This paper aims to show how recent knowledge developed in the field of avalanche research can be used for a real case study, the Taconnaz avalanche path, where passive structures already existed but had to be improved. First a morphological analysis of the site is done and historical data are analysed. Second, each recorded event is back-calculated using a numerical model of dense-flow avalanches. For each surveyed avalanche, parameters at the entry of the runout zone upstream of the defence structures are defined. Third, a statistical analysis of these parameters allows characterization of 100 year return period events. Fourth, physical and numerical models of dense avalanches interacting with defence structures are combined in order to design the most effective passive structure able to contain the reference scenarios. Finally, physical and numerical modelling of the interaction between the powder avalanche and the designed defence structure is performed, to show that the proposed improvements do not increase the residual risk due to the powder part in areas downstream of the defence structures.

Regional climate warming has caused several ice shelves on the Antarctic Peninsula to retreat and ultimately collapse during recent decades. Glaciers flowing into these retreating ice shelves have responded with accelerating ice flow and thinning. The Wordie Ice Shelf on the west coast of the Antarctic Peninsula was reported to have undergone a major areal reduction before 1989. Since then, this ice shelf has continued to retreat and now very little floating ice remains. Little information is currently available regarding the dynamic response of the glaciers feeding the Wordie Ice Shelf, but we describe a Chilean International Polar Year project, initiated in 2007, targeted at studying the glacier dynamics in this area and their relationship to local meteorological conditions. Various data were collected during field campaigns to Fleming Glacier in the austral summers of 2007/08 and 2008/09. In situ measurements of ice-flow velocity first made in 1974 were repeated and these confirm satellite-based assessments that velocity on the glacier has increased by 40–50% since 1974. Airborne lidar data collected in December 2008 can be compared with similar data collected in 2004 in collaboration with NASA and the Chilean Navy. This comparison indicates continued thinning of the glacier, with increasing rates of thinning downstream, with a mean of 4.1 ± 0.2 m a−1 at the grounding line of the glacier. These comparisons give little indication that the glacier is achieving a new equilibrium.

We use velocity profile measurements captured at the Vallée de la Sionne test site, Switzerland, to find experimental evidence for the value of extreme, Voellmy-type runout parameters for snow avalanche flow. We apply a constitutive relation that adjusts the internal shear stress as a function of the kinetic energy associated with random motion of the snow granules, R. We then show how the Voellmy dry-Coulomb and velocity-squared friction parameters change (relax) as a function of an increase in R. Since the avalanche head is characterized by high random energy levels, friction decreases significantly, leading to rapidly moving and far-reaching avalanches. The relaxed friction parameters are near to values recommended by the Swiss avalanche dynamics guidelines. As the random kinetic energy decreases towards the tail, friction increases, causing avalanches to deposit mass and stop even on steep slopes. Our results suggest that the Voellmy friction model can be effectively applied to predict maximum avalanche velocities and maximum runout distances. However, it cannot be applied to model the full range of avalanche behaviour, especially to find the distribution of mass in the runout zone. We answer a series of questions concerning the role of R in avalanche dynamics.

King George Island is the largest of the South Shetland Islands, close to the tip of the Antarctic Peninsula. The annual mean temperature on the island has increased by 1°C during the past three decades, and the ice cap that covers the majority of the island is sensitive to climatic change. We present data from two field campaigns (1997 and 2007): 700 km of global positioning system (GPS) and ground-penetrating radar (GPR) profiles were collected on Arctowski Icefield and on the adjacent central part. The data were analysed to determine the surface and bed topography and the thermal regime of the ice. Average ice thickness is 250 m and maximum thickness is 420 m. The GPR profiles show isochrones throughout the ice cap which depict the uparching of Raymond bumps beneath or close to the ice divides. A water table from percolation of meltwater in the snowpack shows the firn-ice boundary at ∼ 3 5 m depth. The firn layer may be temperate due to the release of latent heat. In the area below 400ma.s.l., backscatter by water inclusions is abundant for ice depths below the water table. We interpret this as evidence for temperate ice. Scatter decreases significantly above 400 m. Ice temperatures below the water table in this part of the ice cap are subject to further field and modelling investigations.

This paper presents an assessment of biological activity associated with ice surface debris (cryoconite) at the ice-sheet scale. Estimates of the mass distribution of cryoconite over the Greenland ice sheet (GIS) and the biological activity associated with it are presented and then coupled with a surface mass-balance model to estimate total carbon fluxes due to respiration and photosynthesis. We find an average loading of 66gm−2 at Kangerlussuaq, southwest Greenland, which compares well with recent estimates from Kronprins Christians Land (17–440 gm−2: Bøggild and others, 2010) in northeast Greenland. We also report a significant microbial biomass in cryoconite at both these places (103–104 cells mg−1) and carbon fluxes of the order of 1–3 μM C g−1d−1 for both respiration and photosynthesis. The modelling indicates that total respiration and photosynthesis fluxes are likely to be ∼101–102 GgCa−1 and thus far from trivial. However, estimation of the net ecosystem impact across the entire ice sheet on atmospheric CO2 concentrations is problematic because photosynthesis rates were almost certainly low during our field campaign. Therefore, like its water balance, the carbon balance of the GIS is now known to be important, but its accurate quantification will remain elusive until more data are forthcoming.

Mass-balance measurements were initiated in 2007/08 on Sørbreen, Jan Mayen, including operation of automatic weather stations in the ablation zone. Mean daily melt rate is 3.6 cmw.e. d−1 for the investigated snow-free period of 115 days in June-September 2008. During this period, the net radiation is the largest contributor to melt. However, the relative contribution is highest in June (81%) and less in September (21%). The net longwave radiation is negative, acting as a heat sink. The climate on Jan Mayen is polar maritime with generally high humidity and overcast conditions. This leads to a positive latent heat flux, which represents condensation to the glacier surface. Persistent temperature inversions on the island lead to non-linear lapse rates and an ablation profile where melt does not necessarily decrease with increased elevation. A comparison of air temperatures on the glacier and twice-daily radiosonde ascents from the meteorological station, ∼ 20 km away from the glacier, shows that air temperatures at corresponding elevations are highly correlated (R2 = 0.94–0.96). This indicates that radiosonde temperature profiles can be valuable for determining lapse rates for melt modeling of the glacier.

The high Himalayan mountains in the north of India are important sources for generating and maintaining the climate over the entire northern belt of the Indian subcontinent. They also influence extreme weather events, such as the western disturbances over the region during winter. The work presented here describes some current trends in weather and climate over the western Himalaya and suggests some possible explanations in the context of climate change. The work also shows how the special features of Indian orography in the western Himalaya affect climate change in the long term, changing the pattern of precipitation over the region. Data analysis of different ranges of the western Himalaya shows significant variations in temperature and snowfall trends in the past few decades. Possible explanations for the changing climate over the western Himalaya are proposed, in terms of variations in cloudiness. The possible effects of climate change on the number of snowfall days and the occurrences of western disturbances over the western Himalaya are also analysed.

Hydrologic and hydrochemical studies have been conducted in Green Lakes Valley, Colorado Front Range, USA, above 3550 m since 1982. They show a classic seasonal hydrograph dominated by snowmelt and an earlier date for the start of spring flow and for peak flow over the period of record. This is consistent with patterns found at lower elevations in Colorado and throughout western North America. They also show an increasing trend in flows in September and October of 2.6 ±0.7 mm a−1 which is not found elsewhere and cannot be accounted for by increased autumn precipitation and the melting of surface ice. Because this late-season increase is not found at the highest elevations or in basins in which there is no evidence of permafrost, it seems best explained by the thawing of alpine permafrost at intermediate elevations. This is corroborated by an increase in the concentration of base cations and silica, and particularly in Ca2+ and SO4–, in the stream discharge starting in 2000. As with the physical hydrology, the geochemical signals have not been detected at the higher elevations in the basin, though they have previously been associated with streamflow from a small rock glacier in the valley. The combined evidence suggests the degradation of ice-rich permafrost on the north-facing slopes of the valley below 3700 m, where it has been detected at 3 m depth by geophysical surveys.

Cyanobacterial communities on a glacier in the Qilian Shan, western China, were investigated using microscopic as well as 16S rRNA and internal transcribed spacer gene analyses. Microscopy revealed that there were abundant cyanobacteria on the entire glacier surface and their community consisted mainly of three morphological types. Low-cycle 16S rRNA gene sequences from six clone libraries were grouped into a total of eight cyanobacterial operational taxonomic units (OTUs), defined as 16S rRNA sequences with similarity of 99%. Although the cyanobacterial community based on morphological types displayed no significant differences among the study sites on the glacier, the community based on OTU groups varied among sites. This inconsistency may be due to simple morphology which might hide a large genetic variability. Phylogenetic analysis revealed that the OTU groups included the orders Oscillatoriales, Chroococcales and unclassified, and the majority of OTUs were Oscillatoriales. From the source environments of the cyanobacterial 16S rRNA gene sequences of each OTU on the glacier estimated by BLAST search (>97% similarity), 39.9% were from soil, 38.2% from fresh water and 1.7% from snow and ice environments. Based on geographical records in the database, all cyanobacterial OTUs were matched to those recorded from the Arctic and Antarctica. The results suggest that the cyanobacterial communities on the glacier are common in cold regions of the world and are likely not to be specialized members of the snow and ice biota but also inhabitants of soil and freshwater environments.

We present, analyse and discuss air-pressure data from finite-volume chute flows of dry fine snow in air. These experiments have the correct similarity criteria to model powder-snow avalanches and demonstrate the transition from a dense to a suspended flow. We measured the dynamic air pressure at the base of the flow, which features a marked negative pressure peak immediately behind the front. This feature is also seen in observations of natural powder-snow avalanches measured in Russia, Japan and Switzerland in direct numerical simulations of non-Boussinesq suspension flows and in ping-pong ball avalanches. This is evidence for large internal motions and suggests that there is a coherent vortex in the avalanche front. This can result in impact pressures many times larger than those expected from the mean flow velocity. We analyse the external air pressures using three models and show how the geometry and velocity of the flow can be found from this single air-pressure measurement. We also measured flow heights and speeds using image analysis and show that the speed is roughly independent of the slope angle and scales with the release size raised to the power 1/4, as predicted by similarity analysis for pseudo two-dimensional (2-D) flows.

Laser-induced fluorescence emission (LIFE) images were obtained in situ from a 27 cm long ice core at Lake Fryxell, Antarctica. The excitation was accomplished with a simple 532 nm green laser pen light, and the fluorescence images were captured with a small compact digital camera. The targets for the experiment were mm-scale cryoconite assemblages found in the ice covers of this perennially frozen Antarctic lake. The fluorescence response originates from photo-pigments in cyanobacteria-dominated cryoconite assemblages with phycoerythrin (PE) exhibiting the optimal target cross section. This inexpensive, low-mass, low-energy method avoids manipulation of the in situ habitat and individual target organisms and does not disturb the microbial community or the surrounding ice matrix. We establish the correlation between fluorescence intensity and PE concentration. We show that cryoconite fluorescence response does not appear to decrease with depth in the ice cover, in agreement with similar findings at Lake Untersee, a perennially ice-covered lake in Dronning Maud Land, Antarctica. Optical reflection and refraction events at the air/ice interface can complicate quantitative estimates of total pigment concentrations. Laser targeting of a single mm-scale cryoconite can result in multiple neighboring excitation events secondary to reflection and refraction phenomena in the multiple air/ice interface of the bubbles surrounding the primary target.

Indian rivers originating in the Himalaya depend on seasonal snow-cover melt during crucial summer months. The seasonal snow cover was monitored using Advanced Wide Field Sensor (AWiFS) data of the Indian Remote Sensing Satellite (IRS) and using the Normalized Difference Snow Index (NDSI) algorithm. The investigation was carried out for a period of 3 years (2004/05, 2005/06 and 2006/07) between October and June. A total of 28 sub-basins of the Ganga and Indus river basins were monitored at intervals of 5 or 10 days. Approximately 1500 AWiFS scenes were analyzed. A combination of area–altitude distribution and snow map was used to estimate the distribution of snow cover in altitude zones for the individual basins and for the western and central Himalaya. Hypsographic curve and snow-free area was used to estimate monthly snow-line elevation. The lowest snow-line altitude in the winters of 2004/05, 2005/06 and 2006/07 was observed at 2480 ma.s.l. on 25 February 2005. In Ravi basin for the year 2004/05, snow accumulation and ablation were continuous processes throughout the winter. Even in the middle of winter, the snow area was reduced from 90% to 55%. Similar trends were observed for 2005/06 and 2007/08. In Bhaga basin, snowmelt was observed in the early part of the winter, i.e. in December, and no significant melting was observed between January and April.

We present simple scaling relationships that allow us to predict the main dynamical characteristics (height, length and velocity) of constant-volume snow avalanches with minimal input data. In particular, we show that both avalanche height and length can be expressed as a function only of the avalanche volume and the distance travelled by the front, independently of the specific rheological parameters of the snow. These scaling relationships are derived from a large-time asymptotic solution to the avalanche dynamic equations, corresponding to a balance between gravity and Voellmy friction (the kinematic wave approximation). Numerical simulations of the complete hydraulic shallow-flow equations confirm that this asymptotic solution, and the predicted scaling relationships, capture the main avalanche characteristics, even for relatively small travel distances. Though derived under restrictive assumptions, we argue that the scaling relationships described in this paper may constitute useful tools for avalanche engineering and design of protective structures.

Photosynthesis by microbes on the surfaces of glaciers and ice sheets has the potential to fix carbon, alter the albedo of ice surfaces via the production of organic matter and so enhance ice melt. It could also be important for supplying labile organic matter and nutrients to in situ and downstream ecosystems. This study compares in situ 24 hour incubation methods for measuring rates of gross photosynthesis, respiration and net community production (NCP) in cryoconite holes on three Svalbard valley glaciers. Rates of gross photosynthesis and respiration measured by the ΔCO2 method were closely balanced, resulting in rates of NCP close to the detection limit (mean of –1.3 μg C g−1 d–1) consistent with previous measurements in Arctic cryoconite holes. This suggests that organic matter within cryoconite holes may be derived largely from allochthonous sources. The molar ratio of ΔO2 to ΔCO2 in incubations gave mean respiratory and photosynthetic quotients of 0.80 ± 0.17 (1 × SD) and 1.24 ± 0.20 (1 × SD), respectively. The 14C method typically underestimated rates of gross photosynthesis (ΔCO2 method) by more than one order of magnitude and measured a rate closer to NCP.

A highly polluted rain event deposited ammonium and nitrate on Midtre Lovénbreen, Svalbard, European High Arctic, during the melt season in June 1999. Quasi-daily sampling of glacial runoff showed elevated ion concentrations of both ammonium (NH4+) and nitrate (NO3−), collectively dissolved inorganic nitrogen (DIN) in the two supraglacial meltwater flows, but only elevated NO3− in the subglacial outburst. Time-series analysis and flow-chemistry modelling showed that supra- and subglacial assimilation of NH4+ were major impacts of this deposition event. Supraglacial assimilation likely occurred while the pollution-event DIN resided within a/the supraglacial slush layer (estimated DIN half-life 40–50 hours, with the lifetime of NO3− exceeding that of NH4+ by 30%). Potentially, such processes could affect preservation of DIN in melt-influenced ice cores. Subglacial routing of event DIN and its multi-day storage beneath the glacier also enabled significant assimilation of NH4+ to occur here (60% of input), which may have been either released as particulate N later during the melt season, or stored until the following year. Our results complement existing mass-balance approaches to the study of glacial biogeochemistry, show how modelling can enable time-resolved interpretation of process dynamics within the biologically active melt season, and highlight the importance of episodic polluted precipitation events as DIN inputs to Arctic glacial ecosystems.

Wet snow avalanches in India are common during the mid- and late winter in the Pir Panjal Range (2000–3000ma.s.l.) and during the late winter in the Great Himalayan Range (3000 ma.s.l. and above). Although it is well known that the presence of liquid water in snow makes the flow behaviour of wet snow avalanches different from that of dry snow avalanches, there exist few actual flow measurements with wet snow. The aim of this investigation is to understand the dynamics of wet snow avalanches by conducting medium-scale experiments (volumes of 3, 6 and 11 m3) on the Dhundi snow chute in Himachal Pradesh, India. We measured flow velocities using video data, as well as optical velocity sensors installed on the side walls and running surface. Measurement results relating to the slip velocity of the front and tail of the moving snow mass, as well as the average slip velocity, are presented. In addition, we use the results of the vertical velocity profile measurements to calculate the effective viscosity of snow at two locations within the flow. We identified a shear thinning type of behaviour, suggesting that a single avalanche rheology cannot describe wet snow avalanche behaviour.

Under melt–freeze conditions crusts may evolve within a snowpack, which may favour avalanche initiation by forming a hard bed surface for weakly bonded faceted grains. We used a parallel-probe saturation profiler (PPSP) to record the distribution of water contents within the snowpack. Diurnal effects of melt–freeze action on the growth of crusts were monitored with the help of the PPSP device. Saturation profiles were collected from a partially wet snow cover. Snow stratigraphy was conducted manually in the morning, after overnight freezing, to identify the location and the granular compositions of the crusts that had evolved. A one-to-one correspondence between the saturation spikes collected using the PPSP and the actual positions of the crusts was established. The PPSP was also used to monitor three-dimensional variations in the maximum percolation depths within a south-facing snowpack. The operation of the PPSP is faster than existing dielectric measurement techniques, so it was applied to study the spatial variability of maximum percolation depths on the slopes of different aspects.

Cyanobacteria inhabit the Antarctic continent and have even been observed in the most southerly ice-free areas of Antarctica (86–87° S). The highest molecular diversity of cyanobacterial communities was found in the areas located between 70° S and 80° S. Further south and further north from this zone, the diversity abruptly decreased. Seventy-nine per cent (33 of 42 operational taxonomic units) of Antarctic terrestrial cyanobacteria have a cosmopolitan distribution. Analysis of the sampling efforts shows that only three regions (southern Victoria Land, the Sør Rondane Mountains and Alexander Island) have been particularly well studied, while other areas did not receive enough attention. Although cyanobacteria possess a capacity for long-range transport, regional populations in Antarctic ice-free areas seem to exist. The cyanobacterial communities of the three most intensively studied regions, separated from each other by a distance of 3000–3400 km, had a low degree of similarity with each other. Further development of microbial biogeography demands a standardized approach. For this purpose, as a minimal standard, we suggest using the sequence of cyanobacterial 16S rRNA gene between Escherichia coli positions 405 and 780.

The topographic effects of differential terrain illumination in optical satellite imagery of rugged mountainous regions have serious consequences for qualitative and quantitative analysis for various snow applications. Therefore, effective removal or minimization of topographic effects is necessary in satellite image data of mountainous regions. Different methods for topographic corrections, including C-correction, Minnaert corrections (including slope) and slope-matching method, are analysed in the context of snow reflectance. Combination of dark-object subtraction models DOS1 and DOS3 is used for image-based atmospheric corrections while considering the effect of Rayleigh scattering on the transmissivity in different spectral bands of AWiFS and MODIS image data. The performance of different models is evaluated using (1) visual analysis, (2) change in snow reflectance on sunny and shady slopes after the corrections, (3) validation with in situ observations and (4) graphical analysis. The results show that the slope-matching technique could eliminate most of the shadowing effects in Himalayan rugged terrain and correctly estimate snow reflectance from AWiFS and MODIS imagery. The validation of results with in situ observations for both types of imagery suggests that all other methods significantly underestimate reflectance values after the corrections.

Two- and three-dimensional avalanche dynamics models are being increasingly used in hazard-mitigation studies. These models can provide improved and more accurate results for hazard mapping than the simple one-dimensional models presently used in practice. However, two- and three-dimensional models generate an extensive amount of output data, making the interpretation of simulation results more difficult. To perform a simulation in three-dimensional terrain, numerical models require a digital elevation model, specification of avalanche release areas (spatial extent and volume), selection of solution methods, finding an adequate calculation resolution and, finally, the choice of friction parameters. In this paper, the importance and difficulty of correctly setting up and analysing the results of a numerical avalanche dynamics simulation is discussed. We apply the two-dimensional simulation program RAMMS to the 1968 extreme avalanche event In den Arelen. We show the effect of model input variations on simulation results and the dangers and complexities in their interpretation.