Snow avalanches and currents of gas and rock released by volcanic eruptions cause significant loss of life around the world.

Avalanche -4-320Martin Kern and Kevin Chetty inspecting the mast in the avalanche path. The bunker can be seen in the background.

Understanding the dynamics of these flows is complex because the majority of the mass is in a thin granular layer that is often hidden by a cloud of suspended material. To determine the flow speed of the dense part of an avalanche, a new instrument has been installed at a test site in Vallée de la Sionne in Switzerland. The results are being used to improve computer models for flow dynamics and therefore improve risk zoning in mountain areas.

How it works

The radar instrument consists of one transmitter and eight receivers. Rather than the old-fashioned dishes, modern radar receivers are made on printed circuit boards and are approximately 15cm by 10cm.

The radar is mounted at the avalanche bunker and looks up the path. It has an operating frequency of 5.3GHz which is a long enough wavelength to pass through the powder cloud and obtain an image of the denser layers of flowing snow beneath. The range of the instrument is over 2000m and the instrument extracts flow data from every 0.75m along the avalanche path 50 times a second.

The radar works on the Doppler principle - it determines the velocity of the avalanche based on the change in frequency of the reflected signal with respect to the transmitted signal. Tests of the instrument so far indicate that the measured velocities are very similar to those recorded from the other instruments installed in the avalanche path at the test site. As a result scientists can start to make detailed inferences about the friction laws for these geophysical mass flows.

Games

Test your knowledge avalanche phenomena with this online quiz.

Videos

This video introduces the research behind this exhibit.

This is a video of a granular flow experiment.

Lead image: A large avalanche at the Vallée de la Sionne test site viewed from the bunker. The instrument tower can be seen just in front of the avalanche. Credit: SLF, Switzerland