Hot lava, volcanic ash, and gases can escape from a magma chamber below the surface through a volcano, which is a rupture in the crust of a planet-mass object like Earth.

Volcanoes are most prevalent underwater and occur most frequently where tectonic plates are diverging or converging. Volcanoes on a mid-ocean ridge, like the Mid-Atlantic Ridge, are the result of divergent tectonic plates, whereas volcanoes on the Pacific Ring of Fire are the result of convergent plates. As in the East African Rift, the Wells Gray-Clearwater volcanic field, and the Rio Grande rift in North America, stretching and thinning of the crust’s plates can also result in volcanoes.

Volcanism away from plate limits has been hypothesized to emerge from upwelling diapirs from the center mantle limit, 3,000 kilometers (1,900 mi) somewhere down in the Earth. Hotspot volcanism, such as the Hawaiian hotspot, is the result of this. When two tectonic plates slide past one another, volcanoes rarely form.

As ash and sulfuric acid droplets obscure the Sun and cool the Earth’s troposphere, large eruptions can change the temperature of the atmosphere. All things considered, enormous volcanic emissions have been trailed by volcanic winters which have caused devastating starvations.