Shinmoedake Volcano Research Articles

Precursory crater contraction associated with the 2017 eruption of Shinmoe-dake volcano (Japan) detected by PALSAR-2 and Sentinel-1 InSAR

The time series of PALSAR-2 and Sentinel-1 images reveal inflation at the volcanic flank and contraction at the crater for approximately 5 months before the 2017 eruption of Shinmoe-dake volcano, Japan. While the observation of inflation at the volcano’s flank is ubiquitous, few studies have reported crater contraction preceding an eruption. The flank inflation stopped after the 2017 eruption, while the contraction at the crater continued until the 2018 eruption. We found that a pipe-shaped deformation source above sea level best fits the observation preceding the 2017 eruption. Suppose the flux of ejected materials constrains the conduit radius during the previous 2011 eruption. In that case, the amount of deformation of the pipe-shaped deformation source, whether open or closed at its top, is too large to be realistic. Although constraining the conduit radius from the eruption flux overestimates the pressure change of the pipe-shaped deformation source, water-saturated fractures along the volcanic conduit could extend the effective conduit radius of the pressure source. We propose one potential scenario for the mechanism of the crater contraction preceding volcanic eruptions based on the combination of compaction due to cooling by ambient groundwater and material withdrawal within the conduit. The groundwater inflows from the ambient aquifer through cracks in the porous conduit wall, which are generated by conduit expansion during the magma ascent. Decoupling from the conduit wall due to a decrease in volume of the material promotes material instability and crater contraction. The interaction between the groundwater and the magma triggers the 2017 eruption of Shinmoe-dake volcano, as previous studies have reported.Graphical

Estimation of seismometer clock time offsets using Kalman Filter towards accurate seismic velocity change

SUMMARY Monitoring seismic velocity changes obtained from ambient noise correlations is widely used to understand changes in rock properties in response to earthquakes, volcanic activities and environmental changes. Since continuous seismic data have been accumulated, this method can estimate long-term changes in seismic velocity, such as crustal recovery after a major earthquake and temporal variations in seismic velocity related to long-term environmental change. Changes in seismic velocity can be estimated with a high temporal resolution by measuring the phase differences of ambient noise correlations based on a seismic interferometry method. Still, these phase differences are influenced not only by seismic wave velocity changes but also by errors in clock timing in seismometers. The clock drift occurs due to out-of-synchronization with the GPS clock and the drift of the internal clock. Therefore, to accurately monitor temporal changes in crustal structure by measuring the phase differences of noise correlations, it is crucial to evaluate the contribution of errors in clock timing to the phase differences. Recently, a method using an extended Kalman filter based on a state-space model was developed for reliable detection of temporal changes in the waveforms of ambient noise correlations, with the state-space model offering the advantage of flexible modelling of time-series data. In this study, we incorporated the time-shifts caused by clock time errors of the seismometer into the state-space model of the temporal changes in ambient noise correlations. We estimated seismic velocity changes, amplitude changes of noise correlations and clock time errors from 2010 April to 2021 September at seismic stations around the Shinmoe-dake volcano in Japan, which experienced eruptions in 2011 and 2018, respectively. Several stations exhibited clear clock time offsets, and the occurrence of clock time-shifts coincided with the dates when the data logger was turned off for seismic station maintenance or replacement of the seismometer. The proposed method provides stable estimations with respect to the signal-to-noise ratio of the waveform, and this stable estimation facilitates accurate timing of seismic recordings, enabling precise analysis of seismic phase arrival times.

Constraints on magma storage conditions based on geodetic volume change and erupted magma volume and application to the 2011 and 2018 eruptions at Kirishima Shinmoe-dake volcano, Japan

We investigated magma storage conditions prior to the 2011 and 2018 eruptions at Kirishima Shinmoe-dake volcano in Japan based on the relationship between geodetic volume change of magma chamber and erupted magma volume. We derived an analytical expression for the ratio of the erupted magma volume to the geodetic volume change (“volume ratio”), which was formulated as a function of parameters related to the magma storage conditions. This expression shows that the volume ratio is strongly dependent on the effective compressibility of the magma chamber, which in turn depends on the rigidity of surrounding host rocks and shape of the chamber. For the Shinmoe-dake eruptions, the magnitude of the volume change (i.e., deflation) of a spherical magma chamber associated with lava effusion was estimated based on geodetic observations. The erupted magma volume was estimated from a SAR image analysis of the lava accumulation inside the summit crater. Based on these observations, we estimated that the volume ratio in 2011 and 2018 was 2.69 and 2.33, respectively. Substituting the estimated volume ratio into the analytical expression revealed that the observed geodetic data and volume ratio can be explained only when the magma chamber, which was assumed to be spherical, is filled with bubble-free magma. This result suggests that efficient gas segregation from the chamber occurred prior to the eruptions. Our results indicate that combining multi-observation data based on the volume ratio provides valuable information about the magma storage process, such as the behavior of the gas phase in the magma chamber.Graphical

Eruption style transition during the 2017–2018 eruptive activity at the Shinmoedake volcano, Kirishima, Japan: surface phenomena and eruptive products

Recent eruptions of the Shinmoedake volcano, Japan, have provided a valuable opportunity to investigate the transition between explosive and effusive eruptions. In October 2017, phreatic/phreatomagmatic explosions occurred. They were followed in March 2018 by a phase of hybrid activity with simultaneous explosions and lava flows and then a transition to intermittent, Vulcanian-style explosions. Evolution of surface phenomena, temporal variations of whole-rock chemical compositions from representative eruptive material samples, and rock microtextural properties, such as the crystallinity and crystal size distribution of juvenile products, are analyzed to characterize the eruption style transition, the conduit location, and the shallow magma conditions of the volcanic edifice. The 2017–2018 eruptive event is also compared with the preceding 2011 explosive–effusive eruption. The chemical and textural properties of the 2018 products (two types of pumice, ballistically ejected lava blocks, and massive lava) are representative of distinct cooling and magma ascent processes. The initial pumice, erupted during lava dome formation, has a groundmass crystallinity of up to 45% and the highest plagioclase number density of all products (1.9 × 106/mm3). Conversely, pumice that erupted later has the lowest plagioclase number density (1.2 × 105/mm3) and the highest nucleation density (23/mm4 in natural logarithm). This 2018 pumice is similar to the 2011 subplinian pumice. Therefore, it was likely produced by undegassed magma with a high discharge rate. Ballistics and massive lava in 2018 are comparable to the 2011 Vulcanian ballistics. Conversely, the high plagioclase number density pumice that occurred in 2018 was not observed during the 2011 eruption. Thus, such pumice might be specific to hybrid eruptions defined by small-scale explosions and lava dome formation with low magma discharge. The observed transitions and temporal variations of the activities and eruption style during the 2017–2018 Shinmoedake eruptions were primarily influenced by the ascent rate of andesitic magma and the geological structure beneath the summit crater.Graphical

Permutation entropy variations in seismic noise before and after eruptive activity at Shinmoedake volcano, Kirishima complex, Japan

Permutation entropy (PE) is a complexity metric that encodes a time series into sequences of symbols and can be used to decipher between deterministic and stochastic behavior. This study investigates PE variations in seismic noise during three eruption cycles in 2011, 2017, and 2018 at Shinmoedake volcano, Japan. The volcano is monitored by a dedicated seismic network and by infrasound microphones that recorded continuously during the aforementioned eruptions. The frequency range 1–7 Hz was used in order to infer temporal changes of PE in seismic noise and minimize any human contributions. The results showed that PE values decreased before the occurrence of each eruption. By combining these results with other observations we can attribute this decrease in PE to two reasons: first, to the occurrence of volcanic tremor that is a deterministic signal, and second, to magma migration at shallower depth beneath Shinmoedake which can attenuate high-frequency seismic waves and thus result in a less stochastic signal. PE also exhibited a spike-like increase just before the onset of the three eruptions. In 2011 and 2017, this feature was probably associated with bubble growth and collapse due to the interaction between the aquifer and high temperature magma. In 2018 the aquifer had mostly evaporated; hence, the spike in PE values was likely generated by fracturing of solidified magma within the conduit as fresh magma was pushing its way upwards. These results show that PE is a potentially useful tool for monitoring seismic noise at volcanoes and can contribute toward forecasting volcanic eruptions in conjunction with other widely used methodologies.Graphical

Shallow crystallization of eruptive magma inferred from volcanic ash microtextures: a case study of the 2018 eruption of Shinmoedake volcano, Japan

The occurrence of groundmass crystals reveals the shallow conduit process of magmas, which affects the behavior of eruptions. Here, we analyzed groundmass microtextures of ash samples from the 2018 eruption of Shinmoedake volcano, Japan, to evaluate the change of magma ascent conditions during the eruption sequence. The eruptive activity changed from ash venting (Phase 1: March 1–6) to lava effusion with continuous ash-laden plumes (Phase 2: March 6–9) and then shifted to Vulcanian explosions (Phase 3: March 10–April 5). Non-juvenile particles were abundant in Phase 1, whereas juvenile particles were dominant in Phases 2 and 3. Vesicular juvenile particles were more abundant in Phase 2 than Phase 3. The lower microlite crystallinity and groundmass SiO2 concentrations of the vesicular particles indicate that they were sourced from magma that ascended rapidly. Abundant nanolites were observed in the black interstitial glass of juvenile particles under an optical microscope, whereas few nanolites were observed in the transparent ones. The presence of nanolites can be explained by the dehydration of silicate melt, as well as cooling and oxidation between fragmentation and quenching. Temporal changes in the ash componentry show that the eruption activity started from the erosion of the pre-existing vent plug (Phase 1), shifted to the simultaneous eruption of bubble-bearing and outgassed magmas (Phase 2), and concluded with explosions of the stagnant lava (Phase 3), thereby demonstrating the sequence of vent opening and extrusion and stagnation of magma. Therefore, ash microtextures are valuable for monitoring the shallow conduit process of eruptive magma.

Behavior of magmatic components in fumarolic gases related to the 2018 phreatic eruption at Ebinokogen Ioyama volcano, Kirishima Volcanic Group, Kyushu, Japan

Direct sampling and analysis of fumarolic gas was conducted at Ebinokogen Ioyama volcano, Japan, between December 2015 and July 2020. Notable changes in the chemical composition of gases related to volcanic activity included a sharp increase in SO2 and H2 concentrations in May 2017 and March 2018. The analyses in March 2018 immediately preceded the April 2018 eruption at Ioyama volcano. The isotopic ratios of H2O in fumarolic gas revealed the process of formation. Up to 49% high-enthalpy magmatic vapor mixed with 51% of cold local meteoric water to generate coexisting vapor and liquid phases at 100–160 °C. Portions of the vapor and liquid phases were discharged as fumarolic gases and hot spring water, respectively. The CO2/SO2 ratio of the fumarolic gas was higher than that estimated for magmatic vapor due to SO2 hydrolysis during the formation of the vapor phase. When the flux of the magmatic vapor was high, effects of hydrolysis were small resulting in low CO2/SO2 ratios in fumarolic gases. The high apparent equilibrium temperature defined for reactions involving SO2, H2S, H2 and H2O, together with low CO2/SO2 and H2S /SO2 ratios were regarded to be precursor signals to the phreatic eruption at Ioyama volcano. The apparent equilibrium temperature increased rapidly in May 2017 and March 2018 suggesting an increased flux of magmatic vapor. Between September 2017 and January 2018, the apparent equilibrium temperature was low suggesting the suppression of magmatic vapor flux. During this period, magmatic eruptions took place at Shinmoedake volcano 5 km away from Ioyama volcano. We conclude that magma sealing and transport to Shinmoedake volcano occurred simultaneously in the magma chamber beneath Ioyama volcano.

Harmonic tremor model during the 2011 Shinmoe-dake eruption, Japan

Summary The Shinmoe-dake volcano started with three sub-Plinian eruptions from 26 to 27 January 2011, followed by a magma effusive stage from 28 to 31 January 2011, and Vulcanian eruptions occurred frequently during 1 to 10 February 2011. During the magma effusive and Vulcanian stages, multiple episodes of harmonic tremors were observed at stations near the summit crater. Although harmonic tremors have been observed at various volcanoes worldwide, the source mechanism remains poorly understood. This paper proposes a source model for harmonic tremors, which is composed of a nonlinear viscous fluid flow in a flexible channel. A simple lumped parameter model is used to consider the process. The dynamics are described by a third-order system of ordinary differential equations using model variables for a cross-sectional area of the constricted segment and the fluid velocities in the upstream and downstream tubes. This model produces various kinds of trajectories for self-sustained oscillations that change the reservoir pressure connected on the upstream channel of the model. Linearization analysis around the stationary point and global analysis employing nullcline planes reveal the mechanism of self-sustained oscillations of the system qualitatively. To consider both the frequency peaks of the harmonic tremor and the characteristics of observed phase spectra, the qualitative characteristics of an observed phase portrait are compared to those of a simulated one. This tremor model simulates the frequency peaks and the phase portraits of typical harmonic tremors observed during the 2011 Shinmoe-dake eruption. Because this model involves several geometrical configuration parameters, it has the potential to reveal the source mechanism of various kinds of harmonic tremors.

Detection of Thermal Changes Related to the 2011 Shinmoedake Volcano Activity, Japan: Spatiotemporal Variation of Singularity of MODIS Data after Discriminating False Changes Due to Cloud

We proposed a cloud discrimination method applicable in Japan using MODIS nighttime data, monitored the singularity of the spatiotemporal correlation of surface temperature anomalies and investigated the possibility of detecting and monitoring lava activity in Shinmoedake. With the aim to detect lava eruption activity in 2011, nine years of data from 2003 to 2011 were analyzed. As a result, the first anomalous singularity in brightness temperature was detected on 26 January 2011. Moreover, the maximum value was detected on 30 January 2011. The values showed larger ones until early February 2011. When an anomalous singularity appeared, it was the only period with the magma-related volcanic activity for Shinmoedake over the analyzed period of nine years. The above facts indicate the effectiveness of the proposed singularity method to monitor the lava activity for Shinmoedake. Therefore, it is concluded that if cloud discrimination is realized with high accuracy, no spurious changes will come to arise, and no false detection of hotspots will be given.

Vault-housed extensometers recorded a rapid initial pulse before precursory magma reservoir inflation related to the 2011 eruption of Shinmoe-dake, Japan

Previous studies of the major eruption at Shinmoe-dake volcano, Japan, in January 2011 suggested that gradual injection of magma from a deep source into a shallow reservoir began in December 2009 and led to the major eruption. To investigate the initial phase of this injection event, we examined extensometer data from the Isa Observatory, ~ 18.5 km from the summit of Shinmoe-dake, and discovered a strain change event that spanned about 3 days in December 2009. The size of the strain change is comparable to those observed during each sub-Plinian eruption in 2011. The source of the rapid strain change appears to be deeper than the estimated location of the magma reservoir that directly supplied magma to the 2011 eruption sequence. These observations suggest that rapid injection of magma from the deep magmatic plumbing system in December 2009 triggered the continuous ascent of additional magma from depth, which in turn drove the climactic eruptions in January 2011. Extensometers also recorded two rapid strain change events of the same order of magnitude and with similar characteristics in December 2006 and August 2008; however, noticeable inflation of the edifice was not detected immediately following either event. This suggests that transient injection of magma into a shallow reservoir is not always followed immediately by a gradual recharge process.

Tracing Volcanic Activity Chronology from a Multiparameter Dataset at Shinmoedake Volcano (Kirishima), Japan

Routine volcano monitoring increasingly involves multiparameter datasets. Databases that include multi-disciplinary datasets have great potential to contribute to the evaluation of ongoing volcanic eruptions and unrest events. Here, we examine the characteristics of a multiparameter dataset from Shinmoedake volcano (Kirishima) in Japan for the period of 2010–2018 to examine how the chronology of volcanic activity can be traced. Our dataset consists of global navigation satellite system (GNSS), seismic, tilt, infrasound, sulfur dioxide (SO2) column amount, and video records. We focus mainly on the period after 2012, particularly a series of ash emissions in 2017 (hereafter the 2017 eruption), lava effusion, and Vulcanian eruptions in 2018 (hereafter the 2018 eruption). Our dataset shows that the GNSS observations successfully captured the gradual inflation of the volcano edifice, suggesting magma intrusion or pressure buildup in the magma storage region prior to the 2017 and 2018 eruptions. The number of volcanic earthquakes also gradually increased from 2016 toward the eruptions, particularly events occurring beneath Shinmoedake. Tilt data captured a precursor tilt event prior to the 2017 eruption and a magma chamber deflation during the lava effusion of the 2018 eruption. Tilt, seismic, infrasound, SO2 gas column, and video data record signals accompanying periodic degassing during the lava effusion and explosive degassing accompanying the Vulcanian eruptions, which have similar characteristics to those reported for past eruptions at Shinmoedake and other volcanoes. This similarity suggests that multidisciplinary databases will be an important reference for future evaluations of ongoing volcanic activity and unrest.

Sulfur isotopic systematics during the October 2017 eruption of the Shinmoe-dake volcano, Japan

Shinmoe-dake, a volcano, in Japan, began to erupt on October 11, 2017, after a 6-year period of quiescence. The pyroclastic materials ejected during October 11–14, 2017, contain sulfur-bearing minerals. Time-series sulfur isotopic compositions of sulfur species in the samples ejected during the 2017 eruption were measured in order to reveal the geochemical characteristics of the volcanic hydrothermal system that developed after the 2011 eruption and its evolution during the 2017 eruption. δ34S values for water-leached sulfate (+16.09‰ to +17.51‰), acetone-leached native sulfur (−1.23‰ to +0.42‰), fine-grained pyrite (−1.81‰ to −0.90‰), and coarse-grained pyrite (−3.48‰ to −2.57‰) remained relatively constant with time. The hydrochloric-acid-leached sulfates of the pyroclastic materials ejected from October 11 to October 12 exhibit a relatively limited range of δ34S (+9.87‰ to +13.17‰). Then, on October 14, the δ34S value suddenly increased to +16.85‰, which is similar to that of the water-leached sulfate from the same day (+16.09‰). δ34S values for all the sulfur species were probably controlled by the disproportionation of magmatic SO2 in the presence of water in the hot (about 400 °C) deep and cooler (about 300 °C) shallow acidic hydrothermal alteration zones below the summit crater. These zones existed separately before and during the first few days of eruption, but were ruptured in succession as the eruption progressed. The sulfur isotopic similarity between the hydrochloric-acid-leached sulfate and the water-leached sulfate of the pyroclastic material on October 14 implies that the mixing, dissolution, and re-equilibration of the recycled sulfate from both alteration zones occurred at about 300 °C after the second day of the eruption.

A non-linear time-series analysis of the harmonic tremor observed at Shinmoedake volcano, Japan

A non-linear time-series analysis of the harmonic tremor observed at Shinmoedake volcano, Japan

Two Active Volcanoes in Japan May Share a Magma Source

Evidence collected following the 2011 eruption of Japan’s Shinmoedake volcano suggests that the powerful event affected the behavior of an active caldera nearby.

Lava Effusion during the March 2018 Activity of Shinmoedake Volcano, Kirishima Volcanic Complex

霧島火山群のほぼ中央に位置する新燃岳では，2018年3月1日に約5か月ぶりに噴火活動が開始し，3月6日からは断続的な爆発的噴火とともに，火口内で溶岩流出も発生した．パンケーキ状の溶岩ドームは3月9日には北西側火口縁に達するまで成長し（写真手前），その後も複数回の爆発的噴火が起こり，3月10日の噴火では大きな噴石が火口から約1.8 kmの地点にまで飛散し，3月25日と4月5日の爆発的噴火では噴石とともに，ごく小規模な火砕密度流が火口縁から400 m程度流下した．新燃岳では5月14日にも宮崎県の太平洋岸にまで降灰をもたらす噴火が発生しており，さらに4月19日と26日には北西へ約5 km離れた硫黄山でごく小規模な噴火が起こるなど，霧島火山群では火山活動が活発な状況となっている．写真中央奥には，尖った山頂をもつ高千穂峰火山と，その右側に大正時代まで頻繁に活動した御鉢火口が見える．朝日新聞社の協力により撮影．

霧島火山新燃岳2011年3月～2012年2月の降灰量調査 : 即時的降灰量推定の予察的検討

霧島火山新燃岳2011年3月～2012年2月の降灰量調査 : 即時的降灰量推定の予察的検討

3-A14 霧島・新燃岳の水蒸気爆発に伴う空気振動(桜島・霧島火山の活動2,口頭発表)

3-A14 霧島・新燃岳の水蒸気爆発に伴う空気振動(桜島・霧島火山の活動2,口頭発表)

P75 霧島火山群新燃岳2011年2月1日ブルカノ式噴火における弾道放出物とその噴出条件(ポスターセッション)

P75 霧島火山群新燃岳2011年2月1日ブルカノ式噴火における弾道放出物とその噴出条件(ポスターセッション)

P12 霧島山(新燃岳)噴火時の避難計画策定等の取組について(ポスターセッション)

P12 霧島山(新燃岳)噴火時の避難計画策定等の取組について(ポスターセッション)

P11 長期間アレイ地震解析からみた新燃岳の噴火活動推移(ポスターセッション)

P11 長期間アレイ地震解析からみた新燃岳の噴火活動推移(ポスターセッション)