A large hydrothermal reservoir beneath Taal Volcano (Philippines) revealed by magnetotelluric observations and its implications to the volcanic activity |
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Authors: | Paul K. B. ALANIS Yusuke YAMAYA Akihiro TAKEUCHI Yoichi SASAI Yoshihiro OKADA Toshiyasu NAGAO |
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Affiliation: | *1Philippine Institute of Volcanology and Seismology, Quezon City, Philippines.;*2School of Earth and Environmental Sciences, Tokai University, Shizuoka, Japan.;*3Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Ibaraki, Japan.;*4Earthquake Prediction Research Center, Institute of Oceanic Research & Development, Shizuoka, Japan. |
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Abstract: | Taal Volcano is one of the most active volcanoes in the Philippines. The magnetotelluric 3D forward analyses indicate the existence of a large high resistivity anomaly (∼100 Ω·m) with a volume of at least 3 km × 3 km × 3 km, which is capped by a conductive layer (∼10 Ω·m), beneath the Main Crater. This high resistivity anomaly is hypothesized to be a large hydrothermal reservoir, consisting of the aggregate of interconnected cracks in rigid and dense host rocks, which are filled with hydrothermal fluids coming from a magma batch below the reservoir. The hydrothermal fluids are considered partly in gas phase and liquid phase. The presence of such a large hydrothermal reservoir and the stagnant magma below may have influences on the volcano’s activity. Two possibilities are presented. First, the 30 January 1911 explosion event was a magmatic hydrothermal eruption rather than a base-surge associated with a phreato-magmatic eruption. Second, the earlier proposed four eruption series may be better interpreted by two cycles, each consisting of series of summit and flank eruptions. |
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Keywords: | magnetotellurics resistivity structure Taal Volcano magmatic-hydrothermal eruptions hydrothermal reservoir |
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