Désenglacement du haut bassin versant du Vorz Massif de Belledonne, Isère, au Tardiglaciaire et à l'Holocène

Abstract

Identification and mapping of glacial heritages in the upper Vorz watershed (Belledonne massif, Western French Alps) have provided a chronology of the glacier retreat during the Lateglacial and the Holocene. The glacier retreat in this area is now largely achieved : it just remains the Freydane glacier, the largest in the massif (0.3 km2), and the tiny relict glacier of Roche Noire. Downstream the present fronts of these two glaciers, thirteen positions were recognized. The last four among the five Holocene positions correspond probably to the end of the Little Ice Age (c.1850), 1890, late 1920s and early 1980s. Beyond the morainic complex of the Holocene-LIA, the mapping of moraines suggests eight Lateglacial positions. Among the periglacial and gravitative forms and formations which cover more or less the moraines, there are four very different rockfalls or rock avalanches, of which the largest (at least several millions m3) could have occurred at the end of the Lateglacial or at the beginning of the Holocene, and probably corresponds to the collapse of a palaeo-summit from the crest line between Roche Rousse and Roche Noire.