Grotta dell'Alume

Grotta dell'Alume is an Italian volcanic cave associated with active fumaroles. Fumarolic gases historically deposited alum and sulfur minerals on parts of the cave interior.

The name refers to alum, a mineral material that accumulated through volcanic alteration and fumarolic activity. Alum from volcanic areas was historically valuable for uses such as dyeing and tanning.

The cave is described as having active fumaroles, meaning volcanic gas and heat remain part of its character. That makes it a geologically active site rather than an ordinary limestone cave.

Alum and sulfur are the best-known mineral deposits associated with the cave. The deposits formed directly along walls and surfaces affected by hot volcanic gases.