Pockmarks, Mounds, and Microbial Activity in a Hydrothermal Lacustrine System: A Case Study from Pantelleria Island (Strait of Sicily)

Pockmarks are crater-like depressions formed by the expulsion of subsurface fluids (Hovland and Judd, 1988). While they are well documented in marine environments, they remain poorly characterized in lacustrine settings (Hovland et al. 2002). This study presents the first detailed morphological and geochemical investigation of over 100 pockmarks and approximately 200 mounded structures on the lakefloor of Bagno dell’Acqua, an alkaline lake located within the Cinque Denti Caldera on Pantelleria Island (Strait of Sicily). High-resolution bathymetry, sub-bottom seismic profiling, SCUBA observations, and gas geochemical analyses were integrated to assess the origin and distribution of these features. The pockmarks, predominantly elliptical and clustered in the lake’s western sector, exhibit signs of active or recent gas seepage and are associated with seismic anomalies such as gas chimneys and acoustic blanking zones. These features likely formed through the migration of biogenic methane and hydrothermal CO₂ emissions. Mounded features, concentrated in deeper lake sectors, are interpreted as gas-charged domes formed by sediment uplift and hydrothermal mineral precipitation, often associated with active bubbling and microbial mats. Gas analyses reveal a mixture of magmatic CO₂ and biogenic CH₄, highlighting the complex interplay of volcanic, sedimentary, and microbial processes. These findings highlight the role of lacustrine hydrothermal systems in fluid migration, microbial processes, and carbon cycling, and provide new insights into the geomorphological and geochemical evolution on Bagno dell’Acqua lake. Finally, the presence of active gas features also has implications for geohazard assessment in volcanic and tectonically active lake basins.