Volcano

A volcano is a vent or fissure in the crust of a planetary body through which hot lava, volcanic ash and gases escape from an underlying magma chamber. Most of Earth's volcanoes form along tectonic plate boundaries, appearing where plates diverge, as along the Mid-Atlantic Ridge, or converge, as around the Pacific Ring of Fire; divergent volcanism is usually non-explosive while convergent volcanism produces violent eruptions. Volcanoes can also form where crust stretches and thins, as in the East African Rift, or away from plate boundaries entirely through mantle plumes rising from roughly 3,000 kilometers deep within the Earth, producing hotspot volcanism such as the island chain built by the Hawaiian hotspot. Volcanoes rarely form at transform boundaries, where plates slide past one another rather than converging or diverging.