Frequency and magnitude of rainfall-triggered debris-flows in Mont Dore valley, Sancy Massif (French Central Massif)

This study reconstructs more than a century of debris-flow (DF) activity in the Mont-Dore valley (Sancy Massif, Puy-de-Dôme department, French Central Massif) through dendrogeomorphology, and rainfall data analysis. Tree-ring records from 75 disturbed Silver firs ( Abies alba Mill.) reveal at least 16 DF events between 1900 and 2021, indicating a mean recurrence interval of approximately 7–8 years. DF event magnitudes, expressed as inundated areas on forested cone, ranged from 3600 to 31,500 m 2 , with ~10,000 m 2 events recurring on a decadal scale and higher magnitude events (>20,000 m 2 ) occurring at multi-decadal intervals. The temporal pattern shows an increase in DF frequency since the 1980s, consistent with a rise in high-intensity rainfall episodes. Meteorological analysis of the documented 1994 DF event suggests that precipitation exceeding 80 mm/day −1 act as a primary trigger, often following several weeks of dry conditions. These findings emphasize the combined influence of abundant volcaniclastic sediment supply and limited catchment area in sustaining recurrent DF activity. By linking long-term magnitude–frequency patterns with hydrometeorological forcing, this study provides one of the first quantitative reconstructions of debris-flow hazards in an inactive volcanic mountain environment in Europe. Our results offer valuable insights for hazard assessment, early-warning thresholds, and climate adaptation strategies in the Mont-Dore touristic valley.