Mt. St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is most famous for its catastrophic eruption on May 18, 1980, which was the deadliest and most economically destructive volcanic event in the history of the United States. The volcano is part of the Cascade Volcanic Arc, a segment of the Pacific Ring of Fire that includes over 160 active volcanoes.