Mud volcanoes as natural laboratories for fluid-driven processes: a comparison between Nirano and Aragona (Italy)

This study presents a comparative analysis of the two key example of sedimentary volcanism in Italy: the mud volcanoes of Salse di Nirano (Northern Italy) and the Maccalube of Aragona (Sicily). Mud volcanoes are not related to magmatic activity but result from the ascent of gas, mainly methane, which transports mud, water and fine-grained sediments to the surface These systems represent natural laboratories for investigating subsurface fluid migration, gas-driven processes, and their surface expressions.

At both sites, mud and fluid samples were collected to perform geochemical, mineralogical, magnetic, and paleontological analyses, providing integrated constraints on fluid sources, sediment provenance, and mud volcano dynamics

Despite their apparent similarities, the two sites display markedly different genetic mechanisms and activity style. The study is carried out within the framework of the INGV-MUR project Pianeta Dinamico, called PROMUD.

The Nirano mud volcanoes are characterized by slow and persistent activity, forming small and stable mud cones and bubbling pools. This behavior reflects the compressional tectonic setting of the Northern Apennines, where fractures facilitate the upward migration of fluids and hydrocarbons. The extruded material mainly consists of ARGILLE SCAGLIOSE, the main constituent of the volcanoes, marly clays rich in CaCO₃, and Plio-Pleistocene clay sediments, while saline waters indicate an ancient marine depositional environment.

In contrast, the Maccalube of Aragona area exhibits highly variable and sometimes violent activity, with bubbling mud pools and sudden eruptive events. Here, the mud composition derives from poorly consolidate shallow clayey sediments, and methane is generated within organic-rich sediments. Brackish waters are likely derived from compaction processes of marine sediments.

The comparison highlights how similar fluid-driven process can produce contrasting surface features, levels of activity and hazard scenarios.