Pardon El Chichon's Dust

By Frederic Golden

A vast volcanic cloud from Mexico may bring a cooler summer

When Mexico's El Chichon volcano came abruptly to life in late March and early April after more than a century, it killed 187 people, forced thousands from their homes and created havoc over a wide area of Mexico. Since then, 3,721-ft. El Chichon (The Lump) has simmered down, giving off only occasional blasts of steamy vapor. But the mountain continues to be an object of intense scientific concern. Though the initial blowup was relatively small. El Chichon pumped so much dust and debris into the upper atmosphere--perhaps more than any other volcano since 1912--that the earth's climate could be adversely affected.

The possibility is not idle speculation. As far back as 1783, when the eruption of Iceland's Laki volcano was followed by an extremely cold winter, Benjamin Franklin pointed out that volcanic dust could partly block sunlight. After the explosion of Indonesia's Tambora volcano in 1815, there were so many frosty nights the following June in Canada and the U.S. that people called it the "year without a summer." Some scientists believe a very large amount of volcanic dust in the atmosphere could send the earth tumbling into another ice age.

No responsible researcher foresees such catastrophic consequences from El Chichon. But there are troubling signs. A huge smoglike cloud from the volcano has been spotted at scattered locations around the globe. At the Kitt Peak National Observatory, near Tucson, astronomers say the brightness of stars has been reduced by 40%, and volcanic dust has created garish sunsets over wide areas of the Northern Hemisphere. Says Atmospheric Physicist James Pollack, of NASA's Ames Research Center, which has used U-2 aircraft to collect samples of El Chichon's dust: "This is the biggest volcanic cloud we have had in the last two decades.

When you screen out that much sunlight, that's an important event." El Chichon's importance caught scientists by surprise. Located in an impoverished area of southeastern Mexico, where the Zoque Indians scratch out a living by farming the volcano's slopes, it erupted with much less fury than Mount St. Helens and gave off only a fourth to a sixth as much debris as its Yankee rival. But as Volcanologist Wendell Duffield of the U.S. Geological Survey notes, "At Mount St. Helens the barrel of the cannon was pointed laterally. At El Chichon it was pointed straight up." The result: the Mexican volcano injected much more dust, ash and sulfur dioxide into the stratosphere, where the particles would be wafted high enough (at least 18 miles) to be carried in a westerly direction by prevailing high-altitude winds. Thus far, the cloud has been spotted over Hawaii, Japan, the Indian Ocean and Africa. U-2s have also detected traces over Kansas and Montana.

El Chichon's cloud covers more than one-quarter of the earth's surface and is constantly changing. Between the equator and 30DEG north, the debris has blocked out as much as 10% of the sun's total radiation. "That's very large," says Atmospheric Physicist John DeLuisi of the National Oceanic and Atmospheric Administration. "That's very significant."

Brian Toon of NASA's Ames center says the cloud could reduce temperatures in the Northern Hemisphere by a degree or so next summer--enough to affect growing seasons and rainfall. Others say the effect will be too negligible, only a few tenths of a degree. Scientists will have plenty of time to decide the issue: it may take up to five years before all the dust from El Chichon settles back to earth. Says DeLuisi: "We've got a nice little experiment going on here."

If Americans think the eruption of Mount St. Helens ended the U.S. volcano threat, they may be in for another shock. California's scenic Mammoth Lakes ski resort area, a few miles east of Yosemite National Park, has been jolted by a series of moderately strong earthquakes since 1978. At first seismologists of the U.S. Geological Survey thought the only risk was more quakes. Now they suspect that there may be a danger in the area of a volcanic eruption.

What set off the warning bell was the observation by Seismologist Alan Ryall of the University of Nevada of volcanic-type earthquake activity. In 1980 the shallowest quakes were originating at a depth of about 3 miles. By last summer, they were occurring only 2 miles below the surface. Roy Bailey, coordinator of the U.S.G.S.'s volcanic hazards program, suggests that the quakes were caused by the slow upward movement of a tongue of magma--the hot molten rock that forms a volcano's lava. Still another sign: the outbreak of new steam vents, or fumaroles, in the seismically active region.

In declaring a "potential volcanic hazard"--the lowest of three possible levels of alert--the U.S.G.S. emphasizes that an eruption is not certain. But the volcano watchers note that there is geological precedent for a major blowup in the region. Mammoth Lakes lies inside a huge 10-mile by 18-mile caldera, or depression, called Long Valley. It was created 700,000 years ago by a volcanic eruption probably more powerful than any the earth has seen since.

--By Frederic Golden. Reported by Laura Lopez/Mexico and Dick Thompson/San Francisco

With reporting by Laura Lopez, Dick Thompson

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