The definition of a volcano is discussed, and a new encompassing version is provided. The discussion focuses on the observations that volcanism is a self-similar process that ranges many orders of magnitude in space and time scales, and that all kinds of geologic processes act on volcanoes.

Former definitions of volcano, such as that from the Glossary of Geology (1997, p. 690)—“a vent in the surface of the Earth through which magma and associated gases and ash erupt” or “the form or structure, usually conical, that is produced by the ejected material” are clearly insufficient. All definitions that we encountered tend to consider volcanoes from the point of view of a single discipline, each of them neglecting relevant aspects belonging to other disciplines. For the two cases mentioned above a volcano is seen only from the point of view of eruptive activity or of morphology.

We attempt to look at volcano holistically to provide a more comprehensive definition. We define a volcano as a geologic environment that, at any scale, is characterized by three elements: magma, eruption, and edifice. It is sufficient that only one of these elements is proven, as long as the others can be inferred to exist, to have existed, or to have the potential to exist in the future.