About 130 volcanic vents belong to the field, whose activity began 1.5million years ago and continued into the Holocene. Three major caldera-forming eruptions took place in the volcanic field prior to the last glacial period. Postglacial volcanic activity has included eruptions with simultaneous explosive and effusive components, as well as eruptions with only one component. The most recent eruptions in the volcanic field took place 2,500 ± 700, 1,400 ± 600 and 800 ± 600 years ago and generated lava flows; today geothermal phenomena occur at Laguna del Maule. Volcanic rocks in the field include basalt, andesite, dacite and rhyolite; the latter along with rhyodacite makes up most of the Holocene rocks. In pre-Colombian times, the field was a source of obsidian with regional importance.