Since Japan has 111 active volcanoes, we living there need to be prepared for the volcanic disasters that we will likely encounter in our lifetime. The Integrated Program for Next Generation Volcano Research and Human Resource Development (INeVRH), a research project of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), started in 2016 and is now in its 7th year. It is approaching its final stage will be ready to make proposals that will improve our knowledge from both scientific and practical points of view. In theme A, the Japan Volcanic Data Network (JVDN) system started its function as a volcanic research platform, providing the observation and analysis data of many universities, governmental agencies, and institutes. The JVDN system promotes collaborative, multidisciplinary study. In theme B, many strategic observation techniques now deployed have revealed the characteristics of volcanoes in detail. For example, a dense seismic and magnetic survey has clarified the fine structure of the hydrothermal system beneath volcanoes, providing information that can be used to evaluate their phreatic eruption potential. In addition, brand-new volcanic gas observation techniques using drones now obtain in-situ information effectively. Theme C has obtained geologic and petrologic findings at many volcanoes and has come to the stage in which systematic compilation of this database would be useful to comparative studies of many volcanoes. These findings are also used in numerical simulations that combine geologic, petrologic, and geophysical formulations to produce more comprehensive models used to interpret volcanic activity. Theme D focuses on the development of practical technologies for volcanic disaster mitigation, mainly related to volcanic ash. A scheme for the quick detection and evaluation of volcanic ash is proposed through observation and numerical simulation, and an experiment is performed to reveal the thickness threshold of volcanic ash deposits on air-conditioners. This special issue reports on some up-to-date topics that could become the basis of dynamic and effective links between themes A, B, C, and D, which may serve as a base and direction for discussions that summarize and conclude this 10-year project.

The identification of anomalies in seismic wave interferometry data is important in the prediction of imminent volcanic eruptions. Herein, we propose using the local outlier probability (LoOP) method to evaluate the degree of anomaly in seismic wave velocities and scattering properties, estimated via seismic wave interferometry. LoOP is the likelihood that an observation is anomalous and is always in the range of 0–1 (0–100%). We quantitatively evaluated the degree of anomaly in seismic wave velocities and scattering properties before and after the eruption of Mt. Aso, Japan, in October 2016 and Mt. Shinmoedake, which lies within the Mt. Kirishima cluster of volcanoes, Japan, in 2017 and 2018. We found that LoOP exceeded 70% 2 to 3 days before Mt. Aso erupted on October 8, 2016, and it exceeded 70% 1 to 5 days before Mt. Shinmoedake erupted on October 11, 2017 and March 6, 2018. Adjusting the reference and quiet periods for the estimation of changes in seismic velocity/scattering property and LoOP calculations can allow the tracking of repeated, significant LoOP increases during times of high volcanic activity. The quantitative evaluation of temporal anomalies in seismic datasets will improve the precision of predictions of imminent volcanic eruptions.

Sharing volcano-related photographic data is necessary for deepening understanding of volcanic phenomena. Therefore, a new function for archiving, displaying, and providing digital photographic data has been added to the Japan Volcanological Data Network (JVDN) system to enable users to share photographs of volcanoes and their related metadata. The new function was developed in order to facilitate widespread use in research involving data owned by individuals or organizations, and it solved a number of issues: the issue of preventing the loss of photographs or their associated metadata, issues related to copyright ownership of photographs, information-management issues related to photographic data, and the issue of the extent of disclosure of photographic data. We have uploaded photographic data related to the eruption disaster of Mount Unzen (1990–1995) onto the JVDN system and have started to provide these data to interested parties. These photographic data are related to various aspects including volcanic-eruption phenomena, volcanic disasters, and disaster countermeasures. We expect that such data will be effectively utilized in various fields in the future. We believe that sharing of photographic data by means of the new functions will contribute toward the development of volcanology and the mitigation of volcanic disasters.

Synthetic aperture radar (SAR), which transmits radar waves from the ground, can detect crustal deformation with high spatial and temporal resolution. To obtain crustal deformation data useful for evaluating volcanic activity, we are developing a portable SAR that can conduct repeated observations without being fixed to the site under Project B of the Integrated Program for Next Generation Volcano Research and Human Resource Development. We named this SAR sensor: SAR for crustal deformation with portable equipment (SCOPE). SCOPE detects crustal deformation over a wide area by repeating observations at several points, which differs from the general ground-based SAR (GB-SAR). SCOPE has four observation types: GB-SAR, car-borne SAR, cart-borne SAR, and man-borne SAR, which are used to conduct such mobile observations efficiently. This study performed repeated observations with a 1-day interval using GB-SAR and car-borne SAR and obtained high coherence and reasonable phase distribution. When using the man-borne SAR type, moderate coherence was obtained. However, focusing on the SAR image was insufficient, and an inappropriate phase slope appeared in the interferogram, suggesting that improvements in the observation and analysis methods remained. We also investigated the temporal persistence of coherence when applying SAR interferometry to the SCOPE data. Sufficient coherence was obtained to detect crustal deformation in sparsely vegetated areas for a data pair at a 1-year interval. Even in densely vegetated areas, sufficient coherence was obtained from the data pair at intervals of several months. These results show that SCOPE has high potential for detecting crustal deformation based on repeated observations.

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 H₂S, SO₂, CO₂, and H₂O, 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 CO₂ ratios and lower H₂O ratios, relative to other gases, being observed. For more accurate estimations of CO₂ and H₂O 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.

Remarkable and continuous geomagnetic field change, suggesting remagnetization at a shallow depth, was detected through repeated geomagnetic field observation of the summit area of Mt. Usu Volcano from 2008 to 2021. Long-term cooling of the remnant magma, that intruded during the 1977–82 eruption, was considered responsible for the remagnetization. A magnetic dipole parallel to the present geomagnetic field well reproduced the observation. The modeled source was located near the Ginnuma crater on the south side of the previously inferred intrusive body beneath the Usu-Shinzan cryptodome. Meanwhile, no magnetic source was detected on the other side of the intrusion, implying asymmetric heat transport paths around the intrusion. Considering previous studies on seismicity, geodetic modeling, and resistivity structure, the magnetic source region is plausibly a high permeability zone through which heat from the intruded magma has been efficiently transported. In other words, the source region can be a key monitoring target for future eruptions as it may be linked to the subsurface magma system.

To understand a field of volcanic activity, a survey on the Earth’s subsurface structure is helpful. In particular, a magnetotelluric survey can image the subsurface structure necessary for volcanic disaster prevention because it is sensitive to high-temperature areas and areas where fluid and clay minerals exist. In 3-D magnetotelluric inversion using the data observed near volcanoes and the coastline, the topography and sea around the survey area need to be considered. Therefore, constructing a mesh of the analysis area by automatically using topography and bathymetry data is necessary. Additionally, the estimated subsurface structure should be compared to the sources of variation estimated from other physical observations, such as earthquakes, ground deformation, and changes in the geomagnetic total field, for interpretation. This study introduces a simple and easy-to-operate graphical pre- and post-processor developed to support the resistivity structure analysis of a volcano and the nearby coastline. In the developed software, the pre-process indicates the mesh construction, and the post-process indicates result derivation, file construction for the sensitivity tests, and file exportation to compare the inversion results with other measured quantities. This pre- and post-process can be performed easily on the same window of the software.

Miyakejima volcano experienced its latest eruption in 2000 with the summit subsidence, and the next event is expected in the near future. An aeromagnetic survey in Miyakejima was conducted in March 2021 in order to investigate the current state of its magnetization structure to identify the potential for another eruption and, thus, mitigate volcanic disaster. The survey flight was conducted using an uncrewed aerial vehicle (UAV), a multirotor drone, to deploy a scalar magnetometer. After processing geomagnetic field data from this survey, in combination with data from previous surveys conducted by using another UAV, an uncrewed helicopter, the average magnetization intensity was determined to be 12.4 A/m. Further, the surrounding area of the crater was relatively highly magnetized; however, the crater rim had a low magnetization intensity. Temporal variation was detected between 2014 and 2021 and dominated the central part of the observation area. Decreased magnetization intensity was identified beneath the caldera, which may become recently demagnetized due to heat supply traveling through fractures in the impermeable layer from the deep heat reservoir.

Numerical simulation is a useful method for studying the magmatic-hydrothermal systems of volcanoes. However, no comprehensive scheme has been established for constructing subsurface permeability structures that have a significant impact on fluid flow within the volcano. In this study, as a first step to establishing such a scheme, numerical simulations of hydrothermal fluid flow incorporating the heterogeneous properties of the permeability structure were performed utilizing the resistivity structure observed at Kusatsu-Shirane Volcano, central Japan. Although the constructed permeability structure was relatively simple, the simulation results closely reproduced some observations, such as the broad resistivity structure and the distribution and discharge patterns of hot springs around the volcano. These results suggest that the uncertainty in generating permeability structures in hydrothermal fluid flow simulations can be greatly reduced by using resistivity structures.

Preexisting fracture systems, including old fissures, dikes, and microfractures in the caldera, are possibly used as channels for magma and hydrothermal fluid intrusions during an eruption. To reveal such a fracture system in the Hakone volcano, we used the fuzzy c-means method to perform clustering on S-wave splitting analysis results. The results show that the fracture system in the Hakone caldera can be divided into two clusters (A and B) or four clusters (A1, A2, B1, and B2). In the central cone vicinity, craters or dikes corresponding to the compressive axis of the regional stress field are dominant, whereas the fault systems with the best orientation to the regional stress field develop around the central cone. Cluster B1 can be explained by the northwest–southeast alignment of micro cracks or dikes corresponding to the direction of maximum horizontal pressure of the regional stress field. The others are likely explained by fault fracture zones, which have an optimal orientation for regional stress fields, or by the alignment of micro cracks affected by the local stress field. Cluster B2 suggests the existence of fracture zones of the Tanna and Hirayama fault systems, which cross the Hakone volcano from north to south. Clusters A1 and A2 are possibly explained by the conjugate system of B2. However, the alignment of micro cracks generated by the local stress field or old volcanic structures can also be a cause of the clusters.

The performance of a multi-channel seismometer system with phase-shifted optical interferometry was improved by newly introduced sensors and a processing unit. The current version of the system consists of three optical wired seismometers and the unit. We deployed the system at Sakurajima Volcano and successfully operated it from June to December 2019. As the Sakurajima Volcano frequently erupts, a number of eruption events were observed during the observation period, as were a number of lightning strikes. In this study, we evaluated the observation performance of the volcanic earthquake and the noise caused by the lightning, using the spectrum and amplitude of the waveform. The results show that this sensor can observe earthquakes caused by eruptions as well as ordinary seismometers do. When the lightning struck, pulsed noise with power in a wide frequency band was observed in the existing seismometer, but not in the new sensor. Therefore, the observation was not affected by lightning. In addition, this system was found to be effective in the array analysis of volcanic earthquakes.

Volcanic activity is diverse. Therefore, a lot of volcanic ejecta need to be analyzed to properly assess the condition of a volcano. However, until now, rapid analysis in this regard has been insufficient. To accurately evaluate both the transition and the characteristics of eruptions, we constructed a platform to efficiently analyze volcanic ejecta incorporating a number of automatic processing functions into a data processing system composed of an electron beam microprobe analyzer (EPMA) and personal computers. A number of time-consuming tasks, such as crystal size distribution analysis and ash particle classification, were automated. Further, the analysis platform is equipped with a database function for collecting various analytical data as the basis for the future development of volcanology. Various quantitative values related to the composition and microtexture of the volcanic ejecta were collected and entered into the database. This paper introduces an outline of the system, collected data, and usage examples.

We have studied four lava dome eruptions which occurred in 45–10 ka in Haruna volcano. Enclave parts (SiO₂ 50.9–55.1 wt%) and host parts (SiO₂ 59.5–64.5 wt%) in lava samples are all products of magma mixing. Characteristics of felsic endmember magmas are the same among four eruptions, while those of mafic endmember magmas vary slightly in terms of bulk composition. The felsic magma had SiO₂ ≥ 63 wt% and a temperature of 760°C–860°C, and contained ≥60 vol% of orthopyroxene, amphibole, plagioclase, quartz, and Fe-Ti oxides. The mafic magma had SiO₂ 48–51 wt% and contained 0–10 vol% of olivine. The enclave magmas resulted from higher contribution of mafic magma and thus had higher temperature than the host magmas, which led to formation of enclave upon their interaction. Similarities of endmember magmas between the four eruptions and the Futatsudake-Ikaho eruption (late 6th–beginning of 7th century) suggest structure of magma plumbing system and eruption triggering process have been basically unchanged in past 45,000 years. The felsic magmas were commonly mush-like and had high viscosity. Therefore, generation of low-viscosity magma through magma mixing, and vent-opening by the low-viscosity magma are mandatory for eruption to initiate. Unlike the Futatsudake-Ikaho eruption, the older four eruptions did not proceed to eruptive phase where felsic magma erupts without mixing and explosively. The absence of quartz only in felsic magma of Futatsudake-Ikaho eruption is consistent with its less-evolved bulk composition and slightly higher temperature than those of older four eruptions.

High-temperature melting and crystallization experiments were carried out at pressures from 1 atm to 196 MPa and under H₂O-saturated conditions on the basaltic andesite melt of the Izu-Oshima 1986B eruption (i.e., the B_M melt), using a 1-atmosphere fO₂-controlled furnace and an internally heated pressure vessel. These data were used to constrain the H₂O-saturated plagioclase liquidus (HSPL) of the melt. The fO₂ conditions were controlled by a mixed H₂-CO₂ gas at the Ni-NiO (NNO) buffer for the 1 atm experiments, but were not controlled for the high-pressure experiments. Plagioclase is the liquidus phase at 1 atm, whereas early saturation of Fe-Ti oxide above the plagioclase liquidus occurred in the high-pressure experiments due to the elevated fO₂ conditions. The HSPL temperature decreases from 1172 ± 8°C to 1030 ± 20°C as the pressure increases from 1 atm to 196 MPa. A combination of previously proposed models for the plagioclase liquidus and melt H₂O-solubility can predict the experimentally determined HSPL temperatures, even if oxidation-induced magnetite crystallization occurs. Using these models and the previously reported pre-eruptive temperature of ∼1100 ± 30°C, we estimate the pre-eruptive pressure conditions of the B_M melt to be 42_-32⁺⁴⁸ MPa, which corresponds to depths of 1.9_-1.4^+1.9 km. The estimated depth is consistent with that of the shallow active dikes previously identified from geophysical studies, suggesting that the B_M melt was derived from a small, shallow magma chamber formed in the shallow dike region.

History and pattern of explosive eruptions at Chokai volcano, Japan, in the last 2500 years were investigated from tephra survey and accelerator mass spectrometry (AMS) radiocarbon dating. The tephrostratigraphy was established based on observations at eight hand-dug trenches and three outcrops. The well-correlated tephra layers were dated at c. 2.5 ka, 2.1–1.9 ka, 1.8 ka, and 1.6 ka, indicating major eruptions occurred at these ages. The tephra from the documented 871 CE eruption was also identified. Componentry analysis of ash was carried out for these five eruption deposits. The changes in tephra facies and ash components within an unbroken series of tephra layers indicate a shift from hydrothermal-dominant phreatic or phreatomagmatic eruption to magma-dominant eruptions in a single episode. Common eruption sequences were identified based on the combination of tephra facies variation and records of witnessed eruptions. Every volcanic activity begins with precursory activity of seismicity, fumaroles, and snow melting for weeks to months, then onset hydrothermal-dominant eruption happens. Then, the eruption evolves to a magma-dominant eruption, or alternatively, the hydrothermal-dominant eruption persistently continues until cessation. The eruption sizes are VEI 2 or more minor. Lahar can occur at any stage of the eruption, resulting in damage to the residential area at the base of the volcano. The eruption patterns and the extent of hazard risks elucidated by this study will be utilized to hazard mitigation plans.

The lahars are one of the most hazardous volcanic phenomena causing the third greatest causalities among the volcanic hazards since the 16th century worldwide. Lahars can flow down a long distance and cause tremendous disaster at the foot of volcanoes often beyond the areas of primary volcanic impacts of pyroclastic fall and pyroclastic density currents. Therefore, the research on lahar history of active volcanoes approaching from an analysis of a geological record in distal volcanic regions is significant for lahar hazard risk evaluation. Zao volcano has high risks of future eruptions, because volcanic tremors have been detected since 2013. The presence of a crater lake at the summit area, and steep slopes at the high altitude of Zao indicates high potential energy for future lahars, if triggered by an eruption starting underneath the crater lake. This study firstly reports the existence of lahar deposits at the western foot of Zao and discusses the depositional features and the origin of these as well as the lahar hazard risk at this volcano. The lahar deposits were exposed during the archaeological excavation of the Fujiki ruin, western foot of the Zao volcano. Two major lahar units, L1 and L2, were recognized. Based on the ¹⁴C dating and stratigraphic relationships, the ages of units L1 and L2 were estimated to be <ca. 4.0 and ca. 4.6 cal ka, respectively. The lithology, granulometry, and componentry features of the lahar deposits revealed the depositional features and the source materials. The upper part of L1 (L1-1) unit and lower part of L2 (L2-2) unit were deposited from a hyperconcentrated flow, whereas, the lower part of L1 (L1-2) unit and upper part of L2 (L2-1) unit were formed by a debris flow. The sources of both units were phreatomagmatic eruption products that may have erupted shortly before the lahar events. This implies that these eruptions were the most plausible trigger for the lahars. These results suggest that lahar risk will increase especially after the phreatomagmatic eruptions as well as phreatic eruptions, even in the western foot of this volcano.

Eruption history of Akanfuji in the Me-akan volcano, eastern Hokkaido, has been examined by comparing multiple natural outcrops. In a previous study, at least 17 layers of scoria fall deposits were recognized. To obtain more detailed geological information and reexamine the eruptive activity of Akanfuji, we conducted trench surveys. At each survey site, the scoria fall deposits from Akanfuji are layered with a total thickness of several tens of centimeters to 1 m. A light brown volcanic ash layer is deposited just under the lowest layer of Akanfuji, and the fresh glass in the light brown volcanic ash shows the glass composition of the volcanic ash that erupted at Tarumai volcano 2500 BP. In addition, volcanic ash ejected from Ponmachineshiri of the Me-akan volcano is deposited on top of the newest deposits in the Akanfuji series with a thin soil layer in between. The volcanic ash ejected from Ponmachineshiri contains patches of volcanic ash from the Mashu volcano that erupted 1000 years ago. Therefore, Akanfuji was active from about 2500 to 1000 years ago. Akanfuji ejected scoria fall deposits at least 17 times (Akf-1 to Akf-17), and assuming that it erupted an average number of times during the activity period, it would be once every 90 years. The eruption rate was estimated to be 0.12 km³ DRE/ka.

We investigated conduit flow dynamics during the 1986 sub-Plinian eruption of Izu-Oshima volcano, Japan, using a 1-D steady conduit flow model. Following observations that the magma plumbing system beneath Izu-Oshima, characterized by the feeding of a dyke, generated a fissure-type sub-Plinian eruption, we considered a dyke-like conduit geometry by applying a pseudo-dyke conduit with an ellipsoidal horizontal cross-section. Under appropriate parameter settings constrained by geological, petrological, and geophysical observations, we identified a conduit geometry that enables steady solutions of a conduit flow that generates the sub-Plinian eruption. A dyke-like conduit geometry allows us to widen the range of geometric parameters of the solution. We found that the distribution of magma overpressure in the conduit strongly depends on conduit geometry. When the conduit geometry is composed of deeper and shallower dykes with large and small aspect ratios, respectively, localized overpressurization occurs in the region before magma fragmentation. This overpressurization in the dyke-like conduit may induce a characteristic crustal deformation similar to that caused by a vertical tensile fault. It is crucial to consider the effects of conduit flow with a dyke-like geometry on deformation for precise monitoring of eruption sequences based on geodetic signals in future eruptions at Izu-Oshima volcano.

Pyroclastic density currents (PDCs) are one of the most dangerous but least understood phenomena of volcanic eruptions. An open-source numerical depth-averaged model of dense granular currents controlled by physical processes such as energy dissipation, basal deposition, and erosion (faSavageHutterFOAM) was applied to investigate the basal concentrated region of a dome-collapse PDC generated on June 3, 1991 at Unzen volcano (Japan) to assess the effects of the physical processes (and their interplay) on the flow dynamics and run-out area of the PDC. Numerical simulations show that energy dissipation process decreases the flow velocity and increases the basal deposition rate, which reduces the run-out distance. The simulations also reveal that erosion process during flow propagation decreases the flow velocity and increases the run-out distance. The numerical results are sensitive to the parameters of energy dissipation (dry friction coefficient μ and collisional or turbulent friction coefficient χ) and erosion (specific erosion energy e_b). The results are fitted to field data for run-out distance and flow velocity when μ is between 0.01 and 0.1 with χ∼10³ m^-1 s^-2 (or when χ is between 10⁴ and 10⁵ m^-1 s^-2 with μ∼0.2) and e_b∼10² m² s^-2. The estimated value of e_b suggests that re-entrainment of deposit mass played an important role in controlling the flow dynamics and run-out area of the PDC. The estimated values of μ and χ are correlated, but the estimation of these parameters might be improved by further constraints from field data. The presented results serve as a basis to make further quantitative estimations of the model parameters (μ, χ, and e_b) for applying the faSavageHutterFOAM model to hazard assessments of PDCs.

This study applied the numerical simulations of lava flows to evaluate the damage caused by volcanic hazards. The accuracy of the numerical simulation was governed by the reliability of the input parameters in the numerical models. One of the most important parameters is the information pertaining to terrain data, which is generally provided as a digital elevation model (DEM). The recently-developed 8K technology, mainly applied in the broadcasting field, provides a precise photographic survey of the terrain and can produce a detailed digital topographic map. The Japan Broadcasting Cooperation (NHK) deployed an 8K drone to generate a digital elevation model of Sakurajima Volcano, Japan. These data were used to formulate the lava flow under certain prescribed conditions. This study analyzes the influence of DEM mesh size on lava flow simulations, showing that high-precision DEM outlines the distribution of inundated areas in detail. Moreover, a smaller mesh resulted in a faster arrival time of the lava flow. The study’s results are useful for both risk and crisis management.

In this study, a new data assimilation method called “particle filter” was applied to the volcanic plume tracking model called PUFF to assimilate the Multi-parameter (MP) radar observations at Sakura-jima volcano. In the particle filter algorithm, the statistical likelihood was computed for each ash particle of the model given the observed MP radar data. Particles with a high likelihood were retained, but particles with a low likelihood were removed from the computation. The removal was followed by resampling of new particles at high-likelihood locations. The results show that the particle filter works properly to generate suitable new particles in the open space between the model and the observed particles. As the plume shape of MP radar observation is an important information source, observed particles were added at the resampling stage of the particle filter. A proper threshold value for removing or retaining the particles was examined using likelihood estimation. In this study, we determined the proper threshold to resample approximately half of the model particles. The results of the analysis show a reasonable mix of observed, predicted, and resampled data at proper locations, filling the open space between the prediction and the observation. It was found that data assimilation using the particle filter is a suitable method for assimilating the MP radar observation to the PUFF model prediction. This study demonstrates that the new PUFF model system, combined with real-time MP radar data using a particle filter, is highly reliable and useful for preventing volcanic hazards around active volcanoes.

At Sakurajima volcano, frequent Vulcanian eruptions have been seen at the summit crater of Minamidake since 1955. In addition to this eruption style, the eruptive activities of Strombolian type and prolonged ash emission also occur frequently. We studied the design of a simulator of advection-diffusion-fallout of volcanic ash emitted continuously. The time function of volcanic ash eruption rate is given by a linear combination of the volcanic tremor amplitude and the volume change of the pressure source obtained from the ground motion. The simulation is repeated using discretized values of the eruption rate time function at an iteration time interval of the simulation. The integrated value of the volcanic ash deposition on the ground obtained from each individual simulation is used to estimate the value of the ash fallout. The plume height is given by an empirical equation proportional to a quarter of the power of the eruption rate. Since the wind velocity field near the volcano is complicated by the influence of the volcanic topography, the predicted values published by meteorological organizations are made in high resolution by Weather Research and Forecasting (WRF) for the simulation. We confirmed that an individual simulation can be completed within a few minutes of iteration interval time, using the PUFF model as the Lagrangian method and FALL3D-8.0 as the Eulerian method on a general-purpose PC. Except during rainfall, the radar reflectivity, the count of particles per particle size, and fall velocity obtained by the disdrometers can be used for the quasi-real time matching of the plume height calculated from the eruption rate and the ash fall deposition rate obtained from the simulation.

A preliminary consideration is conducted on the amount of vertically falling volcanic ash sucked into the horizontal air intakes of the exterior device for air conditioning (AC) using a numerical calculation code consisting of transport equations of airborne ash concentration, equations of motion of ash particles, and a simplified airflow model. This study focuses on the effect of the inertia force acting on the ash particle on the process of ash ingress into the horizontal air intake of AC. The results with the ash particle of sphericity 0.8 indicate that the inertia force reduces the amount of the ash ingress into the air intake by 22, 31, and 51% for the diameters of 67.5, 125, and 250 μm, respectively, as compared to the case neglecting the inertia force. The ashfall depths (thickness of deposited ash) derived as the ones leading to reduction of the performances of AC from our previous laboratory experiment on an open-type cooling tower are re-evaluated with the code. The results suggest that the ashfall depth affecting AC performances can be larger by a factor of 1.6 to 2.1, depending on the particle sphericity, than that obtained in the experiment where the inertia force was neglected in the conversion from the ash amount provided to the test piece to the “actual” ashfall depth. Simulations on the effect of installing a hood over the air intake are also made, indicating limited but substantial reduction of the expected ash ingress. The importance of mitigating ashfall impacts is stressed.

A hydrovolcanic eruption in the early hours of October 8, 2016 triggered a power outage of about 29,000 houses (∼50,000 habitants) in the Aso caldera area, Kyushu, Japan. Although it was recovered naturally by the early morning of that day, the power outage occurred again in the evening following rainfall that began in the afternoon. The power supply in the caldera area had been temporarily maintained despite the heavy landslide damage due to strong earthquakes in April 2016, without the supplemental transmission lines for the normal standard. The power outage is considered to have been due to the insulator flashover in the power substation, Ichinomiya, Aso, around which the mass of volcanic ash was about 3,000 g/m² or less (≤3 mm thick). This outage resulted from high electric conductivity of the volcanic ash that was wetted with strongly acidic water dammed in the crater before the eruption. This may be one example of the power outage incident due to thin ash fall.

Due to an authors' error, the original version of this article contained errors in in-text citations under Section 4.4 and the corresponding references. Reference [55] should be listed as [56] and the following paper should be listed as [55].

K. P. Tao, M. Chong, J. C. S. Pun, J. G. S. Tsun, S. M. W. Chow, C. S. H. Ng, M. H. T. Wang, Z. Chan, P. K. S. Chan, A. M. Li, and R. W. Y. Chan, “Suppression of influenza virus infection by rhinovirus interference at the population, individual and cellular levels,” medRxiv, doi: 10.1101/2021.08.09.21256656, 2021.

The two paragraphs in Section 4.4 (pp. 79–80) should be corrected as follows:

Now reads

Co-infections of the influenza virus and rhinovirus are relatively common, especially in young children. Previous infection with rhinovirus inhibits subsequent influenza A virus infection by the IFN-mediated innate immune system in differentiated human airway epithelium (Fig. 17) [7]. In other words, rhinovirus induces an IFN response that suppresses subsequent influenza virus infection [7].

A recent study revealed that the replication of rhinovirus is not affected by SARS-CoV-2, although the replication of SARS-CoV-2 is inhibited by rhinovirus, indicating that rhinovirus infection protects against SARS-CoV-2 [55]. SARS-CoV-2, similar to the influenza virus and many other viruses, is inhibited by IFNs [55]. Therefore, the number of COVID-19 cases may be reduced due to the inhibitory effects of rhinovirus-induced IFN response.

Should read

Co-infections of the influenza virus and rhinovirus are relatively common, especially in young children. Previous infection with rhinovirus inhibits subsequent influenza A virus infection by the IFN-mediated innate immune system in differentiated human airway epithelium [7]. An another study also reported similar phenomenon (Fig. 17) [55]. In other words, rhinovirus induces an IFN response that suppresses subsequent influenza virus infection [7].

A recent study revealed that the replication of rhinovirus is not affected by SARS-CoV-2, although the replication of SARS-CoV-2 is inhibited by rhinovirus, indicating that rhinovirus infection protects against SARS-CoV-2 [56]. SARS-CoV-2, similar to the influenza virus and many other viruses, is inhibited by IFNs [56]. Therefore, the number of COVID-19 cases may be reduced due to the inhibitory effects of rhinovirus-induced IFN response.

In the Reference list (p. 81), references [55] to [56] should be corrected as follows:

Now reads

[55] K. Dee, D. M. Goldfarb, J. Haney, J. A. R. Amat, V. Herder, M. Stewart, A. M. Szemiel, M. Baguelin, and P. R. Murcia, “Human rhinovirus infection blocks severe acute respiratory syndrome coronavirus 2 replication within the respiratory epithelium: Implications for COVID-19 epidemiology,” J. Infect. Dis., Vol.224, No.1, pp. 31-38, 2021.

Should read

[55] K. P. Tao, M. Chong, J. C. S. Pun, J. G. S. Tsun, S. M. W. Chow, C. S. H. Ng, M. H. T. Wang, Z. Chan, P. K. S. Chan, A. M. Li, and R. W. Y. Chan, “Suppression of influenza virus infection by rhinovirus interference at the population, individual and cellular levels,” medRxiv, doi: 10.1101/ 2021.08.09.21256656, 2021.

[56] K. Dee, D. M. Goldfarb, J. Haney, J. A. R. Amat, V. Herder, M. Stewart, A. M. Szemiel, M. Baguelin, and P. R. Murcia, “Human rhinovirus infection blocks severe acute respiratory syndrome coronavirus 2 replication within the respiratory epithelium: Implications for COVID-19 epidemiology,” J. Infect. Dis., Vol.224, No.1, pp. 31-38, 2021.

The authors regret these errors, and these errors have now been corrected in the PDF version of the article.