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Tavurvur, an active stratovolcano near Rabaul in Papua New Guinea. Credit: Taro Taylor edit by Richard Bartz.


1. An opening or vent in Earth’s crust, through which hot gases, lava, and ash are discharged during the time the volcano is active (an eruption). A volcano may be described as active, dormant, or extinct. About 500 volcanoes around the world are known to be active. 2. A cone-shaped hill or mountain built up around a volcanic vent by lava and ashes. 3. A similar structure found on other planets such as Mars, or found on moons such as Io, a satellite of Jupiter that has at least eight active volcanoes. [Volcano honors Vulcan, the Roman god of fire and metal-working.]