Chronologie holocène des dépôts de mise en place catastrophique dans une haute vallée alpine. Le cas du comblement de l'ombilic du tour (Alpes françaises du Nord) [ Brutal genesis deposits holocene chronology in a high alpine valley : the case of the filling-up of the tour ombilic.

Abstract

The high catchment of the Arve river (upper valley of Chamonix, French Alps) offers a great variety of deposits due to catastrophe. These deposits start during Boreal period with a phase of torrential spasmody activity. The Ancient Atlantic period is marked by the brutal «opening» of the «combe de la Vormaine» catchment, which generates a big upheaveal of the morphogenesis. A contrario, there is a cutting- down phase during the Subboreal period. In the Subatlantic period, and more particularly during the Little Ice Age, a recrudescence of torrentiality in relation with a phase of intense solifluxion on the slopes can be observed. The present dynamic of the river Arve, not very developped during the Holocene period, is the consequence of the recent activation of a slide of great importance on the slope of the Posettes.