TY - JOUR
T1 - Coupled effect of magma degassing and rheology on silicic volcanism
AU - Okumura, Satoshi
AU - Nakamura, Michihiko
AU - Uesugi, Kentaro
AU - Nakano, Tsukasa
AU - Fujioka, Takuma
N1 - Funding Information:
For this study, support was provided to S.O. by the Global Centers of Excellence program of Tohoku University (Global Education and Research Center for Earth and Planetary Dynamics). This study received financial support from Grants-in-aid for Scientific Research in Japan (nos. 21684025 and 24740299 ). The fiber elongation experiments were carried out with the help of Dr. Goto of Tohoku University. Official reviews by Alain Burgisser and Atsuko Namiki greatly improve this manuscript.
PY - 2013/1/5
Y1 - 2013/1/5
N2 - Explosive volcanism such as the 1991 Mt. Pinatubo, Philippines, and the 2008 Mt. Chaitén, Chile, eruptions is caused by violent vesiculation of hydrous magma. However, gas may efficiently separate from magma owing to the enhancement of gas permeability by shear deformation of magma flowing in a volcanic conduit. This makes it difficult to maintain the driving force of explosive volcanism although explosive volcanism is actually common. Here, we propose that shear localization in a volcanic conduit controls the eruption style and explosivity based on deformation experiments of vesicular magma linked with synchrotron radiation X-ray radiography and computed tomography. We observed, for the first time in situ, that the shear localization caused magma fracturing and formed a slip plane, and thus inhibited deformation and outgassing elsewhere. We also observed the compaction of vesicular magma into a dense "lava" as a result of outgassing when shear localization did not occur. In a natural setting, shear localizes along the edges of a volcanic conduit, where the strain rate is high, causing a highly permeable fracturing layer to form at the conduit's edge and leaving less-sheared and less-outgassed magma at its center. The less-outgassed magma in the center may ascend rapidly and cause explosive volcanism. Non-explosive lava effusion may occur only when shear localization does not occur effectively. This new view explains the rapid ascent of viscous magma and the formation of pyroclasts with contrasting vesicularity (pyroclastic obsidian and highly vesiculated pumice).
AB - Explosive volcanism such as the 1991 Mt. Pinatubo, Philippines, and the 2008 Mt. Chaitén, Chile, eruptions is caused by violent vesiculation of hydrous magma. However, gas may efficiently separate from magma owing to the enhancement of gas permeability by shear deformation of magma flowing in a volcanic conduit. This makes it difficult to maintain the driving force of explosive volcanism although explosive volcanism is actually common. Here, we propose that shear localization in a volcanic conduit controls the eruption style and explosivity based on deformation experiments of vesicular magma linked with synchrotron radiation X-ray radiography and computed tomography. We observed, for the first time in situ, that the shear localization caused magma fracturing and formed a slip plane, and thus inhibited deformation and outgassing elsewhere. We also observed the compaction of vesicular magma into a dense "lava" as a result of outgassing when shear localization did not occur. In a natural setting, shear localizes along the edges of a volcanic conduit, where the strain rate is high, causing a highly permeable fracturing layer to form at the conduit's edge and leaving less-sheared and less-outgassed magma at its center. The less-outgassed magma in the center may ascend rapidly and cause explosive volcanism. Non-explosive lava effusion may occur only when shear localization does not occur effectively. This new view explains the rapid ascent of viscous magma and the formation of pyroclasts with contrasting vesicularity (pyroclastic obsidian and highly vesiculated pumice).
KW - In situ fast X-ray CT
KW - Magma degassing
KW - Magma rheology
KW - Shear localization
KW - Volcanic eruption
KW - X-ray radiography
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U2 - 10.1016/j.epsl.2012.11.056
DO - 10.1016/j.epsl.2012.11.056
M3 - Article
AN - SCOPUS:84872194850
VL - 362
SP - 163
EP - 170
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
SN - 0012-821X
ER -