Our story today takes us nearly two millennia back, to the first century when the Roman Empire was in power. The ancient cities of Pompeii and Herculaneum were established in the shadow of Mount Vesuvius at the Bay of Naples.
Both the cities were still recovering from earthquakes, which originated beneath Vesuvius, that had damaged much of their infrastructure. Vesuvius, that stood at nearly 6500 feet, was however not known to be an active volcano then. So when several minor quakes shook the earth beneath the two cities a decade after these earthquakes, the natives didn’t pay much attention to it. Only, this time, Vesuvius was going to end centuries of dormancy.
Mount Vesuvius exploded after noon on August 24, 79 AD, with clouds of ash and pumice blasting off miles into the stratosphere. With the people unprepared for the event and experiencing something unheard of, the damages were bound to be large.
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Within an hour, ash blocked out the sun in Pompei. While Herculaneum was protected by winds during the initial stages of the explosion, a giant cloud of ash and gas later engulfed the city, burning or asphyxiating (dying by being deprived of air) those who remained.
Even though a few thousands are believed to have survived the first night, a second more powerful eruption the following day killed almost everyone in an instant. A flow of rock and ash, mixing with the rain to form a sort of concrete, buried Pompei. Mudslides set off by the eruptions along with accompanying tremors buried Herculaneum as well. This meant that for centuries, after which these cities were finally excavated, the details of the dead and their civilisation were carefully preserved.
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Through the letters of Pliny
While excavations in the last few centuries gave us a glimpse of the damage and life before it in these sites, much of what we know about the eruption is from what was written by Pliny the Younger. The nephew of Pliny the Elder, who was a Roman official and scholar of scientific matters, Pliny the Younger was at Misenum when the eruption took place.
Pliny the Elder is believed to have dispatched ships from his fleet immediately to investigate the issue. Pelted by rocks from the volcano, they could not make a landing, and by August 25, Pliny the Elder died, due to sulphur gases from the volcano.
Pliny the Younger, who was still in his teens, wrote detailed accounts of what he saw in letters to his friend and historian Tacitus. Watching from the town of Misenum, he also interview survivors, before escaping the catastrophe along with his mother. He went on to become a Roman writer and administrator.
Large explosive events that produce plumes of ash that form enormous dark columns of gas and tephra high into the stratosphere are therefore known as Plinian or Vesuvian explosions. The ash in these cases ascends over 11 km and up to 45 km into the stratosphere - much higher than even the freefall altitude record that Joseph Kittinger had set.
ganesh.a.s@thehindu.co.in