Budget of shallow magma plumbing system at Asama Volcano, Japan, revealed by ground deformation and volcanic gas studies
Budget of shallow magma plumbing system at Asama Volcano, Japan, revealed by ground deformation and volcanic gas studies
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DOI：
10.1002/2014jb011715
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发表时间：
2015-05-01
影响因子：
3.9
通讯作者：
Shinohara, Hiroshi
中科院分区：
文献类型：
--
作者：
Kazahaya, Ryunosuke;Aoki, Yosuke;Shinohara, Hiroshi
2000年至2011年，日本浅间火山观测到了多次强烈的火山气体排放和地面变形（膨胀和紧缩）周期。根据火山气体排放速率和地面变形数据，估算了浅层岩浆管道系统的岩浆收支。 2004 年和 2008 年观察到的近期通货膨胀被模拟为浅间火山以西 2-3 公里处的堤坝侵入。先前的研究提出，岩浆从地壳中的岩浆库上升到岩脉，并通过连接岩脉和山顶的蜿蜒管道到达地表。火山中高达4600吨/天的密集火山二氧化硫排放量是通过岩浆通过该岩浆通道的对流脱气来模拟的。由于火山气体排放，储层中的岩浆收缩，火山就会收缩。我们根据 GPS 观测估计了模拟的岩脉体积变化、火山气体排放导致的岩浆体积减少以及产生的脱气岩浆量，以计算岩浆预算。结果表明，膨胀期火山气体排放引起的岩浆体积减少大于岩墙体积变化。这表明至少比岩墙体积变化大2倍以上的大量岩浆从中地壳岩浆库供给到了岩墙。岩脉的体积减少与紧缩时期火山气体排放导致的岩浆体积减少相当。岩脉的长期收缩趋势和脱气岩浆体积(10(8-9)m(3))表明，所产生的脱气岩浆并未储存在岩脉中，岩浆主要由中地壳岩浆库供给。在这两个时期，产生的脱气岩浆的体积都比岩墙的体积变化大1个数量级。这表明中地壳岩浆库供给的岩浆实际体积比岩脉体积变化大1个数量级。这些结果强烈表明，穿过岩浆库的岩浆量可能明显大于通过大地测量观测估计的岩浆库的体积变化。
Multiple cycles of the intensive volcanic gas discharge and ground deformation (inflation and deflation) were observed at Asama Volcano, Japan, from 2000 to 2011. Magma budget of the shallow magma plumbing system was estimated on the basis of the volcanic gas emission rates and ground deformation data. Recent inflations observed in 2004 and 2008 were modeled as a dike intrusion to 2-3km west of Asama Volcano. Previous studies proposed that magma ascends from a midcrustal magma reservoir to the dike and reaches the surface via a sinuous conduit which connects the dike to the summit. The intensive volcanic sulfur dioxide discharge of up to 4600t/d at the volcano was modeled by magma convective degassing through this magma pathway. The volcano deflates as shrinkage of the magma in a reservoir by volcanic gas discharge. We estimated the volume change of the dike modeled based on the GPS observations, the volume decrease of the magma by the volcanic gas discharge, and the amount of degassed magma produced to calculate the magma budget. The results show that the volume decrease of the magma by the volcanic gas discharge was larger than the volume change of the dike during the inflation periods. This indicates that a significant volume of magma at least more than 2 times larger than the volume change of the dike was supplied from the midcrustal magma reservoir to the dike. The volume decrease of the dike was comparable with the volume decrease of the magma by the volcanic gas discharge during the deflation periods. The long-term deflation trend of the dike and the volume of degassed magma (10(8-9)m(3)) suggest that the degassed magma produced is not stored in the dike and the magma is mainly supplied from the midcrustal magma reservoir. In both periods, the volume of degassed magma produced was 1 order of magnitude larger than the volume change of the dike. This indicates that the actual volume of the magma supplied from the midcrustal magma reservoir is up to 1 order of magnitude larger than the volume change of the dike. These results strongly suggest that an amount of magma moved through a magma reservoir is possible to be significantly larger than volume change of the magma reservoir estimated by the geodetic observations.