Slope stability monitoring system via three-dimensional simulations of rockfalls in Ischia island, Southern Italy

Volcanoes are dynamically active systems in continuous evolution. This behaviour is emphasized by many different processes, e.g., fumarolic activity, earthquakes, volcanic slope instabilities and volcanic climax eruptions. Volcanic edifices experience slope instability as consequence of different solicitations such as i) eruption mechanism and depositional process, ii) tectonic stresses, iii) extreme weather conditions; all these events induce the mobilization of unstable fractured volcanic flanks.

Several methods exist to gather information about slope stability and to map trajectories followed by individual falling rocks in individual slopes. These methods involve direct field observation, laser scanning, terrestrial or aerial photogrammetry. Such information is useful to infer the likely location of future rockfalls, and represent a valuable input for the application of three-dimensional models for rockfall trajectories.

The Ischia island is volcano-tectonic horst that is a part of the Phlegrean Volcanic District, Southern Italy. It covers an area of about 46 km² and it has experienced a remarkable ground uplift events due to a resurgence phenomenon. Slope instability is correlated both with earthquakes events and with volcanism phenomena. Specifically, evidences suggest that rockfalls occurred as an effect of the gravitational instability on the major scarps generated by the rapid resurgence, eased by the widespread rock fracturing.

We present results of an analysis relevant to the most probable individual masses trajectories of rockfall affecting the slopes of Ischia island. We first identified the prospective rockfall sources through an expert-mapping of source area in sample locations and statistical analysis on the whole island. Probabilistic sources are the main input of the three-dimensional rockfalls simulation software STONE.

The software assumes point-like masses falling under the sole action of gravity and the constraints of topography, and it calculates trajectories dominated by ballistic dynamics during falling, bouncing and rolling on the ground. Analysis of high-definition critical sector pictures, achieved by using UAV (Unmanned Aerial Vehicle) platform, will allow a detailed localization of source areas and an additional more robust simulations.

The procedure can be viewed as a multiscale analysis and allows besting allocating computational efforts and economic resources, focusing on a more detailed analysis on the slopes identified as the most risky ones during the first, large-scale analysis of the whole area.