Volcano



A volcano is a rupture on the crust of a celestial object or planet, such as the Earth, which allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.

Earth's volcanoes occur because the planet's crust is broken into 17 major, rigid tectonic plates that float on a hotter, softer layer in the Earth's mantle. Therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging. Volcanoes can also form where there is stretching and thinning of the crust's interior plates, e.g., in the East African Rift and the Rio Grande Rift in North America.

Erupting volcanoes can pose many hazards, not only in the immediate vicinity of the eruption. One such hazard is that volcanic ash can be a threat to fliers, in particular those with jet engines where ash particles can be melted by the high operating temperature; the melted particles then adhere to the turbine blades and alter their shape, disrupting the operation of the turbine. Large eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the lower atmosphere (or troposphere); however, they also absorb heat radiated up from theplanet,  thereby warming the upper atmosphere (or stratosphere). Historically, so-called volcanic winters on Terra have caused catastrophic famines.