Magma-hydrothermal System of Hakone Volcano

IF 0.2 Q4 GEOGRAPHY, PHYSICAL
K. Mannen
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引用次数: 3

Abstract

― 831 ― Abstract Hakone volcano has been in an active phase since 2001, as implied by frequent volcanic unrest every 2 ­ 5 years, with each accompanied by deep inflation ( 6 ­ 10 km ) , increase of deep low-frequency events ( DLFEs ) at a depth of ~20 km, increase of CO 2 /H 2 S ratio in fumarole gas, and surge of volcano tectonic earthquakes ( VT; < 6 km deep ) . A series of episodes of volcanic unrest culminated in a small phreatic eruption ( erupted volume; ~100 m 3 ) in 2015; however, lesser unrest in terms of seismic activity occurred in 2017 and 2019. Recent studies on crustal structures based on seismic tomography indicate a magma chamber 10 ­ 20 km beneath the volcano, which might be connected to a large magma chamber beneath Fuji volcano, approxi-mately 30 km NW of Hakone. Interestingly, the DLFEs beneath Hakone volcano seem to take place in a high attenuation zone that connects the magma chambers. Deep inflation beneath Hakone volcano, however, is clearly located at a shallower location than the magma chamber of Hakone. The increases of CO 2 and He within the fumarole of Hakone during its unrest may indicate degassing of magma at depth. The maximum fumarole temperature after the eruption and constraints on subsurface temperature ( ~200°C at 400 m deep indicated by the mineral assemblage and ~370°C at 4 km below sea level where is the lower depth limit of VT ) imply a vapor-dominated hydrothermal system in the volcano from the bottom of the cap structure ( ~100 m deep ) to a depth of possibly 2 ­ 4 km. Such a vapor-dominated system may allow rapid transfers of magmatic gases and their emission from the fumarole area in the very early phase of volcanic unrest, as was observed. Hakone lacks long period events ( LF ) and volcanic tremors, which are common at many active volcanoes. Because such events are considered to be related to fluid migration, the vapor-dominated system can be attributed to their absence in Hakone. An estimation of the water mass balance implies that the amount and rate of inflation in the hydrothermal system are comparable to those emitted from the fumarole area in pre-eruptive calm periods. Thus, continuous inflation at depth can be explained by crystal depositions from the hydro thermal fluid. The high temperature of steam emitted in the fumarole area after the eruption indicates destruction of the container of the hydrothermal system, which also caused the lower VT activity and CO 2 /H 2 S
箱根火山岩浆热液系统
―831―抽象箱根火山自2001年以来一直处于活跃期,每2至5年发生一次频繁的火山动荡,每次都伴随着深度下沉(6至10公里)、约20公里深处低频事件(DLFE)的增加、富马孔气体中CO2/H 2 S比的增加以及火山构造地震(VT;<6公里深)的激增。一系列火山动荡事件最终导致2015年的一次小规模潜水喷发(喷发量约100立方米);然而,2017年和2019年发生的地震活动较少。最近基于地震层析成像的地壳结构研究表明,火山下方10-20公里处有一个岩浆室,可能与箱根西北约30公里处的富士火山下方的一个大型岩浆室相连。有趣的是,箱根火山下方的DLFE似乎发生在连接岩浆室的高衰减区。然而,箱根火山下方的深流显然位于比箱根岩浆室更浅的位置。箱根富马孔内CO2和He在其动乱期间的增加可能表明岩浆在深处脱气。火山喷发后的最大喷孔温度和对地下温度的限制(矿物组合指示的400米深处约200°C,海平面以下4公里处约370°C,这是VT的深度下限)意味着火山中从帽盖结构底部(约100米深)到可能2至4公里深的蒸汽主导的热液系统。正如所观察到的那样,这种以蒸汽为主的系统可能允许岩浆气体的快速转移,并在火山动荡的早期阶段从富马孔区域排出。箱根缺乏长周期事件(LF)和火山震动,这在许多活火山中很常见。由于这些事件被认为与流体迁移有关,蒸汽主导的系统可归因于箱根没有它们。对水团平衡的估计表明,热液系统中的流入量和速率与喷发前平静期从富马孔区域排出的水量和速率相当。因此,水热流体的晶体沉积可以解释深度的连续流动。火山喷发后富马孔区冒出的高温蒸汽表明热液系统的容器遭到破坏,这也导致VT活性和CO2/H2 S降低
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来源期刊
CiteScore
1.50
自引率
33.30%
发文量
28
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