Volcanos

A volcano is a mountain that forms as lava flows through a crack onto Earth's surface.

Mount St. Helens, Washington, is the most active volcano in the Cascade Range. Its most recent series of eruptions began in 1980 when a large landslide and powerful explosive eruption created a large crater, and ended 6 years later after more than a dozen extrusions of lava built a dome in the crater. Larger, longer lasting eruptions have occurred in the volcano's past and are likely to occur in the future. Although the volcano seems to have returned to a period of quiet, scientists with the U.S. Geological Survey and University of Washington Geophysics Program continue to closely monitor Mount St. Helens for signs of renewed activity.  Written by U.S. Geological Survey.

Pompeii an ancient Roman city on the Bay of Naples 15 miles (24 km) southeast of Naples near the southern foot of Mount Vesuvius. In the eruption of Vesuvius in 79 A.D. Pompeii was buried in volcanic rock and ash. Its existence was completely forgotten within a few generations. The site was discovered in the 18th century and excavations were begun. Because it had lain undisturbed and protected from the elements since the time of the disaster, Pompeii gave the world its most precise knowledge of how a Roman city looked and how its inhabitants lived. Written by How Stuff Works.