Study suggests new structure for some volcanos

Ars Technica : Some volcanos, especially those situated in areas where Earth’s crust is thin, have direct connections to the mantle. Others have magma chambers that are not connected to the mantle. Until recently, Irazú in Costa Rica was believed to be one of the latter, but a study of the ash from an eruption that occurred between 1963 and 1965 appears to show otherwise. Philipp Ruprecht and Terry Plank of Columbia University measured the nickel content of olivine crystals in the ash from the eruption. The amount of the metal present in the crystals is tied to the way the crystals were formed, which in turn indicates where the magma came from. They determined that the crystals formed in a shallow chamber filled with melted rock from the mantle. What was surprising was how quickly the chamber refilled—over a period of just a few months—which could only occur if it was directly connected to the mantle. Because that sort of magma flow is similar to that of volcanos in Iceland, the monitoring methods used in Iceland may also be useful for studying Irazú and other volcanos that were not previously believed to be directly connected to the mantle.