Experiments on vertical basement fault reactivation below volcanoes

Scaled modeling has been conducted to study the role played by the reactiva tion of vertical basement faults in the destabilization process of overlyin g volcanoes. Results show that basement fault reactivation induces the form ation of faults within the volcanic edifice. These faults delimits a centra l block which is extruded from between the two undeformed lateral parts of the edifice, Collapse of this central block can occur when heterogeneous co nes are used in experiments, revealing that mechanical interfaces are of pa ramount importance in triggering rockslide avalanches. Collapse structures may display horseshoe shapes in map view and are then surprisingly similar to avalanche scars resulting from failure created by magmatic intrusions in natural volcanoes. Large-scale destabilisation of half the surface of the cone may also occur in a single event depending on the position of the reac tivated basement fault below the edifice. It is emphasized that the process under consideration may occur on a dormant volcano as well, provided that a fault is reactivated below it.