On full-scale avalanche measurements at the Ryggfonn test site, Norway Peter Gauer a,b, ⁎ , Dieter Issler a,b , Karstein Lied a , Krister Kristensen a , Harald Iwe a,b , Erik Lied a , Lambert Rammer c , Helmut Schreiber d a Norwegian Geotechnical Institute, Sognsveien 72, N-0806 Oslo, Norway b International Centre for Geohazards, c/o NGI, Norway c Federal Research and Training Centre for Forests, Natural Hazards and Landscape, Rennweg 1 — Hofburg, A-6020 Innsbruck, Austria d Institute for Communication Technology and Wave Propagation, Technical University Graz, Inffeldgasse 12, A-8010 Graz, Austria Received 1 August 2006; accepted 22 September 2006 Abstract Avalanche measurements carried out at the Ryggfonn test site, Norway, during several winter seasons are analyzed with emphasis on recognizing different flow regimes and estimating flow densities. Measurements include 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. Pressure measurements were combined with velocity estimates based on cross correlations between the load cell readings and, in several cases, on Doppler radar measurements. In most cases a saltation (fluidized) layer in front of a more dense part could be identified. Doppler radar measurements confirm a fast moving head, in some instants preceded by a slower snout, and decreasing speed from the head to the tail. Calculated accelerations (decelerations) indicate that the effective friction parameter varies strongly and depends on the flow regime. © 2006 Elsevier B.V. All rights reserved. Keywords: Avalanche; Full-scale measurements; Impact pressure; Shear stress; Velocity; Acceleration; Density estimates 1. Introduction Measurements and observations from full-scale ava- lanches are indispensable for fully understanding the flow behavior of avalanches. They form the basis for developing and calibrating models. Full-scale measure- ments provide information on the scaling behavior of avalanches and so they are a control for small-scale experiments, such as chute or water tank experiments. However, full-scale experiments are expensive and time consuming. Unlike laboratory experiments, they are only controllable to a certain degree. Local topography and varying snowpack properties set the initial and boundary conditions. Their reproducibility is limited, qualitatively as well as quantitatively. In addition, harsh conditions within an avalanche make measurements a difficult task. Accessibility to the avalanche path prior to a release is usually limited. Sensors have to be placed a long time before an event and might be buried by the time due to previous avalanches. The knowledge of the sensor status is important, a fact that limits the reliability of automatic measurements. Cold Regions Science and Technology 49 (2007) 39 – 53 www.elsevier.com/locate/coldregions ⁎ Corresponding author. Norwegian Geotechnical Institute, Postbox 3930 Ullevål Stadion, N-0806 Oslo, Norway. Tel.: +47 22 02 31 29; fax: +47 22 23 04 48. E-mail address: pg@ngi.no (P. Gauer). 0165-232X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.coldregions.2006.09.010