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The interplay between collapse structures, hydrothermal systems, and magma intrusions: the case of the central area of Piton de la Fournaise volcano

By Jean-François Lénat, Patrick Bachèlery and Aline Peltier

Abstract

International audienceWe explore the possible relationships between a structural heterogeneity, the hydrothermal system, and the intrusive activity at Piton de la Fournaise volcano. Geological and geophysical data show that as the result of repeated collapses (the last one in 2007), a cylinder of faulted, fractured, and crumbled rocks must exist between the surface and the top of a magma reservoir at about sea level. This structure constitutes a major geological heterogeneity. An obvious spatial correlation exists between this column of fractured and brecciated rock and the location of (1) most of the seismic activity, (2) a low-resistivity dome, (3) a huge self-potential anomaly, (4) thermal evidence of hydrothermal activity, and (5) the root of magma intrusions. The dominant factors that make this structural heterogeneity a trap for the activity are probably its higher permeability and its weaker mechanical strength. Evidence exists for the presence of an active hydrothermal system confined in this permeable zone. The long-term stability of the activated zone above sea level and the similarity of the pre-eruptive crises, in spite of the inferred large perturbation of the magmatic system in 1998, suggest a common triggering mechanism for all the eruptions since at least the first data recorded by the observatory in 1980. This mechanism can be purely magmatic, resulting from the pressurization of a reservoir, but we also propose that the hydrothermal system may play a role in the development of volcanic instabilities. A qualitative model is proposed to explain the triggering of magma intrusions by hydrothermal processes, and its speculative aspects are discussed. This work represents a first attempt to integrate the structural and dynamic information in a unified framework at Piton de la Fournaise

Topics: Collapse, Hydrothermal system, Piton de la Fournaise, Eruption, Pre-eruptive crisis, Magma transfer, [ SDU.STU.VO ] Sciences of the Universe [physics]/Earth Sciences/Volcanology, [ SDE.MCG ] Environmental Sciences/Global Changes
Publisher: Springer Verlag
Year: 2012
DOI identifier: 10.1007/s00445-011-0535-3
OAI identifier: oai:HAL:hal-00715675v1
Provided by: Hal-Diderot
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