There are three types of volcanoes: active volcanoes that have erupted recently and may erupt again like Kilauea in Hawaii and Arenal in Costa Rica; dormant volcanoes that are currently inactive like Mount Fuji in Japan; and extinct volcanoes that cannot erupt again like Anatahan volcano which surprisingly erupted in 2003 after being considered extinct. The document discusses Pompeii, an ancient Roman city that was buried and preserved under volcanic ash when Mount Vesuvius erupted in 79 AD, killing many residents. Underwater volcanoes can create new islands as they erupt, such as the Galapagos Islands off the coast of Ecuador which were formed underwater and still experience eruptions today.