Portland, Ore. — Besides being a rare and spectacular geological event for the United States, what is the significance of the Mt. St. Helens eruption? * For those living within about a 500-mile radius of the Cascades Range peak in southwestern Washington, the effects range from dangerous and costly to inconvenient.
* For other areas of the US, from the Rocky Mountains to the Eastern Seaboard , the effect will be mostly visual: spectacular sunsets because of the eastward moving cloud of ash and a daytime pall of varying intensity.
* To geologists and, more specifically, volcanologists it already has posed a test of expertise. Sunday's explosion was the least-expected climax of recent activity on the peak. The volcano presents a continuing subject for study not experienced so close at hand since the last century.
What happened last Sunday morning on Mt. St. Helens was very close to the worst possible scenario earth scientists -- who had been watching and waiting since the mountain first started spewing ash, gas, and steam on March 27 -- had projected. An earthquake that was heard and felt as far north as Vancouver, B.C., and as far south as Roseburg, Ore., was almost simultaneous with the explosion of the mountain. Some 1,300 vertical feet of the top of the 9,677 -foot volcanic cone was sheared away by the violent blast that sent the plume of ash, gas, and steam billowing 60,000 feet into the sky.
Massive avalanches of melting glaciers, ash, and mud raced down the slopes of the mountain. While it continued to erupt, the plume of airborne ash was carried by upper-level westerly winds into a widening span over eastern Washington, Idaho, Montana, and Wyoming and spread out over the Great Plains.
The ash choked residents, contaminated drinking water, and forced closure of schools and highways in Washington, Idaho, and Montana. Thousands of motorists were stranded.
Meteorologists predicted that the leading edge of the ash cloud would reach the East Coast by Wednesday. Climatologists said the thick cloud could affect weather in the Northern Hemisphere for several months.
Heavier fallout will be concentrated closer to the mountains, across eastern Washington, Idaho, and Montana. Several cities -- including Yakima and Spokane, Wash., and Moscow, Idaho, had an eclipse-like experience within a few hours of the eruption. The sun was blotted out and an inches-deep blanket of gritty ash fell like dark snow.
Life and commerce came to a virtual halt under the gloom as roads and airports were closed. Damage to health, property, commerce, and agriculture is massive, and early attempts to put dollar values on the consequences were, at best, speculative.
On Mt. St. Helens itself, surface phenomena sent avalanches of mud, water, and debris crashing down its long ravines and stream courses. The volcanic blast leveled vast forests. Streams were alternately dammed by mud and debris and swamped by melting glaciers. Walls of water crashed down the Toutle River, into the Cowlitz River, and ultimately into the Columbia. Shipping on the Columbia was halted as the channel filled with silt and several ships caught in the river at Longvieww, Wash., and below went aground. Dredging will be necessary to clear the channels.
A jam of logs and debris swept from the devastated banks of the Toutle and Cowlitz Rivers surged into the Columbia in a wraith-like jumble nearly 20 miles long. The jumble, containing much valuable timber, poses an extreme hazard to navigation. Much of it will eventually float out into the Pacific.
Several thousand people were successfully evacuated from communities and recreation areas around the mountain. By late Monday there had been five confirmed fatalities -- loggers and mountainside residents caught in the initial blast and subsequent avalanches and floods. Some 21 persons were officially listed as missing. Among the missing was 84-year-old Harry Truman, who had refused to leave the mountain. His resort at Spirit Lake was believed buried under some 30 feet of mud. The lake no longer exists.
Although no lava had emerged from the mountain as of May 20, geologists pointed out that this kind of eruption is considered likely to lead to lava flow.
Bob Christianson of the US Geological Survey said the eruption approached the magnitude of the largest ever for Mt. St. Helens, which occurred 32,000 years ago. He said a prediction as to how long the present activity will continue "is one of those $64,000 questions."