The gases, mostly carbon dioxide that is dissolved in the champagne, are confined by the heavy, strong bottle and a cork. Volcanic eruptions work in a similar fashion. A magma body forms about a hundred miles beneath a volcano. Lighter than the surrounding rocks, the magma begins to rise. The pressure that keeps the gases dissolved drops, allowing them to boil off.
Carbon dioxide boils first, then sulfur dioxide.
That's ideal, a wonderful thing for forecasting an eruption. If carbon dioxide really is more dependent on pressure, then it should be coming out days or weeks before the eruption. The ratio between carbon dioxide and sulfur dioxide ought be a powerful, better way to forecast an eruption. Williams began studying volcanic gases in the late 1970s with his mentor, Dick Stoiber, at Dartmouth College. The instrument was manufactured by Barringer Research to monitor pollution from coal-fired power plants and smelters.