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Integrated Monitoring of Volcanic Ash and Forecasting at Sakurajima Volcano, Japan

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Integrated Monitoring of Volcanic Ash and Forecasting at Sakurajima Volcano, Japan https://doi.org/10.20965/jdr.2019.p0798 Iguchi, M. et al. Paper: Integrated Monitoring of Volcanic Ash and Forecasting at Sakurajima Volcano, Japan Masato Iguchi∗1,†, Haruhisa Nakamichi∗1, Hiroshi Tanaka∗2, Yusaku Ohta∗3, Atsushi Shimizu∗4, and Daisuke Miki∗1 ∗1Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University 1722-19 Sakurajima-Yokoyama-cho, Kagoshima 891-1419, Japan †Corresponding author, E-mail: [email protected] ∗2University of Tsukuba, Ibaraki, Japan ∗3Tohoku University, Miyagi, Japan ∗4National Institute for Environmental Studies, Ibaraki, Japan [Received February 8, 2019; accepted May 9, 2019] The Sakurajima volcano is characterized by frequent 1. Introduction vulcanian eruptions at the Minamidake or Showa crater in the summit area. We installed an integrated At the Sakurajima volcano in Japan, vulcanian erup- monitoring system for the detection of volcanic ash tions frequently occur at Minamidake crater or Showa (composed of remote sensing sensors XMP radars, li- crater 500 m east of Minamidake. This activity, which dar, and GNSS with different wave lengths) and 13 op- has occurred continuously at the Minamidake crater since tical disdrometers on the ground covering all direc- 1955, features frequent vulcanian and strombolian erup- tions from the crater to measure drop size distribu- tions and the continuous emission of ash. The crater was tion and falling velocity. Campaign sampling of vol- relatively active from 1972 to 1992, with 4,919 vulcanian canic ash supports the conversion of particle counts eruptions and the emission of 240 M tons of volcanic ash. measured by the disdrometer to the weight of volcanic After 1993, this activity gradually decreased and the an- ash. Seismometers and tilt/strain sensors were used nual number of vulcanian eruptions fell to below 10 times to estimate the discharge rate of volcanic ash from per year between 2003 and 2017. Eruptive activity re- the vents. XMP radar can detect volcanic ash clouds sumed in phreato-magmatic style on June 4, 2006, at even under visual difficulty because of weather such the Showa crater, becoming magmatic in February 2008 as fog or clouds. A vulcanian eruption on Novem- with frequent associated vulcanian eruptions. The erup- ber 13 was the largest event at the Sakurajima vol- tive activity of the crater continued until October 2017. cano in 2017; however, the volcanic plume was not We counted 5,921 vulcanian eruptions at the crater dur- visible due to clouds covering the summit. Radar re- ing the period from February 2008 to October 2017, vealed that the volcanic plume reached an elevation and 44 M tons of volcanic ash was emitted. In Novem- of 4.2–6.2 km. Post-fit phase residuals (PPR) from the ber 2017, eruptive activity returned to Minamidake crater. GNSS analysis increased suddenly after the eruption, The heavy and long-term discharge of volcanic ash im- and large-PPR paths from the satellites to the ground- pacted the area around the Sakurajima volcano in vari- based receivers intersected each other at an elevation ous ways. The most severe impact was a reduction in the of 4.2 km. The height of the volcanic plume was also output from agriculture. The government of Kagoshima estimated from the discharge rate of volcanic ash to prefecture estimate the amount of agricultural damage be 4.5 km, which is empirically related to seismic en- due to the Sakurajima eruption at 236 billion yen over ergy and the deflation volume obtained via ground de- the 39 years since 1978, when statistics for the damage formation monitoring. Using the PUFF model, the began to be calculated. The second impact concerns traf- weight of the ash-fall deposit was accurately forecast fic, including airlines, roads, and railways. The wind- in the main direction of transport of the volcanic ash, shields of airplanes were occasionally damaged by vol- which was verified by disdrometers. For further ad- canic lapilli and ash ejected by eruptions that occurred at vances in forecasting of the ash-fall deposit, we must the Minamidake crater in the 1970s [1]. Since then the consider high-resolution wind field, shape of volcanic airspace around Sakurajima was set as a no-fly area, and plume as the initial value, and the particle number dis- the occurrence of this type of damage ceased. Awareness tribution along the volcanic plume. of the air problems that are often caused by volcanic ash has increased since an eruption at Galunggung in 1982, followed by eruptions at Redoubt in 1989, Pinatubo in Keywords: volcanic ash, XMP radar, lidar, vulcanian 1991, and Eyjafjallaj¨okull in 2010. Because of the ef- eruption, Sakurajima volcano fects these events have had on air travel, the possibility 798 Journal of Disaster Research Vol.14 No.5, 2019 © Fuji Technology Press Ltd. Creative Commons CC BY-ND: This is an Open Access article distributed under the terms of the Creative Commons Attribution-NoDerivatives 4.0 International License (http://creativecommons.org/licenses/by-nd/4.0/). Integrated Monitoring of Volcanic Ash and Forecasting at Sakurajima Volcano, Japan of cancelling flights has increased. Roads have on occa- craters cannot be seen visually, and are compared with sion been closed due to heavy ash-fall from Sakurajima, plume height which is estimated from the discharge rate for example, during eruptions on August 24, 1995 and on based on seismic and ground deformation observations. July 24, 2012. Large amounts of ash-fall have also been The actual height of the plume is then confirmed by com- known to cause train derailments and create obstructions parison with the aerial amount of ash produced by simu- to train operations. The third issue is the impact on the lation. health of residents living around Sakurajima. After ana- lyzing the fine volcanic ash particles, Hillman et al. [2] concluded that the potential health hazard of the ash is 2. Remote Sensing for the Detection of Volcanic low, but high exposure and respiratory conditions should Ash still be monitored given the high frequency and duration of such exposure. For this study, we installed an integrated observation Considering this situation, we propose a study for the system to detect volcanic plume at the Sakurajima vol- “Development of a real-time volcanic ash hazard assess- cano. The system is composed of lidar, XMP radar, and ment method” for the Integrated Program for Next Gen- a set of GNSS. These instruments radiate electromagnetic eration Volcano Research and Human Resource Develop- waves with different wavelengths, lidar emits light with ment under the Ministry of Education, Culture, Sports, a wavelength of 532 nm, and XMP radar and GNSS ra- Science and Technology (MEXT). This proposed study is diate waves in the X-band (wavelength: 2.5–3.7 cm) and composed of 1) the detection of volcanic ash using inte- the L-band (wavelength: 20–60 cm), respectively. By us- grated remote sensing immediately after the onset of erup- ing multiple wave-lengths, the integrated system can be tions, 2) a reduction in the time taken to forecast ash-fall, applied at various scales of eruption, which produce dif- based on seismic and ground deformation data, 3) precise ferent spatial concentrations of volcanic ash particles in forecasts of ash-fall deposits based on spatially high reso- the atmosphere. lution wind fields, 4) the technical development of an on- line system for forecasting, and 5) stochastic forecasting of ashfall by statistical processing of precursory ground 2.1. Lidar deformation prior to volcanic eruptions. We studied top- Lidar is usually used for the observation of aerosols in ics 1–3 for the first 4 years under the 10-year project. To the atmosphere [11]. Lidar can detect volcanic ash parti- reduce the time taken before forecasts of ash-fall, we used cles at a distance. For example, volcanic ash particles that the PUFF model [3], considering the emission rate of vol- erupted from Augustine volcano were detected by a lidar canic ash [4]. Grid point values (GPV) for wind direction system at Fairbanks, 700 km away from the volcano [12]. and velocity forecast by the Japan Meteorological Agency For our observation of the Sakurajima volcano, we use a (JMA) were used in the model. At the Sakurajima vol- polarization and dual-wavelength lidar manufactured by cano, the emission rate of volcanic ash is well formulated FIT Leadintex and set the radiative direction of light from by using a linear combination of the seismic amplitudes of the lidar to the area immediately above the crater to detect explosion earthquakes and volcanic tremors and the vol- ash particles independently from wind direction. Lidars ume of deflation due to ground deformation source [5]. were located on the west and east flanks of the volcano For topic 3, high-resolution data for wind fields are re- (Fig. 1). The lidar radiates linearly polarized light pulses quired for a precise forecast of volcanic ash volume, be- at wavelengths of 532 and 1064 nm. Both the parallel and cause the wind field near volcanoes is affected by topogra- perpendicular components of backscatter light at 532 nm phy, and downward flow is dominant leeward of the sum- and the total backscatter at 1064 nm are detected. The mit [6]. The Weather Research and Forecasting (WRF) light pulse is radiated 40 times in the first 2 seconds. Af- model [7] is used to downscale the JMA forecast data and ter 8 s, 40 pulses are radiated again. The sequence is re- the high-resolution meteorological data are then used for peated with a time interval of 10 s. the FALL3D model [8] to forecast the ashfall deposits [9]. The emission rate of volcanic ash can be estimated by the observation of seismic and ground deformation [5]; 2.2.
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