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Tanaka Ryo

Faculty of Science　Institute of Seismology and VolcanologyAssociate Professor

Researcher basic information

■ Degree
  • 博士（理学）, 北海道大学
■ URL
researchmap URLホームページURL■ Various IDs
Researcher number
  • 30804926
ORCID IDJ-Global ID■ Research Keywords and Fields
Research Keyword
  • 火山物理学
  • 熱水流動数値計算
  • 火山測地学
  • 熱観測
  • ドローン
  • 火山の熱水系
  • 火山噴火予知
Research Field
  • Natural Science, Solid earth sciences
■ Educational Organization

Career

■ Career
Career
  • May 2026 - Present
    Hokkaido University, Institute of Seismology and Volcanology Faculty of Science, 准教授, Japan
  • Apr. 2019 - Present
    Hokkaido University, Institute of Seismology and Volcanology Faculty of Science
  • Apr. 2017 - Mar. 2019
    Hokkaido University, Institute of Seismology and Volcanology Faculty of Science
Educational Background
  • Apr. 2014 - Mar. 2017, Hokkaido University, Graduate School of Science
  • Apr. 2012 - Mar. 2014, Hokkaido University, Graduate School of Science
  • Mar. 2012, Hokkaido University, School of Science

Research activity information

■ Awards
  • May 2024, 日本火山学会, 日本火山学会研究奨励賞
    火山浅部熱水系の活動プロセスの理解を目指した多項目観測と数値実験による複合的研究
■ Papers
  • Dense magnetotelluric imaging of the Akan Caldera (Hokkaido, Japan): insights into its magma plumbing system and caldera-forming reservoir
    Tomohiro Inoue; Takeshi Hashimoto; Koki Aizawa; Hiroshi Ichihara; Ryo Tanaka; Yusuke Yamaya
    Earth, Planets and Space, 16 Mar. 2026
    Scientific journal
  • Shallow thermal activity of Tokachidake Volcano (Japan) investigated through repeated drone-borne magnetic surveys
    Toshiaki Hokari; Ryo Tanaka; Takeshi Hashimoto; Takao Koyama
    Earth, Planets and Space, 13 Mar. 2026
    Scientific journal
  • Coupled model of overpressure-driven dike deformation and volcanic conduit flow: implications for non-uniform dike deformation during effusive eruptions
    Sora Nishikawa; Ryo Tanaka
    Earth, Planets and Space, 78, 1, Springer Science and Business Media LLC, 15 Jan. 2026
    Scientific journal, Abstract

    Interactions between the elastic magma chamber and the variable flow resistance of conduits control volcanic eruptions. Recent geodetic observations have revealed complex conduit deformations, especially in inclined dikes, which traditional models have struggled to capture. In this study, we introduce a simplified coupled model that explicitly accounts for magma flow within a nonuniform, elastically deformable inclined dike conduit under the influence of edifice loading. Dimensional analysis reduces the governing equations to an advection–diffusion type equation, controlled by two key dimensionless parameters representing the relative deformability of the conduit and the contribution of gravitational and pressure gradient forces. Numerical simulations demonstrate that these parameters govern the regime of pressure propagation. Specifically, deformation driven by large overpressure can significantly increase effusion rates and induce response delays between different depths. Applying this model to the 2018 Kilauea eruption, we show that the observed response delays and the spatial pattern of deformation (simultaneous expansion and contraction) are well-reproduced in a regime, where advective effects dominate. Our findings provide a refined theoretical framework for understanding volcanic conduit behavior in complex geometries and could explain observed non-uniform deformation phenomena.

    Graphical abstract
  • Hydrothermal sealing process in a volcanic conduit interpreted from the characteristics of subvolcanic hydrothermal alterations at Tokachidake volcano, Japan
    Ryo Takahashi; Shingo Takeuchi; Ryo Tanaka; Kan Fujiwara; Shimpei Uesawa
    Earth, Planets and Space, 77, 1, Springer Science and Business Media LLC, 04 Nov. 2025
    Scientific journal, Abstract

    At Tokachidake volcano, Japan, inflation of the crater area was observed alongside a decrease in fumarolic plume height during 2006–2017, which was attributed to conduit sealing. The accumulation of excess pressure owing to continuous sealing can lead to phreatic eruptions and edifice collapses. To reveal the sealing process, this study investigates the characteristics of hydrothermal alterations in the volcanic conduit by analyzing altered materials from the edifice interior and associated changes in porosity and permeability. The weakly altered rock retained some of its primary minerals and can be interpreted as having formed in an environment, where the supply of volcanic gases and hydrothermal fluids was limited. In contrast, the conduit-filling lava and scoria fragments were intensely leached and cemented by fine alunite and amorphous silica, resulting in consolidated aggregates (strongly altered rock). Porosity and permeability tended to increase as hydrothermal alteration advanced. However, the strongly altered rocks were originally unconsolidated aggregates of lava and scoria fragments. Our data suggest that the consolidation associated with hydrothermal alterations reduced the permeability of the conduit by three to four orders of magnitude, leading to conduit sealing. This decrease in permeability would create excess pore pressure within the conduit, with our estimates ranging from <1 to 13.5 MPa. Such conduit sealing is likely to occur repeatedly in the future. Therefore, to elucidate the present state of the volcano and support hazard mitigation, it is essential to correctly interpret the phenomena occurring beneath the crater area based on our results.

    Graphical Abstract
  • 水準測量による有珠山周辺の地盤変動観測
    平戸 悠登; 青山 裕; 鈴木 敦生; 岡田 和見; 保苅 健陽; 泉 那由多; 立石 悟; 筒井 優斗; 田中 良
    北海道大学地球物理学研究報告, 88, 53, 74, Mar. 2025
  • 火道の粘弾性変形と上昇マグマの物性変化を連成したモデルの構築
    西川空良; 田中 良
    北海道大学地球物理学研究報告, 88, 17, 32, Mar. 2025
  • Sulfur dioxide flux measurement at Mount Tokachi, Japan, with TROPOspheric Monitoring Instrument
    Kensuke Yamaguchi; Ryo Tanaka; Masaaki Morita; Toshiya Mori; Ryunosuke Kazahaya
    Frontiers in Earth Science, 11, Frontiers Media {SA}, 18 May 2023, [Corresponding author]
    Scientific journal
  • A broadband magnetotelluric survey for Mt. Meakandake volcano with special attention to the unrest during 2016–2017
    Tomohiro Inoue; Takeshi Hashimoto; Ryo Tanaka; Yusuke Yamaya
    Earth, Planets and Space, 74, 114, Dec. 2022, [Peer-reviewed]
    English, Scientific journal
  • Simple Graphical Pre- and Post-Processor for 3-D Magnetotelluric Inversion
    Ryo Tanaka
    Journal of Disaster Research, 17, 5, 639, 643, Fuji Technology Press Ltd., 01 Aug. 2022, [Peer-reviewed], [Lead author, Last author, Corresponding author]
    English, Scientific journal, 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.
  • Focal mechanisms and the stress field in the aftershock area of the 2018 Hokkaido Eastern Iburi earthquake (MJMA = 6.7)
    Yuki Susukida; Kei Katsumata; Masayoshi Ichiyanagi; Mako Ohzono; Hiroshi Aoyama; Ryo Tanaka; Masamitsu Takada; Teruhiro Yamaguchi; Kazumi Okada; Hiroaki Takahashi; Shin’ichi Sakai; Satoshi Matsumoto; Tomomi Okada; Toru Matsuzawa; Hiroki Miyamachi; Shuichiro Hirano; Yoshiko Yamanaka; Shinichiro Horikawa; Masahiro Kosuga; Hiroshi Katao; Yoshihisa Iio; Airi Nagaoka; Noriko Tsumura; Tomotake Ueno
    Earth, Planets and Space, 73, 1, Springer Science and Business Media LLC, Dec. 2021, [Peer-reviewed]
    Scientific journal, AbstractThe tectonic stress field was investigated in and around the aftershock area of the Hokkaido Eastern Iburi earthquake (MJMA = 6.7) occurred on 6 September 2018. We deployed 26 temporary seismic stations in the aftershock area for approximately 2 months and located 1785 aftershocks precisely. Among these aftershocks, 894 focal mechanism solutions were determined using the first-motion polarity of P wave from the temporary observation and the permanent seismic networks of Hokkaido University, Japan Meteorological Agency (JMA), and High Sensitivity Seismograph Network Japan (Hi-net). We found that (1) the reverse faulting and the strike-slip faulting are dominant in the aftershock area, (2) the average trend of P- and T-axes is 78° ± 33° and 352° ± 51°, respectively, and (3) the average plunge of P- and T-axes is 25° ± 16° and 44° ± 20°, respectively: the P-axis is close to be horizontal and the T-axis is more vertical than the average of the P-axes. We applied a stress inversion method to the focal mechanism solutions to estimate a stress field in the aftershock area. As a result, we found that the reverse fault type stress field is dominant in the aftershock area. An axis of the maximum principal stress (σ1) has the trend of 72° ± 7° and the dipping eastward of 19° ± 4° and an axis of the intermediate principal stress (σ2) has the trend of 131° ± 73° and the dipping southward of 10° ± 9°, indicating that both of σ1- and σ2-axes are close to be horizontal. An axis of the minimum principal stress (σ3) has the dipping westward of 67° ± 6° that is close to be vertical. The results strongly suggest that the reverse-fault-type stress field is predominant as an average over the aftershock area which is in the western boundary of the Hidaka Collision Zone. The average of the stress ratio R = (σ1 − σ2)/(σ1 − σ3) is 0.61 ± 0.13 in the whole aftershock area. Although not statistically significant, we suggest that R decreases systematically as the depth is getting deep, which is modeled by a quadratic polynomial of depth.
  • Three-dimensional inversion of audio-magnetotelluric data acquired from the crater area of Mt. Tokachidake, Japan
    Ryo Tanaka; Yusuke Yamaya; Makoto Tamura; Takeshi Hashimoto; Noritoshi Okazaki; Ryo Takahashi; Toru Mogi
    Earth, Planets and Space, 73, 1, Springer Science and Business Media LLC, Dec. 2021, [Peer-reviewed], [Lead author, Corresponding author]
    Scientific journal, Abstract

    Subvolcanic hydrothermal systems can lead to hydrothermal eruptions as well as unrest phenomena without an eruptive event. Historical eruptions and recent unrest events, including ground inflation, demagnetization, and a gradual decrease in the plume height, at Mt. Tokachidake, central Hokkaido, Japan, are related to such a subvolcanic hydrothermal system. This study investigates the three-dimensional (3-D) resistivity structure of Mt. Tokachidake to image its subvolcanic hydrothermal system. A 3-D inversion of the magnetotelluric data, acquired at 22 sites around the crater area, was performed while accounting for the topography. Our resistivity model was characterized by a high-resistivity layer at a shallow depth (50–100 m) and two conductors near the active crater and dormant crater. The high-resistivity layer was interpreted to be composed of dense lava, which acts as a caprock surrounding the conductor. The high conductivity beneath the active crater can be explained by the presence of hydrothermal fluid in fractured or leached zones within the low-permeability lava layer, as the sources of ground inflation and demagnetization were identified within the conductive zone immediately beneath the resistive layer. The resistivity structure was used to estimate the volume of hydrothermal fluid within the pore space. The minimum volume of hydrothermal fluid beneath the active crater that can explain the resistivity structure was estimated to be 3 × 106 m3. This estimate is comparable to the water volume that was associated with the long runout and highly fluidized lahar in 1926. The resistivity structure and volume of hydrothermal fluid presented in this study can be used as a reference for further numerical simulations, which aim to reveal the mechanisms of recent unrest events and assess the risk of hazards, such as lahar.
  • Three-dimensional reconstruction of topography model of Tarumae lava dome using UAV (unmanned aerial vehicles)
    Kudo Chisato; Aoyama Hiroshi; Tanaka Ryo
    Geophysical bulletin of Hokkaido University, 83, 103, 114, 北海道大学大学院理学研究院, 19 Mar. 2020, [Domestic magazines]
    Research institution
  • Seismic and geodetic monitoring near the active crater at Tokachidake volcano (preliminary report)
    Aoyama Hiroshi; Tanaka Ryo; Hashimoto Takeshi; Murakami Makoto; Narita Shohei
    Geophysical bulletin of Hokkaido University, 83, 25, 48, 北海道大学大学院理学研究院, 19 Mar. 2020
    Japanese
  • Quantitative relationship between plume emission and multiple deflations after the 2014 phreatic eruption at Ontake volcano, Japan
    Shohei Narita; Makoto Murakami; Ryo Tanaka
    Earth, Planets and Space, 71, 1, Springer Science and Business Media LLC, 30 Dec. 2019
    Scientific journal, Abstract

    The phreatic eruption of Mount Ontake in 2014 caused local-scale subsidence and a mass discharge of water–vapor plumes from vents. A previous study of InSAR data analysis modeled the local subsidence as a deflation of a shallow hydrothermal reservoir (~ 500 m beneath the vents), and speculated that it was associated with plume emission continuing just after the eruption. In addition, combination of the InSAR and GNSS data implies that another, deeper deflation source (~ 3–6 km beneath the vents) contributes to the baseline contraction of the GNSS data. In this study, we estimated daily mass flux of the emitting plumes using photographed images, and compared the temporal behavior of the discharged mass with that of deflation of the two sources in order to clarify their association. The temporal profiles of the shallow deflation volume and the discharge mass both show evidence of decay, but with different characteristics; the deflation volume progress was approximated by a single exponential decay with a long relaxation time (379–641 days), whereas the discharge mass displayed a sum of a linear trend and an exponential decay with shorter relaxation time (47 days). This discrepancy, along with GNSS data, suggests the contribution of a deep deflation source with a short relaxation time (20–40 days). Estimation of mass balance between the emitting plume and fluids discharged from both shallow and deep sources revealed that more than 70% of the discharged mass came from the deep source. Based on the estimated mass balance, phase state of the shallow reservoir was estimated as a single-phase, liquid-rich reservoir. The fast decay of the deep deflation may reflect rapid depressurization due to violent fluid discharge at the onset of the eruption. In contrast, the slow decay of the shallow deflation suggests that it had a minor role in the eruption. However, such a wet reservoir has the potential to induce volcanic hazard such as snow-melting lahar for future eruptions, requiring monitoring the volcano, which will probably shift to pre-eruptive re-pressurized phase, until the future eruption.
  • The 2018 Hokkaido Eastern Iburi earthquake (MJMA = 6.7) was triggered by a strike-slip faulting in a stepover segment: insights from the aftershock distribution and the focal mechanism solution of the main shock
    Kei Katsumata; Masayoshi Ichiyanagi; Mako Ohzono; Hiroshi Aoyama; Ryo Tanaka; Masamitsu Takada; Teruhiro Yamaguchi; Kazumi Okada; Hiroaki Takahashi; Shin'ichi Sakai; Satoshi Matsumoto; Tomomi Okada; Toru Matsuzawa; Shuichiro Hirano; Toshiko Terakawa; Shinichiro Horikawa; Masahiro Kosuga; Hiroshi Katao; Yoshihisa Iio; Airi Nagaoka; Noriko Tsumura; Tomotake Ueno; Koji Miyakawa; Shin'ichi Tanaka; Miwako Ando; Naoki Uchida; Ryosuke Azuma; Ryota Takagi; Keisuke Yoshida; Takashi Nakayama; Satoshi Hirahara; Yoshiko Yamanaka; Yuta Maeda; Shuichiro Hirano; Hiroki Miyamachi; Hiroshi Yakiwara; Takuto Maeda; Masahiro Shimazaki; Youichi Asano
    EARTH PLANETS AND SPACE, 71, Dec. 2019, [Peer-reviewed]
    English, Scientific journal
  • Significance of Electromagnetic Surveys at Active Volcanoes: Toward Evaluating the Imminence of Wet Eruptions
    Takeshi Hashimoto; Wataru Kanda; Yuichi Morita; Midori Hayakawa; Ryo Tanaka; Hiroshi Aoyama; Makoto Uyeshima
    Journal of Disaster Research, 14, 4, 580, 591, Jun. 2019, [Peer-reviewed]
    English, Scientific journal
  • Tiltmerer observation in Avachinsky volcano, Kamchatka, Russia
    Takahashi, H; H. Aoyama; M. Ohzono; R. Tanaka; C. Ito; S. Watanabe; T. Matsushima; Y. Yamashita; H. Miyamachi; S. Okuyama; E. Gordeev; Y. Muraviyev; K. Maguskin; N. Malik; I. Minorov; D. Chebrov
    Geophysical Bulletin of Hokkaido University, 82, 11, 18, Mar. 2019
    Japanese, Scientific journal
  • Contention between supply of hydrothermal fluid and conduit obstruction: inferences from numerical simulations
    Ryo Tanaka; Takeshi Hashimoto; Nobuo Matsushima; Tsuneo Ishido
    Earth, Planets and Space, 70, 1, Springer Berlin Heidelberg, 01 Dec. 2018, [Peer-reviewed], [Lead author, Corresponding author]
    English, Scientific journal
  • Volcanic smoke reduction in visible and thermal infrared imagery
    Hashimoto, T.; Terada, A.; Tanaka, R.
    Earth, Planets and Space, 70, 1, 2018, [Peer-reviewed]
    Scientific journal
  • 全磁力観測：火山体内部構造・熱水流動系のモデル化と火山活動度評価手法の高度化（十勝岳）
    橋本武志; 青山 裕; 田中 良
    北海道地質研究所調査研究報告, 44, 105, 111, Mar. 2017
    Japanese
  • Permeability-control on volcanic hydrothermal system: case study for Mt. Tokachidake, Japan, based on numerical simulation and field observation
    Ryo Tanaka; Takeshi Hashimoto; Nobuo Matsushima; Tsuneo Ishido
    EARTH PLANETS AND SPACE, 69, 1, Mar. 2017, [Peer-reviewed], [Lead author, Corresponding author]
    English, Scientific journal
  • Volcanic plume measurements using a UAV for the 2014 Mt. Ontake eruption
    Toshiya Mori; Takeshi Hashimoto; Akihiko Terada; Mitsuhiro Yoshimoto; Ryunosuke Kazahaya; Hiroshi Shinohara; Ryo Tanaka
    EARTH PLANETS AND SPACE, 68, 1, Mar. 2016, [Peer-reviewed]
    English, Scientific journal
  • Transition in eruption style during the 2011 eruption of Shinmoe-dake, in the Kirishima volcanic group: Implications from a steady conduit flow model
    Ryo Tanaka; Takeshi Hashimoto
    Earth, Planets and Space, 65, 6, 645, 655, Springer Berlin, 2013, [Peer-reviewed], [Lead author, Corresponding author]
    English, Scientific journal
■ Other Activities and Achievements
■ Syllabus
  • 自然史科学特別講義Ⅰ, 2024年, 修士課程, 理学院
  • 自然史科学特別講義Ⅱ, 2024年, 修士課程, 理学院
  • 地球計測実習, 2024年, 学士課程, 理学部
  • 地球惑星科学のための古典力学, 2024年, 学士課程, 理学部
  • 地球惑星科学のための古典力学演習, 2024年, 学士課程, 理学部
■ Affiliated academic society
  • Apr. 2013 - Present
    THE VOLCANOLOGICAL SOCIETY OF JAPAN
  • Feb. 2012 - Present
    Japan Geoscience Union
■ Research Themes
  • 沈み込み帯の火山における噴火位置予測手法の構築に向けた実験的研究
    科学研究費助成事業
    01 Apr. 2024 - 31 Mar. 2027
    田中 良
    日本学術振興会, 若手研究, 北海道大学, 24K17131
  • 水蒸気噴火や山体崩壊の発生場となる活火山内部の熱水変質帯の物質科学的検討
    科学研究費助成事業
    01 Apr. 2023 - 31 Mar. 2026
    高橋 良; 竹内 晋吾; 田中 良; 上澤 真平; 藤原 寛
    日本学術振興会, 基盤研究(C), 地方独立行政法人北海道立総合研究機構, 23K03510
  • 地盤表層域における熱水放出の状態変化に関する実験観測的研究
    科学研究費助成事業
    09 Jul. 2021 - 31 Mar. 2024
    青山 裕; 西村 太志; 田中 良
    初年度である2021年度は，北海道南部のしかべ間歇泉で本研究課題の開始前から実施している多項目連続観測を継続して噴出孔内の映像撮影や圧力測定を試みたほか，鬼首間歇泉で取得した熱赤外カメラ及び空気振動観測のデータ解析，霧島硫黄山の噴気観測，地下構造の深部からの熱水供給率を変化させたときの熱水流動の応答に関する数値計算などを実施した．
    しかべ間歇泉では，間歇泉噴出孔の保守業者の厚意により，6月および9月の作業時に業者所有の孔内撮影用カメラを間歇泉内に挿入し，孔内の状況把握や孔底深度の計測，噴出時の気泡発生状況の動画撮影等を行った．この調査により，掘削深度は約27mであり，ケーシング部分は上部の20mで下部の約7mは裸孔となっていることが始めて確認された．また，井戸の下端には熱水溜まりのような空洞は存在せず，ケーシング下端や裸孔部分の亀裂から井戸内に高温水が流入していることが明らかになった．1月には研究費で購入した圧力センサーを用いて噴出中の孔内圧力を測定し，噴出サイクルを通した井戸内圧力の時系列データを取得した．この調査時には，噴出ごとの熱水噴出体積の推定を試み，過去に見積もられた400L程度であることを確認した．
    鬼首間歇泉では，間欠泉噴出時に観測した熱赤外映像および空気振動観測のデータ解析を進めた．熱赤外映像は時間的な差分を取ることで短周期変動を強調し，熱水の上方への噴出を調べた結果，周期1秒以下の調和振動が見られることを見出した．空気振動にも同様の振動が見られることから，噴出孔の極浅部で共鳴現象が起きていることが示唆された．
    宮崎県の霧島硫黄山では，自然の噴気について熱赤外映像の試験観測を行った．予備的な解析では，連続的な蒸気を噴出する噴気にも調和振動的な振る舞いが認められることから，間歇泉現象や噴気現象には浅部に共鳴現象を励起する類似のプロセスがあることが示唆された．
    日本学術振興会, 挑戦的研究(萌芽), 北海道大学, 21K18784