What Is Going On Inside Snow Avalanches

The data collected should flow into simulations that reproduce the complex events inside avalanches in detail. "Exactly what happens when an avalanche moves down the mountain is not known, because until now you have only observed it from the outside," says Christoph Baer. Findings from the simulations could help to create better avalanche protection devices.

Measure snow density

Basically, it is already known that avalanches consist of several layers that behave like solids, liquids or gases containing dust. The new sensor detects variations in snow density in the dust layer. Among other things, the density affects the impact pressure of the avalanche, which is decisive for its destructive power. Avalanche events can only be correctly simulated by fluid mechanics if the snow density is known.

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The Bochum system uses radar to determine how many snow particles are in the dust layer. The more snow there is, the slower the radar wave spreads. This enables the researchers to draw conclusions about the snow density and record it in real time.

Aircraft aluminum sensor

The sensor is made of aircraft aluminum because it has to withstand the enormous forces of the avalanche during the measurement. It is about one meter long, 30 centimeters thick and weighs 70 kilograms. An avalanche has an impact pressure of up to six bar. "This corresponds to a pressure of 3.5 tons - two cars - on the surface of an A4 sheet," explains Baer. “It rolls directly over our sensor. It is a challenge that he gets stuck on the test mast and delivers useful measurement results.”

The students Patrick Kwiatkowski and Henrik Deis built the sensor as part of their work as scientific assistants at the chair for integrated systems of Prof. Dr. Nils Pohl. At the same chair, Timo Jaeschke is researching the millimeter-wave radar system used as part of his doctorate. Christoph Baer developed the underlying principle for radar-based density measurement in his doctoral thesis at the RUB Chair for Electronic Circuit Technology.

Waiting for the avalanche

In 2016, the team from the Swiss Institute for Snow and Avalanche Research is expecting the first snowfalls in the closed test area Vallée de la Sionne. If there is no avalanche on its own, it will be triggered by a controlled explosion at the end of winter.

Project partners for the development of the sensor were the Swiss Institute for Snow and Avalanche Research in Davos, the Institute for Natural Hazards in Innsbruck, the University of Innsbruck and the Austrian Federal Office for Forests. (jv)