Periodic sulphur dioxide degassing from the Soufrière Hills Volcano related to deep magma supply
T. Christopher, M. Edmonds, B. Taisne, H. Odbert, A. Costa, V. Hards, G. Wadge, 2015. "Periodic sulphur dioxide degassing from the Soufrière Hills Volcano related to deep magma supply", The Role of Volatiles in the Genesis, Evolution and Eruption of Arc Magmas, G. F. Zellmer, M. Edmonds, S. M. Straub
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Soufrière Hills Volcano produced prodigious quantities of sulphur dioxide (SO2) gas throughout 1995–2013. An unprecedented, detailed record of SO2 flux shows that high SO2 fluxes were sustained through eruptive pauses and for two years after the end of lava extrusion and are decoupled from lava extrusion rates. Lava extrusion rates have exhibited strong 1- to 2-year cyclicity. Wavelet analysis demonstrates periodicities of c. 5 months and c. 2 years within the SO2 time series, as well as the shorter cycles identified previously. The latter period is similar to the wavelength of cycles in lava extrusion, albeit non-systematically offset. The periodicities are consistent with pressure changes accompanying deformation in a coupled magma reservoir system whereby double periodic behaviour may arise from limited connectivity between two reservoirs. During periods of lava extrusion SO2 is released together with the lava (yielding the c. 2 year period), albeit with some offset. In contrast, when magma cannot flow because of its yield strength, SO2 is released independently from lava (yielding the c. 5 month period). Our results have implications for eruption forecasting. It seems likely that, when deep supply of magma ceases, gas fluxes will cease to be periodic.
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The subduction zone volatile cycle is key to understanding the petrogenesis, transport, storage and eruption of arc magmas. Volatiles control the flux of slab components into the mantle wedge, are responsible for melt generation through lowering the solidi of mantle materials and influence the crystallizing phase assemblages in the overriding crust. Further, the rates and extents of degassing during magma storage and decompression affect magma rheology, ultimately control eruption style and have consequences for the environmental impact of explosive arc volcanism. This book highlights recent progress in constraining the role of volatiles in magmatic processes.
Individual book sections are devoted to tracing volatiles from the subducting slab to the overriding crust, their role in subvolcanic processes and eruption triggering, as well as magmatic-hydrothermal systems and volcanic degassing. For the first time, all aspects of the overarching theme of volatile cycling are covered in detail within a single volume.