were covered in Volcanic ash and mud from the eruption of nearby Mt. Vesuvius.
By the 1st century, Pompeii was only one of a number of towns located around the base of Mount Vesuvius. The area had a substantial population which grew prosperous from the region's renowned agricultural fertility. Many of Pompeii's neighboring communities, most famously Herculaneum, also suffered damage or destruction during the 79 eruption, which is thought to have lasted about 19 hours, in which time the volcano released about 1 cubic mile (4 cubic kilometres) of ash and rock over a wide area to the south and south-east of the crater, with about 3 m (10 ft) of tephra falling on Pompeii.The white pumiceous ash associated with this eruption was mainly of leucite phonolite composition.
Foreshocks
The 79 eruption was preceded by a powerful earthquake seventeen years beforehand on 5 February 62<8>, which caused widespread destruction around the Bay of Naples, and particularly to Pompeii. Some of the damage had still not been repaired when the volcano erupted <9>. However, this may have been a tectonic event rather than one associated with the re-awakening of the volcano<10>.
Another smaller earthquake took place in 64; it was recorded by Suetonius in his biography of Nero<11>, in De Vita Caesarum, and by Tacitus in Book XV of Annales<12> because it took place whilst Nero was in Naples performing for the first time in a public theatre. Suetonius recorded that the emperor continued singing through the earthquake until he had finished his song, whilst Tacitus wrote that the theatre collapsed shortly after being evacuated.
The Romans grew used to minor earth tremors in the region; the writer Pliny the Younger writing that they "were not particularly alarming because they are frequent in Campania". In early August of 79, springs and wells dried up <13>. Small earthquakes started taking place on 20 August, 79<14>, becoming more frequent over the next four days, but the warnings were not recognised (it is worth noting the Romans had no word for volcano, and only a hazy concept of other similar mountains like Mount Etna, home of Vulcan), and on the afternoon of August 24, a catastrophic eruption of the volcano started. The eruption devastated the region, burying Pompeii and other settlements. By coincidence the date was the Vulcanalia, the festival of the Roman god of fire.
http://en.wikipedia.org/wiki/Mount_Vesuvius