For the past four years, geochemist Tobias Fischer at Arizona State University has been monitoring gas emissions from the 14,000-foot Galeras volcano in southern Colombia. What his measurements now show is that changes in the cocktail of gases emanating from a volcano may signal an imminent eruption.
A volcano is fueled by a pool of molten rock, or magma, at its center, which releases a mix of gases that include hydrochloric acid, sulfur dioxide, and carbon dioxide. The pressure of the escaping gas is so great that it forces out rainwater that has seeped into fissures in the solid rock above. Eventually, some of the fissures become clogged--either by cooling rock at the surface of the magma chamber or by minerals precipitating from volcanic gases dissolved in the water forced from the fissures. The clogged channels slow the flow of gases and pressure builds. That pressure buildup, many geologists suggest, ...
