[S-VC45] 活動的火山

[SVC45-20] VARIATION IN THE CHEMICAL AND ISOTOPIC COMPOSITION OF FUMAROLIC GAS AT TAAL VOLCANO, PHILIPPINE PRIOR TO THE 2020 ERUPTION

*大場 武¹、谷口 無我²、沼波 望¹、笹井 洋一³、Barairo Maria⁴、Alanis Paul⁴、Bornas Ma. Antonia⁴、楠本 成寿⁵、長尾 年恭³、角皆 潤⁶、伊藤 昌稚⁶、新宮原 諒⁶ (1.東海大学理学部化学科、2.気象研究所、3.東海大学海洋研究所、4.PHIVOLCS、5.富山大学大学院理工学研究部環境・エネルギー学域、6.名古屋大学大学院環境学研究科)

キーワード：タール火山、火山ガス、化学組成、安定同位体比

Taal volcano island is located in the southern part of Luzon Island, Philippine, about 50 km south of Manila. Taal volcano island has a mountainous body of about 5 km across surrounded by the lake water in caldera. The Taal Main Crater Lake (MCL) with a diameter of 1 km is located at the center of Taal volcano island. Thirty-three (33) eruptions have been recorded between 1572 and 1977 at Taal volcano island. From the last eruption in 1977 to 2019, the relatively long dormant period has continued. On 12^th January 2020, a large eruption happened at MCL. The plume of eruption raised up to 10km. Fumarolic gas contains components degassed from magma, so it responds to the up and down of volcanic activity, and chemical composition and stable isotopic ratio fluctuate sensitively. In this research, we focused on the time variation of several fumarolic gases discharging at Taal volcano island. From September 2016 to March 2019, the CO₂/H₂O ratio of a fumarole gas gradually decreased. The number of volcanic earthquakes started to increase in May 2019 followed by the enhanced number toward to the eruption in January 2020. The CO₂/H₂O ratio of the fumarolic gas in September 2019 raised to 5 times relative to the ratio in March 2019. Other parameters such as He/CH₄ ratio and apparent equilibrium temperature (AET) defined between H₂O and H₂ provided useful information to deduce the process beneath Taal volcano prior to the 2020 eruption.