Araya Naoki, Nakamura Michihiko, Yasuda Atsushi, Okumura Satoshi, Sato Tomoki, Iguchi Masato, Miki Daisuke, Geshi Nobuo
Department of Earth Science, Graduate School of Science, Tohoku University, 6-3 Aramaki Aza-Aoba, Aoba-ku, Sendai, 980-8578, Japan.
Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan.
Sci Rep. 2019 Feb 13;9(1):1979. doi: 10.1038/s41598-019-38494-x.
Vigorous explosive eruptions that produce continuous high eruption plumes (Plinian eruptions) are generally assumed to tap a magma reservoir. The 1914 Plinian eruption at the Sakurajima volcano located on the Aira caldera rim is one such case, where the main magma reservoir was assumed to be located approximately 10 km beneath the caldera. However, we report that estimated magma storage depths immediately prior to the eruption were much shallower (0.9-3.2 km) on the basis of pressure at which volatiles within the phenocryst melt inclusions and plagioclase rims were finally equilibrated. The same is observed for two historic Plinian eruptions in 1471 and 1779. This depth is even shallower than the shallowest magma reservoir estimated from the pressure source for geodetic deformation during recent Vulcanian explosions (4 km beneath the crater). We propose that the magmas were fed from a thick conduit pre-charged from deeper reservoirs. The ground subsidence observed after 1914 within the Aira caldera may have been caused by conduit recharge following the eruption. Voluminous conduit recharge could be key to forecasting the next possible large eruption at the Sakurajima volcano.
一般认为，产生持续高喷发柱的剧烈爆发性喷发（普林尼式喷发）会连通一个岩浆库。位于阿伊拉火山口边缘的樱岛火山在1914年发生的普林尼式喷发就是这样一个例子，当时主要岩浆库被认为位于火山口下方约10公里处。然而，我们报告称，根据斑晶熔体包裹体和斜长石边缘内挥发物最终达到平衡时的压力，喷发前估计的岩浆储存深度要浅得多（0.9 - 3.2公里）。在1471年和1779年的两次历史普林尼式喷发中也观察到了同样的情况。这个深度甚至比根据近期武尔卡诺式爆炸期间大地测量变形的压力源估计的最浅岩浆库还要浅（火山口下方4公里）。我们认为岩浆是由一个预先从更深储层充注的厚管道供给的。1914年后在阿伊拉火山口内观察到的地面沉降可能是喷发后管道再充注造成的。大量的管道再充注可能是预测樱岛火山下一次可能发生的大型喷发的关键。
