Be-10 cosmic-ray exposure dating of moraines and rock avalanches in the Upper Romanche valley (French Alps) : evidence of two glacial advances during the Late Glacial/Holocene transition

Cosmic-ray exposure (CRE) dating of moraines allow glacier fluctuations and past climate change reconstructions. In the French Alps, there is a lack of moraine dating for the Late Glacial/Holocene transition period. Here we present a chronology of glacier advances in the Upper Romanche valley (French Alps - Massif des Ecrins) based on Be-10 CRE dating. CRE ages of moraines of 13.0 +/- 1.1 ka and 12.4 +/- 1.5 ka provide evidence for two stages of glacial advance or standstill at the end of the Late Glacial. The CRE dating of a rock avalanche deposit at 12.2 +/- 1.5 ka is attributed to post-glacial debuttressing and reveals rapid deglaciation at the end of the Late Glacial. A CRE age of 7.1 +/- 0.7 ka of a second mass wasting, whose triggering factor is unidentified so far, indicates that up to an altitude of 2300 m a.s.l., the valley was ice-free as of similar to 7 kyr at the latest. The re-evaluation of 21 moraine Be-10 CRE ages from nine glacial valleys across the Alps shows multiple glacial advances occurring at the Late Glacial/Holocene transition. These results lead to a re-evaluation of the importance of cooling events during the Allerod and the Younger Dryas in the Alps