Mount Vesuvius was only 9 kilometres away from Pompeii and 7 kilometres from Herculaneum. In 79 CE, local people did not see the volcano as a threat because it had not been active within living memory. On 24 August that year, however, Mount Vesuvius unexpectedly erupted. It was a massive eruption, lasting up to 24 hours and consisting of two phases. During the first phase, the volcano spewed huge clouds of ash and pumice (light volcanic rock) high into the sky. The wind blew these clouds towards Pompeii, depositing a layer about 2.5 metres thick across the town.