Editing Pyroclastic flow (section)

==Causes==
{{Unreferenced section|date=March 2018}}
Several mechanisms can produce a pyroclastic flow:

* ''Fountain collapse'' of an [[eruption column]] from a [[Plinian eruption]] (e.g. [[Eruption of Mount Vesuvius in 79|Mount Vesuvius' destruction of Herculaneum and Pompeii]] in 79 AD). In such an eruption, the material forcefully ejected from the vent heats the surrounding air and the turbulent mixture rises, through [[convection]], for many kilometers. If the erupted jet is unable to heat the surrounding air sufficiently, convection currents will not be strong enough to carry the plume upwards and it falls, flowing down the flanks of the volcano.{{fact|date=January 2025}}
* ''Fountain collapse'' of an eruption column associated with a [[Vulcanian eruption]] (e.g., [[Montserrat]]'s [[Soufrière Hills]] volcano has generated many of these deadly pyroclastic flows and surges). The gas and projectiles create a cloud that is denser than the surrounding air and becomes a pyroclastic flow.
* Frothing at the mouth of the vent during degassing of the erupted lava. This can lead to the production of a rock called [[ignimbrite]]. This occurred during the eruption of [[Novarupta]] in 1912.
* Gravitational collapse of a [[lava dome]] or spine, with subsequent avalanches and flows down a steep slope (e.g., Montserrat's Soufrière Hills volcano, which caused nineteen deaths in 1997).
* The [[Lateral eruption|directional blast]] (or jet) when part of a volcano collapses or explodes (e.g., the [[1980 eruption of Mount St. Helens|eruption of Mount St. Helens on May 18, 1980]]). As distance from the volcano increases, this rapidly transforms into a gravity-driven current.