of this zone, and likely much higher at its center. Brine content decreases, but remains detectable, up to 45 m away along some transects. Hence, we infer a network of subparallel basal crevasses allowing injection of pressurized subglacial brine into the ice. Subglacial brine is routed towards Blood Falls by hydraulic potential gradients associated with deeply incised supraglacial valleys. The brine remains liquid within the subglacial and englacial environments through latent heat of freezing coupled with elevated salt content. Our findings suggest that cold glaciers could support freshwater hydrologic systems through localized warming by latent heat alone.

Evolution of cold dry snow and firn plays important roles in glaciology; however, the physical formulation of a densification law is still an active research topic. We forced eight firn-densification models and one seasonal-snow model in six different experiments by imposing step changes in temperature and accumulation-rate boundary conditions; all of the boundary conditions were chosen to simulate firn densification in cold, dry environments. While the intended application of the participating models varies, they are describing the same physical system and should in principle yield the same solutions. The firn models all produce plausible depth-density profiles, but the model outputs in both steady state and transient modes differ for quantities that are of interest in ice core and altimetry research. These differences demonstrate that firn-densification models are incorrectly or incompletely representing physical processes. We quantitatively characterize the differences among the results from the various models. For example, we find depth-integrated porosity is unlikely to be inferred with confidence from a firn model to better than 2 m in steady state at a specific site with known accumulation rate and temperature. Firn Model Intercomparison Experiment can provide a benchmark of results for future models, provide a basis to quantify model uncertainties and guide future directions of firn-densification modeling.

Hydraulic roughness exerts an important but poorly understood control on water pressure in subglacial conduits. Where relative roughness values are <5%, hydraulic roughness can be related to relative roughness using empirically-derived equations such as the Colebrook–White equation. General relationships between hydraulic roughness and relative roughness do not exist for relative roughness >5%. Here we report the first quantitative assessment of roughness heights and hydraulic diameters in a subglacial conduit. We measured roughness heights in a 125 m long section of a subglacial conduit using structure-from-motion to produce a digital surface model, and hand-measurements of the b-axis of rocks. We found roughness heights from 0.07 to 0.22 m and cross-sectional areas of 1–2 m2, resulting in relative roughness of 3–12% and >5% for most locations. A simple geometric model of varying conduit diameter shows that when the conduit is small relative roughness is >30% and has large variability. Our results suggest that parameterizations of conduit hydraulic roughness in subglacial hydrological models will remain challenging until hydraulic diameters exceed roughness heights by a factor of 20, or the conduit radius is >1 m for the roughness elements observed here.

Feature tracking of approximately annually separated Landsat-7 ETM+ imagery acquired from 1999 to 2010 and speckle tracking of 24-day separated RADARSAT-2 imagery acquired from 2009 to 2015 reveal that motion of the major tidewater glaciers of Devon Ice Cap is more variable than previously described. The flow of almost half (six of 14) of the outlet glaciers slowed over the observation period, while that of the terminus regions of three of 14 of the glaciers sped up in the most recent years of observation. The North Croker Bay Glacier of southern Devon Ice Cap showed the greatest variability in motion, oscillating between multi-year (three or more) periods of slower and faster flow and exhibited a pattern of velocity variability that is different from that of the rest of the ice cap's outlet glaciers. Comparisons between areas of dynamic variability and glacier bed topography indicate that velocity variability is largely restricted to regions where the glacier bed is grounded below sea level. Derived velocities are combined with measurements of ice thickness at the fronts of tidewater glacier to determine a mean annual (2009; 2011–15) dynamic ice discharge of 0.41 ± 0.11 Gt a−1 for Devon Ice Cap. The Belcher Glacier is becoming a larger source of mass loss via ice discharge.

Annual and seasonal surface velocities measured continuously from 1960 to 1970 at White Glacier, a 14 km long polythermal valley glacier spanning ~100–1800 m a.s.l., provide the most comprehensive early record of ice dynamics in the Canadian Arctic. Through comparison with differential GPS-derived velocity data spanning 2012–16, we find reductions in mean annual velocity by 31 and 38% at lower elevations (600 and 400 m a.s.l.). These are associated with decreased internal ice deformation due to ice thinning and reduced basal motion likely due to increased hydraulic efficiency in recent years. At higher elevation (~850 m a.s.l.) there is no detectable change in annual velocity and the expected decrease in internal deformation rates due to ice thinning is offset by increased basal motion in both summer and winter, likely attributable to supraglacial melt accessing a still inefficient subglacial drainage system. Decreases in mass flux at lower elevations since the 1960s cannot explain the observed elevation loss of ~20 m, meaning that ice thinning along the glacier trunk is primarily a function of downwasting rather than changing ice dynamics. The current response of the glacier exemplifies steady thinning, velocity slowdown and upstream retreat of the ELA but, because the glacier has an unstable geometry with considerable mass in the 1300–1500 m elevation range, a retreat of the ELA to >1300 plausible within 25–40 years, could trigger runaway wastage.

Increased summer ice velocities on the Greenland ice sheet are driven by meltwater input to the subglacial environment. However, spatial patterns of surface input and partitioning of meltwater between different pathways to the base remain poorly understood. To further our understanding of surface drainage, we apply a supraglacial hydrology model to the Paakitsoq region, West Greenland for three contrasting melt seasons. During an average melt season, crevasses drain ~47% of surface runoff, lake hydrofracture drains ~3% during the hydrofracturing events themselves, while the subsequent surface-to-bed connections drain ~21% and moulins outside of lake basins drain ~15%. Lake hydrofracture forms the primary drainage pathway at higher elevations (above ~850 m) while crevasses drain a significant proportion of meltwater at lower elevations. During the two higher intensity melt seasons, model results show an increase (~5 and ~6% of total surface runoff) in the proportion of runoff drained above ~1300 m relative to the melt season of average intensity. The potential for interannual changes in meltwater partitioning could have implications for how the dynamics of the ice sheet respond to ongoing changes in meltwater production.

Surface hoar crystals are common on the surface of mountain snow covers. Once buried, layers of large plate-shaped surface hoar crystals are prone to releasing dangerous snow-slab avalanches. Since snow microstructure influences the optical properties of snow, remote sensors could potentially detect the formation of surface hoar and other snow types associated with avalanche release. The spectral reflectance of 377 snow samples was measured with a field spectrometer between 750 and 2500 nm, including 161 samples of surface hoar. Morphological snow shapes associated with critical avalanche layers (surface hoar, near-surface faceted particles and depth hoar) had lower average reflectance factors than non-critical snow shapes at infrared wavelengths. Needle-shaped surface hoar was more reflective than plate-shaped surface hoar, but there were no significant differences between different sizes of surface hoar. Normalized difference indices calculated with reflectance from two wavelength bands is presented as a potential method to classify critical snow surfaces remotely, although melt-freeze crusts near the surface complicated the classification. Accordingly, further studying on the effect of melt-freeze crusts and quantification of the bidirectional reflective properties of critical snow types is needed.

In this study, a modelling approach was used to investigate the cause of the diversion of erratic boulders from Mont Blanc and southern Valais by the Valais Glacier to the Solothurn lobe during the Last Glacial Maximum (LGM). Using the Parallel Ice Sheet Model, we simulated the ice flow field during the LGM, and analyzed the trajectories taken by erratic boulders from areas with characteristic lithologies. The main difficulty in this exercise laid with the large uncertainties affecting the paleo climate forcing required as input for the surface mass-balance model. In order to mimic the prevailing climate conditions during the LGM, we applied different temperature offsets and regional precipitation corrections to present-day climate data, and selected the parametrizations, which yielded the best match between the modelled ice extent and the geomorphologically-based ice-margin reconstruction. After running a range of simulations with varying parameters, our results showed that only one parametrization allowed boulders to be diverted to the Solothurn lobe during the LGM. This precipitation pattern supports the existing theory of preferential southwesterly advection of moisture to the alps during the LGM, but also indicates strongly enhanced precipitation over the Mont Blanc massif and enhanced cooling over the Jura Mountains.

This study investigates the evolution of Greenland ice sheet flux focusing on five of the main fast flowing regions (Petermann glacier, North East Greenland Ice Stream, Kangerdlugssuaq glacier, Helheim glacier and Jakobshavn glacier) in response to 20th and 21st century climate change. A hybrid (shallow ice and shallow shelf) ice-sheet model (ISM) is forced with the combined outputs of a set of seven CMIP5 models and the regional climate model MAR. The ISM simulates the present-day ice velocity pattern, topography and surface mass balance (SMB) in good agreement with observations. Except for the Kangerdlugssuaq glacier, over the 21st century all the fast-flowing areas have exhibited a decrease in ice flux as a result of a negative SMB rather than dynamical changes. Only the fronts of Kangerdlugssuaq and Helheim glaciers have shown an interannual variability driven by dynamical rather than climate changes. Finally, the results predict a substantial inland ice margin retreat by the end of the 21st century, especially along the northern coasts.

Temporal variations of the radionuclide 10Be are broadly synchronous across the globe and thus provide a powerful tool to synchronize ice core chronologies from different locations. We compared the 10Be record of the Akademii Nauk (AN) ice core (Russian Arctic) for the time period CE 1590–1950 to the 10Be records of two well-dated Greenland ice cores (Dye3 and NGRIP). A high correlation (r = 0.59) was found between the AN and Dye3 records whereas the correlation with NGRIP was distinctly lower (r = 0.45). Sources of deviations may include local fluctuations in the deposition of 10Be due to changes in the precipitation patterns, and artefacts due to the core-sampling strategy. In general, the existing age model was validated, confirming the AN ice core to be a unique and well-dated source of palaeoclimate parameters for the Russian Arctic. We further used numerical simulations to test the influence of the core-sampling strategy on the results and derived an optimized sampling strategy for the deeper parts of the ice core.

Using in-situ measured data from Qiyi Glacier, in combination with meteorological and run-off data from stations, a distributed degree-day model was developed for 631 investigated glaciers in the Beida River catchment to explore glacier mass change and its effect on streamflow. The results showed that the average mass balance was −272 ± 67 mm w.e. a−1, with an ice loss of 3.99 Gt during 1957–2013. Assuming a continuous linear trend, equilibrium line altitude rose by 242 m. Compared with morpho-topographic variables, climatic control is a more important factor affecting glacier change. Mass-balance sensitivity to air temperature was −239 mm w.e.°C−1 a−1, while to precipitation it was +1.1 mm w.e. mm−1 a−1. That is, a 210 mm increase in precipitation would be needed to compensate for the net mass loss induced by an air temperature increase of 1°C. Average annual glacier meltwater runoff was 1.51 × 108 m3 from 1957 to 2013, accounting for 15.2% of surface runoff. The time series of meltwater runoff changed abruptly in 2000, and its contribution to surface runoff increased from 13.9 to 20.4%.

Changes of glaciers and glacial lakes and their causes were examined in the Hengduan Shan from 1990 to 2014, based on Landsat TM/ETM+/OLI images. A total glacier area of 1298.8 ± 62.1 km2 and glacial lake area of 255.8 ± 31.6 km were inventoried in 2014. The area of glaciers declined at an average rate of −0.40 ± 0.26% a−1, while glacial lakes expanded at average rate of +0.12 ± 0.03% a−1 over the past 24 years. These changes probably resulted from an observable temperature increase and slight precipitation increase. A ‘corridor-barrier’ effect formed by the longitudinal range–gorge terrain may have had major impacts on the distributions and changes of glaciers and glacial lakes. The Ningjing-Yunling Shan, where glaciers and glacial lakes are sparsely distributed, are an important geographic transition line in the Hengduan Shan because of the barrier effect of the mountain ranges against moisture from the southwest. In contrast, between the south and north, there were small differences with respect to the distributions and changes of glaciers and glacial lakes, owing to a north–south corridor effect for water and heat transport and diffusion through the longitudinal gorges in the Hengduan Shan.

Supraglacial debris thickness is a key control on the surface energy balance of debris-covered glaciers, yet debris thickness measurements are sparse due to difficulties of data collection. Here we use ground-penetrating radar (GPR) to measure debris thickness on the ablation zone of Lirung Glacier, Nepal. We observe a strong, continuous reflection, which we interpret as the ice surface, through debris layers of 0.1 to at least 2.3 m thick, provided that appropriate acquisition parameters were used while surveying. GPR measurements of debris thickness correlate well with pit measurements of debris thickness (r = 0.91, RMSE = 0.04 m) and two-way travel times are consistent at tie points (r = 0.97). 33% of measurements are <0.5 m, so sub-debris melting is likely important in terms of mass loss on the debris-covered tongue and debris thickness is highly variable over small spatial scales (of order 10 m), likely due to local slope processes. GPR can be used to make debris thickness measurements more quickly, over a wider debris thickness range, and at higher spatial resolution than any other means and is therefore a valuable tool with which to map debris thickness distribution on Himalayan glaciers.

Ice-stream dynamics are strongly controlled by processes taking place at the ice/bed interface where subglacial water both lubricates the base and saturates any existing, underlying sediment. Large parts of the former Eurasian ice sheet were underlain by thick sequences of soft, marine sediments and many areas are imprinted with geomorphological features indicative of fast flow and wet basal conditions. Here, we study the effect of subglacial water on past Eurasian ice-sheet dynamics by incorporating a thin-film model of basal water flow into the ice-sheet model SICOPOLIS and use it to better represent flow in temperate areas. The adjunction of subglacial hydrology results in a smaller ice-sheet building up over time and generally faster ice velocities, which consequently reduces the total area fraction of temperate basal ice and ice streaming areas. Minima in the hydraulic pressure potential, governing water flow, are used as indicators for potential locations of past subglacial lakes and a probability distribution of lake existence is presented based on estimated lake depth and longevity.