occurred after 17 October. The volcano ejected a cloud of stones, ashes and volcanic gases to a height of , spewing molten rock and pulverized pumice at the rate of per second, ultimately releasing 100,000 times the thermal energy released by the Hiroshima-Nagasaki bombings. The cities of Pompeii and Herculaneum were destroyed by pyroclastic surges and the ruins buried under tens of metres of tephra. Precursors and foreshocks The AD 79 eruption was preceded by a powerful earthquake in 62, 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. The deaths of 600 sheep from "tainted air" in the vicinity of Pompeii indicates that the earthquake of AD 62 may have been related to new activity by Vesuvius. The Romans grew accustomed to minor earth tremors in the region; the writer Pliny the Younger even wrote that they "were not particularly alarming because they are frequent in Campania". Small earthquakes started taking place four days before the eruption becoming more frequent over the next four days, but the warnings were not recognized. Scientific analysis Reconstructions of the eruption and its effects vary considerably in the details but have the same overall features. The eruption lasted two days. The morning of the first day was perceived as normal by the only eyewitness to leave a surviving document, Pliny the Younger. In the middle of the day, an explosion threw 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, pyroclastic surges in the close vicinity of the volcano began. Lights were seen on the peak, 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. Additional light tremors accompanied these and a mild tsunami in the Bay of Naples. By late afternoon of the second day, the eruption was over, leaving only haze in the atmosphere through which the sun shone weakly. The latest scientific studies of the ash produced by Vesuvius reveal a multi-phase eruption. The initial major explosion produced a column of ash and