Type: Composite volcano
When southern Italy's Vesuvius suddenly came alive on August 24, A.D. 79, no one was prepared. The volcano had been dormant for centuries and didn't give any warnings of the catastrophic explosion to come.
But in just a few hours after it roared to life, Vesuvius's hot volcanic ash and dust had completely buried the Roman towns of Pompeii and Herculaneum. Their ruins were not discovered for more than 1,600 years.
Scientists estimate that the eruption sent a column of ash 20 miles (32 kilometers) into the sky. Then the column suddenly collapsed. Roughly ten feet (three meters) of tephra, or fragments of volcanic rock and lava, hit Pompeii. Everything was buried, except the roofs of some buildings.
In the next stage of the eruption, a superhot river of steam and mud rushed down the volcano's slopes and into the seaside town of Herculaneum, traveling four miles (seven kilometers) in about four minutes.
Victims there died so quickly from the intense heatabout 930°F (500°C)that they did not even have time to raise their hands in self-defense, Italian archaeologists say.
When archaeologists excavated the forgotten town of Pompeii, beginning in the 19th century, they found much of it preserved by the hot ash. By pouring plaster into the hollows left in the hardened ash by decomposed bodies, excavators made macabre body casts. The molds revealed the volcano's victims frozen at the instant of death.
A relatively young volcano, Vesuvius formed probably fewer than 200,000 years ago when the African and Eurasian plates collided in a subduction zone.
Today more than two million people live on and around Vesuvius, still considered a dangerous and potentially deadly volcano.