Short time scales of magma-mixing processes prior to the 2011 eruption of Shinmoedake volcano, Kirishima volcanic group, JapanReportar como inadecuado

Short time scales of magma-mixing processes prior to the 2011 eruption of Shinmoedake volcano, Kirishima volcanic group, Japan - Descarga este documento en PDF. Documentación en PDF para descargar gratis. Disponible también para leer online.

Bulletin of Volcanology

, 75:750

First Online: 06 September 2013Received: 28 February 2013Accepted: 06 August 2013


We estimated time scales of magma-mixing processes just prior to the 2011 sub-Plinian eruptions of Shinmoedake volcano to investigate the mechanisms of the triggering processes of these eruptions. The sequence of these eruptions serves as an ideal example to investigate eruption mechanisms because the available geophysical and petrological observations can be combined for interpretation of magmatic processes. The eruptive products were mainly phenocryst-rich 28 vol% andesitic pumice SiO2 57 wt% with a small amount of more silicic pumice SiO2 62–63 wt% and banded pumice. These pumices were formed by mixing of low-temperature mushy silicic magma dacite and high-temperature mafic magma basalt or basaltic andesite. We calculated the time scales on the basis of zoning analysis of magnetite phenocrysts and diffusion calculations, and we compared the derived time scales with those of volcanic inflation-deflation observations. The magnetite data revealed that a significant mixing process mixing I occurred 0.4 to 3 days before the eruptions pre-eruptive mixing and likely triggered the eruptions. This mixing process was not accompanied by significant crustal deformation, indicating that the process was not accompanied by a significant change in volume of the magma chamber. We propose magmatic overturn or melt accumulation within the magma chamber as a possible process. A subordinate mixing process mixing II also occurred only several hours before the eruptions, likely during magma ascent syn-eruptive mixing. However, we interpret mafic injection to have begun more than several tens of days prior to mixing I, likely occurring with the beginning of the inflation December 2009. The injection did not instantaneously cause an eruption but could have resulted in stable stratified magma layers to form a hybrid andesitic magma mobile layer. This hybrid andesite then formed the main eruptive component of the 2011 eruptions of Shinmoedake.

KeywordsDiffusion Magma chamber Magma mixing Magnetite Sub-Plinian eruption Time scale Editorial responsibility: P. Wallace

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Autor: Akihiko Tomiya - Isoji Miyagi - Genji Saito - Nobuo Geshi


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