Volcán Mentolat is an ice-filled 6-km-wide caldera in the central part of Magdalena Island across the Puyuhuapi strait from Puerto Cisnes. An eruption about 7000 years ago produced a pumice and scoria layer that extends to the SE. A young-looking andesitic lava flow on the W side of the volcano may be its most recent product. Historical reports by Serrano describe an eruption at the beginning of the 18th century that could refer to this lava flow.