Introduction

Volcanoes provide spectacular examples of the way molten silicate melt — magma — interacts with the surface of the Earth. Depending upon the chemical composition of the magma, volcanic eruptions can be violent, sending huge volumes of rock and ash into the atmosphere in extremely short periods of time, or passive where lava simply oozes out without much damage to the surrounding region. In subduction zones, such as Costa Rica, magmas tend to be volatile-rich as a consequence of interactions between the subducting slab and the mantle underlying the volcano. This volatile-rich nature coupled with the fact that magmas can reside in the crust and evolve to more silica-rich — and hence more viscous — magmas, leads to explosive volcanism. The aim of our expedition to Costa Rica is to understand how the various volatile species are added to the source of the magmas, and how volcanoes act to recycle these volatiles between the sediments being subducted and the atmosphere.