At 8:32 a.m. on May 18, 1980, Mount St. Helens, a stratovolcano located in southwestern Washington State, erupted, causing extensive damage and loss of life. To mark the anniversary of this catastrophic event, we've put together these trivia questions...
What Events Led Up to the Eruption?
As with most volcanoes, Mount St. Helens gave some advance warning that an eruption was likely well before the actual event. Beginning in March 1980, seismic activity at the mountain offered a hint that the volcanic peak might once again be active. On March 20, 1980, an earthquake with a magnitude of 4.2 on the Richter Scale was recorded. Over the two days of March 23 and 24, an ominous series of 174 mini-tremors was recorded by seismologists. Then, on March 27, the first actual eruption occurred when ash soared up to 10,000 feet in the air after the opening of a 250-foot-wide vent on the mountain's top. Ash from this first eruption fell on the streets of Spokane, which lies about 300 miles northeast of Mount St. Helens.
Fearful that more was soon to come, authorities posted a hazard watch covering an area within a 50-mile radius of the mountain. Some residents were evacuated from the area, but others refused to budge. A bulge on the north side of Mount St. Helens grew progressively larger throughout the month of April, and on the morning of May 18 a 5.1 earthquake and an eruption shook the mountain and the surrounding region. Ash was propelled from the volcano at a speed of 650 miles per hour, and a wave of ash, gas, glacial ice, and rocks poured down the sides of the mountain into the surrounding valley.
How Much Damage Did the Eruption Cause? By far, the biggest casualty of the volcanic eruption was the loss of 57 lives. Of those 57 killed, the bodies of 27 were never recovered. On top of the many deaths it caused, the eruption demolished a 230-square-mile area around Mount St. Helens. Wiped from the map within that area of destruction were 250 homes, 15 miles of railway line, 185 miles of roads, and 47 bridges. And the effects of the eruption were felt over a far wider area. Ash that shot from the volcano's peak was detected as far away as Minneapolis, Minnesota.
Has Mount St. Helens Erupted Since 1980? Although nothing approaching the magnitude of its 1980 eruption has occurred, Mount St. Helens periodically sends plumes of ash high into the sky, and multiple tremors have been recorded in and around the mountain. In October 2004, magma reached the surface of the volcano and resulted in the creation of a new lava dome on the mountain's south flank. This lava dome grew throughout 2005 and 2006.
Are There Other Volcanoes in the United States?
According to the U.S. Geological Survey, 45 eruptions and 15 cases of significant volcanic unrest have occurred at U.S. volcanoes since 1980. And the USGS reports that there are 169 volcanoes in the United States, although most have long been dormant. Among America's most active volcanoes are those outside the contiguous 48 states, including Hawaii's Mauna Loa, said to be the largest volcano in the world. Nearby and more active is Kilauea, also on the big island of Hawaii. Alaska also has a number of volcanoes, some of which have been active since the 1990s.
Of volcanoes in the 48 contiguous states, the dozen or so in the Cascades mountain chain are considered among the most dangerous. The Cascades extend more than 1,000 miles from Mount Lassen in northern California to Mount Baker near the Canadian border in Washington State. Mount Rainier, north of Mount St. Helens in Washington State and close to the Seattle-Tacoma metro area, has not erupted since 1825 but is considered one of the country's most dangerous volcanoes, according to the USGS.