<P> Reconstructions of the eruption and its effects vary considerably in the details but have the same overall features . The eruption lasted for two days . The morning of the first day, August 22, was perceived as normal by the only eyewitness to leave a surviving document, Pliny the Younger, who at that point was staying at Misenum, on the other side of the Bay of Naples about 30 kilometres (19 mi) from the volcano, which may have prevented him from noticing the early signs of the eruption . He was not to have any opportunity, during the next two days, to talk to people who had witnessed the eruption from Pompeii or Herculaneum (indeed he never mentions Pompeii in his letter), so he would not have noticed early, smaller fissures and releases of ash and smoke on the mountain, if such had occurred earlier in the morning . Around 1: 00 P.M., Mount Vesuvius violently erupted, spewing up a high - altitude column from which ash and pumice began to fall, blanketing the area . Rescues and escapes occurred during this time . At some time in the night or early the next day, August 23, pyroclastic flows in the close vicinity of the volcano began . Lights seen on the mountain were interpreted as fires . People as far away as Misenum fled for their lives . The flows were rapid - moving, dense, and very hot, knocking down wholly or partly all structures in their path, incinerating or suffocating all population remaining there and altering the landscape, including the coastline . These were accompanied by additional light tremors and a mild tsunami in the Bay of Naples . By evening of the second day, the eruption was over, leaving only haze in the atmosphere through which the sun shone weakly . </P> <P> Pliny the Younger wrote an account of the eruption: </P> <P> Broad sheets of flame were lighting up many parts of Vesuvius; their light and brightness were the more vivid for the darkness of the night...it was daylight now elsewhere in the world, but there the darkness was darker and thicker than any night . </P> <Table> <Tr> <Td> </Td> <Td> This section needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (August 2018) (Learn how and when to remove this template message) </Td> </Tr> </Table>

What caused the eruption of mount vesuvius in 79 ad