The mud boils in the barren expanse which occupies part of the valley formed by the Miscano river near Montecalvo Irpino.

 The presence of methane and other gases in the volcanic subsoil produces small volcanoes of mud continuously changing and are known as, in fact, Bolle (Baubles) della Malvizza. An open-air scientific laboratory, where greenhouse gas effects are studied and some new bacteria have been discovered.