Ground deformation cycles in a magma-effusive stage, sub-Plinian and vulcanian eruptions at Kirishima volcanoes, Japan
Ground deformation cycles in a magma-effusive stage, sub-Plinian and vulcanian eruptions at Kirishima volcanoes, Japan
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日本雾岛火山岩浆喷发阶段、次普林尼式和火山喷发的地面变形循环
DOI：
10.1002/jgrb.50278
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
and J. Oikawa
中科院分区：
文献类型：
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作者：
Takeo;M.;Y. Maehara;M. Ichihara;T. Ohminato;R. Kamata;and J. Oikawa
爆炸性喷发的动力学，如普林尼期、次普林尼期、火山期和斯特龙堡期的喷发，是火山物理学中最迷人的学科之一。2011年新莫德火山火山活动初期，先后发生了次普林尼期喷发、岩浆喷发和火山喷发等活动。每次活动都伴随着不同的倾斜运动。本文阐明了火山倾斜运动的特征及其时间序列，为火山喷发的触发机制提供了新的解释。在Shinmoe - dake火山的次普林尼期和火山喷发之前，在山顶附近的浅层深处发生了通货膨胀。在岩浆喷发阶段也记录了膨胀-收缩周期，典型周期为1小时，与火山震动或长周期事件同步。几乎所有的火山喷发之前都有梯形膨胀，其持续时间随着时间的推移而系统地延长，随后是各种时间序列的倾斜运动，在频繁的火山喷发中变得越来越复杂。我们发现，在每个子阶段，前一个持续时间的对数与经过的时间之间存在明显的线性关系，梯度为0.45。这些观测结果可以基于这样的假设得到一致的解释：火山喷发是由岩浆脱气超压引起的最强封闭固体岩浆框架的灾难性破裂引起的，岩浆脱气随时间呈指数递减。
The dynamics of explosive eruptions, such as Plinian, sub‐Plinian, Vulcanian, and Strombolian ones, is one of the most fascinating subjects in volcano physics. During the early period of volcanic activity at the Shinmoe‐dake Volcano in 2011, various kinds of activities, such as sub‐Plinian eruptions, a magma effusion, and Vulcanian eruptions, occurred sequentially. A different kind of tilt motion accompanied each activity. Here we clarify the characteristics of the tilt motions and their time sequences, presenting a new explanation of the triggering mechanism of a Vulcanian eruption. The sub‐Plinian and the Vulcanian eruptions at the Shinmoe‐dake Volcano were preceded by inflations at shallow depths near the summit. The inflation‐deflation cycles were also recorded during the magma‐effusive stage, with a typical period of 1 h, synchronized with volcanic tremors or long‐period events. Almost all Vulcanian eruptions were preceded by trapezoidal inflations, whose durations systematically lengthened as time progressed, and were followed by various time sequences of tilt motions, which became increasingly more complicated throughout the frequent Vulcanian eruptions. We have found clear linearity with a constant gradient of 0.45 between the logarithm of the preceding duration versus elapsed time for each substage. These observations can be consistently explained based on the assumption that a Vulcanian eruption is induced by a catastrophic rupture of the strongest closed, solid magma frame due to magma degassing overpressure, and the degassing from magma declines exponentially with time.