Kuchinoerabujima Volcano Research Articles

Influence of hydrothermal recharge on the evolution of eruption styles and hazards during the 2018\u20132019 activity at Kuchinoerabujima Volcano, Japan

The activity of the 2018–2019 eruption of Kuchinoerabujima Volcano in Japan changed from continuous ejection of ash-laden plumes between October 21 and the middle of December, to intermittent explosive activity accompanied by several pyroclastic density currents until January 2019. To understand the behaviors of magma and hydrothermal fluid that controlled the eruptive sequence, we carried out component analysis, X-ray diffractometry, and leachate analysis for ash samples. The proportion of non-altered volcanic ash particles is ~ 15% in the earlier phase, then it decreased to less than 10% in the later explosive phase. Accordingly, the mineral assemblage of the volcanic ash samples changed from plagioclase-dominant to sulfate minerals-dominant. Concentration of SO42− and Cl/SO4 values of the ash-leachates decreased toward the later activity. These results indicate that the proportion of fresh volcanic rocks decreased and sulfuric acid fluid-derived sulfate minerals increased toward the later activities. Consequently, the 2018–2019 eruption at Kuchinoerabujima Volcano changed from magmatic activity to phreatomagmatic activity. Weak glowing of the crater was observed during the magmatic activity, indicating the volcanic conduit was hot enough to dry up the sub-volcanic hydrothermal system. The following phreatomagmatic activity indicates that the hydrothermal fluid recharged after the magmatic eruption phase. Recharge of the hydrothermal fluid likely caused the variation of the eruption style, and is a process that may control the evolution of hazards during future eruption scenarios at similar active volcanoes in Japan and worldwide.Graphical

Precursors to the 2015 Eruption of Kuchinoerabujima Volcano and Decision Making on Evacuation

Precursors to the 2015 Eruption of Kuchinoerabujima Volcano and Decision Making on Evacuation

Airborne measurements of volcanic gas composition during unrest at Kuchinoerabujima volcano, Japan

Airborne measurements of volcanic gas composition using an unmanned aerial vehicle (UAV) and Cessna aircraft were conducted at Kuchinoerabujima volcano, Japan, between 2014 and 2016. Because eruptions occurred in August 2014, May 2015, and June 2015, access to the summit crater was limited because of the risk of sudden eruption such that airborne measurements were the only viable method to measure the volcanic gas composition. Multi-GAS and alkali-filter pack measurements were made on the leeward side of the crater and around the crater, using the Cessna and UAV, respectively. Observations using the UAV could measure the dense plume and quantify the gas species of H2O, CO2, SO2, H2S, H2, HCl, and HF, while the observations using the Cessna could measure only the diluted plume and quantify CO2, SO2, H2S, and H2. The seven airborne observations enabled us to monitor variations in the volcanic gas composition. Over the observation period, the SO2/H2S ratio decreased from 10 to 1.9. The H2O/SO2 ratio, H2/SO2 ratio, and apparent equilibrium temperatures (AET) estimated using the volcanic gas composition increased after the 2014 eruption. The decrease in the SO2/H2S ratio might be attributed to changes in the pressure of degassing magma and interactions with the hydrothermal system. The airborne methods presented here highlight the utility of using light aircrafts to safely conduct volcanic gas measurements during periods of volcanic unrest when traditional ground-based methods are not possible.

Ground deformation source model at Kuchinoerabu-jima volcano during 2006\u20132014 as revealed by campaign GPS observation

We analyzed campaign Global Positioning System observation data in Kuchinoerabu-jima during 2006–2014. Most benchmarks located around Shin-dake crater showed crater-centered radial horizontal displacements. Horizontal displacements at western rim of the Shin-dake crater were tended to be larger compared to those at eastern rim. In addition, benchmark KUC14 which locates near the cliff at Furu-dake showed westward horizontal displacement rather than crater-centered radial (southward) one. Meanwhile, small displacements were detected at the benchmarks located at the foot of Kuchinoerabu-jima. We modeled the observed displacements applying a finite element method. We set entire FE domain as 100 × 100 × 50 km3. We set top of the domain as a free surface, and sides and bottom to be fixed boundaries. Topography was introduced in the area within Kuchinoerabu-jima using digital elevation model data provided by Kagoshima prefecture and elevation information from Google earth, and elevation of the outside area was assumed to be sea level. We assumed a stratified structure based on a one-dimensional P-wave velocity structure. We applied a vertical spheroid source model and searched optimal values of horizontal location, depth, equatorial and polar radiuses, and internal pressure change of the source using the forward modeling method. A spherical source with a radius of 50 m was obtained beneath the Shin-dake crater at a depth of 400 m above sea level. The internal pressure increase of 361 MPa yields its volume increase of 31,700 m3. Taking effects of topography and heterogeneity of ground into account allowed reproduction of overall deformation in Kuchinoerabu-jima. The location of deformation source coincides with hypocenters of shallow volcano-tectonic (VT) earthquakes and the aquifer estimated from a two-dimensional resistivity model by audio-frequency magnetotellurics method. The obtained deformation source may be corresponding to the pressurized aquifer, and shallow VT earthquakes and demagnetization may be caused by pressure and strain accumulation in the rocks around the aquifer. Applying the obtained spherical source to the tilt change before August 3, 2014 eruption, we found that 520 m3 of volcanic materials were supplied toward shallower in 1.5 h before the eruption. The depth and volume change of deformation source before May 2015 eruption detected by precise leveling surveys is deeper and two orders of magnitude greater compared to that before August 2014 eruption.

B1-10 SAR干渉解析による口永良部島の地殻変動(火山地下構造と地殻変動,口頭発表)

B1-10 SAR干渉解析による口永良部島の地殻変動(火山地下構造と地殻変動,口頭発表)

Background to the Rapid Evacuation from the 2015 Eruption and Education for Disaster Prevention by Residents on Kuchinoerabujima Volcano

Background to the Rapid Evacuation from the 2015 Eruption and Education for Disaster Prevention by Residents on Kuchinoerabujima Volcano

Observations using an unmanned aerial vehicle in an area in danger of volcanic eruptions at Kuchinoerabu-jima Volcano, southern Kyushu, Japan

Observations using an unmanned aerial vehicle in an area in danger of volcanic eruptions at Kuchinoerabu-jima Volcano, southern Kyushu, Japan

Quantification of seismic and acoustic waves to characterize the 2014 and 2015 eruptions of Kuchinoerabujima Volcano, Japan

Quantification of seismic and acoustic waves to characterize the 2014 and 2015 eruptions of Kuchinoerabujima Volcano, Japan

Contribution of monitoring data to decision making for evacuation from the 2014 and 2015 eruptions of Kuchinoerabujima Volcano

Contribution of monitoring data to decision making for evacuation from the 2014 and 2015 eruptions of Kuchinoerabujima Volcano

Sulfur dioxide flux monitoring using a regular service ferry after the 2014 eruption of Kuchinoerabujima Volcano, Japan

Sulfur dioxide flux monitoring using a regular service ferry after the 2014 eruption of Kuchinoerabujima Volcano, Japan

Special Issue on Integrated Study on Mitigation of Multimodal Disasters Caused by Ejection of Volcanic Products

Volcanic eruptions induce often widely dispersed, multimodal flows such as volcanic ash, pyroclastics, layers, and lava. Lahars triggered by heavy rain may extend far beyond ash deposits. Indonesia, which has 127 volcanoes along its archipelago, is at high risk for such disasters. The 2010 Merapi volcano eruption, for example, generated pyroclastic flows up to 17 km from the summit along the Gendol River, killing over 300 residents. The February 13, 2014, eruption of the Kelud volcano produced a gigantic ash plume over 17 km high, dispersing tehpra widely over Java Island. Ash falls and dispersion closed 7 airports and caused many flights to be cancelled. Volcanoes in Japan have recently become active, with the 2014 phreatic eruption at the Ontake volcano leaving 63 hikers dead or missing. The eruption of the Kuchinoerabujima volcano on May 29, 2015, forced all island residents to be evacuated. All of these events undeerscore how underedeveloped Japan’s early warning alert levels remain. The Sakurajima volcano, currently Japan’s most active, maintained high activity in the first half of 2015. Ash from Janaury 2015, for example, was moved down the volcano’s slopes by extremely heavy rain in June and July, accumulating as thick sediment near villages. Regarding such situations of volcano countries, we will develop an integrated system to mitigate many kinds of disasters which are generated by volcanic eruptions and extended by rain fall and wind, based on scientific knowledge. We are developing an integrated warning system to be used by local and national governments to mitigate volcanic and sediment disasters. We are also creating measure against volcanic ash for airlines. This special issue summarizes basic scientific knowledge and technology on the present warning system to be used in the integrated system for decision-making.

Disaster Governance in Disaster Management Planning -Analysis of the Evacuation Planning Process for Kuchinoerabujima Volcano Eruption-

Disaster Governance in Disaster Management Planning -Analysis of the Evacuation Planning Process for Kuchinoerabujima Volcano Eruption-

Phreatomagmatic eruptions of 2014 and 2015 in Kuchinoerabujima Volcano triggered by a shallow intrusion of magma

Phreatomagmatic eruptions of 2014 and 2015 in Kuchinoerabujima Volcano triggered by a shallow intrusion of magma

P22 口永良部島2015年(5/29,6/18)噴出物の構成物(ポスターセッション)

P22 口永良部島2015年(5/29,6/18)噴出物の構成物(ポスターセッション)

GPS 連続観測による口永良部島火山の2014 年噴火10 年前からの地盤変動

2014年8月3日に噴火した口永良部島(くちのえらぶじま)火山の山頂部に おいて，GPS連続観測を噴火直前までの約10年継続して行った．最も近接した観測点は火口までの距離が約230 mであるものの，噴火前1 ヶ月間の短期間に前兆を示す変位は捉えられなかった．しかし長期的にみると，全期間で4回，山頂域の膨張を示唆する変位を観測している．それぞれのイベントは数 cmの変位に数ヶ月かかる緩慢なものであるが，その変位は累積していった．初期のイベントは明瞭な地震の増加を伴ったが，後期になると地震活動の高まりはほとんど見られなくなった．イベントの間隔は次第に長くなるとともに，2009 年頃から長期的トレンドに加えて微少な変動が混在するようになり，この頃から変動のパターンが変化した．詳細な解析により，山頂部の変動は下部地盤の西変位の上に火口浅部の放射状の変動が重なることによって現れていることが明らかになった．2013年からは火口浅部の変動は，膨張からほとんど停止ないし収縮傾向に転じている．さらに山頂部の2観測点に共通の変動が観測されるようになったことから，山頂部のやや深い場所に別の変動源が現れた可能性がある．

Meeting with the May 29, 2015 eruption of Kuchinoerabujima volcano

Meeting with the May 29, 2015 eruption of Kuchinoerabujima volcano

U1-03 2014年8月口永良部島火山噴火発生までの火山活動(緊急学術セッション(口頭発表))

U1-03 2014年8月口永良部島火山噴火発生までの火山活動(緊急学術セッション(口頭発表))

UP-25 口永良部島火山山頂部のGPSによる地殻変動観測と噴気・地中温度観測(緊急学術セッション(ポスター))

UP-25 口永良部島火山山頂部のGPSによる地殻変動観測と噴気・地中温度観測(緊急学術セッション(ポスター))

Evolution of volcanic gas composition during repeated culmination of volcanic activity at Kuchinoerabujima volcano, Japan

Chemical and isotopic compositions of low to medium temperature fumarolic gasses were measured at various fumaroles of Kuchinoerabujima volcano from 1993 to 2009 by the combination of fumarolic gas sampling and Multi-GAS measurement of volcanic plumes. Repeated culmination of the volcanic activity was observed as contemporaneous occurrence of seismic swarms, summit inflation and demagnetization, almost every two years after 1999. Fumarolic activity also increased parallel with these activities; new fumarolic fields of low-temperature fumaroles at boiling point formed at the southern and western rims of the summit crater in 2003 and intense degassing activity started at medium-temperature fumaroles inside the summit crater in 2008. The low-temperature fumarolic gasses have peculiar composition with high H 2/H 2O, CO/CO 2 and SO 2/H 2S ratios, typical features of high-temperature volcanic gasses, but also with low HCl and total S contents, typical features of low-temperature gasses. These features indicate that the gasses are formed by low-temperature differentiation of high-temperature gasses. Variation of H and O isotopic ratios of the low-temperature gasses indicates that the gasses are formed by isoenthalpic processes of vapor–liquid separation at 100 °C of a high-temperature gas and meteoric water mixture, implying that the high-temperature gas was injected into a shallow aquifer without cooling. Temperatures of the high-temperature gasses were estimated as 550–700 °C based on the equilibrium temperature calculation with considering the low-temperature differentiation. The medium-temperature fumarolic gasses from the summit crater have typical compositions of high-temperature volcanic gasses and are estimated as the source gas of the boiling point fumaroles. The H 2/H 2O and CO 2/S t ratios of the low-temperature fumaroles increased from 2004 to 2009, which is interpreted to be caused by the evolution of thermal structure of a shallow gas storage region of a few hundred meters deep. Increase of magmatic gas supply caused enlargement of a high-temperature zone of the gas storage region widening the surrounding temperature transit zone with smaller temperature gradient. The enlargement of the high-temperature zone also reduces the overlying low-temperature aquifer, which caused the decrease of CO 2/S t ratio by reduction of sulfur removal reaction. The enlargement of the high-temperature zone resulted in the leakage of the high-temperature gasses directly to the surface as the medium-temperature gasses from the summit crater.

Temporal change of characteristics of shallow volcano-tectonic earthquakes associated with increase in volcanic activity at Kuchinoerabujima volcano, Japan

Shallow volcano-tectonic (VT) earthquakes recorded at the Kuchinoerabujima island volcano in southwest Japan are analyzed in order to clarify the role of hydrothermal activity in the development of volcanic seismicity. From analysis of shallow VT earthquakes in 2006, two specific episodes of elevated seismicity are observed in April and November 2006. The VT earthquakes have hypocenters at depths of 0–0.4 km beneath the summit crater, and normal fault focal mechanisms with WNW–ESE extension consistent with the tensional stress field indicated by the alignment of craters and fissures. Although the hypocenters and focal mechanisms are found to be largely invariant during these episodes, the corner frequencies of the VT earthquakes underwent a pronounced increase and decrease accompanying the changes in seismicity rates. The corner frequencies increased to 20–25 Hz approximately one month prior to the onset of elevated seismicity, and then decreased to 10–15 Hz in the period of peak seismicity. The rupture length also decreased at the onset of seismicity, thereafter increasing as the seismicity continued. The peak seismicity in terms of the daily number of VT events was accompanied by inflation around the crater, suggestive of a pressure increase in the volcanic system. It is inferred that the increase in shallow VT seismicity and rupture length is related to the development of a fractured zone. The pressure increase in the volcanic system is attributed to the intrusion of hydrothermal fluids, which is supported by an observed increase in fumarolic temperature and activity. The preceding monochromatic events are thus considered to be generated by the effect of fluid-filled cracks. The shortening of rupture length is then inferred to be related to the closing of non-fluid-filled cracks in the fracture zone under the increasing pressure field, leading to a transition from monochromatic events to low-frequency and shallow VT seismicity.