Plinian spine

A Plinian spine is one of the two main explosive regimes, the other being pyroclastic flow.

In a Plinian spine, the mixture of gas and fragments of magma takes in enough air to become lighter than the atmosphere: it is then propelled by Archimedean thrust and forms an atmospheric column that can reach a very high altitude in the atmosphere (several tens of kilometres, i.e. up to the stratosphere).

In the case of a Plinian spine, the erupting column ejects fragments of magma and volcanic gases to very high altitude where the stratospheric winds disperse them over a very wide area. On the ground, the result is a rain of ash which is unpleasant and bad for the health but not fatal. This is not the case of pyroclastic flow ...

Although these two regimes are well defined, things are more complicated in practice. Eruptions sometimes change from one type to the other (like the famous eruption of Vesuvius in the year 79 AD) and are often in an intermediate regime with the two types of flow co-existing. And this is what makes these eruptions particularly dangerous ...