Ryggfonn is one of the few full scale avalanche paths in the world instrumented for full scale experiments. The research here is done in cooperation with many, among others Institut für Lawinen-und Wildbachforschung, Innsbruck, Wildbach-und Lawinenverbauung/WLV Tirol, Universitat de Barcelona and the Norwegian Armed Forces Winter School.
The avalanche path in Ryggfonn has a vertical drop of 900 m and a total length of about 2100 m. The size of the avalanches usually varies from 2 (0.1 Gg) to 5 (100 Gg) measured in the Canadian classification for avalanche (McClung and Schaerer, 1993) and the avalanche speed can reach up to 60 m/s.
From the left: Release with the detonation of explosives, the avalanche starts when the snow-pack on top loosens and cracks. The avalanche and avalanche cloud on the way down the avalanche path. After the landslide has stopped (at the embankment rampart in the bottom of the path).
Link between the model and reality
Probability and risk mapping involves the analysis calculation of the run-out distances for avalanches. Data from Ryggfonn is used to develop, refine and calibrate dynamic models for landslide movement. Small scale tests are more easily available, but the scaling of the models will then be a major challenge. Data from full scale experimental test fields, such as Ryggfonn, therefore provides very important information. In addition, NGI has built an embankment rampart in the run-out area of Ryggfonn to study the impact and effect of such mitigation structures.
Overview and surveillance from opposite side of Ryggfonn during release of avalanche
Instrumentation in Ryggfonn
After extensive investments in recent years, Ryggfonn today is equipped and instrumented so that all avalanches in the slide path path are automatically logged, and thereby provides valuable data about the forces and pressure generated, and the velocity of the avalanche. The fixed instrumentation includes LED sensors, load cells and geophones mounted on steel masts and concrete constructions along the avalanche path, as well as in embankment rampart. During field tests measurements with lasers and doppler radar measurements are made.
In recent years, NGI has invested a substantial amount from own funds into a significant upgrading of measuring and monitoring equipment in this field laboratory, including a new tower system for the artificial release of avalanches (the Wyssen-Tower). The monitoring equipment measures speed and pressure profiles in front of and on the embankment rampart. This provides completely new possibilities to analyze the interaction between the avalanche and the embankment. And it demonstrates both the importance of how high NGI values the Ryggfonn test site, and the potential and the international importance of this experimental test field site.