Beginning at around 1pm on 24 August, Mount Vesuvius sent gas, volcanic ash, and pumice into the stratosphere for up to 20 hours. This was followed by a pyroclastic flow that carried gas and molten rock down from the volcano and which then buried the previously fallen ash.

The belief was that God would intervene to protect Savonarola from the flames, but he and his opponents squabbled for so long that a rainstorm eventually led to the cancellation of the event.