Le Salse di Nirano (Fiorano Modenese, Modena - Italy), mud volcanoes.
A geological phenomenon that originates where fundamentally gaseous hydrocarbon deposits, particularly methane, come into communication with the surface through cracks in the roof of the deposit: the gas leaks out pushing and carrying upward the salty waters associated with the gaseous deposit. The dissolved clays brought to the surface deposit around the opening, creating the typical cones. The Salse, emissions of salty muds, are mistakenly considered pseudo-volcanic in nature. While this is not the only site of this phenomenon in Italy, it is undoubtedly the most important. (source)
The word “salsa” does not mean “sauce” but “salted”, referring to the salty clay soil. Inside the cones, mud seems to boil because of hydrocarbons bubbles, which are actually emitted at ambient temperature.