Geochemical volcano monitoring

The geochemistry of volcanic fluids is increasingly employed at volcano observatories worldwide to assess volcano activity state, and eruption potential. Here, we review the state-of-the-art in the field, with a primary focus on the most recent developments in instrumental gas monitoring that have rendered geochemistry an increasingly effective eruption-forecasting tool. We describe the main geochemical techniques, from both ground and space, and how they each contribute to volcano monitoring. By presenting some selected case studies, we demonstrate that geochemical monitoring strategies need to adapt as volcanic activity state evolves during unrest and in the run-up to eruption. Modern gas-monitoring networks need to integrate different instrumental tools and require collection of a variety of gas-related signals if any subtle change in volcano behavior is to be captured in a timely manner.