THE ROBINSON LIBRARY
|The Robinson Library >> Science >> Geology >> Dynamic and Structural Geology|
|The Eruption of Mount St. Helens
March 20-May 18, 1980
Located in the state of Washington, Mount St. Helens had been quiet for 123 years when, on March 20, 1980, it was shaken by an earthquake. Over the next seven days more than 100 major earthquakes and thousands of small ones were recorded. On March 27, just after noon, a boom came from the mountain that was heard miles away, and steam and ash began shooting into the air. Steam, gases, ash, ice, and rocks continued to spew from the volcano for the next few weeks, and small earthquakes and explosions continued to rock the mountain and surrounding area.
Volcanologists and other scientists began flocking to the area, as did tourists. The scientists warned that a major eruption was imminent, and people living on the mountain were evacuated. A "Red Zone" was marked offmon a map, and only scientists were allowed inside. As time went by and nothing dramatic happened, however, residents began defying the Red Zone, and even began selling maps showing tourists how to avoid the barricades by using logging roads.
At 8:30 a.m. on May 18, Mount St. Helens was rattled by an earthquake, followed by several smaller ones. The quakes triggered a massive landslide that roared down the north slope. At 8:32, the top of the mountain exploded with a blast that was heard 200 miles away. Seconds later the north slope exploded out to the side. The second explosion instantly leveled trees and structures over more than 150 square miles, and triggered a massive mudflow that lasted for hours and caused even more devastation "downstream" from the mountain.
Volcanologist David Johnston was monitoring the
volcano's activity from an observation post about 5 miles
north of the crater on May 18, and reported the blast --
"Vancouver, Vancouver. This is it!" -- just
before his radio went silent.
When Mount St. Helens blew, 1.3 billion cubic yards of ash shot up 12 miles into the air, and also billowed out. Many people who weren't killed by the explosion or mudflow died in the suffocating ash "fallout." As the ash cloud moved with the wind northeastward across the sky, it "turned day into night" for hundreds of towns in its path, some over a hundred miles away.
|The Robinson Library
>> Science >> Geology >> Dynamic and Structural Geology
This page was last updated on 02/02/2018.