Updated on 2024/10/23

写真a

 
GESHI NOBUO
 
Organization
Faculty of Science Department of Earth and Planetary Sciences Professor
School of Sciences Department of Earth and Planetary Sciences(Concurrent)
Graduate School of Sciences Department of Earth and Planetary Sciences(Concurrent)
Title
Professor
Contact information
メールアドレス
Profile
I promote the study of the subsurface behavior of magmas that drives volcanic eruptions, using the combinative approaches of geological and petrological methods. How magma rises in the crust forms magma reservoirs, what triggers magma accumulated in magma reservoirs to start rising toward the surface, and what kind of dynamic balance is required for the formation of magmatic conduit. The formation processes of volcanic conduits and calderas caused by the collapse of magma chambers are also the subject of my research. I also study the transition mechanism of explosive eruptions by analyzing the microstructure and chemical composition of volcanic ash and other eruptive products. I am also studying the history of eruption activities of volcanoes using the geological analysis of the lithofacies and stratigraphy of the volcanic products. Though I have studied many volcanoes in Japan and international, recently I have studied mainly the volcanoes and volcanic fields in the Kyushu area, such as Sakurajima and Aira Caldera. Recently, I have been introducing various automated analysis methods for the volcanic ejecta and volcanic outcrops.
External link

Research Areas

  • Natural Science / Solid earth sciences

  • Natural Science / Solid earth sciences

Degree

  • PhD in Science

Research Interests・Research Keywords

  • Research theme: Research of Volcanic activity and eruption mechanism

    Keyword: volcano, eruption, magma,

    Research period: 2024.4

  • Research theme: intrusion

    Keyword: intrusion

    Research period: 2024

  • Research theme: volcano

    Keyword: volcano

    Research period: 2024

  • Research theme: large-scale eruption

    Keyword: large-scale eruption

    Research period: 2024

  • Research theme: eruption

    Keyword: eruption

    Research period: 2024

  • Research theme: magma

    Keyword: magma

    Research period: 2024

  • Research theme: caldera

    Keyword: caldera

    Research period: 2024

Awards

  • 日本火山学優秀学術賞

    2017.5   非特定営利活動法人日本火山学会   Award of prominent academic research

  • 日本火山学会優秀論文賞

    2007.5   非特定営利活動法人日本火山学会   Award of prominent research paper

  • 日本火山学研究奨励賞

    2004.5   非特定営利活動法人日本火山学会   Incentive Award

Papers

  • Voluminous magma formation for the 30-ka Aira caldera-forming eruption in SW Japan: contributions of crust-derived felsic and mafic magmas

    Ayumu Nishihara, Yoshiyuki Tatsumi, Katsuya Kaneko, Jun-Ichi Kimura, Qing Chang, Nobuo Geshi, Takashi Miyazaki, Bogdan Stefanov Vaglarov, Hironobu Hinata, Keiko Suzuki-Kamata

    Frontiers in Earth Science   11   2024.1   eISSN:2296-6463

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

    Understanding the origin, assembly, and evolution of voluminous magma that erupts in catastrophic caldera-forming eruptions (CCFEs) is a community imperative. A CCFE of the Aira caldera at 30 ka discharged over 350 km<sup>3</sup> of magma, which can be grouped into petrographically and geochemically distinct types: voluminous rhyolite, small amounts of rhyodacite, and andesite magmas. To further understand the magma plumbing system of the Aira CCFE, we examined the geochemical characteristics of whole rock and plagioclase from its eruptive deposits. The trace element and <sup>87</sup>Sr/<sup>86</sup>Sr signatures recorded in the plagioclase phenocrysts of these magmas indicate that the three magmas were originally produced by partially melting an identical source rock, which was estimated to be a mafic amphibolite with an <sup>87</sup>Sr/<sup>86</sup>Sr signature of ∼0.7055 that comprised the lower crust. Melting of mafic amphibolite produced both felsic and mafic magmas by low and high degrees of partial melting, respectively. The mafic magma assimilated uppermost crustal materials and crystallized to produce an andesite magma type. The andesitic magma consists of phenocrysts (∼39 vol%) and melt with a dacitic (∼70 wt% SiO<sub>2</sub>) composition. The felsic magma mixed with ∼10% of the andesite magma and crystallized, forming the rhyolite magma. The mixing between the andesite and rhyolite magmas before the Aira CCFE produced the rhyodacite magma. The 30-ka Aira CCFE magmas were generated only by melting two kinds of crustal materials with different geochemical characteristics and had geochemical variations due to different conditions of partial melting and mixing between various crustal melts. The lack of definitive evidence of the mantle component mixing with the Aira CCFE magmas suggests that the mantle-derived magmas worked only as a heat source for crustal melting.

    DOI: 10.3389/feart.2023.1283844

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  • Redox state of magma recorded in volcanic glass from an ash-forming eruption at Bromo volcano, Indonesia: Insights into the degassing process

    Takahiro Miwa, Hidemi Ishibashi, Ryunosuke Kazahaya, Satoshi Okumura, Masato Iguchi, Genji Saito, Atsushi Yasuda, Nobuo Geshi, Hiroyuki Kagi

    Bulletin of Volcanology   85 ( 9 )   2023.8   eISSN:1432-0819

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

    DOI: 10.1007/s00445-023-01660-1

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    Other Link: https://link.springer.com/article/10.1007/s00445-023-01660-1/fulltext.html

  • Importance of long-term shallow degassing of basaltic magma on the genesis of massive felsic magma reservoirs: A case study of Aso caldera, Kyushu, Japan

    Isoji Miyagi, Hideo Hoshizumi, Taichi Suda, Genji Saito, Yasuo Miyabuchi, Nobuo Geshi

    Journal of Petrology   2023.2   ISSN:0022-3530 eISSN:1460-2415

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    Language:Others   Publishing type:Research paper (scientific journal)   Publisher:Oxford University Press (OUP)  

    Abstract

    This paper presents the chemical composition (including H2O and CO2) of matrix glass, melt inclusions in phenocrysts, and their host minerals in eruptive products from Aso caldera. We found a group of melt inclusions with clearly lower potassium (0.6–2 wt.% K2O at 50–70 wt.% SiO2) than previously reported high-K2O whole-rock compositions (3–5 wt.% K2O at 55–70 wt.% SiO2). While most of the high-K2O intermediate to felsic melt inclusions are vapor undersaturated and show the features of H2O, CO2, and K2O accumulation, the low-K2O basaltic melt already has higher H2O and CO2. We reconcile this discrepancy with a model in which (1) the volatile-rich basalt magmas degas near the surface, (2) migrate back to depths of ≥12 km in the crust, and (3) crystallize feldspar and quartz to produce high-K2O felsic melt, (4) magma mixing among the undegassed, degassed, and evolved magmas. By crystallization, about five times as much low-K2O basaltic magma is required to produce high-K2O felsic magma. The quantity of felsic magma ejected from 270 ka (Aso-1) to 90 ka (Aso-4) requires a basalt magma supply rate of 18-31 km3/ka. This magma supply rate is comparable to or less than the present-day production rate of degassed magma (73 km3/ka) at an active center of Aso, Nakadake. These findings suggest volcanic gas flux monitoring has the potential to be a ‘basalt usage meter’ during the dormant period of caldera volcanoes.

    DOI: 10.1093/petrology/egad009

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  • Influence of hydrothermal recharge on the evolution of eruption styles and hazards during the 2018–2019 activity at Kuchinoerabujima Volcano, Japan

    Yusuke Minami, Keiko Matsumoto, Nobuo Geshi, Hiroshi Shinohara

    Earth, Planets and Space   74 ( 1 )   2022.12   eISSN:1880-5981

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    <title>Abstract</title>The activity of the 2018<bold>–</bold>2019 eruption of Kuchinoerabujima Volcano in Japan changed from continuous ejection of ash-laden plumes between October 21 and the middle of December, to intermittent explosive activity accompanied by several pyroclastic density currents until January 2019. To understand the behaviors of magma and hydrothermal fluid that controlled the eruptive sequence, we carried out component analysis, X-ray diffractometry, and leachate analysis for ash samples. The proportion of non-altered volcanic ash particles is ~ 15% in the earlier phase, then it decreased to less than 10% in the later explosive phase. Accordingly, the mineral assemblage of the volcanic ash samples changed from plagioclase-dominant to sulfate minerals-dominant. Concentration of SO<sub>4</sub><sup>2−</sup> and Cl/SO<sub>4</sub> values of the ash-leachates decreased toward the later activity. These results indicate that the proportion of fresh volcanic rocks decreased and sulfuric acid fluid-derived sulfate minerals increased toward the later activities. Consequently, the 2018<bold>–</bold>2019 eruption at Kuchinoerabujima Volcano changed from magmatic activity to phreatomagmatic activity. Weak glowing of the crater was observed during the magmatic activity, indicating the volcanic conduit was hot enough to dry up the sub-volcanic hydrothermal system. The following phreatomagmatic activity indicates that the hydrothermal fluid recharged after the magmatic eruption phase. Recharge of the hydrothermal fluid likely caused the variation of the eruption style, and is a process that may control the evolution of hazards during future eruption scenarios at similar active volcanoes in Japan and worldwide.


    <bold>Graphical Abstract</bold>

    DOI: 10.1186/s40623-022-01580-y

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    Other Link: https://link.springer.com/article/10.1186/s40623-022-01580-y/fulltext.html

  • Long-term change of the eruption activities of Sakurajima volcano, Japan, inferred from the fallout tephra deposits

    Nobuo Geshi, Hideto Naruo

    Frontiers in Earth Science   10   2022.11   ISSN:2296-6463

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    Language:Others   Publishing type:Research paper (scientific journal)   Publisher:Frontiers Media {SA}  

    <jats:p>Stratigraphic analysis of fallout tephra deposits in and around a volcano provides a framework for understanding the long-term temporal change in the volcano’s activities. Here, we reconstruct the evolution of the volcanic activities of Sakurajima volcano based on reconstructed tephra stratigraphy by original field surveys, compilations of geological and archeological data, and new <jats:sup>14</jats:sup>C dating. We define three eruption stages of Stage 1 (30–24 ka), Stage 2 (12.8–4.8 ka), and Stage 3 (4.5 ka–present), based on a major hiatus and shifting of the volcanic centers. Stages 2 and 3 are further subdivided according to the predominant mode of volcanic activity. Revised distribution of tephra deposits indicates that a total of 14.5 km<jats:sup>3</jats:sup> (5.8 km<jats:sup>3</jats:sup> dense rock equivalent) of fallout tephra has erupted from Sakurajima. Among them, Stage 2a (13–8 ka) produced the largest volume of tephra fallout deposits, suggesting that Sakurajima peaked in magma discharge during Stage 2a (2.9 km<jats:sup>3</jats:sup>/kyr) and then decreased rapidly toward Stage 2b (8–4.8 ka; 0.07 km<jats:sup>3</jats:sup>/kyr). The eruption of large-volume tephra deposits in Stage 2a, followed by the development of a thick volcanic ash layer in Stage 2b, indicates the eruption style shifted from explosive pumice eruptions in Stage 2a to ash-producing Vulcanian activity in Stage 2b, with decreasing magma discharge rate. Thick volcanic ash deposits covered by several fallout tephra deposits during Stage 3 also reflect a shift in activity from repeated Vulcanian explosions with lava effusions in Stage 3a (4.5–1.6 ka) to predominantly pumice eruptions during the historical period (Stage 3b) with an increasing magma discharge rate. The case study of Sakurajima presented here demonstrates that the combined analysis of the distribution, stratigraphy, and age of pumice fall layers with the lava and pyroclastic cone deposits on the volcanic edifice is a powerful tool for deciphering the growth history of complex stratovolcanoes.</jats:p>

    DOI: 10.3389/feart.2022.988373

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Books

  • 火山のきほん

    下司信夫, 斎藤雨梟(Role:Joint author)

    誠文堂新光社  2023.9 

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    gateway to volcanology

  • gateway to volcanology

    Nobuo Geshi, Ukyo Saito(Role:Joint author)

    誠文堂新光社  2023.9    ISBN:9784416523292

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  • 火山のきほん : マグマってなんだろう?噴火はなぜ起きる?地球の活動を読み解く火山の話

    下司 信夫 , 斎藤 雨梟

    誠文堂新光社  2023    ISBN:9784416523292

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    Language:Japanese  

    CiNii Books

  • 火山全景: 写真でめぐる世界の火山地形と噴出物

    下司 信夫, 白尾 元理

    誠文堂新光社  2017.8 

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    Responsible for pages:総ページ数:191   Language:Others  

  • 日本の地形・地質―見てみたい大地の風景116 (列島自然めぐり)

    斎藤 眞, 下司 信夫, 渡辺 真人, 北中 康文(Role:Joint author)

    文一総合出版  2012.3 

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    Responsible for pages:総ページ数:288   Language:Others  

MISC

  • Tephrostratigraphy and Eruptive History of Aso-4/3 Tephra Group, Aso Volcano: Preparatory Process for Aso-4 Ignimbrite Eruption

    星住英夫, 宮縁育夫, 宮城磯治, 下司信夫, 宝田晋治

    火山   67 ( 1 )   2022   ISSN:0453-4360

  • Development of an efficient method of outcrop survey using image analysis and machine learning technology

    Noguchi Rina, Haruyama Junichi, Geshi Nobuo, Shoji Daigo, Fujimoto Keiichiro

    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN   2022   106 - 106   2022   ISSN:2433-5320 eISSN:2189-7190

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    Language:Japanese   Publisher:The Volcanological Society of Japan  

    DOI: 10.18940/vsj.2022.0_106

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  • Phreatomagmatic stratigraphy and eruptive history of maar cluster at the southern coastal area, Miyakejima Volcano, Japan

    渡部将太, 及川輝樹, 下司信夫, 長谷川健

    日本地球惑星科学連合大会予稿集(Web)   2022   2022

  • Shallow magma pre-charge during repeated Plinian eruptions at Sakurajima volcano Reviewed

    Naoki Araya, Michihiko Nakamura, Atsushi Yasuda, Satoshi Okumura, Tomoki Sato, Masato Iguchi, Daisuke Miki, Nobuo Geshi

    Scientific Reports   2019.12

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    © 2019, The Author(s). Vigorous explosive eruptions that produce continuous high eruption plumes (Plinian eruptions) are generally assumed to tap a magma reservoir. The 1914 Plinian eruption at the Sakurajima volcano located on the Aira caldera rim is one such case, where the main magma reservoir was assumed to be located approximately 10 km beneath the caldera. However, we report that estimated magma storage depths immediately prior to the eruption were much shallower (0.9–3.2 km) on the basis of pressure at which volatiles within the phenocryst melt inclusions and plagioclase rims were finally equilibrated. The same is observed for two historic Plinian eruptions in 1471 and 1779. This depth is even shallower than the shallowest magma reservoir estimated from the pressure source for geodetic deformation during recent Vulcanian explosions (4 km beneath the crater). We propose that the magmas were fed from a thick conduit pre-charged from deeper reservoirs. The ground subsidence observed after 1914 within the Aira caldera may have been caused by conduit recharge following the eruption. Voluminous conduit recharge could be key to forecasting the next possible large eruption at the Sakurajima volcano.

    DOI: 10.1038/s41598-019-38494-x

  • Salt shell fallout during the ash eruption at the Nakadake crater, Aso volcano, Japan: evidence of an underground hydrothermal system surrounding the erupting vent

    Hiroshi Shinohara, Nobuo Geshi, Akihiko Yokoo, Takahiro Ohkura, Akihiko Terada

    Earth, Planets and Space   2018.12

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    © 2018, The Author(s). A hot and acid crater lake is located in the Nakadake crater, Aso volcano, Japan. The volume of water in the lake decreases with increasing activity, drying out prior to the magmatic eruptions. Salt-rich materials of various shapes were observed, falling from the volcanic plume during the active periods. In May 2011, salt flakes fell from the gas plume emitted from an intense fumarole when the acid crater lake was almost dry. The chemical composition of these salt flakes was similar to those of the salts formed by the drying of the crater lake waters, suggesting that they originated from the crater lake water. The salt flakes are likely formed by the drying up of the crater lake water droplets sprayed into the plume by the fumarolic gas jet. In late 2014, the crater lake dried completely, followed by the magmatic eruptions with continuous ash eruptions and intermittent Strombolian explosions. Spherical hollow salt shells were observed on several occasions during and shortly after the weak ash eruptions. The chemical composition of the salt shells was similar to the salts formed by the drying of the crater lake water. The hollow structure of the shells suggests that they were formed by the heating of hydrothermal solution droplets suspended by a mixed stream of gas and ash in the plume. The salt shells suggest the existence of a hydrothermal system beneath the crater floor, even during the course of magmatic eruptions. Instability of the magmatic–hydrothermal interface can cause phreatomagmatic explosions, which often occur at the end of the eruptive phase of this volcano.

    DOI: 10.1186/s40623-018-0798-4

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Professional Memberships

  • 日本火山学会

  • 日本地質学会

  • International Association of Volcanology and Chemistry of the Earth's Interior

Committee Memberships

  • International Association of Volcanology and Chemistry of the Earth’s Interior   commissioner   Foreign country

    2023.7 - 2027.6   

  • 日本火山学会   Executive   Domestic

    2022.7 - 2024.6   

  • 日本火山学会   編集委員長   Domestic

    2022.7 - 2024.6   

Academic Activities

  • 火山

    2022.7 - Present

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Research Projects

  • 岩相の特徴量自動認識による火山性露頭その場調査手法の研究

    Grant number:23K22597  2022.4 - 2025.3

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (B)

    春山 純一, 庄司 大悟, 藤本 圭一郎, 野口 里奈, 下司 信夫

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    本研究では、属人的な知識と経験および人力踏査に頼っていた露頭の記載・層序分類に対して、岩相の特徴量自動認識と可視化を行い、効率的なその場調査手法の開発を目指す。具体的には、1)聞き取りやワークショップにより、専門家の火山性露頭での岩相判断プロセスや基準を整理分類、それをもとに2)岩相の特徴的な地質テクスチャを認識、分類する岩相の特徴量自動認識アルゴリズムを開発、3)開発されたアルゴリズムを国内の露頭調査に適用検証し改良を行う。このアルゴリズムを可搬型計算機に搭載し、計算機上で岩相判断を行うことで、野外調査における岩相判断のための情報取得の効率化(迅速化、高精度化、自動化)を図ることを目指す。

    CiNii Research

  • 岩相の特徴量自動認識による火山性露頭その場調査手法の研究

    Grant number:22H01326  2022 - 2024

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Grant type:Scientific research funding

  • マグマ過剰圧とその時間変化の追跡による爆発的割れ目噴火推移過程の解明

    Grant number:22K03785  2022 - 2024

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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  • 火道構造から推測する噴火駆動力と爆発的噴火挙動との関係

    Grant number:19K04024  2019 - 2022

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Grant type:Scientific research funding

  • 浅部マグマ過程のその場観察実験に基づく準リアルタイム火山学の構築

    Grant number:16H06348  2016 - 2020

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Grant type:Scientific research funding

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Travel Abroad

  • 2012.9 - 2014.3

    Staying countory name 1:Italy   Staying institution name 1:ローマ第三大学