Gravitational instability of submarine volcanoes offshore Campi Flegrei (Naples Bay, Italy)

Slope instability processes have sculpted numerous morphological features on the flanks of the submerged volcanoes in Naples Bay off Campi Flegrei. Geophysical data were used to define the time and spatial evolution of sediment failures. Four types of volcanic slopes were recognized: (1) highly inclined slopes with low-relief morphologic features resulting from shallow translational slump complexes; (2) highly inclined slopes with high-relief morphologic features associated with deep, rotational slump complexes; (3) highly inclined slopes corresponding to scars and slump deposition at the base on a subhorizontal surface; and (4) gently inclined slopes with a staircase morphology associated with shallow rotational slumps. All slumps occur immediately after the emplacement of the volcanoes with some of them remaining active for a long time after their formation. The volcanic landslides under study were characterized by different concomitant triggering factors (angle of slope margin, seismic activity, basement architecture, rapid sea-level changes, sea currents and high pore-fluid pressure) and featured volumes of up to 200 million m3. The identification of recurrent events of flank instability affecting submarine volcanoes should be considered when evaluating the potential risk that tsunamis pose to the densely populated Naples Bay coast.