The “Piscine” coastal depressions of the southern Pontine Plain (Central Italy): evidence from historical cartography and GIS analysis

Valerio Vitale¹, Sergio Madonna², Stefania Nisio¹ & Aldo Annunziatellis^3
1ISPRA - Dip. Servizio Geologico d'Italia, Via V. Brancati 48, 00144 Roma.
²University of Tuscia, Via S. Camillo de Lellis snc, 01100 Viterbo.
³ISPRA - Dip. per il monitoraggio e la tutela dell'ambiente e per la conservazione della biodiversità, Via V. Brancati 48, 00144 Roma.
Corresponding author e-mail: valerio.vitale@isprambiente.it

A multidisciplinary analysis was conducted of numerous surface depressions termed Piscine, exhibiting subcircular morphology. These landforms, which characterized the southern sector of the Pontine Plain (Central Italy), have been documented in historical maps since the eighteenth century, and remain of uncertain origin. To investigate their genesis, bibliographic sources, historical cartography, and geognostic data were integrated to reconstruct the geological and stratigraphic settings in which these depressions developed. These landforms were digitized from pre-reclamation maps and analyzed to explore their distribution patterns and relationships with selected subsurface variables. The results indicate that the depressions are primarily located in areas characterized by outcropping ancient coastal dune sands and display distinct spatial patterns. A consistent spatial correlation was identified between depression density and peat deposit thickness, whereas no clear relationship was observed with fault density. These findings suggest that compaction processes affecting peat-rich sediments, which lead to differential subsidence of overlying deposits, may be a mechanism for depression formation. However, owing to data limitations, alternative processes (piping-related sinkhole activity or dissolution of continental carbonate rocks), cannot be entirely excluded. Further detailed geognostic investigations are required to refine the interpretation and improve the understanding of the subsurface controls governing the development of these landforms.

coastal depressions, piping sinkholes, historical cartography, peat collapse, Pontine Plain.