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.

Muography is an innovative imaging technique used for inspecting and monitoring density-length variations of large-sized natural or human-made objects based on the measurement of the absorption rate of cosmic-ray muons. The first large-sized, high-resolution muography observatory based on Multi-Wire Proportional Chamber (MWPC) technology is being developed to monitor the mass density variations in the vicinity of Minami-dake crater of Sakurajima volcano. We found that the track rates provided by five ongoing tracking systems with a total surface area of 4 m² are stable within ±3% from the backward direction, which demonstrates that the MWPC-based Muographic Observation System (MMOS) is applicable for the detection of average density variations above 2%, which is well below the practical limit of 5%. We quantified the time resolution of the designed muography observatory by modeling the muon flux across the volcano; the average density-length variation of 5 (10)% is expected to be detected within 5–20 (2–8) days at a 1σ (68%) confidence level (CL) with an MMOS orientation of 10.86° above the horizon. An automated analysis framework was developed as a data base for raw data reconstruction, analysis, and preparation, and which is accessible via web-server. We observed a more than 2σ CL decrease in average density across the West side of Crater A during the ongoing data collection period. The observed density decrease suggests that the amount of material has decreased inside Crater A due to the consecutive eruptions of Minami-dake during the data collection period from November 30, 2018 to January 11, 2019.

Spaceborne synthetic aperture radar (SAR) and ground-based radar interferometers (GBRIs) can be used to detect spatially detailed crustal deformations that are difficult to detect by on-site observations, the Global Navigation Satellite System, tiltmeters, and so on. To make such crustal deformation information readily available to those engaged in evaluating volcanic activities and researching the mechanisms, we are preparing a database within the Japan Volcanological Data Network data sharing system to store crustal deformation detected by spaceborne SAR and GBRIs (Subtheme 2-1, Project B, the Integrated Program for Next Generation Volcano Research and Human Resource Development). In this study, we examined methods to reduce atmospheric delay noise in SAR interferometry using the numerical weather model and determined the methods for resampling the analytical values of the numerical weather model and estimating atmospheric delay to efficiently determine atmospheric delay. We show that the atmospheric delay can be estimated with higher accuracy by properly combining the isobaric surface and ground surface data of the mesoscale model (MSM) provided by the Japan Meteorological Agency. We are developing a multi-type portable SAR system as a GBRI system such that it would allow campaign observations whenever increased volcanic activities are observed and acquire crustal deformation with a higher temporal resolution than spaceborne SAR for storage in the database. This system employs L-band radar, which has a higher penetrability against vegetation. Two modes of observations are possible: ground-based SAR and car-borne SAR. The prototype was fabricated to conduct experiments necessary to develop a working model. The experimental observations was carried out around Asama volcano, and we confirmed that clear fringe was obtained.

In 2016, we launched the “Promotion Project for Next Generation Volcano Research B2 (Theme B: Development of Cutting-edge Volcano Observation Technology, subtheme 2: Development of Remote Sensing Techniques for Volcano Observation), subtopic 2-2 (Development of Remote Sensing Techniques for Surface Phenomena of Volcano)” under the “Integrated Program for Next Generation Volcano Research and Human Resources Development” [1], aiming at the development of an optical multispectral remote sensing system for measuring volcanic surface phenomena. With subtopic 2-2, we are planning to develop a new observation device called a surface phenomena imaging camera (SPIC), which is technically superior to current remote sensing techniques, i.e., optical remote observation techniques used to observe volcanic surface phenomena from aircrafts or ground. We are also aiming at applying the developed observation system to quantify volcanic activities and determine volcanic eruption potentials (degrees of urgency) or branching of event trees for volcanic crises with high accuracy, contributing to better predictions of volcanic eruption transitions. To achieve the above-mentioned aims, we started the development of the SPIC by equipping it with camera-type sensors, based on preliminary analyses of the experimental observations made with the airborne spectral imaging system ARTS-SE, which consists of a pushbroom scanner and a camera system, developed by the National Research Institute for Earth Science and Disaster Resilience in FY 2015. We have already developed its components, such as the prototype filter-type multiband cameras SPIC-UC, a prototype uncooled infrared camera, SPIC-C, a cooled camera, and SPIC-SS, a visible-light camera. The SPIC-UC is a two-band camera with the function of visualizing temperature and SO₂ gas concentration distributions. The SPIC-C has the function of measuring temperatures between 2 and 1075^◦C with high accuracy (noise equivalent temperature difference, NETD: 16 mK); it is equipped with a sensor and a filter wheel that work in the middle wave infrared region (MWIR). The SPIC-SS is a six-lens multiband camera system that estimates the measured images from multiband spectra (6 bands) to hyper spectra (300 bands). Further, we studied a method to estimate digital surface model with a ∼30-m error. As our plan has progressed as scheduled, we intend to complete the prototype SPIC by 2020.

Crustal deformation is essential information for monitoring volcanic activity. In the summit area of the Kusatsu-Shirane Volcano (KSV), a dense Global Navigation Satellite System (GNSS) network has been operating near the recent volcanic center, Yugama crater. This network is sensitive to shallow depth activity, such as phreatic eruptions at the summit area, but is not applicable to deep magmatic activity, suggested to have been occurring for thousands of years by recent geological studies. Aiming to detect magmatic activity at a certain depth, we installed a new GNSS network near KSV. The observation sites were selected based on the crustal deformation pattern calculated for several intrusive events of the deep-seated magma. First, the GNSS sites for campaign observation were installed at eight locations in 2017. Then, four continuous sites commenced operation after a phreatic eruption at Mt. Motoshirane in January 2018. Here, we show the results of the first and second observation campaigns, operating in October 2017 and February 2018. Coordinate values are computed by precise point positioning with ambiguity resolution (PPP-AR) analysis and are used to calculate the displacement and the baseline length change during this period. The uncertainties of the calculated coordinate values are sufficiently small (less than 4.5 mm) except at some sites for which the data possibly include multipath errors due to trees and snow. Although any deformation associated with the 2018 eruption of Mt. Motoshirane is not detected, subsequent observations would contribute to monitoring long-term activity near KSV.

The Esan volcanic complex (EVC), northern Japan, is an active volcanic complex. The EVC represents a potential threat owing to its close proximity to inhabited areas, and abundant phreatic deposits occur around its volcanic aprons. Eleven samples of black paleosol and charcoal were collected from trenches dug at two sites (A and B) for the purpose of ¹⁴C dating. Sites A and B are located 2.6 km and 2.2 km from the source crater, respectively, and the deposits at these sites represent a proximal facies. At least 11 (at site A) and 12 (at site B) volcaniclastic units are identified. A newly identified Holocene phreatic unit (Es-0) is dated at ca 11 ka and is older than the EsMP unit that is a Holocene lava-dome building episode at ca 9 ka. Holocene phreatic episodes Es-1 and Es-3 can be divided into three and five subunits, respectively, and include a pyroclastic surge deposit that would have posed a threat to current local communities. The sequence of Holocene eruptions includes at least 11 tephra events over 11,000 years. The material ejected during phreatic explosions is characterised by highly heterogeneous grain size. Therefore, grain size analysis of erupted phreatic material might not effectively discriminate the processes of deposition, in contrast to such analysis of magmatic ejecta. The topography of the EVC largely constrains the area of deposition of phreatic ejecta.

Repeated magmatic eruptions of Tokachidake volcano have caused severe volcanic disasters on three occasions during the 20th century. To prepare for the next eruptive activity, understanding the structure of the magma plumbing system by using petrological analysis of juvenile materials is crucial. Here, we perform petrological analysis of juvenile materials to investigate the difference between two contrasting eruptions in 1962 and 1988–1989, respectively. All these juvenile materials are composed of mafic andesite, which were formed by mixing of olivine-bearing basaltic and pyroxene andesitic magmas. The compositional zonations of olivine phenocrysts in all of these rocks suggest that the injection of the basaltic magma into the andesitic magma occurred several months prior to the 1962 eruption and about six months before the 1988–1989 eruption. In the case of the 1962 activity, the mixed magma rapidly ascended without stagnation from the magma chamber and erupted as a sub-Plinian type. However, the juvenile materials of the 1988–1989 eruptions show distinct petrological features such as higher crystallinity of the matrix, orthopyroxene reaction rims around the olivine, and overgrowth mantle zones around Ti-magnetite phenocrysts. These features suggest that the mixed magma ascended slowly and possibly stagnated at shallower levels prior to eruption. The stagnated magma became a cap rock of the vent system and caused a series of Vulcanian eruptions. These distinct modes of magma ascent can be explained by differences in the magma supply rate. In the case of the 1962 eruption, the volume of magma that erupted in a period of less than 24 h was 7.1 × 10⁷ m³. On the contrary, 23 explosions occurred over three months of the 1988–1989 activity and generated 1 × 10⁵ m³ of ejecta including juvenile and non-juvenile materials. These large eruption rate differences can be attributed to the distinct ascent rates of the magma between the two eruptive activities.

The speciation of water in volcanic glass, as indicated by the relative proportions of H₂O and OH^-, provides information on the processes of volcanic eruptions. Earlier studies of water species used ultraviolet–visible–near-infrared (UV–Vis–NIR) dispersive spectroscopy to examine the NIR spectra of volcanic glass but were unable to confirm whether areas as small as 100 μm across could be studied. Here, UV–Vis–NIR dispersive microspectroscopy was applied in a study of hydrous rhyolitic glass synthesized by decompression in a cold-seal pressure vessel at 880°C. The concentrations of water species were determined by transmittance spectroscopy, with results consistent with those of Fourier-transform infrared microspectroscopy. The measured total water contents were consistent with the known solubility of water in rhyolitic magma, and, therefore, it is concluded that UV–Vis–NIR microspectroscopy can be applied in determining the concentrations of H₂O and OH^- in hydrous rhyolitic glass.

A high-resolution forecast methodology for the ash hazard at Sakurajima volcano, Japan, is presented. The methodology employs a combined modeling approach and utilizes eruption source parameters estimated by geophysical observations from Sakurajima, allowing for a proactive approach in forecasting. The Weather Research and Forecasting (WRF) model is used to downscale Japan Meteorological Agency (JMA) forecast data over the area of interest. The high-resolution meteorological data are then used in FALL3D model to provide a forecast for the ash dispersal and deposition. The methodology is applied for an eruption that occurred on June 16, 2018. Disdrometer observations of ashfall are used along with ash dispersal modeling to inform the choice of the total grain size distribution (TGSD). A series of pseudo-forecast ash dispersal simulations are then carried out using the proposed methodology and estimated TGSD, initialized with meteorological forecast data released up to ∼13 hours before the eruption, with results showing surprising consistency up to ∼10 hours before the eruption. Using forecast data up to 4 hours before the eruption was seen to constrain observation to model ratios within a factor of 2–4 depending on the timing of simulation and location. A number of key future improvements for the methodology are also highlighted.

The Sakurajima volcano is characterized by frequent vulcanian eruptions at the Minamidake or Showa crater in the summit area. We installed an integrated monitoring system for the detection of volcanic ash (composed of remote sensing sensors XMP radars, lidar, and GNSS with different wave lengths) and 13 optical disdrometers on the ground covering all directions from the crater to measure drop size distribution and falling velocity. Campaign sampling of volcanic ash supports the conversion of particle counts measured by the disdrometer to the weight of volcanic ash. Seismometers and tilt/strain sensors were used to estimate the discharge rate of volcanic ash from the vents. XMP radar can detect volcanic ash clouds even under visual difficulty because of weather such as fog or clouds. A vulcanian eruption on November 13 was the largest event at the Sakurajima volcano in 2017; however, the volcanic plume was not visible due to clouds covering the summit. Radar revealed that the volcanic plume reached an elevation of 4.2–6.2 km. Post-fit phase residuals (PPR) from the GNSS analysis increased suddenly after the eruption, and large-PPR paths from the satellites to the ground-based receivers intersected each other at an elevation of 4.2 km. The height of the volcanic plume was also estimated from the discharge rate of volcanic ash to be 4.5 km, which is empirically related to seismic energy and the deflation volume obtained via ground deformation monitoring. Using the PUFF model, the weight of the ash-fall deposit was accurately forecast in the main direction of transport of the volcanic ash, which was verified by disdrometers. For further advances in forecasting of the ash-fall deposit, we must consider high-resolution wind field, shape of volcanic plume as the initial value, and the particle number distribution along the volcanic plume.

Lahar flow is recognized as among the worst secondary hazards from volcanic disaster. Intense rainfall with long duration is frequently associated with lahar flow. In this study, estimation of a rainfall threshold likely to trigger lahar flow is presented in the first part. The second part discusses its implementation by assessing the growth of observed and predicted rainfall, including the uncertainties. The study area is Merapi Volcano, one of the most active volcanoes in Indonesia, including rivers on the flank of Mount Merapi that are vulnerable to debris flow. The rainfall indices needed to describe the conditions that generate lahars or not were determined empirically by evaluating the hourly and working rainfall using X-band multiparameter (X-MP) weather radar. Using past records of lahar flow, the threshold lines separating rainfall that triggers lahars or not were analyzed for the Putih, Gendol, Pabelan, and Krasak Rivers. The performance of several critical lines was evaluated using Bayesian probability based on skill rates from a contingency matrix. The study shows that the line intercept of the critical lines after a significant eruption in 2010 was higher than those lines developed before 2010, indicating that the rivers are currently at lesser risk. Good representation was shown by the thresholds verified with actual rainfall progression and lahar event information on February 17, 2016, at the Gendol and Pabelan Rivers. These rainfall critical lines were the basis for judging the debris flow occurrence by analyzing the track record of predicted rainfall progression. The uncertainty of rainfall short-term prediction from the extrapolation model was evaluated by perturbing the advection vector of rain echo motion. This ensemble forecast product could provide a plausible range of prediction possibility as assistance in gaining the confidence with which a lahar could be predicted. The scheme presented herein could serve as a useful tool for a lahar early warning system in the area of the Merapi Volcano.

Applied trans-disciplinary research focusing on enabling open dialogue, volcano disaster resilience, and governance was conducted in Japan after the Mt. Ontake eruption in 2014 through a three-year project. The researchers and practitioners involved in this project aimed to develop methods to reinforce volcano disaster resilience and governance at the local level. A trans-disciplinary research method of clinical environmental studies was applied. First, it was diagnosed as insufficient for local actors to intentionally coordinate with each other, keeping in mind the whole picture of volcano disaster management and the diverse positionalities of those involved in it. “Ba” (a shared time and space for emerging relationships among individuals and groups to create knowledge) development, or study meetings and workshops, functioned step-by-step to share and collate problems first, and then to share ideas of actions after the project was prescribed and executed. It was evaluated that ba development was effective for open dialogue free from positionality, face-to-face relationship building, and capacity development for local actors involved in volcano disaster management. Action research revealed that through ba development, beliefs and value systems regarding the roles of local governments and universities, as well as the relationship between these two, will be transformed within Japan: Local governments will become facilitators, and universities will function as centers of trans-disciplinary research. Universities and researchers can function as producers, coordinators, and facilitators of ba development in collaboration with local government.

Based on Japan’s experience of establishing and operating the Extreme Disaster Management Headquarters following the Great East Japan Earthquake of 2011, the authors conclude that it is necessary to deepen the discussion on the following issues and identify a proper direction to be pursued for establishing a disaster management administration system capable of responding appropriately to huge disasters in the future: 1) Expansion and strengthening of the Disaster Management Bureau of the Cabinet Office; 2) Establishment of the Ministry of Disaster Management or Disaster Management Agency [(a) Its relation to the Cabinet Secretariat and Cabinet Office, (b) Jurisdiction (matters related to overall coordination and duties)]; 3) Organizational design that will contribute towards establishing an effective disaster management administration system [(a) Mandatory and full-time appointment of Minister of Disaster Management, (b) Staffing system of designated posts and higher-ranking senior officials, (c) Establishment of Regional Disaster Management Bureaus, (d) Staff size, (e) Desirable approaches to human resources management (accumulation and deepening of experience in disaster response, clarifying working conditions etc.)]; etc.