Language：English   Publishing type：Research paper (scientific journal)   Publisher：Canadian Science Publishing  

<jats:p> For the first time ever, samples were collected from volcanic lake waters in Costa Rica using an unmanned aerial vehicle (drone), which represents a major achievement in human–machine interaction and innovation in the technology sector. A Matrice 600 Pro drone was used for remote sampling in the hyperacid crater lake of the Poás volcano, the mildly acidic Lake Botos, and the nearly neutral Lake Hule. A bailer bottle of 250 mL and a HOBO temperature probe, mounted on the drone, were deployed using a specially designed delivery retrieval system. A comparison was carried out relating to the geochemistry of lake water collected by drone as opposed to the hand-collected samples. The SO<jats:sub>4</jats:sub><jats:sup>−2</jats:sup>/Cl ratios of the two samples at Poás hyperacid crater lake were similar, (1.1 ± 0.2) on average, an indication of a lake with homogenous water composition. The Lake Hule showed a similar composition to that registered 20 years ago. The waters from Lake Botos showed some differences, which may be explained by the influence of springs at the bottom of the lake, but the Wilcoxon's signed-rank test showed a good exhibit of a satisfactory level of similarity. Autonomous navigation proves to be very useful for faster, more efficient, reliable, and less hazardous sampling of volcanic lakes. </jats:p>

DOI： 10.1139/dsa-2022-0023

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DOI： 10.1186/s40623-022-01630-5

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Abstract

We repeatedly measured isotopic compositions of noble gases and CO₂ in volcanic gases sampled at six fumaroles around the Kusatsu-Shirane volcano (Japan) between 2014 and 2021 to detect variations reflecting recent volcanic activity. The synchronous increases in ³He/⁴He at some fumaroles suggest an increase in magmatic gas supply since 2018. The increase in magmatic gas supply is also supported by the temporal variations in ³He/CO₂ ratios and carbon isotopic ratios of CO₂. The ³He/⁴⁰Ar* ratios (⁴⁰Ar*: magmatic ⁴⁰Ar) show significant increases in the period of high ³He/⁴He ratios. The temporal variation in ³He/⁴⁰Ar* ratios may reflect changes in magma vesicularity. Therefore, the ³He/⁴⁰Ar* ratio of fumarolic gases is a useful parameter to monitor the current state of degassing magma, which is essential for understanding the deep process of volcanic unrest and may contribute to identifying precursors of a future eruption. These results provide additional validation for the use of noble gas and carbon isotopic compositions of fumarolic gases for monitoring magmatic–hydrothermal systems.

DOI： 10.1038/s41598-022-22280-3

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Other Link： https://www.nature.com/articles/s41598-022-22280-3

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Fuji Technology Press Ltd.  

<jats:p>Recent developments in unmanned aerial vehicle (UAV) technology have made it possible to measure gas compositions in volcanic plumes using lightweight compact gas sensors. However, the differences in the responses of each gas sensor can be critical in estimating gas compositions based on regression scatter plots, particularly for small plumes emitted during volcanic unrest and non-eruption periods. Based on the laboratory experiments, we show that air blowers easily adjust sensor responses and improve correlation on regression scatter plots, allowing quick composition estimates without the use of mathematical applications. Applying our measurement system, lightweight compact gas sensors for H<jats:sub>2</jats:sub>S, SO<jats:sub>2</jats:sub>, CO<jats:sub>2</jats:sub>, and H<jats:sub>2</jats:sub>O, with air blowers suspended from a UAV, were used to determine the compositions of a small plume at Io-yama, Kirishima volcano, Japan. The compositions of the plume estimated by our system were reasonably consistent with those obtained by laboratory analysis of volcanic gas collected at ground level near the vent, with fluctuations in CO<jats:sub>2</jats:sub> ratios and lower H<jats:sub>2</jats:sub>O ratios, relative to other gases, being observed. For more accurate estimations of CO<jats:sub>2</jats:sub> and H<jats:sub>2</jats:sub>O concentrations, low humidity conditions at a distance from the fumarole are preferable for analysis of plumes diluted by ambient dry air. Our measurement system is simple, easy to set up, and useful for estimating the compositions of small passive fumarolic gas plumes during volcanic unrest and non-eruption periods, without mathematical applications.</jats:p>

DOI： 10.20965/jdr.2022.p0620

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DOI： 10.3389/feart.2021.740671

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Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

Interpreting the triggering mechanisms for phreatic eruptions is a key to improving the hazard assessment of crater lakes. Yugama Crater Lake at Kusatsu-Shirane volcano, Japan, is the site of frequent phreatic eruptions with the recent eruptions in 1982–83, 1989, and 1996, as well as volcanic unrest, including earthquake swarms in 2014 and 2018. To understand the magma–hydrothermal interaction beneath Yugama Crater Lake, we analyzed lake waters from November 2005 to May 2021. From 2005 to 2012, Cl and SO₄ concentrations decreased slowly, suggesting the development of a self-sealing zone surrounding the crystallizing magma. We focused on Ca, Al, and Si concentrations as representatives of the breach and dissolution of minerals comprising the self-sealing zone and the Mg/Cl ratio as an indicator for enhanced interaction between groundwater and hot plastic rock within the self-sealing zone. In 2006–2007, the Ca, Al, Si concentrations and the Mg/Cl ratio increased. No Cl and SO₄ increase during this period suggests the self-sealing zone was leached by deep circulating groundwater rather than by magmatic fluids injection. After the 2014 earthquakes, Ca, Al, and Si increased again but were associated with a significant Cl increase and a pH decrease. We believe that the HCl-rich magmatic fluids breached the self-sealing zone, leading to fluids injection from the crystallizing magma to the Yugama crater. During this period, the Mg/Cl ratio did not increase, meaning that magmatic fluids ascending from the breached area of the self-sealing zone inhibited deep intrusion of groundwater into the hot plastic rock region. In 2018, magmatic fluids ascended through the self-sealing zone again with less intensity than in 2014. All eruptions since 1982 have been accompanied by a Mg/Cl ratio increase and a Cl decrease, whereas, when a significant HCl input occurs, as in 2014, no eruptions and no Mg/Cl ratio increase occurred. This demonstrates that the groundwater–hot plastic rock interaction, rather than the magmatic fluids input, played an essential role in triggering phreatic eruptions; i.e., phreatic eruptions can potentially occur without clear signs of fresh magma intrusions.

DOI： 10.3389/feart.2021.741742

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Abstract

On January 23, 2018, a small phreatic eruption (VEI = 1) occurred at the Motoshirane Pyroclastic Cone Group in the southern part of Kusatsu-Shirane Volcano in central Japan. The eruption ejected ash, lapillus, and volcanic blocks from three newly opened craters: the main crater (MC), west crater (WC), and south crater (SC). Volcanic blocks were deposited up to 0.5 km from each crater. In contrast, the ash released during this eruption fell up to 25 km ENE of the volcano. The total mass of the fall deposit generated by the eruption was estimated using two methods, yielding total masses of 3.4 × 10⁴ t (segment integration method) and 2.4 × 10⁴ t (Weibull fitting method). The calculations indicate that approximately 70% of the fall deposit was located within 0.5 km of the craters, which was mainly attributed to the low height of the eruption plume.

DOI： 10.1186/s40623-021-01468-3

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Other Link： https://link.springer.com/article/10.1186/s40623-021-01468-3/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

<title>Abstract</title>We estimate the mass and energy budgets for the 2018 phreatic eruption of Mt. Motoshirane on Kusatsu–Shirane volcano, Japan, based on data obtained from a network of eight tiltmeters and weather radar echoes. The tilt records can be explained by a subvertical crack model. Small craters that were formed by previous eruptions are aligned WNW–ESE, which is consistent with the strike of the crack modeled in this study. The direction of maximum compressive stress in this region is horizontal and oriented WNW–ESE, allowing fluid to intrude from depth through a crack with this orientation. Based on the crack model, hypocenter distribution, and MT resistivity structure, we infer that fluid from a hydrothermal reservoir at a depth of 2 km below Kusatsu–Shirane volcano has repeatedly ascended through a pre-existing subvertical crack. The inflation and deflation volumes during the 2018 eruption are estimated to have been 5.1 × 10⁵ and 3.6 × 10⁵ m³, respectively, meaning that 1.5 × 10⁵ m³ of expanded volume formed underground. The total heat associated with the expanded volume is estimated to have been ≥ 10¹⁴ J, similar to or exceeding the annual heat released from Yugama Crater Lake of Mt. Shirane and that from the largest eruption during the past 130 year. Although the ejecta mass of the 2018 phreatic eruption was small, the eruption at Mt. Motoshirane was not negligible in terms of the energy budget of Kusatsu–Shirane volcano. A water mass of 0.1–2.0 × 10⁷ kg was discharged as a volcanic cloud, based on weather radar echoes, which is smaller than the mass associated with the deflation. We suggest that underground water acted as a buffer against the sudden intrusion of hydrothermal fluids, absorbing some of the fluid that ascended through the crack.

DOI： 10.1186/s40623-021-01475-4

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Language：Japanese   Publisher：The Volcanological Society of Japan  

The Kusatsu-Shirane Volcano is one of the most active composite volcanoes in Japan. All the historical eruptions, except for the 2018 eruption of the Motoshirane Pyroclastic Cone Group, have occurred in and around the Shirane Pyroclastic Cone Group (SPCG). Thus far, the eruption ages and styles of the Yumi-ike Maar and the Shirane-Minami Crater Chain (SMCC), located at the southern foot of SPCG, are not understood. In this study, we re-examine the eruption history of the volcano based on the stratigraphy revealed by three trench surveys, petrography, whole-rock composition, hydrothermal mineral assemblages, and new radiocarbon ages. Three 3 m-deep trenches (RH, SJ, and KSE trenches) were dug on the southern to eastern foot of the SPCG and four key deposits were identified. In ascending order, there are (A) the thick heterogeneous white clayey ash deposit rich in hydrothermal alteration minerals derived from the SPCG; (B) a mixture of pyroclastic surge and fallout deposits with juvenile jointed pyroclasts derived from the Yumi-ike Maar; (C) fallout ash from the AD 1882 eruption, a stratigraphically uppermost thin white clayey ash-fall deposit derived from the SPCG. Additionally, the funnel-shaped pyroclastic dyke is found only at the RH trench at the southern end of the SMCC; its strike coincides with the alignment of the SMCC craters, and it is accompanied by white clayey ash-fall deposits. Our study revealed that these key deposits (except for the ash-fall from the AD 1882 eruption) correspond to three eruptions, with the largest phreatic eruption occurring at the SPCG after ca. 7,000 cal BP; the phreatomagmatic eruption that formed the Yumi-ike Maar at ca. 1,400 cal BP (ca. 600 cal AD); and the phreatic eruptions that formed the SMCC after ca. 1,000 cal BP (ca. 1,000 cal AD). The eruption of the Yumi-ike Maar is likely to be the latest magmatic eruption at the Kusatsu-Shirane Volcano.

DOI： 10.18940/kazan.66.1_1

DOI： 10.3389/feart.2021.741742_references_DOI_FKVsU9bgwiN5VhrV4LHZZkDEDtW

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

<title>Abstract</title>Kusatsu-Shirane volcano hosts numerous thermal springs, fumaroles, and the crater lake of Yugama. Hence, it has been a particular study field for hydrothermal systems and phreatic eruptions. On 23 January 2018, a phreatic eruption occurred at the Motoshirane cone of Kusatsu-Shirane, where no considerable volcanic activity had been reported in observational and historical records. To understand the eruption process of this unique event, we analyzed seismic, tilt, and infrasound records. The onset of surface activity accompanied by infrasound signal was preceded by volcanic tremor and inflation of the volcano for ~ 2 min. Tremor signals with a frequency band of 5–20 Hz remarkably coincide with the rapid inflation. We apply an amplitude source location method to seismic signals in the 5–20 Hz band to estimate tremor source locations. Our analysis locates tremor sources at 1 km north of Motoshirane and at a depth of 0.5–1 km from the surface. Inferred source locations correspond to a conductive layer of impermeable cap-rock estimated by magnetotelluric investigations. An upper portion of the seismogenic region suggests hydrothermal activity hosted beneath the cap-rock. Examined seismic signals in the 5–20 Hz band are typically excited by volcano-tectonic events with faulting mechanism. Based on the above characteristics and background, we interpret that excitation of examined volcanic tremor reflects small shear fractures induced by sudden hydrothermal fluid injection to the cap-rock layer. The horizontal distance of 1 km between inferred tremor sources and Motoshirane implies lateral migration of the hydrothermal fluid, although direct evidence is not available. Kusatsu-Shirane has exhibited unrest at the Yugama lake since 2014. However, the inferred tremor source locations do not overlap active seismicity beneath Yugama. Therefore, our result suggests that the 2018 eruption was triggered by hydrothermal fluid injection through a different pathway from that has driven unrest activities at Yugama.

DOI： 10.1186/s40623-020-01349-1

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-020-01283-2

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Language：Japanese   Publisher：The Geological Society of Japan  

Kusatsu-Shirane Volcano is one of the most active volcanoes in Japan. The summit of the volcano comprises three young pyroclastic cones: the Motoshirane Pyroclastic Cone Group (MPCG), which erupted on January 23, 2018, with almost no eruptive precursors; the Ainomine Pyroclastic Cone, of unknown age; and the Shirane Pyroclastic Cone Group (SPCG), which is the site of numerous historical phreatic eruptions. In this study, we present the results of an investigation of the stratigraphy and eruption history of the MPCG. The MPCG consists of overlapping pyroclastic cones including, from south to north, Motoshirane-nishi, the Older and Younger Motoshirane, Kagamiike, and Kagamiike-kita. The stratigraphic relationships and geochemical characteristics of the erupted material suggest that construction of most of these cones involved initial lava flow and subsequent cone-forming stages. Four lava flows, the Daimyozawa, Ishizu, Sessho, and Furikozawa lavas, form the bases of the Motoshirane-nishi, Older Motoshirane, Kagamiike, and Kagamiike-kita cones, respectively. The subsequent cone-forming stages included Vulcanian and phreatomagmatic eruptions. Products of the Kagamiike and Kagamiike-kita eruptions can be correlated with the ca. 4800 cal yr BP 12L Volcanic Sand (Hayakawa and Yui, 1989), which lies at the eastern foot of the volcano, and the juvenile jointed block-rich horizon (after ca. 1500 cal yr BP) on the southern flank of the Kagamiike cone, respectively. In summary, the MPCG eruption sites shifted from south (the Motoshirane-nishi cone) to north (the Kagamiike-kita cone), and magmatic eruptions continued until just after ca. 1500 cal yr BP. Petrological analyses of the erupted material suggest that the MPCG eruptions were fed by a mixture of dacitic magma from the long-lived crustal magma chamber, and repeatedly recharged mafic magmas with different compositions for each pyroclastic cone.

DOI： 10.5575/geosoc.2020.0022

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DOI： 10.30909/vol.03.01.67114

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Language：Japanese   Publisher：The Geological Society of Japan  

We report petrographic characteristics and whole-rock chemical compositions of the Stage 3 (after 16 ka) eruption products of Kusatsu-Shirane Volcano, central Japan. The Stage 3 eruption products analyzed in this study are from the Shirane Pyroclastic Cone Group (SPCG), the Ainomine Pyroclastic Cone, and the Yumi-ike Maar, which are all located in the northern summit area of Kusatsu-Shirane Volcano. All lavas and juvenile pyroclasts of the Stage 3 eruption products contain phenocrysts of plagioclase, orthopyroxene, clinopyroxene, and opaque minerals. In addition to these minerals, some rocks contain rare olivine, quartz, and biotite phenocrysts. The lavas that were erupted during the early activity of the SPCG (the Hebei-ike, Kagusa, and Shirane-higashi lavas) have wide variations in SiO₂ content from andesitic to dacitic and in some outcrops exhibit a heterogeneous mingled appearance. In contrast, the lavas and pyroclasts that were erupted during the later stage of the SPCG (Shirane Pyroclastic Deposits and the Mizugama Lava Dome), as well as the Ainomine and the Yumi-ike Pyroclastic Deposits, are homogeneous in appearance and have andesitic compositions. Irrespective of the relative eruption ages, the analyzed Stage 3 eruption products are all associated with the calc-alkaline and medium-K series.

DOI： 10.5575/geosoc.2019.0046

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DOI： 10.20965/jdr.2020.p0053

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DOI： 10.20965/jdr.2019.p0755

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We collected information on non-magmatic unrest events reported mainly of Japanese volcanoes that have been monitored for extended time periods, with the aim of conducting a statistical evaluation of these phenomena, which can sometimes lead to an eruption. We assessed the geomagnetic field changes and ground deformation, which indicate demagnetization and inflation, respectively. We then compiled the source depth, intensity, and the rate (i.e., magnetic moment rate / deformation rate), based on the single magnetic dipole model or the Mogi model, since these models are the most frequently cited in the literature. We found clear positive correlations between the source depth and its intensity and rate, exhibiting a linear trend on the log-log scatter plots. We confirmed that all the magnetic events and some of the deformation events were plotted markedly above the cutoff line related to the detection limit. We suspected that the geometry of the monitoring network and/or the simplistic point-source modeling could contribute to these positive correlations; otherwise some physical requirements such as subsurface structure might be the cause.

Although the number of unrest events collected was small, we investigated the validity of the evaluation of these unrest events from different viewpoints. Upward deviation from the linear trend on the scatter plot was found to be a potentially useful criterion, whereas the source depth had no definitive relationship with the subsequent occurrence of eruptions.

We assert that observable non-magmatic unrest events should be plotted within a diagonal area between the lower-right and upper-left domains in a scatter plot of source intensity (or rate) and depth. This is because weak sources at great depths cannot be detected, while overly strong sources close to the ground surface are physically impossible. In the intermediate zone, “unerupted” and “erupted” unrest events both occur. Based on this idea, we propose a statistical evaluation of the severity of unrest events, by measuring the deviation from the “unerupted unrests”, although this hypothesis must be tested with a sufficient number of unrest events in the future. Meanwhile, care must be taken in interpreting the data collected here, since they are based on the simplified point-source models that assume a uniform half-space, and they may not accurately recreate the physical entities.

Further studies that can relate the physical conditions and their time evolution in the subsurface to geophysical monitoring records at the ground surface will be necessary to evaluate how such unrest events are related to eruptions.

DOI： 10.18940/kazan.64.2_103

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Language：English   Publisher：Springer Berlin Heidelberg  

DOI： 10.1186/s40623-018-0798-4

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DOI： 10.1186/s40623-018-0835-3

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Publishing type：Research paper (scientific journal)   Publisher：Springer Nature  

DOI： 10.1186/s40623-018-0886-5

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Language：Japanese   Publisher：The Geological Society of Japan  

This paper reviews the hydrothermal systems of Kusatsu-Shirane volcano, Japan, which are associated with phreatic eruptions. The existence of hydrothermal systems at this volcano is easily explained: hot springs are derived from unique thermal water that results from condensation of magmatic gas. Kusatsu-Shirane also exhibits fumaroles characterized by high H₂S and CO₂ contents, which are separate from the condensation of magmatic gas. Clay layers composed of smectites control the subsurface flow of thermal water. Hypocenter distributions of microearthquakes approach from depth to a bell-shaped impermeable clay layer underlying the Shirane pyroclastic cone, indicating the clay layer’s role in storing thermal water supplied from depth. Sources of low-frequency earthquakes, ground deformation, and demagnetization/magnetization are located around the bell-shaped impermeable clay. These observations indicate that a hydrothermal reservoir exists under the clay layer. Phreatic eruptions seem to result from the growth of cracks connecting the reservoir to the surface. Precursory changes in volcanic activity precede phreatic eruptions at Kusatsu-Shirane in most cases; however, the contents of such precursors do not correlate with the ejecta mass, locations, and lead times of eruptions. Kusatsu-Shirane has been continuously monitored since the 1970s. The phreatic eruption of 1976 was predicted based on geochemical observations, but no precursor warning was detected before the onset of a series of phreatic eruptions in 1982-1983. Microearthquake swarms that occurred in 1989-91 and 2014 were followed by demagnetization and changes in the chemical composition of the water in Yugama Crater Lake and the fumaroles. These changes were similar to precursors of past phreatic eruptions at Kusatsu-Shirane, but no phreatic eruption occurred at Yugama Crater within 2-3 years of either set of changes. Multiparameteric monitoring, including geophysical and geochemical observations, is a powerful tool for detecting changes in volcanic activity, but it is difficult to identify precursors of phreatic eruptions.

DOI： 10.5575/geosoc.2017.0060

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Language：Japanese   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2018.0_76

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Language：Japanese   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2018.0_75

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DOI： 10.1002/2017JB014387

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DOI： 10.1186/s40623-016-0418-0

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Language：Japanese   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2016.0_150

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Language：English   Publishing type：Part of collection (book)   Publisher：Springer Berlin Heidelberg  

DOI： 10.1007/978-3-642-36833-2_13

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Language：Japanese   Publisher：Volcanological Society of Japan  

DOI： 10.18940/kazan.57.4_235

DOI： 10.3389/feart.2021.741742_references_DOI_67LjOiRR5F74DwdebUQyXTuBYv9

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DOI： 10.1016/j.geothermics.2012.01.003

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DOI： 10.1007/s00445-011-0550-4

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Language：Japanese   Publisher：The Volcanological Society of Japan  

We produced an SO₂ imager of a low-cost version with the use of digital cameras of consumer use. General configuration and characteristics of the instrument are presented. Calibration with SO₂ cells of known column concentration confirmed a comparable absorption coefficient to the device which is previously invented by Mori and Burton (2006). Although simultaneous shooting with two cameras is necessary to overcome the temporal change of an object because of somewhat long exposure time (5 to 10 sec) required, this device operates without external power or control PCs, and thus, is suitable for mobile use. We performed a field test of the instrument at Sakurajima volcano and confirmed its validity as an SO₂ imager. However, further improvement of the optical system or a special care with UV scattering in front of a plume is necessary for quantitative applications in a field operation.

DOI： 10.18940/kazan.57.4_219

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Language：Japanese   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2011.0_148

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Language：Japanese   Publisher：Volcanological Society of Japan  

DOI： 10.18940/kazan.55.3_155

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DOI： 10.18940/vsj.2010.0_154

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The heat balance model can be used to readily calculate the total heat-discharge rate through steaming ground based on the distribution of surface temperature obtained by an infrared radiation (IR) thermometer. This method is convenient; however, the model involves some critical assumptions and large uncertainties. With the aim of developing a simple method for reliable measurements of the total heat-discharge rate, we carried out field experiments at the geothermal field of Yoshioka hot springs, Aso volcano, Japan. To directly measure the heat-discharge rate at each measurement site, we used Ice Box Calorimetry (IBC), which can be used to measure the combined conductive and convective heat-discharge rate, Q(W/m^2), from the ground surface, based on the time required to melt ice housed within an aluminum box placed on the ground. At the same time, we used an IR thermometer to measure the ground-surface temperature, T(℃), at each site. Our observations revealed the relationship between the heat-discharge rate anomaly ΔQ(=Q-Q_0^^-) and the temperature anomaly ΔT(=T-T_0^^-), where Q_0^^- and T_0^^- were the average ground-surface temperature and the average heat-discharge rate outside the geothermal area, respectively. Although the obtained data show a degree of scatter, the value of ΔQ increases almost linearly with ΔT, consistent with the heat balance model: ΔQ=CΔT, where C is the proportional coefficient, which is estimated to be 51±2(W/m^2/℃) from the least squares method. We consider that this empirical relationship is applicable in obtaining accurate estimates of the total heat-discharge rate from steaming ground. To assess the reliability of the linear relation and determine appropriate values of C, it would be necessary to conduct additional accurate, simultaneous observations of Q and T at sites on many different volcanoes and under various meteorological conditions. Furthermore, we carried out measurements when the ground surface was wet due to rainfall. As a result, we obtained Q_0 of 220W/m^2, larger than the value obtained with a dry ground surface. This experiment suggests that the presence of rainwater enhances heat convection, including latent heat, near the ground surface.

DOI： 10.18940/kazan.54.5_199

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DOI： 10.1016/j.jvolgeores.2009.08.001

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Language：Japanese   Publisher：THE GEOTHERMAL RESEARCH SOCIETY OF JAPAN  

We describe direct observation techniques for inaccessible and extremely acidic crater lakes surrounded by steep crater walls. Observation equipment and an attached weight suspended beneath a pulley are lowered to the lake surface or lake bottom under gravity along a rope stretched between opposite sides of the crater rim. The weight is tied to the observation equipment using paper string that dissolves in the lake water. This enables the rapid descent of the system from the top of the crater rim to the lake, the automatic deployment of the weight from the observation equipment once the system reaches the lake, and the simple manual retrieval of the system from the lake to the crater rim following the completion of observations.<br>Using the above technique, we deployed two temperature telemetry buoys, including wireless thermometers, upon the crater lake of Aso volcano, Japan, to monitor water temperature. We manually ran a 400 m polypropylene rope (8 mm diameter) between opposite sides of the crater rim. The strength of the rope was sufficient to lower 3-5 kg of equipment to the lake surface. The protective buoy housing the wireless thermometer is made of expanded polystyrene (EPS), enabling it to float on the lake surface. The buoy has a 1-mm-thick coating of polyurethane resin to prevent UV damage. The buoys were fixed at the lake bottom using anchors and 18 m fluororesin ropes initially tied to the system using paper string, enabling the system to readily descend to the lake surface along the stretching rope. The paper strings dissolved several minutes after the equipment had landed on the lake surface, at which point the anchor descended to the lake bottom.<br>To obtain samples of lake sediments, we developed a mud sampler that consists of a stainless steel frame covered by a polyester mesh net. A doughnut-shaped fluororesin block, designed to prevent chemical contamination of the dredged sample, was used as a weight inside the net. The mud sampler and an attached weight suspended beneath two pulleys were lowered to the lake bottom under gravity along the polypropylene rope. The attached weight was tied to the sampler using paper string. We also obtained a sample of lake water using a polypropylene bottle with a weight tied beneath the bottle using paper string.<br>These techniques are expected to contribute to the monitoring of active crater lakes and the underlying hydrothermal system.

DOI： 10.11367/grsj.31.117

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Language：Japanese   Publisher：日本地熱学会  

We estimate heat-discharge rates for a geothermal area formed during the 2000 eruption of Usu volcano, Japan. Field observations carried out in September 2006 reveal that heat-discharge rates from fumaroles, areas of steaming grounds and crater lakes are 8, 9.2, and 2 MW, respectively. The total heat-discharge rate measured in September 2006 represents just 1% of the rate immediately following the eruption.<BR>Integration of the heat-discharge rate from April 2000 to September 2006 yields an accumulated discharge of approximately 2.3×10¹⁶J, equating to the cooling of 8×10⁶m³ of magma. This amount of magma corresponds to several percent of the total intruded magma volume estimated from analyses of ground deformation associated with the 2000 eruption.<BR>Compared with the 1977 eruption, the 2000 eruption involved the discharge of large amounts of heat from fumaroles. Fumaroles that developed during the 2000 eruption showed a decline in activity in short time. Areas of steaming ground associated with the 2000 eruption showed more rapid growth compared with those of the 1977 eruption but discharged less heat. We suspect that differences in the hydrological environments of the two eruptions (e. g., permeability around the intruded magmas) led to contrasting patterns of propagation of the hydrothermal systems around the intruded magmas.

DOI： 10.11367/grsj1979.30.259

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Language：Japanese   Publisher：Volcanological Society of Japan  

We conducted AMT, VLF-MT and high resolution electrical resistivity survey in the northeastern foot of the Unzen Volcano in order to compare shallow resistivity structure with temperature profile of the borehole (USDP-1). These surveys revealed that a low resistivity layer (40Ω・m) lies at 40-50m depth and a high resistivity layer (200Ω・m) lies below 60m depth. The low and high resistivity layers correspond to the high temperature zone (37℃, 42m depth) and temperature-decreasing zone, respectively. To examine the factor which decreases the resistivity and increases temperature at around 40m depth, we observed the feature of the drillcore samples of USDP-1 precisely. As a result, argillaceous impervious layer was found at 67-100m depth, just beneath the low resistivity and high temperature zone. This suggests that groundwater is maintained shallower than 67m depth and that geothermal water decreases the resistivity of this zone.

DOI： 10.18940/kazan.53.4_131

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Language：Japanese   Publisher：THE GEOTHERMAL RESEARCH SOCIETY OF JAPAN  

Morphometric observations of the crater lake at Aso Volcano, Japan, was carried out and the change of its water level, surface area and water volume between Aug 2000 and Aug 2003 were estimated. The lake water was sampled three times during this period and the concentrations of chloride in the water were measured. Mass balance was evaluated by solving the water and chloride budgets simultaneously.Results showed that the lake water was mainly supplied by volcanic input (3500-6200 ton/day) which occupied at least 60% of the water influx.Meteoric water flux (420-2500 ton/day) was not dominant, which occupied less than 20% of the water influx between Aug 2000 and Apr 2003. Lake water was mainly dissipated by evaporation from the lake surface (3800-5900 ton/day). Seepage from the lake bottom (880-2200 ton/day) occupied about 13-37% of the water outflux. Heat balance indicated that thermal energy of volcanic input was about 150-200MW, which occupied more than 95% of energy influx.Most heat loss occurred at the lake surface through evaporation (100-150MW). The specific enthalpy of volcanic input was estimated to be about 2500-4200kJ/kg, which corresponds to the enthalpy of superheated steam at several hundred degrees C.It was suggested that mass and heat are input into the lake by the addition of superheated steam at several hundred degrees C.Water flux and enthalpy of volcanic input between Apr 2003 and Aug 2003 were estimated to be larger than those between Aug 2000 and Apr 2003.This is consistent with the observation that the water temperature became higher, the water level was decreased and small mud eruption was occurred.Our results indicate that the crater lake at Aso ranks among the peak-activity volcanic lakes in the world.

DOI： 10.11367/grsj1979.30.107

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/bf03353133

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DOI： 10.1186/BF03353134

DOI： 10.1186/bf03353134

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Language：Japanese   Publisher：Volcanological Society of Japan  

New geothermal activities occurred at the Yoshioka hot spring of Aso Volcano from June 2006. We found a new fumarole named "a3" in a new steaming ground called "A". The maximum temperature of the steams from it exceeded 98 degrees centigrade. In August, a vigorous fumarole "b1" and new steaming grounds "B" and "C" were formed. Vapor fluxes from these fumaroles obviously increased in October, and the daily mean heat and water discharge rates of the fumarole "b1" were estimated approximately to be 15-30MW and 6.7-13kg/s (580-1,100ton/day), respectively. Especially, "b1" ejected over 10 tons of ash on 16 October. After November 2006, the temperatures of the steaming grounds fell, and heat and the water discharge rates of the fumarole "b1" decreased to be about 4.6MW and 2.0kg/s (170ton/day), respectively. The average heat discharge rate from "b1" is more than tens times higher than that of existing natural fumaroles in the Yoshioka, Yunotani, Jigoku and Tarutama hot springs in the usual period. We infer that the vigorous geothermal events were caused by the temporal increase of vapor flux from the deep geothermal hot water.

DOI： 10.18940/kazan.52.6_335

DOI： 10.1186/s40623-017-0646-y_references_DOI_I0KrJC4SomaNFdHAvksKDQfBoFX

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jvolgeores.2007.04.001

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2006GL026827

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Language：Japanese   Publisher：The Geological Society of Japan  

Warm wind hole swarms were found at the top of the Yasukajigamori lava dome of the Mikurasima volcano, Japan. A white steam column with height of less than 1-2m was seen rising from the major hole Y-a only during the depth of winter. The results of temperature and relative humidity measurements in and around the Y-a hole indicate that temperature and density of vapor in the Y-a hole strongly depend on the temperature of the outer air. This suggests air circulation involving outer air percolating through porous lava dome. Thermal energy discharged from the Y-a hole is estimated to be about 22 GJ in each year, similar to the value reported from at the Nakayama wind holes in Shimogo, Fukushima. As a result of measurements of temperature, pH and electric conductivity of water around the lava domes, we have found no evidence to suggest volcanic thermal activities. Some of wind holes at other active volcanoes could be mistaken as volcanic fumaroles.

DOI： 10.5575/geosoc.112.503

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Language：Japanese   Publisher：Volcanological Society of Japan  

From February to April 2003, four small eruptions occurred in Asama volcano, central Japan. During these eruptions, movements of volcanic clouds were automatically recorded by video cameras. Based on these camera records, we studied the features of ascent processes of volcanic clouds. The volcanic cloud on 6 February 2003 had mostly isolated symmetric shape and expanded linearly with height as it ascended. The squares of heights from virtual origin are proportional to time. These features are consistent with the characters of a thermal, which is well known from dimension analyses and experiments. To evaluate the masses of ejected ash we developed a simple model for volcanic clouds based on thermal assumption, and described the ascent velocity as a function of mean temperature and mass of ash in a volcanic cloud. In this model, a volcanic cloud is composed of ash and ideal gas, driven only by buoyancy. Any fall-out of particles was neglected. We compared the model with the video records of the volcanic cloud on 6 February 2003, and deduced that the volcanic cloud had less than about 400 ton of ash. We found new vents at the bottom of the main crater. Volume of the most prominent vent is comparable with the ash volume derived from our model. Chemical compositions of the products resemble those of Maekake stage, the youngest stage of Asama volcano, suggesting that the ash were derived from the shallow part of the volcanic edifice. It is interpreted that the small explosion occurred at the shallow part beneath the main crater. We propose that high temperature of ejecta was responsible for the formation of unusual volcanic cloud.

DOI： 10.18940/kazan.50.3_183

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Language：Japanese   Publisher：The Volcanological Society of Japan  

Some fundamental features of ascending volcanic clouds have been revealed using images of the clouds that were automatically recorded by video cameras for some eruptions at Asama volcano on 15 to 18 September, 2004. According to the analysis of 17 volcanic clouds that are nearly isolated and of a symmetrical shape, the radius of a cloud increases linearly with increasing height, meeting self-similarity of ascending motion nearly up to its maximum height. If the height is measured from a suitable virtual origin, the ratio of the radius to the height can be a constant that is identified with the entrainment constant. The entrainment constants determined in this way have a mean value of about 0.24 in good agreement with those obtained from previous laboratory experiments, even if the values are greater than 0.25 or less than 0.20 for 35% of the analyzed volcanic clouds. During the ascent of a cloud the height squared is nearly proportional to the time and the product of the radius and the ascent velocity is almost constant. These empirical relations are consistent with well-known characters of a thermal that moves in incompressible uniform surroundings. Coupling these kinematic features of the volcanic clouds with the Scorer&#039;s relation and the equation of state, we evaluate the total buoyancy, the total mass, the density and the mean temperature of the clouds that are regarded as thermals. The total buoyancy of most volcanic clouds did not change significantly during their ascent process. The cloud on 17 September has a relatively great density contrast and small total buoyancy, probably reflecting hot ash particles in it supplied by a Strombolian eruption at that time. The volcanic cloud discharged at 11:54, September 15 contained ash of 2,500-3,700 tons or less with the mean temperature of 310-360K or higher, and the volcanic cloud discharged at 8:38, September 18 contained ash less than 8,300-9,100 tons with the mean temperature higher than 310K or higher.

DOI： 10.18940/kazan.50.6_555

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Language：Japanese   Publisher：Volcanological Society of Japan  

Using commercial Windows PC and digital cameras, we have developed an automatic image recording system, which is inexpensive, small and lightweight. This system automatically records camera images in a digital form and transfers them to a remote server through telephone lines. This system can be flexibly applied to the observation and monitoring of eruption columns even under severe conditions. With this system we have receded images of the eruption columns of Miyakejima Volcano, Japan, every 10 seconds from 12 August 2000 to 13 May 2002. These images revealed how the vents of volcanic gas ejection developed during August 2000. The images after September 2000 showed that the column was relatively high in summer, probably reflecting the amount of vapor in the ambient atmosphere.

DOI： 10.18940/kazan.48.6_445

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Other Link： https://ndlsearch.ndl.go.jp/books/R000000004-I6661268

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Language：Japanese   Publisher：Volcanological Society of Japan  

DOI： 10.18940/vsj.2015.0_35

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Language：Japanese   Publisher：Volcanological Society of Japan  

DOI： 10.18940/vsj.2015.0_32

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Language：Japanese   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2015.0_140

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Language：Japanese   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2014.0_125

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Language：Japanese   Publisher：東京 : 気象庁  

コレクション : 国立国会図書館デジタルコレクション > 電子書籍・電子雑誌 > 国の機関 > 中央省庁 > 国土交通省 > 気象庁

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Other Link： https://ndlsearch.ndl.go.jp/books/R000000004-I025299669

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Other Link： https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-22710171/

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Other Link： https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-22710171/

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Other Link： https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-22710171/

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As a part of the joint geophysical and geochemical observations of Usu volcano in 2006, the airborne infrared thermal survey was conducted at Usu volcano, Noboribetsu geothermal area and Tarumai volcano. The observation was operated by the helicopter which has a hole on the floor for aerial photo of vertical direction. The portable infrared thermal camera (AVIO TVS-620) was fixed on the hole to face the ground perpendicularly using the stand designed for this survey. The position and horizontal direction of the camera were measured by GPS. The vertical angle of the camera was determined by two crossing electronic clinometers placed on the stand. The thermal images (one second interval) ware transferred directly from the camera to computer through the USB cable. The number of the pixel of each frame is 320 for horizontal direction and 236 for vertical direction. The instant view of one pixel is 1.4 mrad. The altitude of the flight was 2300m so that the temperature at a pixel represents the mean temperature of about 3 m2 and the each frame corresponds to the area of 1030 m × 730 m. The detective wavelength of the camera is 8 -14 ìm and the signal attenuation by the atmosphere was ignored in the analysis of the surface temperature. The helicopter kept the constant height during the measurement. The thermally active area was covered by 6, 2 and 3 measurement lines in Usu, Noboribetsu and Tarumai, respectively. The selected thermal images with suitable condition were combined (about 90 frames in Usu volcano) considering the horizontal orientation, vertical angle and the position. The resultant image represents the overall surface temperature distribution at respective field. The surface temperature distribution of Usu volcano shows that the thermally active area is mainly composed from four parts: Nishi-yama crater, Kompira-yama crater, summit area and Showa-shinzan. Nishiyama and Kompira-yama craters were newly formed craters at 2000 eruption activity. The surface temperature distribution of Noboribetsu shows the fumarole activity at Ohyu-numa and Jigoku-dani thermal area and that of Tarumai shows the fumarole activity at A and B craters, respectively. The detailed thermal structure at respective field is cleared by this observation. It is confirmed that this convenient observation system is satisfied for the practical use.

DOI： 10.14943/gbhu.75.43

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Language：Japanese   Publisher：北海道大学大学院理学研究院自然史科学部門（地球物理学）  

Aerial IR surveys were carried out in September 2010 over geothermal areas at Usu,Noboribetsu and Hokkaido-Komagatake volcanoes, Japan. The heat discharge rate from steaminggrounds that formed during the 2000 eruption of Usu volcano is estimated to be 5.6 MW, whichis half the rate measured in September 2006. Integration of the heat discharge rate from April2000 to September 2010 yields an accumulated discharge of approximately 2.4 × 1016 J. This amount of heat corresponds to several percent of the total intruded magma heat estimated fromanalyses of ground deformation associated with the 2000 eruption. Areas of steaming groundassociated with the 2000 eruption showed rapid growth compared with those of the 1977 eruptionbut discharged less heat. We suspect that differences in the hydrological environments of thetwo eruptions, led to contrasting patterns of propagation of the hydrothermal systems around theintruded magmas. The heat discharge rate from the summit areas of Usu volcano, Showa-shinzan andNoboribetsu volcano in 2010 are estimated to be 40, 6.2 and 22 MW, respectively, similar to therates measured in September 2006. No high-temperature grounds were detected at the vents and fissure formed during the1942 eruption of Hokkaido-Komagatake volcano. We observed no geothermal activities at ventsassociated with the 1929, 1996, 1998 and 2000 eruptions, due to the absorption effect ofatmospheric cloud.

DOI： 10.14943/gbhu.75.25

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Language：Japanese   Publishing type：Book review, literature introduction, etc.  

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Language：Japanese   Publisher：Volcanological Society of Japan  

DOI： 10.18940/kazan.56.6_213

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Language：Japanese   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2011.0_150

J-GLOBAL

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Language：Japanese   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2011.0_44

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DOI： 10.18940/vsj.2011.0_137

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DOI： 10.18940/vsj.2011.0_134

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Language：Japanese   Publisher：特定非営利活動法人日本火山学会  

DOI： 10.18940/vsj.2009.0_85

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Language：Japanese   Publisher：北海道大学大学院理学研究院自然史科学部門（地球物理学） = Department of Natural History Sciences (Geophysics), Graduate School of Science, Hokkaido University  

We estimate heat-discharge rates for a geothermal area formed during the 2000 eruption of Usu volcano, Japan. Field observations carried out in September 2006 reveal that heat-discharge rates from fumaroles, areas of steaming grounds and crater lakes are 8, 9.2, and 2 MW, respectively. The total heat-discharge rate measured in September 2006 represents just 1% of the rate immediately following the eruption. Integration of the heat-discharge rate from April 2000 to September 2006 yields an accumulated discharge of approximately 2.3 × 10^[16]J, equating to the cooling of 8 × 10^6 m^3 of magma. This amount of magma corresponds to several percent of the total intruded magma volume estimated from analyses of ground deformation associated with the 2000 eruption. Compared with the 1977 eruption, the 2000 eruption involved the discharge of large amounts of heat from fumaroles. Fumaroles that developed during the 2000 eruption showed a decline in activity in short time. Areas of steaming ground associated with the 2000 eruption showed more rapid growth compared with those of the 1977 eruption but discharged less heat. We suspect that differences in the hydrological environments of the two eruptions (e.g., permeability around the intruded magmas) led to contrasting patterns of propagation of the hydrothermal systems around the intruded magmas.

DOI： 10.14943/gbhu.72.139

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Language：Japanese   Publisher：北海道大学大学院理学研究院自然史科学部門（地球物理学） = Department of Natural History Sciences (Geophysics), Graduate School of Science, Hokkaido University  

We developed a new technique, Ice Box Calorimetry, for estimating heat discharge rates through steaming ground. Ice within an aluminum box provides a powerful tool for measuring the total heat transfer from the ground surface, including conductive heat, convective heat, and latent heat within vapor. Using this method, we are able to rapidly measure heat discharge rates without the need for specialized apparatus. Applying Ice Box Calorimetry to the Nishiyama steaming ground at Usu volcano, Japan in September 2006, we identified local variations in heat discharge rates. The total heat discharged from the steaming ground in September 2006 is estimated to be 16 MW.

DOI： 10.14943/gbhu.72.125

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Publisher：京都大学理学研究科地球熱学研究施設火山研究センター  

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Language：Japanese   Publisher：特定非営利活動法人日本火山学会  

DOI： 10.11367/grsj1979.30.259

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Language：Japanese   Publisher：Volcanological Society of Japan  

地熱地域では,地下深部から供給される火山ガスが地表に噴出するとともに帯水層に付加されて周辺に拡散していると考えられる.鍵山(2006)は,霧島火山群において地下浅部の帯水層の比抵抗が火口中心から周辺に向かうにつれてしだいに高くなるとともに,通常は高比抵抗であることが一般的な表層の比抵抗も中心部ほど低くなる傾向が見られること,地熱活動の活発な火山ほど低比抵抗域の面積が広くなることを示している.こうした傾向を他の火山でも検討するために,伽藍岳周辺において2007年3月および2008年4月にVLF-MTによる表層の比抵抗分布調査を行い,以下の結果を得た.

DOI： 10.18940/vsj.2008.0_162

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Language：Japanese   Publisher：大分県温泉調査研究会  

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Language：Japanese   Publisher：京都大学防災研究所  

For quantitative evaluations of geothermal activities of Aso volcano, Japan, an aerial infrared survey was carried out on early morning by use of a helicopter. At Nakadake, one of the central cones of Aso volcano, aerial infrared photographs reveal that no temperature anomalies exist out of the 1st Crater of Nakadake. The total heat-discharge rate from Aso volcano is estimated to be 200 - 300 MW in the calm period. The most of heat is discharged from hot crater lake of the Nakadake 1st Crater. Heat-discharge rate from the Western slope geothermal field (WSGZ) is estimated to be 9.9 MW. The Yoshioka hot spring (one of the WSGZ) that notable geothermal events occurred in 2006 releases over 5 MW of heats corresponding to the half of the heat-discharges from the WSGZ.

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J-GLOBAL

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Language：Japanese   Publisher：特定非営利活動法人日本火山学会  

DOI： 10.1016/j.jvolgeores.2007.04.001

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Language：Japanese   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2006.0_99

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DOI： 10.18940/vsj.2005.0_71

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DOI： 10.14943/gbhu.68.127

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Other Link： http://hdl.handle.net/2115/14365

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DOI： 10.15083/0000032550

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Other Link： http://id.ndl.go.jp/bib/7240817

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DOI： 10.14943/gbhu.67.327

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Other Link： http://hdl.handle.net/2115/14352

Language：Japanese   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2004.0_197

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Language：Japanese   Publisher：海洋出版  

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Volcano earthquakes and volcano deformation had been observed to be active around the Iwate Volcano since 1998. Authors have repeated precise leveling seven times on the southern foot of the volcano in the period July 1998 to May 2000. Uplifts of 1 to 3 cm at the volcano are observed in the every survey epoch. Authors estimate the point pressure sources from the uplift using the Mogi solution.Estimated pressure sources are shifted to northwest of 5 km with the depth of 2 km from the Amihari Spa.The total volume of intrusion is estimated to be 1.4 x 106 m3 and the rate of intrusion is decreasing with time.

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Other Link： http://hdl.handle.net/2433/80509

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Earthquake swarm is observed around the Iwate-san Volcano, Northeast Japan since 1998. The leveling route with distance of 36 km was set up around the volcano and the precise levelings have been repeated to discuss the crustal deformation four times in July, September, September and November in 1998. When the precise levelingis doing in September 3, 1998, earthquake of M6. 1 was occurred close to the volcano. One leveling team was making leveling in the epicenter area, Re-levelings were repeated since the next day of the earthquake, and coseisimic deformations of 20 cm are detected along the leveling route. However the precursor of the vertical movements is not recognized in the leveling data made just before the earthquake. Uplift of the Iwate-san Volcano is observed and which amounts to 4 cm in the period of July to November in 1998. The pressure sources of the vertical deformations are estimated to be under the west side of the volcano with depth of 3 kim, which is the almost the same location of the pressure estimated by GPS measurements and the DInSAR (Differential Interferometric SAR).

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Other Link： http://hdl.handle.net/2433/80398

Language：Japanese   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.1998.2.0_8

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Since noble gases are chemically inert and their abundance ratios vary only by physical processes, compositional variations in volcanic gases are relatively simple. Variations in 3He/40Ar* ratios (40Ar* = 40Ar excess from atmospheric Ar) of fumarolic gases reflect variations in magmatic He/Ar ratios because both 3He and 40Ar* of fumarolic gases are mostly magmatic in origin. We have measured the concentrations and isotopic compositions of noble gases and CO2 of fumarolic gases collected on the north side of Mt. Shirane since 2015. As a result, the 3He/4He and 3He/CO2 ratios increased after May 2018, suggesting an increase in the supply of magmatic gas with high 3He/4He and 3He/CO2 ratios. The 3He/40Ar* ratios of the fumarolic gases significantly increased when the 3He/4He ratios were high. It has been suggested that He/Ar ratios in gas phases of magma increase with increasing magma vesicularity. Thus, the increase in the 3He/40Ar* ratios suggests an increase in magma vesicularity at the Kusatsu-Shirane volcano. In summary, 3He/40Ar* ratios of fumarolic gases might be an important indicator to evaluate a state of magma.

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Chemical composition of the lake water in Yugama crater at Kusatsu-Shirane volcano were analyzed to investigate magma-hydrothermal activity beneath this volcano. At Yugama crater, unrest event such as earthquake swarms and discoloration of lake water have been sometimes observed since the last eruptions in 1982-83. Also in 2019, the increase of earthquakes and discoloration of lake water were observed. The Mg/Cl ratio of the lake water has increased sharply before and after the eruptive period in 1982-1983 (Ohba et al., 2008), but such change is not observed in 2019, at least as of July 1.

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Noble gas and carbon isotope ratios of volcanic and hot-spring gases collected at Kusatsu-Shirane volcano, Japan were determined. No temporal change in 3He/4He ratios was observed even after volcanic unrest since June 2014. The carbon isotope ratio and CO2/3He ratios are typical values for subduction zone volcanic fluid samples, with dominant contribution of marine carbonates.

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Event date： 2015

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Event date： 2015

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Event date： 2015

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Event date： 2015

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Event date： 2015

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Event date： 2014.11

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Event date： 2014.11

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Event date： 2014

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Event date： 2014

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Event date： 2014

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Event date： 2013

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Event date： 2013

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Event date： 2012.10

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Event date： 2011

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Event date： 2011

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Event date： 2011

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Event date： 2011

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Event date： 2011

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Event date： 2011

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Event date： 2010.10

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Event date： 2010

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Event date： 2010

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Event date： 2009.10

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Event date： 2009

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Event date： 2009

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Event date： 2009

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Event date： 2008.10

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Event date： 2008.10

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Event date： 2008

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Event date： 2008

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Event date： 2008

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Event date： 2008

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Event date： 2007

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Event date： 2007

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Event date： 2007

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Event date： 2007

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Event date： 2006.10

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Event date： 2006

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Event date： 2006

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Event date： 2006

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Event date： 2006

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Event date： 2005

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Event date： 2005

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Event date： 2005

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Event date： 2004

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Event date： 2003

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Event date： 2002

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Event date： 2001

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Event date： 1999

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Event date： 1999

Language：Japanese  

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