Mount St. Helens erupted on May 18, 1980. The volcano, located in southwestern Washington, used to be a beautiful symmetrical cone about 9,600 feet (3,000 meters) above sea level. The eruption, which removed the upper 1,300 feet (396 meters) of the summit, left a horseshoe-shaped crater and a barren wasteland. Today the land is healing, having recovered its natural beauty, but the landscape has been permanently altered.
Native Americans in the Pacific Northwest called the mountain "Louwala-Clough" or "Smoking Mountain." The modern name came from Capt. George Vancouver of the British Royal navy, who named it in honor of Alleyne Fitzherbert, the British Ambassador to Spain, who also held the title Baron St. Helens.
The volcano was relatively active in the early 19th century, and may have had a major explosive eruption in 1800, according to the Mount St. Helens Forest Learning Center. There were minor eruptions in 1898, 1903 and 1932, but for most of the 20th century, the mountain was seen as a peaceful, beautiful mountain and recreation area. That serenity was shattered in 1980.
source: Livescience.com