Circulation of Magma in Volcanic Conduits as a Degassing Mechanism at Active Volcanoes: A Geochemical and Fluid-Dynamic Approach

University Of Washington, Seattle WA

Investigators

Abstract

Kress 9980566 The goal of this project is to better understand the volcanic gas source and the mechanism for non-explosive, passive degassing at high-gas-flux volcanoes. We hypothesize that "excess" gas emission at passively degassing volcanoes may be explained by circulation of magma in the volcanic conduit at both mafic and silicic subduction zone volcanoes. Two contrasting volcanoes, Popocatepetl (Mexico) and Villarrica (Chile), are the focus of the proposed research. Popocatepetl has been passively degassing enormous quantities of SO2 vapor for the last 5 years despite very limited magma production. Villarrica has had an actively degassing lava lake perched in its summit crater for the last 15 years. High rates of heat and gas transfer associated with conduit circulation may be able to explain the observed phenomena at Popocatepetl and Villarrica. We will adopt a two-step investigative process for this study. First, geochemical analysis of rock samples from Popocatepetl and Villarrica will enable us to define pre-eruptive conditions in the magma chamber (e.g., temperature and pressure) and quantify the composition and size of the volcanic gas source. Second, using multiphase, fluid dynamic modeling of magma circulation in the conduit, we will quantify the rates of passive degassing at the two volcanoes under scrutiny. In addition to the laboratory and modeling studies described above, a field campaign at Villarrica will make COSPEC measurements of SO2 flux, directly sample gas from summit fumaroles, and collect rock samples from representative explosive and effusive eruptions. Results of this study will shed light on the differences between the dynamics of explosive and non-explosive volcanic activity as well as help quantify the contribution of volcanic gases to the atmosphere from passive volcanic degassing.