Investigation and preliminary assessment of the Casamicciola landslide in the island of Ischia (Italy) on November 26, 2022

Active volcanic environments, due to their rapid processes of growth and deformation, can be considered a typical setting for the formation of both subaerial and subaqueous gravitational instabilities. Occasionally, such conditions - coupled with heavy rainfalls or earthquakes - can trigger sudden and rapid mass movements such as mud-debris flows and/or debris avalanches, representing serious hazards for human settlements.

The active volcanic island of Ischia is localized within the Gulf of Naples and its complex volcanism began prior to 350ka and continued, with centuries to millennia of quiescence, until the last eruption occurred in the historical period (AD 1302). 56ka a caldera-forming eruption occurred, followed by a resurgence process that has affected the caldera floor and generated a net uplift of about 900m since 33ka. Thus, the main morphostructural feature is the Mt. Epomeo resurgent block.

From a geological point of view, the island is composed of volcanic rocks, epiclastic deposits, and terrigenous sediments, demonstrating an alternation of constructive and destructive phases. In this context, the continuous occurrence of landslides on the island, even causing death to humans, is historically documented. In the last decades, the risk has been greatly exacerbated by the high level of human exposure due to not properly planned urban development.

On November 26, 2022, as a consequence of heavy rainfall, diffuse landslide events occurred along the island, the main of which affected a small catchment basin in the vicinity of an urban settlement within the Casamicciola Municipality. The area affected by the landslide events is located along the northern slope of Mt. Epomeo. On the summit, Mt. Epomeo is characterized by the strongly weathered Green Tuff Formation. The generated debris flow affected about 30 buildings causing 12 casualties, 5 injured, 230 people displaced, and severe damages to roads and properties. It should be pointed out that the maximum occurred rainfall - recorded by the local weather station - for durations from 1 to 24 hours are all higher than the corresponding maximum values recorded in the years 2007÷2021.

The present work shows the first outcomes, in terms of landslide types, volumes, extent, etc., from a preliminary multidisciplinary investigation carried out immediately following the event by using desk research, on-field survey, geomorphological mapping, remote sensing, and numerical modeling.