WHEN MOUNTAINS FIZZ.

This article discusses the mechanics of volcanic eruptions. On May 18, 1980, Mount St. Helens blew its top. Contrast that event with the latest activity of Hawaii's Kilauea volcano, an event that began early in 1983 and is still under way. Although the mountain occasionally spews fountains of lava, the molten rock it exudes usually just flows down the slopes. Two volcanoes. Two eruption styles. Geologists have long sought to uncover what underlies such variation, which sometimes gives a volcano different temperaments at different times. The more these researchers delve into these pursuits, the more convinced they become that the world's volcanoes have a lot in common with soda pop.