Volcano

A volcano is a rupture on the crust of a planetary mass object, 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... This type of volcanism falls under the umbrella of "plate hypothesis" volcanism. Volcanism away from plate boundaries has also been explained as mantle plumes. These so-called "hotspots"... 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 aircraft, 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 Earth's lower atmosphere (or troposphere); however, they also absorb heat radiated up from the Earth, thereby warming the upper atmosphere (or stratosphere). Historically, so-called volcanic winters have caused catastrophic famines. [Volcano. Wikipedia]