FAST VERSUS SLOW AVALANCHE IMPACT DYNAMICS: INSIGHTS FROM MEASUREMENTS AT LAUTARET PASS AVALANCHE TEST-SITE, FRANCE

The present paper describes preliminary re-analyses of field-based data on past well-documented snow avalanches that have impacted an instrumented tripod structure in one of the paths at Lautaret avalanche test-site, France. The re-analyses done include data on velocity and pressure measurements , as well as new data on flow-depth measurements. The latter data was obtained with the help of re-analyses of pressure signals. The various techniques used and assumptions made are presented and discussed, which allows us to infer how the thickness of the dense flow, and both the velocities and pressures over depth, all change simultaneously over time. The present work pays attention to the gravity-dominated flow regime occurring after the passage of the avalanche front. That regime is characterized by a mean pressure on the tripod structure that is essentially controlled by the flow thickness, unlike the inertia-dominated regime which is deemed to be driven by the square of the flow velocity during the passage of the avalanche front. Moreover, a change in dynamics is well identified during the gravity-dominated flow regime, while moving from the avalanche core to the avalanche tail.