Today in the year 79, Mount Vesuvius, a volcano east of Naples, Italy, erupted. As a consequence, Pompeii and Herculaneum were buried, along with multiple other settlements.
When the volcano erupted, it put out a cloud of ash, stones and volcanic gas that was twenty-one miles high. It was so violent, the force of the explosion put out over a hundred thousand times more thermal energy than the Hiroshima and Nagasaki nuclear bombings combined.
The eruption claimed the lives of at least a thousand people. There is only one known eyewitness account of the eruption, written by Pliny the Younger in two letters to Tacitus, the historian.
Vesuvius is still an active volcano. It's the only volcano on mainland Europe that's erupted in the last hundred years. It is regarded as one of the world's most dangerous volcanoes.
There are roughly three million people that live within the blast zone, making it the most densely populated active volcanic area on Earth.