The catastrophic failure of a mountain slope, a snowcover, or a lava dome generates a flow of material downslope driven by gravity. These flows of material are an extremely dangerous natural hazard in many parts of the world. The aim of this project is to develop a radar imaging system that can enhance our understanding of these complex flow processes.

Existing radar used for studying such flows tend to give information on the flow velocity in just one dimension (towards the instrument), and tend to obtain a speed averaged over a distance of 50 metres or so. This is useful for providing general information on how the flow speed changes with alterations to terrain, but this is far too coarse a resolution to gain an understanding of exactly how these flows work. That is, what is the appropriate flow law for describing their dynamics? Once we have a good idea what this is, we can improve the mathematical models used in risk and hazard zoning.

The Radar
Our instrument employs a phased-array to give two components to the velocity. Hence, we are able to see how the flow spreads or interacts with obstacles in the path. The high resolution of our instrument yields these velocity estimates over a distance of less than one metre. This is important as it permits a direct comparison with other instruments in the avalanche path, meaning that we are in a position to determine exactly how the flowing material interacts with the radar beam. This resolution is also close to the scale of the dynamical processes within the flow. Thus, for the first time, we are able to image the whole flow at a resolution that is relevant dynamically.

The Test Site
In this project we are validating the radar data using snow avalanches released at the [
Vallee de la Sionne] avalanche test site in Switzerland. The nice thing about working with avalanches is that because the snow melts, instrumentation can be recovered and repaired in the summer. Contrast this with pyroclastic flows that leave a town such as Plymouth on Montserrat under a layer of rock and ash [http://www.mvo.ms/]. It is also possible to trigger avalanche release using explosives in a much more simple and more controlled manner than is possible with related flow processes. For example, the [SATSIE website] shows such a release in Norway. Hence, for the duration of this project we will be concentrating on snow avalanche phenomena, with the intention of working on other flows once the instrument is fully verified and validated.