On Avalanche Measurements at the Norwegian Full-Scale Test-Site Ryggfonn

Avalanche measurements and observations, which were carried out at the Ryggfonn test-site, Norway, on 16 April 2005, are analyzed. The data include pulsed Doppler radar measurements, impact pressure readings from load cells mounted at two locations within the track and stress readings from load plates flush with the upstream slope of a catching dam. The radar measurements are used to deduce velocities and estimates on the retarding accelerations. The retarding accelerations show a wide discrepancy with commonly used model assumptions. Pressure measurements were correlated with velocity measurements. The measurements infer that commonly used drag factors are not sufficient to describe the forces exerted by slow moving wet snow. These measurements also depict transitions in the flow behavior. Measurements with load plates imply plastic failure rather than Coulomb-type friction. Field observations of the avalanche track suggest that erosion/abrasion due to (saltating) particles is one possible entrainment mechanism.