Volcanoes are openings in a planet's surface where hot, molten (melted) rock, ash and gas escape from below the surface. Most volcanoes occur along subduction zones where ocean plates collide and dive beneath the continental plates.
The Pacific Ring of Fire is an area where large numbers of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean and as the ocean plates are colliding with the continental plates.
The word ‘volcano’ comes from the Ancient Romans who named the violent and destructive events and resulting mountains after their fire god Vulcan. Vulcanology is the study of volcanoes, and vulcanologists are the scientists that study volcanoes.
The Greek philosopher Empedocles, who described the world as being divided into four elemental forces of Earth, Air, Fire and Water, maintained that volcanoes were the manifestation of Elemental Fire. BTW- legend has it that Empedocles threw himself into Mt. Etna.
Super eruptions locations include Lake Taupo (NZ), Lake Toba and Tambora (Indonesia), Yellowstone (WY), La Garita Caldera (CO), and Valles Caldera (NM).
The Decades Volcano* project lists sixteen volcanoes as worthy of close watching because of their history of large, destructive eruptions and proximity to populated areas.