St. Helens eruption may yield clues to climate changes

The explosive eruption of Mt. Helens may held important new light on the complex and controversial relationship between volcanic activity and world climate.

This is the hope of the scientists who are trying to unravel the mysteries of the ice ages and other aspects of Earth's prehistoric climate. Their expectation has been strengthened by the fact that an especially equipped U-2 aircraft was on hand to sample the particles and gases that the volcano blasted as much as 70,000 feet into the atmosphere.

"It [the eruption] came at a good time for us," explains Dr. James Pollack of Ames Research Center, the National Aeronautics and Space Administration facility that sent up the U-2. "We're going to learn quite a lot from it."

Space agency researchers were prepared for the event because they have been studying the climatic effects of minute particles -- like those given off by volcanic eruption -- in the stratosphere for a year and a half. Besides the highflying aircraft, several satellites scrutinized the volcanic plume as well.

Rheories that involve the impact of volcanic activity on climate have appeared sporadically in the last century.

Recently, analysis of volcanic dust in ice cores and deepsea sediments has strengthened these arguments. Researchers have found increases in volcanic activity coinciding with periods of climatic cooling.

Last year, James A. Coakley of the National Center for Atmospheric research reported that Australian follow-up studies of the 1963 Agung eruption in Bali showed twice the expected amount of atmospheric cooling.

While a single eruption like Agung or Mt. St. Helens cools the world climate by only a few tenths of a degree, an amount of no practical significance, it is possible that a major increase in the tempo of volcanic eruptions worldwide could have significant climatic effects.

Even if volcanic activity proves not to be the factor that triggers ice ages, climatologist Reid Bryson of the University of Wisconsin has argued that prediction of future volcanic activity is necessary is climatic changes are to be adequately forecast.

Dr. Bryson points out that frequency of volcanic eruptions has been increasing since 1945.

"From 1945 to 1970, the annual eruption numbers roughly doubled -- from 16 to 18 per year to 37 to 40 per year," he wrote in an article two months ago in the journal Science.

This increase has been accompanied by a decline in the clarity of the atmosphere. Volcanic ash and particles change the way sunlight warms Earth's atmosphere.

According to the current theory, particles in the stratosphere have the most pronounced climatic effects.

These particles, particularly sulfates, remain in the upper atmosphere for a long period of time, as much as years, and absorb sunlight. As a result, the upper atmosphere is heated while the planet's surface is cooled.

Just how profound this effect is, however, depends on the chemical composition of the particles, the mean size of the particles released how much energy they absorb, and how rapidly they age.

The equipment on the U-2 was designed to obtained this information, Dr. Pollack says. And, although it may take a number of months to analyze and interpret the information gathered from the Washington eruption, it holds the promise of adding substantially to scientific understanding of this subject.