The potential failure of Monte Nuovo at Ischia Island (Southern Italy): numerical assessment of a likely induced tsunami and its effects on a densely inhabited area

Ischia is the emergent top of a large volcanic complex that rises more than 1,000 m above the sea floor, at the north-western end of the Gulf of Naples. Caldera resurgence in the central part of the island has resulted in the formation of differentially displaced blocks, among which Mt. Epomeo (787 m a.s.l.) is the most uplifted. Deformation and slope instability have been recognised as common features induced by a block resurgence mechanism that causes uplift and favours gravitational loading and flank failure. The Monte Nuovo block, a topographic high on the north-western flank of Mt. Epomeo, has recently been interpreted as a block affected by deep-seated gravitational slope deformation. This block may undergo a catastrophic failure in the case of renewal of magmatic activity. This paper investigates the potential failure of the Monte Nuovo block as a rockslide-debris avalanche, the consequent tsunami generation and wave propagation, and discusses the catastrophic effects of such an event. Mobilization-prone volume has been estimated at about 160.10(6) m(3) and would move from a maximum elevation of 400 m a.s.l. The landslide itself would sweep away a densely populated territory as large as 3.5 km(2). The highest waves generated by the tsunami, on which this paper is mainly focussed, would hit the northern and western shores of Ischia. However, the high coast would prevent inundation and limit devastation to beaches, harbours and surrounding areas. Most of the tsunami energy would head towards the north-east, hitting the Campania coast. Severe inundation would affect an area of up to 20 km(2) around the mouth of the Volturno river, including the urban area of Castel Volturno. In contrast, less energy would travel towards the south, and the Gulf of Naples would be perturbed by long persisting waves of limited damaging potential.