BACK-CALCULATION OF SMALL AVALANCHES WITH THE 2D AVALANCHE DYNAMICS MODEL RAMMS: FOUR EVENTS ARTIFICIALLY TRIGGERED AT THE SEEHORE TEST SITE IN AOSTA VALLEY (NW ITALY). M. Maggioni 1 *, M. Freppaz 1 , M. Christen 2 , P. Bartelt 2 and E. Zanini 1 1 Dipartimento di Scienze Agrarie, Forestali e Alimentari and NatRisk-LNSA, University of Torino, Italy 2 WSL-SLF Davos, Switzerland ABSTRACT: Avalanche dynamics models are widely used to simulate extreme avalanches for hazard mapping purposes; they are well developed and calibrated on numerous real events. Only recently have small avalanches been studied, mainly for problems related to the safety of ski runs and roads. For small avalanches the physical processes within the avalanche flow are important, as they are not included in the calibrated Voellmy friction coefficients μ and ξ. Presently, researchers have started to develop avalanche dynamics models that include the physical processes associated with granular characteristics of the avalanche. Snow entrainment and deposition processes along the avalanche path are likewise modeled. In this work, we use one of these newly developed models, RAMMS, to back-calculate four well-documented avalanches artificially triggered at the experimental test site of Seehore in Aosta Valley (Northwest Italy), operative since 2009. The events are mostly small-size dense slab avalanches, triggered for scientific investigations. Snow characteristics and flow characteristics were recorded with field work, laser scan measurements, photogrammetry and specific instruments on an obstacle placed along the track to measure impact forces. The collected data are used to tune the RAMMS input parameters in order to reproduce the real events. We present the simulations results and highlight the importance of including erosion and deposition parameters in the investigation of small avalanches. 1. INTRODUCTION Avalanche dynamics models are widely used to simulate extreme avalanches for hazard mapping purposes; they are well developed and calibrated on numerous real events (e.g. Barbolini et al, 2000). Only recently have small avalanches been studied, mainly for problems related to the safety of ski runs and roads. For small avalanches the physical processes within the avalanche flow are important, as they are not included in the calibrated Voellmy friction coefficients μ and ξ (Salm, 1993). Presently, researchers have started to develop avalanche dynamics models that include the physical processes associated with granular characteristics of the avalanche (Naaim et al., 2003; Bartelt and Buser, 2009; Buser and Bartelt, 2009). Snow entrainment and deposition processes along the avalanche path are likewise modeled (Naaim et al., 2003; Sovilla et al, 2006 e 2007; Christen et al, 2010a). In this work, we use one of these recent models, RAMMS developed by the WSL-SLF of Davos (CH), to back-calculate four well-documented avalanches artificially triggered at the experimental test site of Seehore in Aosta Valley (North-western Italian Alps) operative since 2009. This model was used by other authors (see for ex. Casteller et al. (2008) and Christen et al. (2010b)) to back calculate avalanches of larger dimension. This is the first work where small avalanches of release volumes of about 200 m 3 are simulated with an avalanche dynamics model. Correspondig author address: Margherita Maggioni, Dipartimento di Scienze Agrarie, Forestali e Alimentari and NatRisk-LNSA, University of Torino, Via L. Da Vinci 44, 10095 Grugliasco (TO), Italy; tel. +39 011 6708522, fax. +39 011 6708692; email: margherita.maggioni@unito.it Proceedings, 2012 International Snow Science Workshop, Anchorage, Alaska 591