The Pyrenees: glacial landforms from the Bølling–Allerød Interstadial (14.6–12.9 ka)

International audienceThe Bølling–Allerød (B-A) Interstadial (14.6–12.9 ka) was a period of intense glacier recession in the Pyrenees. All available proxies indicate that environmental conditions became substantially wetter and warmer than during the preceding post-LGM interval between 18.9 and 14.6 ka (early Last Glacial to Interglacial transition, LGIT). Most of the Pyrenean trunk glaciers vanished, being confined to the cirques and promoting the onset of paraglacial rock slope failures and the formation of rock glaciers. At lower elevations, forest expansion promoted a sharp decrease in catchment erosion rates. Braided glaciofluvial stream channels narrowed and gave way to meandering river styles. The detailed chronology of deglaciation during those 1700 years of rapid change has been documented for only a very small number of valleys, mostly relying on 10Be or 36Cl exposure ages obtained from glacially-polished bedrock steps on valley floors, with also a few results from ice-marginal boulders and/or rock glaciers. A period of glacier re-expansion occurred at the end of the B-A Interstadial in response to decreasing temperatures heralding the Younger Dryas