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Surface exposure dating and geophysical prospecting of the Holocene Lauvitel rock slide (French Alps) |
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| Authors: | Romain Delunel Didier Hantz Régis Braucher Didier L Bourlès Philippe Schoeneich Jacques Deparis |
| Institution: | 1. Centre Européen de Recherche et d’Enseignement des Géosciences de l’Environnement (CEREGE), UMR 6635 CNRS–Aix Marseille Université, BP 80, 13545, Aix en Provence, France 5. Laboratoire de Géodynamique des Cha?nes Alpines, Université Joseph Fourier, BP 53, 38041, Grenoble, France 2. Laboratoire de Géophysique Interne et de Tectonophysique, Université Joseph Fourier, BP 53, 38041, Grenoble, France 3. Institut de Géographie Alpine—UMR 5194-PACTE/Territoires, Université de Grenoble, Grenoble, France 4. BRGM, 3 avenue Claude-Guillemin, 45060, Orléans Cedex 2, France |
| Abstract: | Large rock falls and rockslides represent a risk for human communities in mountainous areas as they can cause fatalities and destruction of settlements and infrastructures. Assessing the associated hazard requires constraining the time frequency of such events. Since large rockslides are not common, estimating their frequency requires recording them over a long period of time. The Holocene period then appears as pertinent, which implies that rockslide features have to be dated with absolute chronology methods. This paper presents a characterisation and dating of the Lauvitel rockslide, one of the largest Holocene rockslides in the French Alps. Combining field observation with electrical tomography profiles performed on the rockslide deposit that constitutes the Lauvitel Lake dam allows estimating its volume at a minimum of 12?×?106?m3. In addition, cosmic ray exposure dating using in situ-produced 10Be concentration measurements has been applied to date seven samples collected both on the main sliding surface and on blocks lying on the dam and further downstream. Ages obtained are consistent with a single large rockslide event, which occurred at 4.7?±?0.4 10Be-ka and formed two distinct deposits. However, from a mechanical point of view, these clearly separated deposits could hardly result from a single movement. A comparison of their reach angles with those reviewed in the literature highlights that the lower deposit must result from rock avalanches larger than 107?m3, while the upper one (the Lauvitel dam) must result from several events smaller than 106?m3. In the context of hazard assessment for land use planning, these events can, however, be considered as a unique event. |
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