The Destruction of Pompeii    [Print whole story]

Pyroclastic flows
After about 12 hours of activity a change occurred that would be fatal to 1000s of people around Vesuvius. The volcano began to lose energy, but was still able to push out vast quantities of rock. Instead of flying up into the sky and dispersing over a wide area, this rock immediately fell back onto the upper slopes of the volcano.

The eruption column, or cloud, was said to be collapsing. As the rock gathered on the upper slopes of Vesuvius it began to surge down the volcano as a terrifying, glowing avalanche called a pyroclastic flow.

The first flow hit the town of Herculaneum, to the north, at about 1am on the 25th August. Hundreds of Herculaneum residents had gathered at the beach to escape the flows but were trapped in their boat houses and killed instantly by heat and suffocation.