Pompeii and Herculaneum Notes The Eruption Portents of the eruption: ● The major earthquake of 62 CE likely to have been a sign that the volcano was becoming active after a period of dormancy ● From midAugust up to the 24th there were: A series of tremors of increasing frequency and strength Large waves off the coast Signs of disturbance in animals Drying up of springs and wells as the volume of gas in the crater increased Minor steam explosions caused by the interaction of magma and ground water, leading to the showering of fine ash over the slopes of Vesuvius Sources for the Eruption: ● Written account of Pliny the Younger, resident at Misenum, who used the accoutns of others present with his uncle on the beach at Stabiae to substantiate and expand on his own impressions ● Evidence of deposits from the buried cities, studied by forensic archaeologists ● Studies by volcanologists, using these sources, evidence from other volcanic explosions, and their knowledge of geological phenomena ● Cooley: “the nature of the eruption governed both what was left behind for archaeologists to dig up, and how it was sealed by the deposits of the volcano” Stages of the Eruption ● Two phases: Plinian eruption (named for the account provided by Pliny in his letters) Pelean eruption (named for Mt Pelee on Martinique, which erupted and killed 30,000 people in 1902) ● Plinian eruption characterised by a vast ash cloud and the depositing of thousands of tons of pumice and ash over a wide area to the south and east of Vesuvius ● This phase of the eruption lasted from noon on the 24th August until early the next morning when the Pelean phase began ● Pelean eruption characterised by six devastating pyroclastic density currents that overwhelmed first Herculaneum and then Pompeii Plinian Phase: ● Cloud of gas, ash, pumice and the lithic lining of Vesuvius that was carried by the prevailing wind over a large area (including Pompeii and Oplontis) but not over Herculaneum ● After 6 hours buildings began to collapse under the weight of the deposits
● By the early hours of the 25th, 150,000 tonnes of matter was being discharged every second, and carried 30 Kms into the air ● The absence of horses and other beasts of burden (and the fact that only 324 bodies or cavities have been discovered) at Pompeii indicates that most of the approx. 10,000 inhabitants fled during the early phase Plinian phase ● The absence of boats on the beach at Herculaneum indicates that many residents must have fled during the early Plinian phase Pelean Phase: ● Between 1:00 and 2:00 am on the morning of August 25th, the first two of six pyroclastic current deposits (or pyroclastic surges and flows) swept down over Herculaneum and areas to the South and West of Vesuvius ● Two distinct parts: Superheated gases and ash (100 400 degrees celsius) travelling at 200 km/h Ground hugging liquid flow with larger deposits, travelling at 80 km/h ●
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