World of Science | ISSW 2016 Part 1

In contrast to many other conferences, the ISSW also provides interested laypeople with one or two exciting and understandable presentations. On the one hand, there is a lot of focus on highly technical topics such as avalanche dynamics, snowpack modeling and measurement technology, but on the other hand, winter sports practice is also increasingly being discussed. In the following, we summarize a few new insights of the more technical kind, while the more practical topics will be dealt with in separate articles in the near future. Many thanks at this point to the organizers of the Innsbruck Snow Table, especially to Christoph Mitterer and Sasha Bellaire, who were at the ISSW and told us about some interesting studies.

Model chains

Model chains are increasingly being used in avalanche and snowpack modelling. This means that different models are combined into one large construct and no longer just calculate individually.

For example, weather models are linked to snowpack models, for example to better predict the "liquid water content" (LWC) of the snowpack - an important factor in wet snow avalanches. To date, the SNOWPACK snowpack model has been fed with weather station data to calculate the LWC. By its very nature, however, the maximum that is possible is "nowcasting" - predicting something that has actually already happened or is about to happen. If you feed the snowpack model with high-resolution weather forecasts instead, you can predict the LWC for the future accordingly. Bellaire and his colleagues have tested whether and how well this works, with promising results that may make it easier to predict wet snow avalanches in the future.

(Study: Regional Forecasting of Wet Snow Avalanche Cycles: an Essential Tool for Avalanche Warning Services? Sascha Bellaire, Alec van Herwijnen, Christoph Mitterer, Nora Helbig, Tobias Jonas, Jürg Schweizer, Proceedings, International Snow Science Workshop, Breckenridge, Colorado, 2016)

Another study takes a closer look at the anti-crack model and the difficulty of reconciling theory and practice. In contrast to the classic idea of shear fracture, the anti-crack theory can conclusively explain the planar collapse of the weak layer (and thus the mechanics of remote releases). However, the theory also indicates that the slope inclination does not play a significant role in fracture propagation, which is not quite consistent with observations. In a new approach, the elasticity of the snowpack above the weak layer is now included. This results in a new way of calculating the critical length for the onset of crack propagation. This parameter measures how long the initial fracture must be for fracture propagation to occur. It is the distance that the snow saw is driven into the weak layer in a PST until a fracture occurs. With this method, the dependency of the critical length on the slope inclination is between the pure shear model (the steeper the PST, the less distance you have to cut for a break) and the anti-crack model (how far you have to cut with the PST is more or less independent of the slope inclination).

(Study: Critical Length for the Onset of Crack Propagation in Snow: Reconciling Shear and Collapse, Johan Gaume, Alec van Herwijnen, Guillaume Chambon, Nander Wever, Jürg Schweizer, Proceedings, International Snow Science Workshop, Breckenridge, Colorado, 2016)

Avalanche detection

A study from Norway deals with a sliding snow avalanche that occurs every year in the same place above a road. The road should of course be closed when the avalanche starts, but you don't want to close it for weeks because the avalanche might start. Deformations of rock faces are often measured using radar. This technique was also used for the Norwegian sliding snowmelt. In contrast to normal cameras, the radar sees how quickly the sliding snow crack opens up, even when it is dark or foggy. Before it leaves, the gliding snow mouth moves faster and faster and the radar measures this movement. This acceleration phase could be used to predict shortly beforehand that the gliding snow avalanche is about to go down (and the road can be closed).

(Study: Use of Ground Based INSAR Radar to Monitor Glide Avalanches, Ingrid Skrede, Lene Kristensen, Carlo Rivolta, Proceedings, International Snow Science Workshop, Breckenridge, Colorado, 2016)

Another radar system was used in Switzerland, on the access road to Zermatt. Here, two Doppler radar units monitor the slope above the road. If they detect movement in the slope (avalanche!), traffic lights linked to the system on the road to the left and right of the avalanche path switch to red. All avalanches that have occurred have been detected in this way, although there have been false alarms from time to time (e.g. when helicopters fly through the picture, which often happens in Zermatt). The observers on site are well attuned to the system and check within a few minutes whether an avalanche has actually occurred. If not, they switch the lights back to green. This system was presented for the first time in 2010 and was successfully put into operation last winter - a very rapid development from idea to completion.

(Study: Real-time Avalanche Detection with long-range, wide-angle radars for road safety in Zermatt, Switzerland, Lorenz Meier, Mylène Jacquemart, Bernhard Blattmann, and Bernhard Arnold, Proceedings, International Snow Science Workshop, Breckenridge, Colorado, 2016)