D.S. Cronan, A.G. Johnson & R.A. Hodkinson
Department of Geology, Imperial College of Science, Technology & Medicine, London, SW7 2BP
Island arc volcanoes have the capacity to be highly destructive when in eruption, the potential hazards of which include explosive events, pyroclastic flows and, in the case of submarine eruptions, tsunamis. Examples in the Caribbean island arc include the past eruptions of Mont Pelee, Martinique, Soufriere, St. Vincent and the current eruption on Montserrat. We report the results of a study of hydrothermal discharges before and during the Montserrat eruption. We show that offshore hydrothermal springs there, unlike those onshore, exhibit long-term compositional variations an order of magnitude greater than those occurring during an observed, short lived, volcanic event. Manganese, Fe and As contents which were low in fluids prior to the eruption, had increased dramatically by nine days after its start and then decreased to intermediate values as the eruption continued. These variations may be related to stages of the volcanic cycle and could have important implications for eruption prediction of coastal and submarine volcanoes.