Facts about Mount St. Helens
May 15, 2010 0
Mount St. Helens Eruption
TDN file photo / Roger Werth
1. During the past 4,000 years, Mount St. Helens has erupted more frequently than any other volcano in the Cascade Range.
2. Most of Mount St. Helens is younger than 3,000 years old (younger than the pyramids of Egypt).
3. 3,600 years ago, Native Americans abandoned hunting grounds devastated by an enormous eruption four times larger than the eruption on May 18, 1980.
4. March 20, 1980: A 4.2 earthquake signaled the reawakening of the volcano after 123 years.
5. Spring 1980: Rising magma pushed the volcano's north flank outward five feet per day.
6. On the morning of May 18, 1980, the largest landslide in recorded history reduced the summit by 1,300 feet and triggered a lateral blast. Within 3 minutes, the blast, traveling at more than 300 mph, blew down and scorched 230 square miles of forest. Within 15 minutes, a vertical plume of ash rose more than 80,000 feet.
7. The volcanic ash cloud drifted east across the United States in three days and circled Earth in 15 days.
8. Mudflows damaged or destroyed 27 bridges and 200 homes.
9. The May 18, 1980 eruption was the most economically destructive volcanic event in U.S. history.
10. The May 18 eruption was not the only big eruption of 1980: explosive eruptions on May 25, June 12, July 22, Aug. 7, and Oct. 16-18 rocked Mount St. Helens and sent ash to distant communities. Only the one on May 25 dropped significant amount of ash on the Kelso-Longview area.
11. October 1980 to 1986: Over the course of 17 episodes, lava eruptions began filling the crater, building a lava dome that reached 876 feet above the crater floor.
12. Since 1986, snow and rock accumulating in the deep, shaded crater formed Crater Glacier, the youngest glacier on Earth.
13. In September 2004, Mount St. Helens reawakened, and it erupted continuously until January 2008. During this time a second lava dome displaced and then divided Crater Glacier into east and west lobes.
14. During the 2004 to 2008 eruptions, Mount St. Helens settled one half inch due to magma withdrawal beneath the volcano, like a balloon shrinking from air release.
15. During the 1980 to 1986 and the 2004 to 2008 eruptions, lava oozed onto the crater floor, building domes taller than the Empire State Building and restoring 7 percent of the volume the mountain lost in 1980.