Pinatubo's Aerial Impact Scientists Assess Volcano's Effect on Weather, Atmospheric Chemistry
Robert C. Cowen, writer of The Christian Science Monitor, The Christian Science Monitor
KEEP an eye on the sky this autumn.
Arlin Krueger at the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center in Greenbelt, Md., says that "people can expect ... rosy sunsets" over much of the Northern Hemisphere as the volcanic plume spreads from Mt. Pinatubo's eruption in the Philippines.
But atmospheric scientists such as Dr. Krueger are interested in more than sunsets.
Pinatubo's eruption has given them an unplanned opportunity to study the effect that such a massive stratospheric injection of volcanic material has on weather and atmospheric chemistry.
Krueger has explained it is "possible that the cloud will reflect back into space some of the sunlight that would have reached the ground, resulting in a small change in the heat balance of the Earth." Many scientists will be watching for a possible cooling over the Northern Hemisphere, or even globally, of a few tenths of a degree.
Michael Coffey is a member of a team at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., that is analyzing the cloud's composition. He uses spectroscopic data gathered from an aircraft to identify chemical compounds. By establishing early conditions in the cloud and watching how these change, he and his colleagues hope to learn more about the complex chemistry that converts volcanic gases into climate-driving aerosol particles.
Dr. Coffey also notes that the unexpected eruption "is going to test" the prediction of his NCAR colleague Guy P. Brasseur that these particles will provide reaction sites for chemistry that will enhance destruction of stratospheric ozone.
Until now, the biggest eruption of this century, in terms of material shot to stratospheric heights, was that of El Chichon in Mexico in 1982.
Plume-tracker Lamont Poole, assistant head of the aerosol-research branch at the NASA Langley Research Center in Hampton, Va., estimates that Pinatubo's cloud "certainly is at least in the same class as El Chichs, if not larger."
Not all eruptions have major atmospheric implications. Speaking recently at his agency's regional office in Menlo Park, Calif., United States Geological Survey volcanologist Robert I. Tilling explained the difference, saying:
"Volcanoes are similar in that they all offer channels for molten rock (magma) from deep below to travel to the surface. Volcanoes differ, however, in that the type of rock that forms the magma and the amount of gas in the rock determines whether the material will flow as a heavy molten liquid (as in Hawaii) when it reaches the surface, or whether it will explode from the volcano as ash and other bits of volcanic material."
He added, "Some of this explosive material can travel at high speeds down the sides of a volcano in destructive pyroclastic flows, and other material rises high into the atmosphere and later falls to earth as volcanic ash."
This spring's eruption of Pinatubo and of Mount Unzen in Japan, which involved pyroclastic flows, reflect the relative movement of great pieces (plates) of Earth's crust along the western Pacific rim. Here, an oceanic plate slides beneath the plate carrying the Philippines and Japan. Their interaction generates molten rock that rises and eventually erupts explosively. …