TY - JOUR
T1 - Origin and deformation of high porosity bands in the Takanoobane Rhyolite lava of Aso volcano, Japan
AU - Furukawa, K.
AU - Uno, K.
N1 - Funding Information:
We thank Dr. Y. Sudo and the staff of Aso Volcanological Laboratory, Kyoto University, for access to the drilling cores of the Takanoobane rhyolite lava. We also thank Dr. N. Ishikawa for permission to use the rock and paleomagnetic laboratory of Kyoto University. We thank Ms. Y. Kaneshige for her assistance in the measurement of the HPZ dip angle. This work has benefited from extensive discussions with Dr. T. Kanamaru. Microscopic observation was partly done at Nagoya University by the help of Dr. K. Tsukada. We are also grateful to Dr. T. Oikawa for the impregnation of cavities by colored resin. We acknowledge Dr. J.M. Castro and an anonymous reviewer for their constructive comments on the manuscript. This study was partly supported by a Grant-in-Aid for Scientific Research ( 15K05313 ) from the Japan Society for the Promotion of Science .
Publisher Copyright:
© 2015 Elsevier B.V.
PY - 2015/10/15
Y1 - 2015/10/15
N2 - In rhyolite lavas, the high porosity bands are often developed. They potentially act as pathways for gas movement to the lava surface. Since explosive activities of lavas are generally considered to be controlled by degassing system, understanding the origin and deformation process of the high porosity bands is important to assessing volcanic hazards. The Takanoobane rhyolite lava in the middle of Kyushu Island in SW Japan is effused at 51±5ka. The volume, flow length, and thickness are 0.14km3, >2km, and about 90m, respectively. The central crystalline part of the lava is characterized by the light-colored bands defined by the high porosity zone (HPZ). On the basis of geological and petrographical studies, we revealed that the HPZ was primary formed by ductile-brittle tearing of the lava (known as cavitation). According to the AMS results, the HPZs were subsequently stretched and flattened laterally during the concentric spreading of the lava. This deformation process could stretch the HPZ not only radially but also laterally. This effective stretching developed the HPZ into pervasive thin bands. Since the HPZs act as degassing pathways to the lava surface, the pervasive HPZ bands may play a role in providing volcanic gasses to void spaces created in surface fold hinges of rhyolite lavas. Thus, this degassing system may promote explosive activity of the lava surface.
AB - In rhyolite lavas, the high porosity bands are often developed. They potentially act as pathways for gas movement to the lava surface. Since explosive activities of lavas are generally considered to be controlled by degassing system, understanding the origin and deformation process of the high porosity bands is important to assessing volcanic hazards. The Takanoobane rhyolite lava in the middle of Kyushu Island in SW Japan is effused at 51±5ka. The volume, flow length, and thickness are 0.14km3, >2km, and about 90m, respectively. The central crystalline part of the lava is characterized by the light-colored bands defined by the high porosity zone (HPZ). On the basis of geological and petrographical studies, we revealed that the HPZ was primary formed by ductile-brittle tearing of the lava (known as cavitation). According to the AMS results, the HPZs were subsequently stretched and flattened laterally during the concentric spreading of the lava. This deformation process could stretch the HPZ not only radially but also laterally. This effective stretching developed the HPZ into pervasive thin bands. Since the HPZs act as degassing pathways to the lava surface, the pervasive HPZ bands may play a role in providing volcanic gasses to void spaces created in surface fold hinges of rhyolite lavas. Thus, this degassing system may promote explosive activity of the lava surface.
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U2 - 10.1016/j.jvolgeores.2015.09.021
DO - 10.1016/j.jvolgeores.2015.09.021
M3 - Article
AN - SCOPUS:84943376880
VL - 305
SP - 76
EP - 83
JO - Journal of Volcanology and Geothermal Research
JF - Journal of Volcanology and Geothermal Research
SN - 0377-0273
ER -