bluuebunny/crossref_metadata_2025 huggingface dataset:
Metamorphism of fine-grained snow due to surface curvature differences
Authors: Brown R.L. , Edens M.Q , Sato A.
Published: September 2017

The metamorphism of snow in the absence of a significant temperature gradient was investigated. The first part of the study involved analytical modeling of the exchange of mass between grains of differing surface curvature and the process of intergranular sintering. Physical models were developed to evaluate these two processes. For the first process, it was assumed that mass exchange took place primarily by vapor transport between neighboring grains. The principles of mass balance, momentum balance and energy balance were utilized to evaluate time and spatial variations in temperature, vapor velocity, vapor pressure and mass exchange between the two grains. For the second process, mass exchange was also assumed to be dominated by vapor flow from the grain surface to the neck surface. The same variables were solved for in this second process. Results obtained show that, as expected, the exchange rates between grains of different surface curvature depend upon the radii of curvature, pore size and temperature. The rate of sintering, as determined by the rate of vapor deposition on the neck is determined by temperature, grain curvature, and neck curvature. In addition to the physical modeling, an experimental program was undertaken to measure rates of metamorphism in specially prepared snow consisting of fine-grained spherical particles. This snow was made using specialized instrumentation developed in Japan. The mean grain size was 20 μm, which, while very small, allowed the observation of measurable changes in snow microstructure over short time spans. Test results showed that the grain size increased markedly with time and that the small grains were sacrificed as the large grains acquired mass from the smaller grains.
Characteristics of snow gliding on rock
Authors: Mcclung D.M , Walker Simon , Gollen W.
Published: September 2017

Field measurements were made of snow gliding on steep, smooth rock slabs. Supporting dala included snowpack properties, snow rock interface temperatures, air temperatures and precipitation. In this paper, the temporal and spatial dependence of gliding is discussed from two seasons of measurements. The results showed that the basic temporal and spatial characteristics repeated from year to year at the site. The relationship of the measurements to snow-gliding constitutive relations and applications is briefly discussed.
Basal debris entrainment and transport in glaciers of southwestern Bylot Island, Canadian Arctic
Authors: Zdanowicz C. M. , Michel F. A. , Shilts W. W.
Published: September 2017

Glaciers on southwestern Bylot Island in the Canadian Arctic flow from an alpine setting in high-grade crystalline Archean terrane, on to coastal lowlands underlain by clastic sedimentary strata of Cretaceous to Tertiary age. We have used the contrasting mineralogy of the substrate as a tool to study subglacial entrainment and transport of debris in two large piedmont glaciers on Bylot Island. High chlorite/ and mica-illite/smectite ratios indicate that most basal debris is derived from crystalline rocks underlying the upper reaches of the glaciers. The subglacial accretion of Cretaceous–Tertiary sediments appears restricted to the lowermost part of the basal zone and is most noticeable near the glaciers’ termini. Ice associated with discrete silly–sandy debris layers is characterized by an isotopic signature indicative of refreezing of meltwater at the glacier sole. The compositional, textural and isotopic characteristics of basal sediment and ice lead us to conclude that subglacial entrainment through basal ice accretion occurs in both the upper and marginal parts of the glaciers.
The marine record of the Russell Fiord outburst flood, Alaska, U.S.A.
Authors: Cowan Ellen A. , Carlson Paul R. , Powell Ross D.
Published: September 2017

The advance of Hubbard Glacier, near Yakutat, Alaska, U.S.A., in spring 1986 blocked the entrance to Russell Fiord with an ice-and-sediment dam, behind which a lake formed. The water level in Russell Lake rose to 25.5 m a.s.l. The dam catastrophically failed in October 1986, releasing 5.4 km3 of water into Disenchantment Bay. High-resolution seismic-reflection profiles show a 7.5 km long channel system cut into and buried by glacimarine sediment, represented by continuous, parallel reflections. The chaotic seismic facies filling the channel is interpreted to be debris flow deposits. A gravity core from channel-overbank deposits contained sandy diamicton with mud clasts. Above the channel a 1–2 m thick sediment drape extends across the bay. Laminated mud, fining-upward sand beds and diamicton were recovered from this unit. The sediment-drape deposits were produced by suspension settling from turbid plumes and non-channelized turbidity currents generated by the outburst flood.
Morainal-bank sediment budgets and their influence on the stability of tidewater termini of valley glaciers entering Glacier Bay, Alaska, U.S.A.
Authors: Hunter Lewis E. , Powell Ross D. , Lawson Daniel E.
Published: September 2017

Investigations of grounding-line sedimentation in front of tidewater termini of temperate valley glaciers demonstrate that sediment yields and dynamics provide a second-order control on glacier stability by influencing water depth at the grounding line. Sediment is delivered to the grounding line by two routes: (1) debris transported in, on and beneath the glacier, and (2) sediment transported in glacial outwash streams. Glacial streams in Glacier Bay, Alaska, U.S.A., deliver 106 to 107 m3 year−1 of sediment to the grounding lines. The glacial debris flux transports 105 to 106 m3 year−1 of debris to the ice cliffs, where approximately 10% is released at the grounding line, the remainder being transported downfjord by iceberg-rafting. An additional 105 m3 year−1 of sediment may be transported to the grounding line by shearing and advection of a deformable bed.
Water and sediment discharge from a large surging glacier: Bering Glacier, Alaska, U.S.A., summer 1994
Authors: Merrand Yann , Hallet Bernard
Published: September 2017

The water and sediment output from Vitus Lake, in Front of Bering Glacier, was monitored starting in July 1994, Instrumentation was placed in the lake outlet to record stage, turbidity, conductivity and temperature and velocity of flow of river water. Two outburst floods punctuated the termination of the 1993–94 Bering Glacier surge in August 1994. The better-documented flood lasted about 10 d, during which the flood discharge averaged 1100 m3 s−1, in excess of normal discharge (1550 m3 s−1) during this part of the ablation season, and about 9.5 × 108 m3 of water drained from Bering Glacier. The excess water volume discharged during this flood corresponds to a 0.4 m thick layer of water extending over the 2500 km2 of Bering Glacier that was surging in early summer. The suspended-sediment flux from Vitus Lake during the summer of 1994 was two orders of magnitude less than rates of sediment production by other fast-moving glaciers in southern Alaska. This implies that most of the sediment produced is being stored in Vitus Lake, under the glacier, or in both locations.
Thrusting and debris entrainment in a surging glacier: Bakaninbreen, Svalbard
Authors: Hambrey Michael J. , Dowdeswell Julian A. , Murray Tavi , Porter Philip R.
Published: September 2017

Bakaninbreen, a 17 km long glacier terminating in fjord waters in central Spitsbergen (77°45′ N, 17°20′E), began to surge between the springs of 1985 and 1986. By summer 1994 the surge front had reached a position 3 km from the terminus and had almost ceased propagation. Structural investigations were undertaken to characterise the tectonic evolution of this thermally complex surge-type glacier, and the role played by thrusting and its effect on debris entrainment. Much of the glacier surface, particularly within and below the surge front, displayed transverse high-angle thrusts, defined by discrete fractures bounded by coarse clear ice. Some fractures were associated with a film of mud, whereas in others a discrete laver of diamicton, with interstitial ice several decimetres thick, was evident. Within the surge front, and genetically related to the thrusts, was a number of shear zones several metres wide. These were defined by fine-grained ice that was the product of the grinding up of crystals during shear (mylonitization). Three main sedimentary facies are associated with the thrusts: mud, gravelly mud and clast-rich muddy diamicton. The diamicton has the character of basal glacial debris: grain-size distribution ranging from clay to cobble size, clasts with a predominance in the sub-angular and sub-rounded classes, and striated and faceted clasts. Hot-water drilling through the glacier revealed several englacial layers above the surge front, and debris brought up on the drill stem suggests a basal origin. At least some of these englacial layers are probably the sub-surface continuations of the thrusts. The observed facies indicate that the glacier is moving over a soft, deformable bed and that thrusting is an important process in transferring debris to the surface, especially when the surge front is propagating down-glacier.
The role of sediment transport in the mechanics of jökulhlaups
Authors: Fowler A. C. , Ng F. S. L.
Published: September 2017

The classical theory of jökulhlaups used Röthlisberger’s earlier theory of ice-channel drainage to describe the development of the flood hydrograph. This theory has some drawbacks: the mechanism of initiation (breaking the seal) is opaque, the Manning roughness coefficient is too large and the hydrographs can reveal a sudden switching from channel opening to channel closure which is not simulated by the model. In this paper, we examine these features by exploring a more detailed model, which takes into account the physics of sediment erosion and its effect on channel morphology. We propose a theory in which channels need not be semicircular, but have shapes determined by a local balance between closure and melting, and in which erosion of the tunnel margins is taken into account; in particular, we derive theoretical predictions for sediment discharge, and we also propose a mechanism whereby the pressure seal over the caldera rim at Grímsvötn in Vatnajökull, Iceland, can be broken when the lake-level water pressure is still some 6 bar below the maximum overburden ice pressure.
Erosion rates and sediment yields of glaciers
Authors: Bogen Jim
Published: September 2017

Sediment yields and glacial erosion rates are evaluated for four Norwegian glaciers during the years 1989-93. Annual erosion rates were determined from measurements of sediment load and water discharge in glacial meltwater rivers. The mean sediment yield and the corresponding erosion rate of the valley glaciers Engabreen and Nigardsbreen were found to be 456 t km−2 year−1 (0.168 mm year−1) and 210 t km−2 year−1 (0.078 mm year−1), respectively. A small and slow-moving cirque glacier Øvre Beiarbre yielded a rate of 482 t km−2 year−1 (0.178 mm year−1), and the sub-polar Svalbard glacier Brøggerbreen yielded 613 t km−2 year−1 (0.226 mm year−1). The erosion rates are low compared to glaciers elsewhere. There are also considerable variations in sediment yields at each glacier from year to year. However, different factors are found to control the variability on each individual glacier. Analysis of the relationship between water discharge and sediment concentration in meltwater rivers suggests that changes in subglacial drainage systems cause variations in sediment availability and the way sediments are melted out from the ice. When water pressure drops, the drainage system in fast-moving, thick valley glaciers deforms at a more rapid rate than in thin, slow-moving ones. New volumes of debris-laden ice are thus more readily available for melting when water pressure next increases. Beneath the thin, slow-moving Øvre Beiarbre, single years with high transport rates and evacuation of sediment are followed by periods of low availability lasting for 2 years or longer. It is suggested that this pattern results from exhaustion of sediment in a stable drainage system, with more sediment becoming available when the position of the subglacial drainage system is changed.
Glacier debris accumulation and sediment deformation influenced by permafrost: examples from Svalbard
Authors: Etzelmüller B. , Hagen J. O. , Vatne G. , Ødegård R. S. , Sollid J.L.
Published: September 2017

The formation of ice-cored moraines and push moraines is discussed in the light of glacier thermal regime and glacier dynamics. Data from two Svalbard valley glaciers, Erikbreen and Usherbreen are presented. On Erikbreen, fossil forms were investigated, while on Usherbreen a surge ending in 1985 caused the formation of new push-moraine ridges. The push moraines are considered as a soil-mechanical problem. In a theoretical discussion the stress transmitted by the glaciers to the proglacial sediments is estimated. On Usherbreen, the compressive flow results in deformation both in old front ridges and in undisturbed frozen sediment layers in the front sandur. Thus, folding, thrust faulting and overriding all occur. Deformation of proglacial sediments seems to be highly dependent on the mechanical properties of the sediments. The sediments are strongly influenced by permafrost conditions. The unfrozen water content in the sediments governs the deformability, which in turn is partly determined by pore-water salinity. The distribution of push moraines in Svalbard is therefore restricted to areas below the Holocene marine limit, and they occur most frequently in areas of sedimentary bedrock. This study concludes that push moraines and ice-cored moraines require permafrost conditions. Push-moraine ridges are not formed in direct contact with the glacier, so they are geomorphologically not moraines, but deformed permafrost sediments. A model for glacier debris sedimentation and deformation is outlined for Svalbard glaciers ending on land.
The origin of till sequences by subglacial sediment deformation beneath mid-latitude ice sheets
Authors: Boulton G. S.
Published: September 2017

A theory of erosion and deposition as a consequence of subglacial sediment deformation over beds of unlithified sediment is reviewed and applied to large-scale till sequences formed on the southern flanks of the North American and British and European ice sheets during the last glacial cycle. The distribution of till thickness, till lithology in relation to source materials and intra-till erosion surfaces along a flowline in the Michigan lobe of the North American ice sheet are shown to be compatible with the deformational theory but not with other modes of till genesis. It is then demonstrated, in the case of the British ice sheet, how the assumption of a deformational origin for tills can be used to infer time-dependent patterns of ice-sheet dynamic behaviour. By reference to an example from the Netherlands, it is argued that many till sequences interpreted as melt-out tills are more likely to have formed by subglacial sediment deformation.
Snowpack water-equivalent estimates from satellite and aircraft remote-sensing measurements of the Red River basin, north-central U.S.A.
Authors: Josberger E. G. , Mognard N. M. , Lind B. , Matthews R. , Carroll T.
Published: September 2017

Most algorithms to extract dry snowpack water equivalent (SWE) from satellite passive-microwave observations are based on point measurements of SWE or extrapolation of point measurements to the 30 km footprint of the satellite observations. SWE observations on a scale comparable to the satellite observations can be obtained from airborne gamma-ray attenuation techniques from flight lines that are approximately 10 km long. During the winter of 1989, the NOAA National Operational Hydrologic Remote Sensing Center (NOHRSC) flew 92 of these night lines over a 200 × 250 km area of the Red River basin which is located in the north-central part of the United States of America. These observations provide a unique dataset of snow water-equivalent determinations on spatial scales similar to the satellite passive-microwave observations as acquired by the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager (SSM/I) F-8 satellite. Land-classification determinations from the Advanced Very High Resolution Radiometer (AVHRR) show that the eastern part of the region contains a coniferous forest of varying coverage, while the remainder is farmland or prairie. SSM/I data, including observations from a no-snow case in the preceding fall, the flight-line data and the AVHRR data were all co-registered to a common 20 km grid. The resulting dataset was analyzed using linear regression, artificial intelligence and general linear models. The results showed that the passive-microwave response was similar to the response predicted by Mie scattering theory. A comparison of the three techniques found that the artificial intelligence technique and the general linear model explained significantly more of the variance in the dataset, as evidenced by R2 values of 0.97 compared to 0.88 for the linear multiple-regression analysis. Hence, a neural network approach which was continually trained on new datasets as they became available, could provide better estimates of snowpack water equivalent than algorithms based on linear-regression techniques.
Validation of an application for forecasting blowing snow
Authors: Guyomarc’h Gilbert , Mérindol Laurent
Published: September 2017

Wind effects on snow distribution and increasing avalanche hazard are well known. Forecasting such phenomena is based on empirical rules and experience. For two years, the CEN has tested a new analysis program for forecasting blowing-snow events at an Alpine site. The aim is to improve avalanche-forecasting tools so as to increase the accuracy of avalanche-hazard forecasts. Our understanding of blowing-snow mechanisms began with observations and field measurements at a high altitude site during periods of strong wind. Using an empirical approach, snow-grain morphology, cohesion between snow particles and grain-size have been combined to define a function for the calculation of a “driftabilily index”. By comparing this index with the wind thresholds observed in field, a snowdrifting index has been defined. Snow profiles calculated by SAFRAN (estimation of relevant meteorological parameters for snow models) and Crocus (snowpack-evolution model) were analysed using an application called PROTÉON. Forecasts of wind velocity and snow profiles have been used to discriminate between periods with or without snow transport. For the subsequent 24 hours and for each snow layer, the value of this snowdrifting index is calculated and displayed on a graph. Validation consists of a comparison of forecasted blowing-snow periods with the field observations and measurements at a pass situated at 2700 m a.s.l. Meteorological and snow-parameter data are available at this site.
Dependence of new-snow density on slope angle
Authors: Endo Yasoichi , Kominami Yuji , Niwano Shouji
Published: September 2017

The mass per unit horizontal area, vertical height and density of new snow accumulated on various slopes of 0° to 75° were measured. Although the mass of new snow on these slopes was nearly the same, vertical height increased and density decreased with increase of slope angle. Differences in heights and densities of new snow due to slope angle were explained by considering both accumulation and densification processes on the slopes.
Snowmelt modelling on signy island, South Orkney Islands
Authors: Gardiner Michael J. , Ellis-Evans J. Cynan , Anderson Malcolm G. , Tranter Martyn
Published: September 2017

The ability of the Utah energy-balance and snowmelt model (UEB) to simulate decline in snow water equivalent (SWE) at an extreme location was assessed. Field data were collected at Paternoster Valley, Signy Island, South Orkney Islands (60°43′S) during the austral summer of 1996–97. This is the first application of UEB in a maritime Antarctic site. UEB is a physically based snow melt model using a lumped snow-pack representation with primary state variables SWE and snow pack-energy content (U). Meteorological inputs are air temperature, wind speed, humidity, precipitation and total incoming solar and longwave radiation. The Paternoster Valley catchment was subdivided into eight non-contiguous terrain classes for sampling and modelling using a geographical information system (GIS). Simulations of SWE in each of these classes were compared พ with field observations. It is shown that initial U and snow-surface thermal conductance (Ks) affect model simulations. Good approximations of SWE depletion are obtained using measured incoming solar radiation to drive the model but there are shortcomings in the characterization of long wave radiation and sensible-heat fluxes.
Blowing and drifting snow in Alpine terrain: numerical simulation and related field measurements
Authors: Gauer Peter
Published: September 2017

A physically based numerical model of drifting and blowing snow in three-dimensional terrain is developed. The model includes snow transport by saltation and suspension. As an example, a numerical simulation for an Alpine ridge is presented and compared with field measurements.
Simulation of blowing snow over the antarctic ice sheet
Authors: Gallée Hubert
Published: September 2017

A preliminary simulation of blowing snow over the Antarctic continent made with a mesoscale atmospheric model is presented. Sensitivity experiments show that the increase of surface friction arising in conjunction with blowing snow has a relatively more important impact on the dynamics of strong katabatic winds than previously supposed. Sublimation in blowing snow over the Antarctic continent also contributes to the global sea-level budget. It is found that this contribution is of the same order of magnitude as the estimated present sea-level rise.
Field experiments on “living” snow fences
Authors: Naaim-Bouvet Florence , Mullenbach Pierre
Published: September 2017

In Franee, drifting snow is generally controlled using artificial snow fences. Living snow fences are not a new concept but they have only been used on a limited scale. Research directly related to natural plant barriers is limited. We therefore decided to study the behaviour of species that would survive and grow satisfactorily in the French Alps.

In the first experiment, we compared the storage capacity of several different kinds of living fences consisting of pruned spruces, unpruned spruces and sorbs.

Field observations during the winter of 1995-96 proved that deciduous trees such as sorbs are effective, and that pruning the lower 50 cm is not effective at the end of the season because of the weight of snow on low branches.

However, the use of natural plant barriers has disadvantages: a living snow fence takes time to reach an effective height and is difficult to establish on windy sites at a high altitude. This is a real problem. Therefore, in a second experiment, we studied the death rate of larches planted behind a fence. We noticed that the snow fence had several effects, snow accumulation (until the planted trees grew up) and protection of the planted trees.
Passive snow removal with a vortex generator at the Pegasus runway, Antarctica
Authors: Lang R.M. , Blaisdell George L.
Published: September 2017

During the construction phase of the Pegasus runway on the McMurdo Ice Shelf, relatively large amounts of snow and ice were cleared to meet basic grade requirements for the runway surface. A considerable amount of material remains adjacent to the runway in two north–south extending mounds (berms). The runway was originally constructed on an experimental basis so attention was not focused on developing and executing a snow-removal/accumulation plan. After the runway was successfully constructed and supporting routine flight operations, concern developed over the possibility of snow accumulation adjacent to the berm area eventually inundating the runway. The intent of this project was to analyze snow accumulation and to recommend passive methods for removing some of the berm material and snow adjacent to the berm. We found that large quantities of excess snow could be removed by use of vortex fences which cause erosion on the leeward side of the fence. The vortex fence was designed to be portable (unlike traditional jet or blower fences) and self-orienting into the wind to allow snow removal regardless of the wind direction. The vortices generated by the fence do not dissipate rapidly, providing effective and sustained erosion.
Physical modelling of avalanches using an aerosol cloud of powder materials
Authors: Bozhinskiy A.N. , Sukhanov L. A.
Published: September 2017

The problem of physically modelling snow avalanches with an aerosol cloud is considered. Using the simplest model of avalanche-body motion, the criteria of similarity for transit and deposit zones are written. The transit relations between model and natural scales for dynamic parameters of the avalanche body are established. On the basis of the similarity criteria, an approximate physical model of avalanches with an aerosol cloud is made using a mixture of ferromagnetic sawdust and aluminium dust. The setup allows us to start and stop the model avalanche during any stage of its motion and to model actual avalanches. A series of experiments was completed. It is shown that the basic mechanism of aerosol cloud generation for model avalanches is related to the hydraulic jump of fluid when a stormy flow changes to a calm one. A comparison of parameters for model and “home” avalanches (the vicinity of Elbrus) showed that the ratios of the sizes of dense and aerosol components and deposition zones of those avalanches are close to the geometric scale factor and the ratios of velocities, and durations of processes are close to the square root of this coefficient. The latter corresponds to modelling the process by Froude number.
Modelling of snow entrainment and deposition in powder-snow avalanches
Authors: Issler Dieter
Published: September 2017

Following Norem’s description of powder-snow avalanche formation and structure, we propose a mathematical model that consists of a suspension layer and a so-called saltation layer. The latter is only a few meters deep and is modelled by depth-averaged mass and momentum balances. In the suspension layer, the mass and momentum balance equations for the mixture are supplemented by the snow mass balance and the transport equations for turbulent kinetic energy and dissipation. Mass and momentum exchange between the two layers is determined by particle settling, turbulent diffusion against the concentration gradient and aerodynamic shear forces. The net erosion or deposition rate is a function of the kinetic energy of the impacting particles. The saltation layer reacts on the suspension layer in that saltating particles extract momentum from the air flow. The preliminary estimates of the model parameters can be refined by means of saltation-trajectory simulations. Three-dimensional simulations with a simplified model have clearly shown the importance of snow erosion and deposition in practical applications. This approach is well suited for coupling to a dense-flow avalanche model.
Simulations of dense-snow avalanches on deflecting dams
Authors: Irgens Fridtjov , Schieldrop Bonsak , Harbitz Carl B. , Domaas Ulrik , Opsahl Runar
Published: September 2017

Two models simulating snow avalanches impacting retaining dams at oblique angles of incidence are presented.

First, a lumped-mass model applying the Voellmy-Perla equation is used to calculate the path of the centre-of-mass along the side of a retaining dam.

Secondly, a one-dimensional continuum model, applying depth-integrated equations of balance of mass and linear momentum, is expanded to take into account that real avalanche flows are three-dimensional. The centre-line of the avalanche path is determined by the flowing material as it progresses down the channelized avalanche path. The nonlinear constitutive equations comprise viscosity, visco-elasticity and plasticity.

Both models are calibrated by simulations of a registered avalanche following a strongly curved channel. The path and the run-up height of the avalanche on the natural deflecting dam with oblique angle of incidence as calculated by the two models, are compared with the observations made.
Limiting stress states in granular avalanches
Authors: Tai Y.C. , Gray J.M.N.T.
Published: September 2017

The Savage-Hutter theory for granular avalanches assumes that the granular material is in either of two limiting stress states, depending on whether the motion is convergent or divergent. At transitions between convergent and divergent regions, a jump in stress occurs, which necessarily implies that there is a jump in the avalanche velocity and/or its thickness. In this paper, a regularizaron scheme is used, which smoothly switches from one stress state to the other, and avoids the generation of such singular surfaces. The resulting algorithm is more stable than previous numerical methods but shocks can still occur during rapid convergence in the run-out zone. Results are presented from two-dimensional calculations on complex geometry which illustrate that some necking features observed in laboratory experiments can be explained by the regularized Savage-Hutter model.
On the inclusion of a velocity-dependent basal drag in avalanche models
Authors: Gray J.M.N.T. , Tai Y.C.
Published: September 2017

The Savage-Hutter model is generalized by including a velocity-dependent drag in addition to the usual Coulomb dry friction at the base of the avalanche. Both linear and quadratic velocity dependencies are considered, with either constant or asymptotically constant drag coefficients for large thickness h. The singular nature of the constant coefficient model for small h is demonstrated and it is shown that the asymptotic model allows the tail of the avalanche to move at a finite velocity. The inclusion of velocity drag changes the stress state in the avalanche and new earth-pressure relations are derived and investigated.
Prototype for operational seismic detection of natural avalanches
Authors: Leprettre B. , Navarre J.P. , Panel J. M. , Touvier F. , Taillefer A. , Roulle J.
Published: September 2017

A compact, operational prototype for automatic seismic detection of natural avalanches, named SARA, is proposed as a means to improve real-time estimation of natural avalanche activity. A software combining multi-component signal analysis and fuzzy logic has been set up to reject spurious signals automatically. The average success rate of our system, estimated from a set of previously identified signals, is somewhat over 90%. Two prototypes have been installed in the French Alps dur ing the winter of 1996–97. The SARA system enables the user to follow up the evolution of natural avalanche activity with a high time resolution. Results obtained in 1997 are presented and compared with other data related to avalanche activity.
Infrasonic monitoring of snow-avalanche activity: What do we know and where do we go from here?
Authors: Adam V. , Chritin V. , Rossi M. , Lancker E. Van
Published: September 2017

The first recordings of acoustic signals associated with avalanches go back to the 1970s when premonitory low-frequency acoustic emission was observed in the snow cover just before the setting off of natural avalanches (Sommerfeld, 1977; Sommerfeld and Gubler, 1983). Recently, it has been demonstrated that avalanches also produce strong infrasonic vibrations in air during their movement. These infrasonic vibrations propagate great distances and can follow the natural relief. It was then a question of automatically detecting this emission to monitor avalanche activity, with a view to improving forecasting and assisting in the study of certain aspects of avalanche dynamics.

With the double aim of pursuing investigations on the mechanics of the acoustic emission from avalanches and designing an automatic detection system, our laboratory has developed specific instrumentation, the essential link of which is an array of infrasonic microphones associated with a goniometer. Systematic measurements of the infrasonic emissions are being carried out, not only of the natural or released avalanches themselves but of all events with the aim of characterizing the former in relation to “infrasonic noise”.
Spatial characteristics of avalanche activity in an Alpine valley — a GIS approach
Authors: Stoffel Andreas , Meister Roland , Schweizer Jürg
Published: September 2017

Adataset of daily avalanche activity observed consistently for 14 years in the surroundings of Zuoz in the Engadine valley (eastern Swiss Alps) is analyzed. All medium-sized and larger avalanches had been mapped by the local snow and avalanche observer. They were digitized into a geographic information system (GIS) and linked to the daily snow and avalanche observations. Thus the avalanche activity and its spatial distribution could be analyzed and visualized. A classification for avalanche size and avalanche activity is proposed. In 52% of the potential starting zones an avalanche is released at least once in 14 years. The avalanche area decreases strongly with the frequency of avalanche occurrence. Preliminary analysis of the relation of daily avalanche activity to weather, snow and snow cover revealed a wide variety of contributory factors. Even for large amounts of new snow, snow-cover conditions prior to snowfall or temperature evolution might decide the extent of the avalanche activity. For six examples, the avalanche hazard (five degree European scale) is visualized by means of avalanche activity. The GIS approach will be followed to build a tool for local avalanche forecasting in Zuoz.
Global distribution of snow avalanches and changing activity in the Northern Hemisphere due to climate change
Authors: Glazovskaya T. G.
Published: September 2017

Snow avalanches occur in the mountains of all continents and climatic zones. The lower boundary of avalanche distribution rises from sea level in polar and temperate zones to 6000 m in the tropics. Four altitudinal belts of avalanching are distinguished: (I) permanent snow; (II) stable seasonal snow cover; (III) unstable snow cover; and (IV) rare snowfalls. Most avalanche-danger areas of the world belong to the stable seasonal snow-cover bell.

Using data from a GFDL Q-flux Model, we estimated possible changes of the main characteristics of the avalanche regime in the Northern Hemisphere: depth of snow cover, duration of the avalanche-prone period and number of days with avalanche-prone snowfalls. At the beginning of the twenty-first Century, there will likely be a smoothing of the sharp differences in avalanche activity between various mountain regions of the World. Avalanche activity should be less in the most active regions and it is likely to increase in regions with low avalanche activity.
Energy balance and formation of sun crust in snow
Authors: Ozeki Toshihiro , Akitaya Eizi
Published: September 2017

The mechanism of sun-crust formation was investigated through laboratory experiments in a cold wind tunnel. The experiments were carried out by controlling the energy balance and the sun crust formed was consistent with that observed in Nature, i.e. a thin ice layer composed of ice particles and cavities due to internal melting beneath the sun-crust layer. The surface-cooling rate was between −50 and −100 W m−2, and the absorption of shortwave radiation exceeded 200 W m−2. The energy balance during the formation of the sun crust is consistent with the data observed in Nature.

The sources of H2O for the sun-crust formation were investigated through changes in δ18O. Taking into account that the δ value of sun crust was larger than that of the snow beneath it and the calculations of the latent-heat emission with the sun-crust formation, it was concluded that the retention of meltwater by capillary force and refreezing in a thin layer was the dominant mechanism of this metamorphism.
Short-term numerical avalanche forecast used operationally at Météo-France over the Alps and Pyrenees
Authors: Durand Yves , Giraud Gérald , Mérindol Laurent
Published: September 2017

Avalanche-hazard estimation for the present and the following days is one of the main tasks of the avalanche forecaster. For 4 years, some have used the results of a series of automatic numerical models in the Alpine massifs of France. Thee programs describe in real time the main meteorological conditions (SAFRAN), the evolution of the snow cover (Crocus) and the resulting avalanche risks [MÉPRA) at different elevations, slopes and aspects of the massifs considered.

This paper presents the latest evolution of this automatic tool. With the new version it is now possible to provide 1 day forecasts of the state of the snow cover over the massifs of both the Alps and Pyrenees, including the main characteristics of the snowpack and an assessment of the corresponding avalanche hazards.

To achieve this result, the main changes were with SAFRAN. Two combined methods are used within the same package: adaptations of larger-scale meteorological forecasts and use of observations of analogous weather situations from the past. These two approaches are complementary especially for evaluating precipitation where the second solution has important fine-scale information while the first exhibits important local biases.

Validation of this new application was done carefully and proved the quality of the method, now used in real-time by local forecasters. We present some validation results, concerned both with forecasted precipitation fields at the scale of the massif and forecasted avalanche risks deduced from MÉPRA.
Inferential statistics to verify prediction models
Authors: Bolognesi R.
Published: September 2017

Models are powerful tools if their outputs are relevant!

Therefore, knowing the reliability of models is essential for people who wish to use them, as well as for researchers who attempt to improve them. Whatever the nature of the model output, objective evaluation consists of comparing predicted or calculated events with observed events.

Such comparison can only focus on available samples of observed events. Obviously, the results depend on the choice of the sample. However, inferential statistics enable one to extend results obtained from a random sample to general use.

An unbiased method of testing boolean avalanche-prediction models is suggested: the validity of this type of model should be characterized by the probability that the proportion of correct forecasts is within a given confidence interval. This interval is calculated from the sample size, according to the Gaussian table.

This unrestricted principle can be used to prove all kinds of static models, if ever their outputs are verifiable, enabling one to calculate the ratios of correct forecasts as well as the ratios of well-predicted events and can also be extended to verify probabilistic predictions.
Hemispherical–directional reflectance measurements of natural snow in the 0.9–1.45 μm spectral range: comparison with adding–doubling modelling
Authors: Sergent Claude , Leroux Catherine , Pougatch Evelyne , Guirado Florence
Published: September 2017

The authors present the results of snow hemispherical–directional reflectance measurements on natural snow in the 0.9–1.45 μm spectral range. The measurements were made in a cold laboratory on snow collected in the field. Some of the samples have been subjected to controlled metamorphism in the laboratory before measurements were made. In the first part, the adding–doubling model, experimental assumptions and methodology are described. In the second part, experimental results are discussed and compared with theoretical values for different typical snow types and for different stages of snow evolution when subjected to temperature-gradient and wetness metamorphisms.
Viscous compression model for estimating the depth of new snow
Authors: Kominami Yuji , Endo Yasoichi , Niwano Shoji , Ushioda Syuichi
Published: September 2017

This paper describes a method for estimating the depth of new snow, using hourly data of total snow depth and precipitation. As the snow cover is compacted continuously due to its own weight, the depth of new snow deposited since the previous time-step to the present time is given by a difference between the height of the present snow surface and the present is impacted height of the previous snow surface. Thus, based on viscous compression theory and an empirical relation between compressive viscosity and the density of snow, an equation has been derived to compute the time variation of the thickness of a snow layer due to viscous compression. Using this equation, the present height of the previous snow surface, which cannot be measured by simple means, was computed and the depth of daily new snow was estimated as its difference from the present measured total snow depth. The approximated results were found to be in good agreement with data measured in Tohkamachi during the three winters from 1992–93 to 1994–95. The standard deviation was 1.71 cm and the maximum difference between estimated values and observed values was ± 8 cm.
Formation of ice layers by infiltration and refreezing of meltwater
Authors: Pfeffer W. T. , Humphrey N. F.
Published: September 2017

Melt-layer frequency and magnitude in polar and sub-polar ice cores have been interpreted as measures of past summer temperature, and calibrations have been proposed relating frequency of occurrence of ice layers in ice cores to past summer temperatures. But, observations in the percolation facies in Greenland and an analysis of the combined processes of meltwater infiltration and refreezing of water in snow indicate that, in addition to unusually high rates of meltwater input, formation of ice layers will also be facilitated by unusually cold initial conditions or early onset of melt. Uniform warming of both summer and winter conditions has the opposite effect and suppresses ice-layer formation in favor of uniform wetting and refreezing of the snowpack. Numerical modeling of infiltration and refreezing at a stratigraphic fine-to-coarse transition allows quantification of the effects of significant parameters (initial temperature, grain-size and density contrast across the stratigraphic transition, water-input rate and minimum impermeable-layer thickness). Calculations are made to distinguish threshold values of parameters at which infiltration progresses faster than refreezing, resulting in a break-through of water across the stratigraphic transition, from values leading to the formation of an ice layer when refreezing progresses faster than infiltration.
Temporal evolution of physical and dielectric properties of sea ice and snow during the early melt season: observations from SIMS ’90 experiment
Authors: Shokr Mohammede.E , Barber David G.
Published: September 2017

The first field experiment in the 5 year seasonal Sea Ice Monitoring Site (SIMS) program was conducted in Resolute Passage, Canadian Eastern Arctic, between 15 May and 8 June 1990. This period signals the early melt season of sea ice in that region. A standard array of ice and snow measurements was collected on a daily basis from first-year and multi-year ice to monitor temporal evolution. Measurements included ice salinity, ice temperature and ice-surface roughness, snow salinity, snow temperature, snow density and snow depth. The complex dielectric constant of sea ice was computed from these measurements. Rapid desalination of first-year ice was noticed in the surface layer. Towards the end of the experiment period, salinities of the snow-hoar layer were higher than those of the ice-surface layer. Variation in air temperature is replicated by ice-surface temperature but not by the salinity or dielectric properties. No temporal variation in permittivity and dielectric loss was observed for first-year ice, but a slight increase in both parameters was observed for multi-year ice. As a result, a slight decrease in the microwave-penetration depth was observed for multi-year ice. Physical properties of ice and snow were compared against results obtained from other experiments conducted in different ice-formation regions in the late winter and in the early melt season.
Winter Sea-ice mapping from multi-parameter synthetic-aperture radar data
Authors: Rignot Eric , Drinkwater Mark R.
Published: September 2017

The limitations of current and immediate future single-frequency, single-polarization, space-borne SARs for winter sea-ice mapping are quantitatively examined, and improvements are suggested by combining frequencies and polarizations. Ice-type maps are generated using multi-channel, air-borne SAR observations of winter sea ice in the Beaufort Sea to identify six ice conditions: (1) multi-year sea ice; (2) compressed first-year ice; (3) first-year rubble and ridges; (4) first-year rough ice; (5) first-year smooth ice; and (6) first-year thin ice. At a single polarization, C- (λ = 5.6 cm) and L- (λ = 24 cm) band frequencies yield a classification accuracy of 67 and 71%, because C-band confuses multi-year ice and compressed, rough, thick first-year ice surrounding multi-year ice floes, and L-band confuses multi-year ice and deformed first-year ice. Combining C- and L-band improves classification accuracy by 20%. Adding a second polarization at one frequency only improves classification accuracy by 10–14% and separates thin ice and calm open water. Under similar winter-ice conditions, ERS-1 (Cvv) and Radarsat (CHH) would overestimate the multi-year ice fraction by 15% but correctly map the spatial variability of ice thickness; J-ERS-1 (LHH) would perform poorly;and J-ERS-1 combined with ERS-1 or Radarsat would yield reliable estimates of the old, thick, first-year and thin-ice fractions, and of the spatial distribution of ridges. With two polarizations, future single-frequency space-borne SARs could improve our current capability to discriminate thinner ice types.
Short-term velocity variations and basal coupling near a bergschrund, Storglaciären, Sweden
Authors: Hanson Brian , Hooke Roger leb
Published: September 2017

Distance measurements using an automated electronic distance-measurement system in the north cirque of Storglaciären, Sweden, during the summer of 1989, revealed a diurnal variation in glacier speed. Amplitude and timing of the diurnal cycle correlate well with the timing and intensity of the diurnal temperature cycle, indicating that speed responds to variations in daily melt with a lag of approximately 4 h. One 2 d period of non-diurnal velocity variations corresponded with a large rainfall event. Finite-element modeling suggests that these velocity variations must be closely related to water inputs in the cirque rather than to longitudinal coupling with lower parts of the glacier.
An Observation of roll waves in a supraglacial meltwater channel, Harlech Gletscher, East Greenland
Authors: Carver Steve , Sear Dave , Valentine Eric
Published: September 2017

Observations of pulsating flow conditions in a supraglacier meltwater channel on Harlech Gletscher, East Greenland, are reported. Waves of water with turbulent wave fronts and smooth recessive limbs were observed passing downstream at regular intervals of 6-7 s. Peak channel discharge was estimated at 0.5-1.0 m3 s−1, in between which discharge was zero. It is suggested that the phenomenon as observed was due to the formation of roll waves in response to channel morphology and prevalent discharge conditions. Measurements of channel morphology are given together with calculations of critical flow conditions, supporting the hypothesis of roll waves in a natural ice channel. A brief introduction to roll waves and the theory regarding their formation is included.