Understanding the dynamics of an avalanche
(25 November 2016)
Professor Jim McElwaine of the Department of Earth Sciences talks about new research, published in the Journal of Geophysical Research: Earth Surface, which has given some of the first detailed measurements of what takes place inside an avalanche.
Tell us a bit about the research?
The aim of the project was to understand what processes are taking place inside an avalanche as it travels down a mountain. The internal processes of avalanches are difficult to measure as they are often obscured by the powder cloud of snow that is thrown up during the event.
In this study the research group, which included the Swiss Federal Institute for Snow and Avalanche Research, used explosives to artificially trigger five avalanches in Switzerland’s Vallée de la Sionne. We then used a mix of innovative radar technology, pylon-mounted sensors and video to get the best look yet at what is taking place inside an avalanche.
Artificially-triggered avalanches were necessary as naturally-caused avalanches are unpredictable and hard to observe.
How did you measure what was taking place inside an avalanche?
Past studies have used Doppler radar to detect the speed of an avalanche under the powder cloud. However, this has poor resolution which prevents us from seeing the avalanche’s internal structures, such as where the moving snow is deeper or faster.
In this study we used avalanche-specific radar called GEODAR, which was developed by Professor Paul Brennan and Doctor Matt Ash at the Department of Electronic & Electrical Engineering at University College London. This bespoke equipment is able to give high-resolution observations of the internal structures of avalanches.
Radar measurements were complimented with measurements of velocity profiles and impact pressures.
What has the study found?
Until now it has been thought that an avalanche behaved as one single mass, moving at a roughly constant speed down the mountain.
However, our study shows that avalanches are far more complex, containing multiple internal surges of snow moving at very different speeds. These internal surges can frequently overtake one another as the avalanche gathers snow and moves downhill – something that has not been clearly shown before.
Why are these findings important?
Avalanches kill around 100 people a year in the European Alps alone and can cause significant damage to infrastructure. By understanding the dynamics of avalanches we can more accurately predict the distances they may travel, which in turn could help to mitigate their destruction.
Increasingly scientists need to rely on models of avalanche behaviour as statistics from historical events may no longer be reliable for future prediction. Therefore, making these models as accurate as possible is hugely important.
What is the next stage for this research?
We would like to continue this work by undertaking more measurements and adding lateral views of avalanches to the data collected, to help understand how and why these different surges are occurring within a single avalanche.
Differences in speed and the presence of surges may be due, in part, to differences in friction within the avalanche. Some parts of the avalanche have greater contact with the ground than others, and therefore greater friction, which will slow those sections down.
Who else worked on this project?
The project was a collaboration between the Durham University and the Swiss Federal Institute for Snow and Avalanche Research.
The specialist avalanche radar technology was developed by Professor Paul Brennan and Doctor Matt Ash at the Department of Electronic and Electrical Engineering at University College London
The research was originally funded by the Royal Society, then Natural Environment Research Council and most recently by the Swiss National Science Foundation.
The full research paper, The dynamics of surges in the 3 February 2014 avalanches in Vallée de al Sionne, is available here.