Is Mt. St. Helens Preparing To Erupt Again?

By James Donahue

Oct. 4, 2005

The last major volcanic eruption in the United States occurred in Washington State on May 18, 1980, when Mt. St. Helens blew its top. New activity on the mountain suggests that something is brewing again deep below its surface and another eruption may be in the offing.

The 1980 event will long be remembered by many people throughout the Northwestern United States. The skies were darkened by the ash from that massive explosion for months. Fifty-seven people perished and of these, 21 bodies were never recovered.

The eruption that year was triggered by a 5.1 magnitude earthquake centered directly under the mountain. The blast removed 1,314 feet from the top of the mountain, reducing it from 9,677 feet to 8,363 feet, left a large crater and changed the local landscape forever.

The ash cloud reached a height of 80,000 feet within 15 minutes and drifted to the east coast in three days. Most of the ash fell within 300 miles of the mountain, but the fine ash in the upper altitudes circled the earth in 15 days and continued to stay there for years afterward, filtering the sunlight and affecting the climate in the Northern Hemisphere.

Not only did the mountain blast shoot upward, it also blew out of the north side, causing a 230 square mile area of devastation that reached a distance of 17 miles from the crater. The blast brought temperatures as high as 660 degrees Fahrenheit and carried the power of 24 megatons of thermal energy, snapping large trees and stripping their bark.

Mighty rock from the mountain top rolled down the mountain at speeds of 70 to 150 miles an hour, burying the North Ford of the Toutle River. Some areas were buried under as much as 600 feet of material.

Not only rock, but the snow on the mountain was instantly evaporated into steam by the heat. It formed large mudflows that rolled down the mountain in a super landslide that destroyed 27 bridges, 200 homes, 185 miles of roads and 15 miles of railway.

Lava with searing heat nearing 1,300 degrees Fahrenheit, also flowed from the crater covering six square miles before stopped.

After all of that, the mountain went dormant for about 20 years. The people of Washington State cleaned up their neighborhoods and got on with their lives. But the mighty mountain’s current episode may not be through.

As many volcano watchers know Mt. St. Helens sprang back to live with a series of earthquakes and spits of smoke and heat last September. Lava has been flowing from the crater in a steady stream that one writer said was measured as “a dump-truck load every second.”

And even more ominous is a that new dome that has appeared inside the massive crater left by the 1980 blast. Geologists studying the mountain say it is growing up to 16 feet a day..

Because the magma was first coming from the pool created by the volcano’s 1980 eruption, geologists were not expressing concern that the mountain would explode again.

But experts who recently examined some new lava rocks on the mountain found that fresh magma now is mixing with the old, and that has generated concern. It means, they say, that a deeper reservoir of fresher, more explosive magma has now opened. And it means that the danger of another large eruption has increased.

One story said an earthquake analysis at the site has yielded tangible evidence of a crack in the Earth’s crust extending for miles beneath the volcano. It is a weak spot in the crust that is providing a path for the molten rock to follow when it comes to the surface.

“The volcano is there because magma has been rising through that zone of weakness for tens of thousands of years,” said volcanologist Dan Dzurisin.

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