Every winter, snowy landscapes are smoothed by snow deposition in calm conditions (no wind). In this study, we investigated how vertically falling snow attenuates topographic relief at horizontal scales less than or approximately equal to snow depth (e.g., 0.1–10 m). In a set of three experiments under natural snowfall, we observed the particle-scale mechanisms by which smoothing is achieved, and we examined the cumulative effect at the snowpack scale. The experiments consisted of (a) a strobe-light box for tracking the trajectories of snowflakes at deposition, (b) allowing snow to fall through a narrow gap (40 mm) and examining snow accumulation above and below the gap, and (c) allowing snow to accumulate over a set of artificial surfaces. At the particle scale, we observed mechanisms enhancing (bouncing, rolling, ejection, breakage, creep, metamorphism) and retarding (interlocking, cohesion, adhesion, sintering) the rate of smoothing. The cumulative effect of these mechanisms is found to be driven by snowpack surface curvature, introducing a directional bias in the lateral transport of snow particles. Our findings suggest that better quantification of the mechanisms behind smoothing by snow could provide insights into the evolution of snow depth variability, and snow-vegetation interactions.

Despite previous studies, glacier–lake interactions and future lake development in the Poiqu River basin, central Himalaya, are still not well understood. We mapped glacial lakes, glaciers, their frontal positions and ice flow from optical remote sensing data, and calculated glacier surface elevation change from digital terrain models. During 1964–2017, the total glacial-lake area increased by ~110%. Glaciers retreated with an average rate of ~1.4 km2 a−1 between 1975 and 2015. Based on rapid area expansion (>150%), and information from previous studies, eight lakes were considered to be potentially dangerous glacial lakes. Corresponding lake-terminating glaciers showed an overall retreat of 6.0 ± 1.4 to 26.6 ± 1.1 m a−1 and accompanying lake expansion. The regional mean glacier elevation change was −0.39 ± 0.13 m a−1 while the glaciers associated with the eight potentially dangerous lakes lowered by −0.71 ± 0.05 m a−1 from 1974 to 2017. The mean ice flow speed of these glaciers was ~10 m a−1 from 2013 to 2017; about double the mean for the entire study area. Analysis of these data along with climate observations suggests that ice melting and calving processes play the dominant role in driving lake enlargement. Modelling of future lake development shows where new lakes might emerge and existing lakes could expand with projected glacial recession.

The West Kunlun Shan lie close to, or are perhaps part of, two significant glaciological phenomena – the High Mountain Asia surge ‘supercluster’ and the Karakoram Anomaly. However, glaciological studies, and particularly surge studies, in the range are limited. Here, we extend the database of known surges in the region using Landsat imagery and cross-correlation feature tracking. We examine 88 glaciers larger than 1 km2 in the Hotan Prefecture of Xinjiang, China, and find evidence of nine surges occurring between 1972 and 2017. Glaciers display low active phase velocities (~0.2–1.5 km a−1) that show seasonal acceleration in the summer, active phase periods as short as 2 years, and build-up and deceleration phases of months--years. Although these observations display characteristics indicative of both the classic hydrological and thermal switch mechanisms, the surging observed displays a close resemblance to that in the adjacent Karakoram ranges. Furthermore, the majority of the surges occur clustered at the end of a decadal-scale warming period, corroborating previously proposed causal links between climate and surging in the Karakoram. We suggest that the two regions should be considered part of one larger system when considering surge dynamics in High Mountain Asia.

We present the first general theory of glacier surging that includes both temperate and polythermal glacier surges, based on coupled mass and enthalpy budgets. Enthalpy (in the form of thermal energy and water) is gained at the glacier bed from geothermal heating plus frictional heating (expenditure of potential energy) as a consequence of ice flow. Enthalpy losses occur by conduction and loss of meltwater from the system. Because enthalpy directly impacts flow speeds, mass and enthalpy budgets must simultaneously balance if a glacier is to maintain a steady flow. If not, glaciers undergo out-of-phase mass and enthalpy cycles, manifest as quiescent and surge phases. We illustrate the theory using a lumped element model, which parameterizes key thermodynamic and hydrological processes, including surface-to-bed drainage and distributed and channelized drainage systems. Model output exhibits many of the observed characteristics of polythermal and temperate glacier surges, including the association of surging behaviour with particular combinations of climate (precipitation, temperature), geometry (length, slope) and bed properties (hydraulic conductivity). Enthalpy balance theory explains a broad spectrum of observed surging behaviour in a single framework, and offers an answer to the wider question of why the majority of glaciers do not surge.

Submarine melting of tidewater glaciers is proposed as a trigger for their recent thinning, acceleration and retreat. We estimate spring submarine melt rates (SMRs) of Kangiata Nunaata Sermia in southwest Greenland, from 2012 to 2014, by examining changes in along-fjord freeboard and velocity of the seasonal floating ice tongue. Estimated SMRs vary spatially and temporally near the grounding line, with mean rates of 1.3 ± 0.6, 0.8 ± 0.3 and 1.0 ± 0.4 m d−1 across the tongue in 2012, 2013 and 2014, respectively. Higher melt rates correspond with locations of emerging subglacial plumes and terminus calving activity observed during the melt season using time-lapse camera imagery. Modelling of subglacial flow paths suggests a dynamic system capable of rapid re-routing of subglacial discharge both within and between melt seasons. Our results provide an empirically-derived link between the presence of subglacial discharge plumes and areas of high spring submarine melting and calving along glacier termini.

Small mountain glaciers are an important part of the cryosphere and tend to respond rapidly to climate warming. Historically, mapping very small glaciers (generally considered to be <0.5 km2) using satellite imagery has often been subjective due to the difficulty in differentiating them from perennial snowpatches. For this reason, most scientists implement minimum size-thresholds (typically 0.01–0.05 km2). Here, we compare the ability of different remote-sensing approaches to identify and map very small glaciers on imagery of varying spatial resolutions (30–0.25 m) and investigate how operator subjectivity influences the results. Based on this analysis, we support the use of a minimum size-threshold of 0.01 km2 for imagery with coarse to medium spatial resolution (30–10 m). However, when mapping on high-resolution imagery (<1 m) with minimal seasonal snow cover, glaciers <0.05 km2 and even <0.01 km2 are readily identifiable and using a minimum threshold may be inappropriate. For these cases, we develop a set of criteria to enable the identification of very small glaciers and classify them as certain, probable or possible. This should facilitate a more consistent approach to identifying and mapping very small glaciers on high-resolution imagery, helping to produce more comprehensive and accurate glacier inventories.

We investigated the effects of microparticles and grain size on the microstructural evolutions and mechanical properties of polycrystalline ice. Uniaxial compression tests were conducted using fine-grained pure ice and silica-dispersed ice under various conditions. Deformation behavior of fine-grained ice was found to be characterized by stress exponent n ≈ 2 and activation energy Q ≈ 60 kJ mol−1. The derived strain rates of fine-grained ice were ≈ 1 order of magnitude larger than those of coarse-grained ice obtained in previous studies, and they were found to be independent of particle dispersion and dependent on the mean grain size of ice, with grain size exponent p ≈ 1.4. Work hardening was observed in dislocation creep, while the strain rate continued to decrease. These results indicate that the deformation mechanism of fine-grained ice is different from typical dislocation creep, often associated with n = 3. Although microparticles restricted grain growth, there was little direct effect on the deformation of fine-grained ice. Microstructural observations of the ice samples indicated that the grain boundaries were straight and that the subgrain boundary densities increased after deformation. Our experiments suggest that grain size and boundaries play important roles in the deformation processes of polycrystalline ice.

The Martian mid-latitudes contain numerous small water-ice deposits, collectively termed viscous flow features (VFFs). The shape and topography of the deposits contain information on their past flow history and formation process. In order to access this information, it is imperative to get information on their deformational properties. Here we use a high-resolution digital topography map and ice-penetrating radar data in combination with an inverse method to constrain the deformational properties of a lobate debris apron, a class of VFF, in the southern hemisphere of Mars. We find that while the creep parameter and accumulation rates are not well constrained in absolute values, their ratio is robust. We also find that the creep exponent is most likely n ≤ 3.

Analysis of a recent surge of Morsnevbreen, Svalbard, is used to test predictions of the enthalpy balance theory of surging. High-resolution time series of velocities, ice thickness and crevasse distribution allow key elements of the enthalpy (internal energy) budget to be quantified for different stages of the surge cycle. During quiescence (1936–1990), velocities were very low, and geothermal heat slowly built-up enthalpy at the bed. Measurable mass transfer and frictional heating began in 1990–2010, then positive frictional heating-velocity feedbacks caused gradual acceleration from 2010 to 2015. Rapid acceleration occurred in summer 2016, when extensive crevassing and positive air temperatures allowed significant surface to bed drainage. The surge front reached the terminus in October 2016, coincident with a drop in velocities. Ice plumes in the fjord are interpreted as discharge of large volumes of supercooled water from the bed. Surge termination was prolonged, however, indicating persistence of an inefficient drainage system. The observations closely match predictions of the theory, particularly build-up of enthalpy from geothermal and frictional heat, and surface meltwater, and the concomitant changes in ice-surface elevation and velocity. Additional characteristics of the surge reflect spatial processes not represented in the model, but can be explained with respect to enthalpy gradients.

Glacier changes in the Jankar Chhu Watershed (JCW) of Chandrabhaga (Chenab) basin, Lahaul Himalaya were worked out based on Corona and Sentinel 2A images between 1971 and 2016. The JCW consists of 153 glaciers (>0.02 km2) with a total area of 185.6 ± 3.8 km2 that include 82 glaciers with debris-covered ablation zone, comprising 10.9% of the total glacierized area as in 2016. Change analysis based on Corona (1971), Landsat (2000) and Sentinel 2A (2016) was restricted to 127 glaciers owing to the presence of cloud cover on 26 glaciers in 1971. A subset of glaciers was also mapped using Landsat Thematic Mapper (TM; 1989) image. The total glacier area decreased by 14.7 ± 4.3 km2 (0.3 ± 0.1 km2 a−¹). The number of glaciers in the JCW increased by four between 1971 and 2016 due to fragmentation. More recently (2000–16), recession rate has increased. Clean-ice area decreased by 21.8 ± 3.8 km2 (0.5 ± 0.1 km2 a−¹) while debris-covered ice increased by 7.2 ± 0.4 km2 (0.2 ± 0.01 km2 a−¹). Field observations of select glaciers also support derived recession trend in the JCW. Retreat rates in the JCW have been observed to be much lower than previously reported.

The accelerated retreat of glaciers and the reduction of glacier ice reserves caused by climate change can significantly affect regional water resources and hydrological cycles. Changes in glacier thickness are among the key indicators that reflect this process. We analyzed changes observed in the elevation of glacier surfaces in the Gongga Mountains (GGM) using multi-temporal Digital Elevation Models (DEMs) derived from topographic maps, SRTM, ICESat and ZY-3 data. The results showed that the mean rate of change in glacier surface altitude in the GGM was ~−26.7 ± 2.03 m (0.54 ± 0.04 m a−1) between 1966 and 2015. The mean melt rates differed over different time periods, latterly showing an accelerating trend. As a general rule, glaciers appear to be losing more volume at lower than at higher elevations. Further analysis of these results suggests that supraglacial debris coverage in the GGM promotes higher rates of mass loss.

In this work we tested the suitability of thermistor strings as automatic tools for the continuous measurement of glacier ice ablation. Experimental data collected in summer 2017 over an Italian glacier provided ice ablation readings with accuracy similar to manual measurements with ablation stakes and other automatic systems, like the draw-wire method and the Bøggild ablatometer. Thermistor strings have potential for future applications in remote glacier monitoring, thanks to their flexibility, simple construction, and robustness.

A total of eight floating glacier tongues have shrunk in area by >85% from the Yelverton Bay region of Northern Ellesmere Island since 1959, with unusually large losses since 2005. To better understand the causes of these losses, this study undertakes the first examination of ice tongue changes in this region, including an assessment of changes in surrounding marine ice (i.e. sea ice, sikussak and mélange), and atmospheric and oceanographic forcings. From 1959 to 2017, the total ice tongue area decreased by 49.07 km2, with the majority of this loss occurring from 2005 to 2009 (34.68 km2). The loss of ice tongues since 2005 occurred when open water replaced multi-year landfast sea ice (MLSI) and first-year sea ice in the regions adjacent to the ice tongues. These changes were accompanied by an increase in mean annual mid-depth (i.e. 100 and 200 m) ocean temperatures from −0.29°C from 1999 to 2005 to 0.67°C from 2006 to 2012. Despite the recent return of ocean temperatures to below pre-2006 levels, atmospheric summer temperatures have continued to rise (+0.15°C decade−1 between 1948 and 2016), with open water continuing to occur. Without the sustained presence of MLSI in this region the ice tongues are unable to stabilize, making it unlikely that they will re-form in the current climate.

Microorganisms are the most abundant organisms on Earth, and microbial abundance records preserved in ice cores have been connected to records of environmental change. As an alternative to high resolution abundance records, which can be difficult to recover, we used culture-dependent and culture-independent methods to examine bacteria in glacier ice from the Tibetan Plateau (TP). We recovered a total of 887 bacterial isolates from ice cores of up to 164 m in depth retrieved from seven glaciers, located across the TP. These isolates were related to 53 genera in the Actinobacteria, Firmicutes, Bacteroidetes, and Proteobacteria, with 13 major genera accounting for 78% of isolates. Most of the genera were common across the geographic region covered by our sampling, but there were differences in the genera recovered from different depths in the ice, with the deepest portions of the ice cores dominated by a single genus (Sporosarcina). Because microorganisms deposited on glaciers must survive atmospheric transport under a range of temperatures, temperature tolerance should be an important survival mechanism. We tested isolate growth across a range of temperatures (0–35 °C), and found psychrotolerance to be common. Together, our results show that ice depth, and by extension age, are characterized by different types of microorganisms, providing new information about microbial records in ice.

The Southern Patagonia Icefield (SPI) withdrawal in recent decades shows contrasting behaviours between adjacent basins. One of the basins with highest volumetric losses is located at northernmost SPI. We refer to Jorge Montt tidewater glacier (48° 30′S/73° 30′W, 445 km2 in 2018), which retreated 2.7 km between 2011 and 2018 and thinned at rates of up to 21 m a−1 over this period. Based on the retreat record, remote-sensing imagery, field data, a mass-balance model and a calving parameterisation, we attempted to differentiate climatic-induced changes (i.e. surface mass balance) and dynamic responses (i.e. calving fluxes). The surface mass balance reached −4.15 km3 w.e. a−1 between 2012 and 2017. When frontal ablation is included, the net mass balance is −17.79 km3 w.e. a−1. This represents a change of trend compared with modelling estimations of positive surface mass balance prior to 2010. This shift is attributed to higher ablation rates given that accumulation is known to have increased between 1980 and 2015. The available evidence, therefore, indicates that frontal ablation is the main factor, supported by observed rates at Jorge Montt as high as 3.81 km3 w.e. a−1 in 2015, with ice velocities peaking at 11 km a−1.

Supraglacial streams are a significant part of the glacial hydrological system and important for understanding glacial hydrology and dynamics. Here we infer factors that influence the long-term development of perennial supraglacial streams, particularly in reference to canyon, incised and surface stream formation. Orthophotos and digital elevation models generated from high-resolution aerial imagery taken with unmanned aerial vehicles or piloted helicopters between 2010 and 2017 were used to compare seven streams on Fountain Glacier, Bylot Island, Canada over time. Results show canyon formation occurs from a combination of fluvial processes and the impact of solar radiation. The greater the discharge or slope, the faster the incision and higher the sinuosity. With greater sinuosity, the distance between the top of the valley banks increases, and cutoffs cause trapezoidal canyon-like valleys to form. Solar radiation causes the backward migration of the valley walls, further enhancing canyon area. Canyons are less likely to occur in areas of low discharge and slope. Less incised channels are also more likely to have water flow jumping the channel banks, changing the channel path. The presence of medial moraines and crevasses also increases rerouting of small streams. Lastly, windblown created snow-plugs may lead to stream diversion.

We present a workflow to track icebergs in proglacial fjords using oblique time-lapse photos and the Lucas-Kanade optical flow algorithm. We employ the workflow at LeConte Bay, Alaska, where we ran five time-lapse cameras between April 2016 and September 2017, capturing more than 400 000 photos at frame rates of 0.5–4.0 min−1. Hourly to daily average velocity fields in map coordinates illustrate dynamic currents in the bay, with dominant downfjord velocities (exceeding 0.5 m s−1 intermittently) and several eddies. Comparisons with simultaneous Acoustic Doppler Current Profiler (ADCP) measurements yield best agreement for the uppermost ADCP levels (~ 12 m and above), in line with prevalent small icebergs that trace near-surface currents. Tracking results from multiple cameras compare favorably, although cameras with lower frame rates (0.5 min−1) tend to underestimate high flow speeds. Tests to determine requisite temporal and spatial image resolution confirm the importance of high image frame rates, while spatial resolution is of secondary importance. Application of our procedure to other fjords will be successful if iceberg concentrations are high enough and if the camera frame rates are sufficiently rapid (at least 1 min−1 for conditions similar to LeConte Bay).

Glaciers on active volcanoes are subject to changes in both climate fluctuations and volcanic activity. Whereas many studies analysed changes on individual volcanoes, this study presents for the first time a comparison of glacier changes on active volcanoes on a continental scale. Glacier areas were mapped for 59 volcanoes across Latin America around 1986, 1999 and 2015 using a semi-automated band ratio method combined with manual editing using satellite images from Landsat 4/5/7/8 and Sentinel-2. Area changes were compared with the Smithsonian volcano database to analyse possible glacier–volcano interactions. Over the full period, the mapped area changed from 1399.3 ± 80 km2 to 1016.1 ± 34 km2 (−383.2 km2) or −27.4% (−0.92% a−1) in relative terms. Small glaciers, especially in tropical regions lost more of their area compared to large and extra–tropical glaciers. Interestingly, 46 out of 59 analysed glaciers (78%) showed a decelerating shrinkage rate in the second period (−1.20% a−1 before 1999 and −0.70% a−1 after 1999). We found a slightly higher (but statistically not significant) area loss rate (−1.03% a−1) for glaciers on volcanoes with eruptions than without (−0.86% a−1).

The Ross Ice Shelf (RIS) is host to a broadband, multimode seismic wavefield that is excited in response to atmospheric, oceanic and solid Earth source processes. A 34-station broadband seismographic network installed on the RIS from late 2014 through early 2017 produced continuous vibrational observations of Earth's largest ice shelf at both floating and grounded locations. We characterize temporal and spatial variations in broadband ambient wavefield power, with a focus on period bands associated with primary (10–20 s) and secondary (5–10 s) microseism signals, and an oceanic source process near the ice front (0.4–4.0 s). Horizontal component signals on floating stations overwhelmingly reflect oceanic excitations year-round due to near-complete isolation from solid Earth shear waves. The spectrum at all periods is shown to be strongly modulated by the concentration of sea ice near the ice shelf front. Contiguous and extensive sea ice damps ocean wave coupling sufficiently so that wintertime background levels can approach or surpass those of land-sited stations in Antarctica.

In the current ice-sheet models calving of ice shelves is based on phenomenological approaches. To obtain physics-based calving criteria, a viscoelastic Maxwell model is required accounting for short-term elastic and long-term viscous deformation. On timescales of months to years between calving events, as well as on long timescales with several subsequent iceberg break-offs, deformations are no longer small and linearized strain measures cannot be used. We present a finite deformation framework of viscoelasticity and extend this model by a nonlinear Glen-type viscosity. A finite element implementation is used to compute stress and strain states in the vicinity of the ice-shelf calving front. Stress and strain maxima of small (linearized strain measure) and finite strain formulations differ by ~ 5% after 1 and by ~ 30% after 10 years, respectively. A finite deformation formulation reaches a critical stress or strain faster, thus calving rates will be higher, despite the fact that the exact critical values are not known. Nonlinear viscosity of Glen-type leads to higher stress values. The Maxwell material model formulation for finite deformations presented here can also be applied to other glaciological problems, for example, tidal forcing at grounding lines or closure of englacial and subglacial melt channels.