Modelling Erosion and Floods in Volcanic Environment: The Case Study of the Island of Vulcano (Aeolian Archipelago, Italy)

Abstract

The re-mobilization of volcaniclastic material poses a hazard factor which, although it decreases with time since the last eruption, remains present in the hydrographic basins of volcanic areas. Herein, we present the results of the numerical modelling of erosive phenomena of volcanic deposits, as well as of flooding in the volcanic area. The proposed approach includes runoff estimation, land use analysis, and the application of hydraulic and erosion modelling. It exploits the Iber software, a widely used and validated model for rainfall-runoff, river flooding, and erosion and sediment transport modelling. The methodology was applied to the Island of Vulcano (Italy), known for the erosion phenomena that affect the slopes of one of its volcanic cones (La Fossa cone). The rainfall excess was calculated using a 19-year dataset of hourly precipitations, and the curve number expressed by the information on soil cover in the area, derived from the land cover and land use analysis. The erosion and flow models were performed considering different rainfall scenarios. Results show a particularly strong erosion, with thicknesses greater than 0.4 m. This is consistent with field observations, in particular with some detailed data collected both after intense events and by long-term observation. Results of the hydraulic simulations show that moderate and torrential rainfall scenarios can lead to flood levels between 0.2 and 0.6 m, which mostly affect the harbours located in the island’s inhabited area.

The last 1100 years of activity of La Fossa caldera, Vulcano Island (Italy): new insights into stratigraphy, chronology, and landscape evolution

“…The lava flow in question acted as a natural barrier, resulting in the constriction of sediment-laden water flow (i.e., debris floods) to a narrow area, thereby channeling the sediments towards Ponente Harbour. The diagram features primary flow lines, distinguished in blue, derived from Bonasia et al ( 2022 ). In e , stratigraphic logs corresponding to panels a , b , and c are shown …”

“…14 c) whereas the entire watersheds of the island became sealed with very fine-grained, cohesive ash, with abundant clay minerals of hydrothermal origin (Capaccioni and Coniglio 1995 ). VT had hydraulic characteristics of making the surface impermeable and resistant to erosion, with a following catastrophic increased runoff, exacerbating erosion and transport downstream towards the Porto plain volcano of both fine ash and ancient deposits (Bonasia et al 2022 ). During this phase, the coastline and in particular that at the foot of the Lentia ridge rapidly migrated northwards.…”

“…Since then, the caldera, which hosts an important hydrothermal system (Fulignati et al 1998 ), has experienced several periods of unrest, the last one starting in August–September 2021 and still ongoing at the time of writing (September 2023), which culminated in a partial evacuation of the island because of strong degassing increase in inhabited areas (Aiuppa et al 2022 ; Di Traglia et al 2023 ). All these factors, combined with the remarkable vulnerability of the island due to uncontrolled urban development over the past 70 years and a significant seasonal variation of the exposed population, result in a high volcanic risk (Galderisi et al 2013 ; Biass et al 2016a , b ; Bonadonna et al 2022 ; Bonasia et al 2022 ). For these two main reasons (high risk and state of unrest), an improved assessment of the eruptive history and volcanic hazards has become fundamental and timely.…”