GIS-based sinkhole susceptibility mapping in a karst mountain environment: the Vallepietra area and the Holy Trinity Sanctuary (Monti Simbruini, Central Italy)

This study aims to identify areas with high susceptibility to natural sinkholes within a park area of the Municipality of Vallepietra (Rome), surrounding the Sanctuary of the Holy Trinity, a site of significant cultural and religious value and a destination for approximately 500,000 pilgrims per year. The area has been affected by collapse and landslide phenomena, which appear to be associated with intense karst processes. The genesis of sinkholes in the study area is strictly related to karstification, which is amplified and/or triggered by seismic events, as well as by additional factors linked to anthropogenic activities and uncontrolled infiltration, cause the presence of abundant springs and aqueducts. The analyses indicate that ensuring the safety of the Sanctuary requires multidisciplinary interventions based on a multi-risk assessment approach that considers the interaction among geological, geomorphological, and hydrogeological processes. Within an area of 160 km², 215 relict karst landforms were inventoried and georeferenced, supported by three field surveys at Monte Autore (1,669 m a.s.l.). The integration of all datasets within a GIS environment and their use in predictive modelling, through correlations with morphological, geological, and tectonic predictors, allowed the production of a first sinkhole susceptibility map for the Vallepietra area. Five karst depressions were analyzed in detail above the Sanctuary: three solution sinkholes and two rock-collapse sinkholes. Additionally, five hypogeal karst environments were identified beneath the Sanctuary, partly modified by anthropogenic activity. These features represent a critical element due to intense water infiltration, which may induce sudden roof-collapse phenomena directly beneath the structure. Anthropogenic activities, meteorological events, and seismic activity may act as triggering factors for further collapse events.