Complete dynamic modeling calibration for the Thurwieser rock avalanche (Italian Central Alps)

Few rock avalanches have been witnessed and no exact real time description is available. The 2.5 M m(3) Punta Thurwieser rock avalanche (September 2004, Italian Central Alps) is a unique event for which many quantitative observations have been gathered. This is the first case ever of a natural rock avalanche being recorded on video, and for which an almost exact value of the total time duration, from initial detachment to final deposition, is available. The landslide travelled over 2.9 km from its source partially in a glacial environment. The initial failure and the time for the complete evacuation of the source area were studied and assessed by a series of photos. The mean front velocities along the path have been estimated from the video. The final geometry and the characteristics of the deposit have been obtained by GPS measurements, aerial photos, field surveys and laboratory tests. A quasi-3D continuum dynamic analysis of the landslide motion has been performed assuming both a Voellmy and a frictional rheology in the model DAN 3D. For the first time the landslide front velocities have been used for back analyses and calibration of the rheological parameters, together with the final shape and thickness of the deposit, and its developing extension. The dynamic flow resistance parameters, initially calibrated with DAN, were adopted and validated in DAN 3D, showing good consistency. They are consistent with the existing database for calibrated landslides of similar type and scale. Flow velocities on the path segment underlain by glacial deposits (up to 55-65 m s(-1)) are more accurately predicted by adopting a frictional rheology (up to 50-55 m s(-1)) with zero pore pressure and a 26 degrees friction angle than by a Voellmy rheology (up to 40-45 m s(-1)). Both observations and modelling show that glacial ice plays a substantial role in increasing the rock avalanche mobility. (C) 2008 Elsevier B.V. All rights reserved.