Volcanic Gas Chemistry: Measurements, Models and Mysteries

Clive Oppenheimer
Department of Geography, Downing Place, Cambridge CB2 3EN


Volcanoes are "large scale chemical engineering". The key to understanding volcanic activity is the behaviour of the gas phase, which depends primarily on magma chemistry and pressure. Degassing can trigger eruptions and dictates eruption style: whether lavas seep out of the vent passively or are discharged with such violence and heat that they punch plumes tens of kilometres into the atmosphere. Volcanic degassing is also critical to understanding atmospheric composition and climate change. Volcanoes contribute significant fractions of the global atmospheric inventory of radiatively and environmentally significant sulfur, halogen and heavy metal compounds. But volcanoes are not easy to measure. A highly promising approach to sampling volcanic gases (and aerosol) is the application of spectroscopic methods, and I summarise here recent observations made by ultraviolet and infrared remote sensing. These techniques are now being adopted by volcano observatories worldwide for routine monitoring and eruption forecasting. They are also illuminating the exotic atmospheric chemistry of volcanic plumes, highlighting the need to develop models for the high-temperature chemical evolution of the gas and aerosol phases in the first seconds after emission from the vent into the atmosphere.