Mitterer C.,Institute for Snow and Avalanche Research |
Hirashima H.,Japan National Research Institute for Earth Science and Disaster Prevention |
Schweizer J.,Institute for Snow and Avalanche Research
Annals of Glaciology | Year: 2011
Wet-snow avalanches are difficult to forecast, as the change from stable to unstable snow conditions occurs rapidly in a wet snowpack, often in response to water production and movement. Snow stratigraphy plays a vital role in determining flux behaviour. Capillary barriers or melt-freeze crusts can impede and divert water horizontally over large areas and thus may act as a failure layer for wet-snow avalanches. We present a comparison of measured and modelled liquid water content, θ w, and snow stratigraphy during periods of wet-snow instabilities. Special attention is given to the reproducibility of capillary barriers, ponding of water on melt-freeze crusts and the timing of first wetting and of water arrival at the bottom of the snowpack, because these factors are believed to play a major role in the formation of wet-snow avalanches. In situ measurements were performed in the vicinity of automatic weather stations or close to recent wet-snow avalanches in order to compare them with model results. The simulations are based on two different water flux models incorporated within the 1-D snow-cover model SNOWPACK. The comparison of the two model runs with observed θ w and stratigraphy revealed that both water-transport models reproduced the ponding of water on melt-freeze crusts. However, in both models melt-freeze crusts were transformed to normal melt forms earlier than observed in nature, so still existing ponding was not captured by the models. Only one of the models was able to reproduce capillary barriers in agreement with observations. The time of the first wetting at the surface was well predicted, but the simulated arrival time of the wetting front at the bottom of the snowpack differed between the simulations; it was either too early or too late compared with the observation.
Schweizer J.,Institute for Snow and Avalanche Research |
Bruce Jamieson J.,University of Calgary
Annals of Glaciology | Year: 2010
Information on snowpack instability is crucial for assessing avalanche risk in backcountry operations as well as for operational forecasting of the regional avalanche danger. Since slab avalanche release requires both fracture initiation and fracture propagation in a weak snowpack layer, field observations should ideally provide reliable information on the probability or propensity of both fracture processes. Even simple field observations that do not require digging a snow pit can provide useful information. Traditional snowpack tests include the shovel shear test, the shear frame test, the compression test (CT) and the rutschblock test (RB). Interpretation of the test results for the CT and RB has been improved by considering the appearance or type of the fracture in addition to the score. More recently, two tests have been developed that focus on fracture propagation rather than initiation: the extended column test (ECT) and the propagation saw test (PST). We compare the sensitivity, specificity and unweighted average accuracy of various stability tests. Comparative studies indicate that the RB, ECT and PST have comparable accuracy. For most test methods the unweighted average accuracy of a single test was 70-90% depending on the dataset. Test methods such as the RB, ECT and PST, which fracture an area large enough to include fracture propagation, are generally more accurate than test methods that fracture smaller areas (e.g. the CT). The threshold-sum method was also less accurate. Even with very experienced observers for the RB, ECT and PST an error rate of at least about 5-10% has to be expected. Performing a second, adjacent test on the same slope improves test reliability.
Grunewald T.,Institute for Snow and Avalanche Research |
Lehning M.,Institute for Snow and Avalanche Research
Annals of Glaciology | Year: 2011
The spatial distribution and the local amount of snow in mountainous regions strongly depend on the spatial characteristics of snowfall, snow deposition and snow redistribution. Uniform altitudinal gradients can only represent a part of these influences but are without alternative for use in larger-scale models. How well altitudinal gradients represent the true snow distribution has not been assessed. We analyse altitudinal characteristics of snow stored in two high-alpine catchments in Switzerland. Peak winter snow depths were monitored using high-resolution airborne laser scanning technology. These snow depths were transferred to snow water equivalent by applying simple density estimations. From these data, altitudinal gradients were calculated for the total catchment areas and for selected subareas characterized by different accumulation patterns. These gradients were then compared with gradients resulting from automated snow depth measurements obtained from several snow stations on different height levels located in the catchments, and with estimations from climatological precipitation gradients. The analysis showed that neither precipitation gradients nor flat-field stations estimate catchment-wide snow amounts accurately. While the climatological gradient showed different trends for different areas and years, the snow stations tended to overestimate mean snow amounts.
Christen M.,Institute for Snow and Avalanche Research |
Bartelt P.,Institute for Snow and Avalanche Research |
Kowalski J.,Institute for Snow and Avalanche Research
Annals of Glaciology | Year: 2010
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 twodimensional 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.
Bartelt P.,Institute for Snow and Avalanche Research |
Buser O.,Institute for Snow and Avalanche Research
Annals of Glaciology | Year: 2010
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.
News Article | November 30, 2016
A new radar sensor grants insights into the processes inside snow avalanches. The measuring system has been installed at a test slope in the Swiss canton Valais, where the Swiss Institute for Snow and Avalanche Research intends to use it to perform measurements in winter 2016/17.
News Article | February 19, 2017
Those rejoicing in the beauty of fascinating mountain range of Swiss Alps are in for bad news. A huge percentage of the beautiful mountain's snow cover will be lost by 2100. This dry land scenario was revealed in a study which said falling snow cover will be accentuated by the reduced span of the ski seasons. Researchers at the Swiss Federal Institute of Technology in Lausanne, EPFL and Institute for Snow and Avalanche Research who conducted the study, projected Alps snow coverage scenario on the basis of precipitation conditions and temperature variations. The study has been published in The Cryosphere journal. For skiers, a disappointing December just passed when the Swiss Alps had the driest snowfall in over 150 years. Since temperature and rainfall are factors that affect snow fall, global warming alone has not been analyzed as an influence on snow cover. The side effects of low snow formation include the duration of Alpine winter season becoming a casualty as adequate natural snow to facilitate winter sports will not be available. The start of ski season will also be pushed back by weeks or even months. "The Alpine snow cover will recede anyway, but our future emissions control by how much," noted lead-author Christoph Marty, a scientist with the SLF. The simulated projections by the researchers showed snowfall patterns in the mountains with a skewed distribution of snow at different elevations and time frames. Indications were that instead of snow fall, more winter rains will be coming. Sebastian Schlögl, a researcher at SLF said meteorological data and climate change scenarios were applied in modeling the future snow cover at the twin Alpine catchments. According to the study, snow cover loss will be drastic at elevations above 3,000 meters and may induce big commercial loss as 25 percent of all Alps ski resorts are below this threshold. "Since many Alpine villages are heavily dependent on winter tourism, the economy and society of regions with such tourism centers will suffer," added Schlögl. The scientists, however, noted that the snow cover loss can be minimized from 70 to 30 percent if global warming is managed below 2°C. The study reminded that if carbon emissions continue unabated, the formation of snow cover will be confined to heights above 2,500 meters in the coming decades. Meanwhile, a new airline dedicated to the winter snow sports has been announced for Switzerland. The airliner PowdAir will start operations in December with direct flights from UK airports and other places. For skiers, this will be a boon as it cuts travel times to Swiss resorts. The airline will operate a 109-seat Fokker 100 aircraft for five days a week, from Thursday to Monday. "We are in talks with local tour operators and resorts to putting in place infrastructure for skiers' onward travel from Sion," said Rob Stewart, a spokesman for PowdAir. He said skiers who get to Sion will have an efficient way to reach resorts without depending on taxis. © 2017 Tech Times, All rights reserved. Do not reproduce without permission.
News Article | April 4, 2016
Looking for skis to maximize the fun as you hurtle down the slopes? The ideal ski can withstand high levels of pressure in turns yet also be easy to maneuver. These two features usually require two different types of skis: the rigid skis preferred by expert skiers or the flexible ones that intermediate skiers opt for. But a new type of ski offers a two-in-one solution thanks to a design based on turtle scales. These skis are easy to maneuver while entering and exiting turns but stiffen up in the middle of turns to improve the skis' grip on the snow. This 'turtle shell' design is the result of a joint effort of EPFL, the Institute for Snow and Avalanche Research (SLF) in Davos and Stöckli, the Swiss ski manufacturer. The idea of mimicking the morphology of turtles occurred to Véronique Michaud, a researcher at EPFL's Laboratory of Polymer and Composite Technology, while she was attending a seminar on bioinspired materials. "The scales of a turtle interlock, like a jigsaw puzzle, and are connected by a polymer," said Michaud. "When turtles breathe, the scales separate slightly and the shell becomes flexible. But when an external shock occurs, the shell tightens and stiffens. It struck me immediately that we could build these features into skis." Michaud's idea took form during a yearlong Commission for Technology and Innovation (CTI) project in partnership with Stöckli. The project team ran many studies in their effort to replicate the natural phenomenon in skis. The best results were achieved by embedding aluminum plates with a snake-shaped fissure into the skis at precise locations at both ends. When the skis bend in a turn, the plates on each side of the gap come together and the ski stiffens, allowing the skier to execute stable and precise turns. As the skier comes out of the turn, the gap reopens making the ski flexible again and easy to handle. "The aluminum plates work like the scales," said Michaud, "and a special type of rubber between the plates is like the polymer in the turtle shell." Michl Leitner, a former professional speed skier, tested the skis for a day together with Tina Maze, the double Olympic ski champion. "We were pleasantly surprised," said Leitner. "It was easier to start the turn. And as the pressure on the skis' edges rose gradually during the turn, the skis really gripped the snow and were very stable. I was impressed by the ease with which the plates come together and separate." These skis, which went on sale in early March, were designed both for average skiers, who will find it easier to start their turns, and for experts skiers seeking to get the most out of their skis. Explore further: Signal opportunities on the slopes -- with RFID
News Article | February 16, 2017
After long-awaited snowfall in January, parts of the Alps are now covered with fresh powder and happy skiers. But the Swiss side of the iconic mountain range had the driest December since record-keeping began over 150 years ago, and 2016 was the third year in a row with scarce snow over the Christmas period. A study published today in The Cryosphere, a journal of the European Geosciences Union, shows bare Alpine slopes could be a much more common sight in the future. The new research, by scientists based at the Institute for Snow and Avalanche Research (SLF) and at the CRYOS Laboratory at the École Polytechnique Fédérale in Switzerland, shows that the Alps could lose as much as 70% of snow cover by the end of the century. However, if humans manage to keep global warming below 2°C, the snow-cover reduction would be limited to 30% by 2100. In addition to the changes in snow cover, the new research reveals the Alpine winter season -- the period when natural snow is deep enough for winter sports -- is set to become shorter. The team say that, as temperatures rise, the ski season could start half a month to a month later than it does at present. Moreover, if we don't cut emissions, enough snow for winter sports can only be guaranteed above 2500 m by the end of the century. "The Alpine snow cover will recede anyway, but our future emissions control by how much," explains lead-author Christoph Marty, a research scientist at SLF. Higher greenhouse gas emissions will bring higher temperatures to the Alps. But scientists were less sure about how global warming would affect snowfall in the region. "The majority of the climate models used project slightly increasing winter precipitation towards the end of the century. However, since temperatures are clearly increasing simultaneously we may experience increasing rainfall and not snow fall," Marty explains. "We hope our results convincingly show that even increasing winter precipitation cannot compensate for the effect of the strongly increasing temperatures." By simulating future snow cover in the Alps for various temperature and snowfall projections, the team was able to make more robust projections of how Alpine snow will change in the future, and how sensitive this change will be to different global-warming scenarios. Co-author Sebastian Schlögl, also from SLF, explains: "We used meteorological data and many different climate change scenarios to model the future snow cover in two Alpine catchments with ALPINE3D." ALPINE3D is an open-source computer model designed to simulate how snow is distributed in mountainous regions. The team's projections show that the layer of snow covering the Alps will get less deep "for all elevations, time periods and emission scenarios," they write in their The Cryosphere paper. "The most affected elevation zone for climate change is located below 1200 m, where the simulations show almost no continuous snow cover towards the end of the century." About a quarter of the ski resorts in the Alps are located fully below this altitude, according to the skiresort.info website. Ski resorts at higher altitude could also see drastic reductions in snow depth. If global warming isn't limited to 2°C, snow depth could decrease by about 40% at the end of the century even for elevations above 3000 m. The Zugspitze, the highest mountain in Germany, has an altitude of 2962 m. The two highest ski resorts in the Alps, the French Aiguille du Midi in Chamonix, Mount Blanc and the Swiss-Italian Matterhorn ski paradise, have maximum elevations of about 3900 m and minimum heights of around 1000 m and 1500 m, respectively. The decreasing snow depth and a shorter snow season will impact tourism in the Alps. "Since many Alpine villages are heavily dependent on winter tourism, the economy and society of regions with such tourism centres will suffer," says Schlögl. In the long term, the increased rainfall in winter, the smaller snow cover and disappearing Alpine glaciers will alter how much water flows into Alpine creeks and rivers and how the water volume changes over time. "This will not only impact the ecology, but also the management of water for irrigation, power production or shipping," he adds. Despite these impacts, the new research highlights how much we could save in the Alps by mitigating climate change. "The fact that we lose 30% of the Alpine snow cover with the 2°C global warming scenario is sad, but at the same time encouraging compared to the 70% loss when we go on with business as usual," concludes Marty. Please mention the name of the publication (The Cryosphere) if reporting on this story and, if reporting online, include a link to the paper or to the journal website.
News Article | February 17, 2017
Alpine ski resorts are facing the loss of up to 70% of their snow cover by the end of the century, experts have said. Even in the best-case scenarios, global warming is likely to see snowfall replaced by rain across the Alps, according to a report in the European Geosciences Union (EGU) journal the Cryosphere. It says mathematical climate models predict that “bare alpine slopes could be a much more common sight in future”. “Since many alpine villages are heavily dependent on winter tourism, the economy and society of regions with such tourism centres will suffer,” Sebastian Schlögl, one of the report’s authors wrote. Last year the Swiss Alps had their driest December since records began 150 years ago. 2016 was the third year in a row with little snow at Christmas, when many families go skiing. If global warming is limited to 2C, the target set in the Paris climate change agreement, the loss of snow cover in the Alps would be 30% by 2100, the report said. Were the temperature to rise above this target, the snow cover would dwindle by 70%, it added. The research was carried out by scientists at the Institute for Snow and Avalanche Research (SLF) and the Cryos Laboratory at the École Polytechnique Fédérale in Switzerland. It also suggests that the season when natural snow is deep enough for winter sports such as skiing and snowboarding is likely to become shorter. In a report entitled How much can we save? Impact of different emission scenarios on future snow cover in the Alps, the lead author Christoph Marty, SLF’s research scientist, writes: “The alpine snow cover will recede anyway, but our future emissions control by how much. “The majority of the climate models used project slightly increasing winter precipitation towards the end of the century. However, since temperatures are clearly increasing simultaneously, we may experience increasing rainfall and not snowfall.” Marty added: “We hope our results convincingly show that even increasing winter precipitation cannot compensate for the effect of the strongly increasing temperatures.” The team’s projections show that the layer of snow covering the Alps would lose depth “for all elevations, time periods and emission scenarios”. The report says: “The most affected elevation zone for climate change is located below 1,200m, where the simulations show almost no continuous snow cover towards the end of the century.” About a quarter of the ski resorts in the Alps are below this altitude.