General study on the eruption at Shinmoedake volcano, Kirishima, in 2011

2011年1月，新竹（雾岛）火山发生了岩浆喷发事件，造成了大约300年的间歇。1月26日和27日发生了三次地下爆炸，随后在山顶火山口积聚了4天的熔岩。从2月到4月，火山爆发反复发生，2011年6月和9月，一系列火山爆发以潜水式爆炸结束。在这次喷发事件之前，2008年和2010年的两次潜水爆炸以及雾岛周围地区的地震活动加剧。GPS观测显示，位于Shinmoedake陨石坑西北约6公里处的岩浆库自2009年底以来一直在持续显著膨胀。岩浆房的收缩伴随着明显的俯冲爆炸和火山口的熔岩堆积。应变计观测显示，在次平面爆炸前几十分钟，压力有小幅上升。更多的火山爆发表明，火山震动发生在山顶火山口下方及其与岩浆库之间，支持岩浆从岩浆库向火山口的迁移。后者是由岩浆房上方的绝对重力测量证实的。火山喷发前观察到峰顶区域的膨胀、浅层地震的增加和火山口喷出的火山气体的减少，这强烈暗示了火山喷发前管道顶部的密封。由于最早阶段的产物由两种不同成分的岩浆组成，因此认为岩浆混合发生在喷发事件发生之前。这次喷发的岩浆总量估计约为2500万立方米，约为300年前那次喷发的1/3。在本研究中，我们根据300年前这座火山的喷发记录以及日本国内外类似火山的喷发记录，两次尝试制作喷发场景，其中显示了喷发顺序。这次喷发没有发生明显的泥石流。认为喷发产物主要为浮石，具有较高的雨水渗透性。2011年1月火山喷发后，岩浆库的膨胀很快恢复，并持续到2011年底，达到喷发前的水平。2012年初，它几乎停止了喷发，这表明岩浆供应已经停止。少

A magmatic eruption event took place at Shinmoedake (Kirishima) Volcano in January 2011, leaving about 300 years of hiatus. Three subplinian explosions occurred on 26 and 27 January, which were followed by 4-day accumulation of lava at the summit crater. Vulcanican explosions were repeated from February to April, and a series of eruptions ended with phreatic explosions which occurred in June and September 2011. This eruption event was preceded by both phreatic explosions in 2008 and 2010 and elevated seismic activity in the regions surrounding Kirishima. GPS observation indicated that significant swelling of the magma chamber which located about 6 km NW of the Shinmoedake crater had continued since the end of 2009. Deflation of the magma chamber accompanied clearly subplinian explosions and the lava accumulation in the crater. The strain-meter observation showed small increases in pressure several tens of minutes prior to the subplinian explosions. Seismic array-observation during a se … More ries of vulcanian explosions showed that volcanic tremors occurred beneath the summit crater and between it and the magma chamber, supporting magma's migration from the magma chamber to the crater. The latter was confirmed by the absolute gravity measurement at the place just above the magma chamber. Inflation of the summit area, ncrease in the shallow earthquakes and decrease in the volcanic gas emitted from the crater were observed prior to the vulcanian explosions, strongly implying sealing of the conduit top preceding the explosions. It is considered that magma mixing occurred just before the eruption event because the products of the earliest stage consisted of two magmas with different compositions. The total volume of magma erupted in this event is estimated about 25 million m3, which is about 1/3 volume of the eruption 300 years ago.During this study, we tried two times to make the eruption scenario in which sequences of eruptions are indicated, based on records of eruptions of this volcano 300 years ago and of analogous volcanoes in and outside Japan. No significant mudflows occurred in this eruption event. It is considered that the reason is that the eruption products were mainly of pumice which has high permeability of rain water. Inflation of magma chamber resumed soon after the eruptions in January 2011 and continued by the end of 2011, reaching the same level before the eruption event. It almost stopped in the beginning of 2012, suggesting a halt of the magma supply from depth. Less