Fault scarp degradation along the avalanche volcanic complex in French Massif Central

The degradation of fault scarps along the avalanche volcanic complex and collapses are rarely studied in relation to the climate changes. During intense rainstorms, reworked avalanche deposits can be transformed into high-velocity debris flows, which represent a subsequent hazardous flow. This study investigates the relationships between the spatial distribution and the morphological data of the fault scarp degradation associated with retrogressive avalanche surfaces observed along 50 well-exposed surfaces in the Cantal and Mont-Dore volcanoes and 23 craters in the Chaîne des Puys volcanic field in the French Massif Central. From field observations, the Lidar data, and precise topographic maps, a semi-quantitative analysis helps correlate the avalanche mobility, height, and slope gradient of the collapsed edifices. To provide complementary information about the avalanche fault zone, we focused on the run-out distance, the ratios of the vertical drop with run-out distance, and flow area. Few correlations are established between spatial distributions, climatic change, and morphological variations of avalanche surfaces. The run-out distance, the ratios of the vertical drop with run-out distance, and flow area are constrained by the elevation and slope gradient of the collapsed edifices. Erosion, nival surface conditions, and high-intensity rainstorms constrained the debris avalanche mobility and the transformation into debris flow. These results provide information about the fault scarp degradation along the volcanic complex and gravitational collapse leading to fluidization during intense rainfall episodes, related to the effects of regional climate change.