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CRE dating on the head scarp of a major landslide (Séchilienne, French Alps), age constraints on Holocene kinematics

Olivier Le Roux 1 Stéphane Schwartz 1 Jean-François Gamond 1 Denis Jongmans 1 Didier Bourles 2 Regis Braucher 2 William Mahaney 3 Julien Carcaillet 4 Laetitia Leanni 2
1 LGIT - Laboratoire de Géophysique Interne et Tectonophysique
2 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
3 Geomorphology and Pedology Lab
4 LGCA - Laboratoire de Géodynamique des Chaines Alpines
Abstract : Cosmic Ray Exposure (CRE) dating applied to the active Séchilienne landslide (Romanche valley, Belledonne Massif, French Alps) provides information about its Holocene dynamics from initiation to present day activity. Glacier retreat at 1100 m a.s.l. is estimated at 16.6±0.6 10Be ka from glacially polished bedrock samples, with total deglaciation of the valley achieved at least by 13.3 ka. Application of the CRE method along vertical profiles sampled with a high spatial resolution of 3 m on the head scarp yields: (1) an initiation of the rock-slope failure at 6.4±1.4 10Be ka and (2) a continuous rock-slope failure activity with a mean head scarp exposure rate of 0.6 cm/yr. The data suggest an increase of the head scarp exposure rate between 2.3 and 1.0 ka. After this acceleration phase, the exposure rate is similar to that obtained by the present day monitoring data over 20 years in the depletion zone (1.3 cm/yr). Since the failure initiation occurred more than 5400 yr after the total deglaciation of the valley the slope failure does not appear as an immediate consequence of debutressing in the Romanche valley. This result is consistent with studies of other large alpine rockslides in the Alps. Failure initiation of the Séchilienne landslide occurred during the Holocene Climatic Optimum, a hot and wet period. The temperature and precipitation changes of this climatic optimum seem to have a worsening effect at the regional scale to trigger large mass wasting in this glacial alpine valley.
Keywords : cosmic ray exposure method Séchilienne landslide kinematics head scarp dating Holocene climatic optimum
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https://hal-insu.archives-ouvertes.fr/insu-00411150
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Submitted on : Wednesday, August 26, 2009 - 12:59:29 PM
Last modification on : Saturday, October 3, 2020 - 3:12:43 AM

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Olivier Le Roux, Stéphane Schwartz, Jean-François Gamond, Denis Jongmans, Didier Bourles, et al.. CRE dating on the head scarp of a major landslide (Séchilienne, French Alps), age constraints on Holocene kinematics. Earth and Planetary Science Letters, Elsevier, 2009, 280 (1-4), pp.236-245. ⟨10.1016/j.epsl.2009.01.034⟩. ⟨insu-00411150⟩

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