Monitoring the magmatic activity and volatile fluxes of an actively degassing submarine caldera in southern Japan
Monitoring the magmatic activity and volatile fluxes of an actively degassing submarine caldera in southern Japan
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监测日本南部活跃排气的海底破火山口的岩浆活动和挥发通量
DOI：
10.1016/j.gca.2021.10.023
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发表时间：
2022
影响因子：
5
通讯作者：
Sano Yuji
中科院分区：
文献类型：
--
作者：
Nakajima Ma. Teresa Escobar;Takahata Naoto;Shirai Kotaro;Kagoshima Takanori;Tanaka Kentaro;Obata Hajime;Sano Yuji
水下破火山口的突然爆发可能对附近社区构成迫在眉睫的危险。因此，密切监测这些环境中挥发性废水的变化至关重要。与陆上火山不同，水下火山活动难以观察。若见湖是日本南部的一个水下破火山口，与活跃的陆上火山山有着共同的岩浆源。樱岛经过多年的不活动，火山爆发在山。樱岛火山在2009年变得更加频繁;然而，邻近的若见子火山口在这种活动激增中的表现尚不确定。在这项研究中，我们评估的热液喷发内若见湖山最近的干扰状态。樱岛根据2015年获得的样品的气泡、海水和沉积物孔隙水测量结果，富含3 He的酸性流体似乎继续排放到海底。自2010年以来，水柱中的3 He过剩量没有明显变化，但岩浆源的氦同位素比值继续升高，为107.2 Ra。这一比例的岩浆成分是高于以前观察到的1986年（106 Ra）。这种差异可能与岩浆源区的脱气活动和地幔成分的变化有关。利用沉积物孔隙水的新数据，我们估计3 He和4 He通过海底的扩散通量分别为16.05个原子cm-2s-1和1.52 × 106个原子cm-2s-1。我们还计算了3.38 × 104 atoms cm−2s−1处的vent 3 He通量。利用3 He通量，我们计算了若见湖的CO2扩散通量为1.41 × 106 mol yr− 1，喷口通量为3.72 × 108 mol yr−1。现有的数据仍然有限，需要更频繁和更长时间的观测来推断若见湖的时间变化及其与火山活动的关系。樱岛
The sudden eruption of submerged calderas can potentially pose imminent danger to nearby communities. Hence, it is crucial to closely monitor the changes in volatile effluents in these environments. Unlike subaerial volcanoes, underwater volcanic activity is difficult to observe. Wakamiko, a submerged caldera in southern Japan shares a magma source with the active subaerial volcano, Mt. Sakurajima. Following years of inactivity, the volcanic eruptions in Mt. Sakurajima became more frequent in 2009; however, it is undetermined how the neighboring Wakamiko caldera has behaved in relation to this upsurge in activity. In this study, we assess the state of hydrothermal venting inside Wakamiko following recent disturbances in Mt. Sakurajima. Based on gas bubbles, seawater, and sediment pore water measurements of samples obtained in 2015, it appears that acidic fluids enriched in3He continue to be discharged to the seafloor. Excess3He in the water column shows no apparent change since 2010; however, the helium isotopic ratio of the magmatic source continues to be elevated at ∼7.2 Ra. This ratio for the magmatic component is higher than previously observed in 1986 (∼6 Ra). The difference could be related to changes in the degassing activity as well as the mantle composition of the magmatic source. Using the new data from sediment pore water, we estimate the diffusive fluxes of3He and4He through the seafloor at 16.05 atoms cm−2s−1and 1.52 × 106atoms cm−2s−1, respectively. We also calculated the vent3He flux at 3.38 × 104atoms cm−2s−1. With the use of the3He flux, we calculated the diffusive CO2flux from Wakamiko at 1.41 × 106mol yr−1and the vent flux at 3.72 × 108mol yr−1. The available data that we have are still limited and a more frequent and longer observation is necessary to deduce the temporal changes in Wakamiko and its relation to the volcanic activity of Mt. Sakurajima.