[In Depth] Gas changes signal eruptions
By monitoring gases emitted from the mouths of volcanoes, scientists could provide days to weeks of warning before an eruption. The latest evidence comes from studies of volcanoes monitored as part of the Volcano Deep Earth Carbon Degassing initiative, where scientists used hardy, long-lived sensors to measure the ratio of carbon to sulfur gases emitted before eruptions. In principle, a jump in the ratio can signal when a fresh injection of magma is rising from deep in the crust—a prelude to an eruption. The ratio changes because carbon dioxide dissolved in rising magma bubbles out at depths of 10 kilometers or more, as the pressure drops. Sulfur-rich gases, in contrast, stay in solution up to shallower depths. A spike in the ratio provides warning that a batch of magma has risen above a deep threshold. A subsequent drop in the ratio could indicate that the magma has climbed farther still,...