A volcanic eruption occurs when molten rock, ash and steam pour through a vent in the earth's crust.
Some volcanoes explode.
Others are slow-flowing fountains of lava, which is hot fluid rock. The following are examples of famous volcanic eruptions. The eruption of Mount Vesuvius buried the towns of Pompeii and Herculaneum under 20 feet of ash and lava, killing an estimated 20,000 people. The ash that buried the town and the people also preserved them. The work of uncovering the ancient cities began in 1748 and continues to this day.