Evaluating Holocene natural hazards in the French Massif Central from a regional lake sediment approach

International audienceGeophysical surveys in the Lakes Tazenat, Aydat, Chambon and Lacassou combined with a multiproxy study of sediment cores highlight Late Holocene abrupt environmental changes in the northern part of the French Massif Central (FMC). Dating landslide-induced dust layers and subaqueous slope failures impacting lake basin sedimentary fills suggest regional triggering by palaeo-earthquakes (cluster of events) either in the Puy-de-Sancy volcano area, or along the regional Limagne fault. In the present study, a cluster of palaeo-earthquakes occurring in the Sancy area between AD 1243 and 1270 are documented in the Lakes Montcineyre, Chauvet, Pavin and Guéry, as well as by the formation of Lake Lacassou following the last emplacement of the Dent du Marais landslide in the Chaudefour glacial valley around AD 1250 ± 30. Former cluster of earthquakes occurring near the Limagne fault between AD 580 and 650 are evidenced in Lake Tazenat and in maar Lake Pavin. Lake Pavin present lake-level was similarly favoured by the cluster of earthquakes between AD1243 and 1270 and the occurrence of a slump and an outburst flood event resulting in the bypassing of a palaeo-outlet. Holocene earthquakes near the Limagne fault are suggested in maar Lake Tazenat by coeval mass wasting deposits (MWDs) around 2250 ± 50 cal. BP and around 2730 ± 30 cal. BP. A landslide-induced dust layer dated between 2760 and 2520 cal. BP at the transition from paludal to lacustrine deposits in the Chaudefour glacial valley is suggesting that the formation of Lake Chambon resulted from a first emplacement of the Dent du Marais landslide. Radionuclides and radiocarbon dating in Lake Tazenat suggest variable sedimentation rates over the last millennia due to: (i) floods during the Little Ice Age, (ii) coeval MWDs at the basin edges and an erosive turbidite in the central basin between AD 575 and 625 and (iii) lake eutrophication since AD 1945. More gravity cores are needed to directly sample and date the youngest generation of coeval MWDs detected on seismic profiles in order to test the impact in this lake of the cluster of major historical earthquakes in the FMC between AD 1450 and 1490 near the Limagne fault