An up-to-date Holocene catalog of sedimentary events recorded in volcanic lakes from the French Massif Central
Résumé
A decade of scientific investigation, combining subsurface geophysical mapping techniques and coring operations, highlighted several sedimentary events in volcanic lakes of the French Massif Central1,2,3. Here, we present a synthesis of recent studies dedicated to lakes located around the Puy-de-Sancy stratovolcano (i.e., Pavin, Chauvet, Aydat, Montcineyre, Guéry, and Crégut) with new data collected in Lake Lacassou, nearby Lake Chambon, and in the northernmost maar lake Gour de Tazenat. A multi-proxy characterization allowed the identification of mass-movement deposits and coarse-bed turbidites related to subaqueous slope failures. The radiocarbon-based chronological framework allows the creation of a catalog of sedimentary events over the late Holocene that give insights about past geohazards in a low-medium seismogenic area. The dating of coeval deposits between sites was attributed to historical earthquakes documented during the VIth, XIIIth and XIXth centuries. Among them, an undocumented earthquake has been identified as the regional trigger for synchronous deposits in AD 1275 in four lakes around the Puy-de-Sancy stratovolcano1. New chronological constrains from Lake Lacassou suggest this event could have also triggered the `Dent du Marais` collapse and the subsequent formation of Lake Chambon. Regular occurrences of single sedimentary events suggest either a growing human pressure and/or unsettled climatic conditions have also been involved in the generation of extreme events such as for the 5500 cal BP slope failure in Lake Cregut, the AD 180 delta collapse in Lake Aydat, and the AD 600 outlet break in Lake Pavin. The absence of deposit related to the major earthquake dated AD 1490 (Mw > 6) also suggest studied lakes are too distant and/or sediment loadings were too low since the last slope failures two centuries prior. Finally, we reported unusual deposits across the subaqueous plateau (oxic waters) in Lake Pavin during late XVIIIth and early XXth centuries. Their iron-rich signature suggests a formation under an iron-rich mixolimnion consecutive of a lake rollover carrying dissolved iron species from anoxic deep waters to oxic waters2. Consequently, these layers constitute first evidences of recent roll-over phenomena in Lake Pavin and may support further work about similar hazards in volcanic settings.
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