Pompeii: The Last Day – Youtube Video embedded here
On 24 August AD79, the sleeping giant Mount Vesuvius erupted with horrifying force, destroying the prosperous Roman cities Pompeii and Herculeneum.
Their inhabitants were subjected to 24 hours of untold horror. Four million tonnes of pumice, rock and ash rained on the towns, suffocating the life out of the cities, and burying alive those who had been unable to flee.
The animation shows eruption, and the processes leading up to the eruption, of a volcano. It explains that pressure of gases builds up underground until, eventually, it becomes so great that there is a violent explosion hurling dust and debris in to the sky and the surrounding area.
As the pressure is released the remaining gases in the magma (molten rock) cause lava to flow out and down the side of the volcano destroying everything in its path. Eventually the lava cools and forms a solid plug and the process begins again.