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Micro-tilt changes preceding summit explosions at Semeru volcano, Indonesia

机译：印度尼西亚Semeru火山在山顶爆炸前微倾角变化

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A two-axis tiltmeter installed at the summit of Semeru volcano, Indonesia, reveals two different modes of deformation, short-term and longer-term. The short-term variations are inflations precursory to the occurrence of summit explosions. The time intervals between the explosions range from several minutes to several tens of minutes, and the maximum precursory tilt change observed is about 0.1-0.2 μrad. This change in tilt is interpreted to reflect a shallow pressurization source, just beneath the active crater. The longer-term tilt changes are displayed over a period of several days to weeks, and a steady inflation during a period of nearly 2 weeks preceded the occurrence of pyroclastic flows on December 22, 2005. Both short-term and longer-term changes are confined to the radial tilt component, pointing toward the active crater and conduit. To explain both of these tilt changes we propose relatively shallow conduit pressurization, although at somewhat deeper levels in the case of longer-term deformation. The causative mechanisms involve gas exsolution, microlite crystallization, and rheological stiffening, which results in greater flow resistance and dynamic pressure in the upper conduit, thus causing the edifice tilts observed. The gas pore pressure in the magma builds until the threshold required to trigger explosive fragmentation is reached.
机译：安装在印度尼西亚Semeru火山山顶的两轴倾斜仪显示了两种不同的变形模式，即短期变形和长期变形。短期变化是发生顶峰爆炸之前的通货膨胀。爆炸之间的时间间隔从几分钟到几十分钟不等，观察到的最大前体倾斜变化约为0.1-0.2μrad。倾斜的这种变化被解释为反映了处于活动火山口下方的浅压力源。长期倾斜变化显示在几天到几周的时间内，并且在2005年12月22日发生火山碎屑流之前的近两周时间内，出现了稳定的通货膨胀。短期和长期变化都是仅限于径向倾斜分量，指向活动的弹坑和导管。为了说明这两种倾斜变化，我们建议采用相对较浅的导管增压，尽管在长期变形的情况下要稍微深一些。其原因包括气体逸出，微晶结晶和流变硬化，这导致上部导管中的流动阻力和动压力更大，从而导致建筑物倾斜。岩浆中的气体孔隙压力会不断增加，直到达到触发爆炸性碎片所需的阈值为止。

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