A new type of volcano flank failure: The resurgent caldera sector collapse, Ischia, Italy

This study is the first description of recurrent and rapid lateral failure of the resurgent portion of a caldera complex. The sliding planes and the characteristics of debris avalanche deposits resemble those of cone sector collapses, but the main triggering mechanism proposed at Ischia caldera (Italy) is related to intermittent resurgence. During the last 33 ka, the increase in resurgence rate produced major collapses southward due to three main mechanisms that contributed to an increase in shear stress: i) magma-driven uplift, which produced increase in static loading, ii) faulting and associated deformation, which induced tilting and steepening of the original layering, and iii) earthquake shaking due to coseismic faulting. The largest episodes of flank failure occurred in the interval 8.6-5.7 ka BP. These were followed by magma eruption and a decrease in the resurgence rate. Recognition of this phenomenon is particularly important in recent/active calderas located near the coast, as it can trigger tsunamis.