At 1 p.m. on August 24, A.D. 79, it began. Nineteen hours later, the two wealthy Roman cities of Pompeii and Herculaneum were almost erased from history. Signs of the incoming blast included a minor earthquake and underground water sources running out a few days prior [source: Stewart]. A plume of smoke rocketed 20 miles (32 kilometers) into the air from Vesuvius' opening, spewing forth its blisteringly hot contents.
The only eyewitness to account the eruption, Pliny the Younger, compared the smoke shooting up from Mount Vesuvius to a pine tree. Soon, the city was engulfed in smoke and noxious gasses from the mountain. Although most people escaped Pompeii, at least 2,000 who stayed behind were crushed or buried alive in the ash and rock that rained from the sky that day.
On the other side of the mountain at the Bay of Naples, the seismic storm travelled to Herculaneum. In addition to clouds of ash and rock came a heat wave of almost 900 degrees Fahrenheit (482 degrees Celsius) [source: Lorenzi]. Many were able to escape the wrath of the volcano, but 80 bodies were found -- seemingly frozen in time -- killed instantly by extreme thermal shock.
The A.D. 79 eruption buried Herculaneum in 75 feet (22 meters) of ash, while Pompeii remained under about 9 feet (2.7 meters). Since the area surrounding Mount Vesuvius was uninhabitable for centuries following the explosion, the cities eventually drifted from history, until 1748. Because of the fine dust and the speed at which it fell, Pompeii in particular was for the most part preserved intact. Architectural elements, artifacts and the hundreds of bodies stood unchanged until their excavation.
What archeologists didn't know until more recently was that the famous eruption was not the first or the largest from Mount Vesuvius. About 3,780 years ago, it burst open with more power, converting thousands of miles of landscape into desert for more than 200 years [source: Than]. Referred to as the Avellino eruption, it evidently caught thousands of inhabitants by surprise as well -- archeologists discovered deeply embedded footprints in the surrounding area.
A 1631 eruption killed 4,000 people and destroyed six villages [source: Woods]. In modern times, only one minor eruption occurred in 1944, resulting in 26 fatalities. Although geologists today can predict the severity of the next eruption, they cannot pinpoint a date, making Mount Vesuvius a ticking time bomb.
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