Updated on 2025/06/03

写真a

 
OHTA Ryoga
 
Organization
Academic Assembly Institute of Humanities and Social Sciences JINBUN KAGAKU KEIRETU Assistant Professor
Faculty of Humanities Department of Humanities Assistant Professor
Title
Assistant Professor
Other name(s)
Ohta J. Ryoga
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Research Interests

  • Slope deformation

  • Mountain river

  • GIS

  • Lightning Geomorphology

  • Geoarchaeology

  • Tephrochronology

  • Geospatial Information Science

  • Radiocarbon Dating

  • cosmogenic nuclide analysis

  • Quaternary geology

  • Anthropocene

  • Disaster Risk Cognition and Reduction

  • Critical zone

  • Geomorphology

  • Physical geography

Research Areas

  • Humanities & Social Sciences / Geography  / Physical Geography

  • Natural Science / Human geosciences  / Geomorphology

Research History (researchmap)

  • Niigata University   Faculty of Humanities   Assistant Professor

    2025.4

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    Country:Japan

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  • Niigata University   Institute for Research Administration

    2025.4

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    Country:Japan

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  • Meiji University   School of Arts and Letters   Lecturer (part-time)

    2024.4 - 2025.3

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  • Chuo University   The Institute of Science and Engineering   JSPS Research Fellow PD

    2022.10 - 2025.3

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  • Kyoto University   Disaster Prevention Research Institute   JSPS Research Fellow DC1

    2019.4 - 2022.9

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Research History

  • Niigata University   Institute of Humanities and Social Sciences, Academic Assembly   Assistant Professor

    2025.4

  • Niigata University   Department of Humanities, Faculty of Humanities   Assistant Professor

    2025.4

Education

  • Kyoto University   Graduate school of Science   Division of Earth and Planetary Science

    2019.4 - 2022.9

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    Country: Japan

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  • Kyoto University   Graduate School of Science   Division of Earth and Planetary Science

    2017.4 - 2019.3

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    Country: Japan

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  • Senshu University   School of Letters   Department of Geography

    2013.4 - 2017.3

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    Country: Japan

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  • Iwaki High School, Fukushima

    2010.4 - 2013.3

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    Country: Japan

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Professional Memberships

  • Japan Association for Quaternary Research

    2020

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  • American Geophysical Union

    2019

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  • JAPANESE GEOMORPHOLOGICAL UNION

    2017

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  • THE ASSOCIATION OF JAPANESE GEOGRAPHERS

    2016

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  • JAPAN GEOSCIENCE UNION

    2015

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  • Geographic Information System Association

    2025

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  • Tokyo Geographical Society

    2023

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  • Japanese Society for Active Fault Studies

    2022

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Committee Memberships

  • 国土地理院   全国活断層帯情報整備検討委員会  

    2025.4   

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    Committee type:Government

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  • 国土地理院   全国活断層帯情報整備検討委員会(調査協力者)  

    2023.4 - 2025.3   

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Papers

  • Late Pleistocene tephras found in the vicinity of Mt. Kushigata, the Koma Mountains in central Japan Reviewed

    Ryoga Ohta, Tatsuki Watanabe, Yoshihiko Kariya

    The Quaternary Research (Daiyonki-Kenkyu)   64 ( 1 )   1 - 12   2024.10

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    Authorship:Lead author, Corresponding author   Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.4116/jaqua.64.2402

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  • Transient Response and Adjustment Timescales of Channel Width and Angle of Valley-Side Slopes to Accelerated Incision Reviewed

    Naoya O. Takahashi, J. Bruce H. Shyu, Shinji Toda, Yuki Matsushi, Ryoga J. Ohta, Hiroyuki Matsuzaki

    2023.6

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Wiley  

    DOI: 10.1029/2022JF006967

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  • Use of terrestrial cosmogenic 10Be to quantify anthropogenic sediment yield from mountainous watersheds: Application in reconstructing environmental change in the Tanakami Mountains, central Japan Reviewed

    Ryoga Ohta, Yuki Matsushi, Hiroyuki Matsuzaki

    Geomorphology   405 ( 108201 )   1 - 17   2022.3

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    Authorship:Lead author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Elsevier BV  

    DOI: 10.1016/j.geomorph.2022.108201

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  • Quantification and reconstruction of anthropogenically-accelerated hillslope erosion: Changes in soil sustainability and transition of watershed environment as responses to the longstanding consumption of forest resources Reviewed

    Ryoga OHTA

    Kyoto University   2022.9

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    Authorship:Corresponding author   Publishing type:Doctoral thesis  

    DOI: 10.14989/doctor.k24170

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Books

  • 1:25,000活断層図「柳ヶ瀬・関ヶ原断層帯及び湖北山地断層帯とその周辺」

    金田平太郎, 石村大輔, 堤浩之, 中田高, 太田凌嘉

    国土地理院  2024.10 

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MISC

  • Three-stage evolution of particle shape in headwater streams

    Naoya Ono Takahashi, Daisuke Ishimura, Keitaro Yamada, Ryoga J. Ohta, Yuki Arai, Yuki Yamane

    EGUsphere   2025.3

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    Publishing type:Internal/External technical report, pre-print, etc.   Publisher:Copernicus GmbH  

    Abstract. Given the importance of sediments in fluvial morphodynamics, studying how sediment particle shapes change during mass loss is important for understanding the morphology and change rates of fluvial landscapes. Particles of riverbed materials tend to become more rounded and circular downstream, but this trend can often be obscured because it results from processes that increase or decrease shape parameters to various degrees. This study unravels such complex interactions by evaluating the contributions of each process and revealing the factors that determine the rates of change in shape. We investigated changes in the roundness and circularity of basalt and shale particles in headwaters using the automated image analysis software Rgrains. The observed evolution of the roundness and circularity comprised three stages with different rates of increase. Both shape parameters initially increased rapidly, remained nearly constant, and then slowly increased downstream, indicating that the dominant process affecting the particle shape changed during a few kilometers of transport. These punctuated shape changes result from the hillslope sediment supply and the addition of rock fragments produced by chipping and fragmentation, of which finer fragments were found to significantly alter the downstream evolution of the shape. The rate of increase in the roundness and circularity of the particle shape depended on the rock type and grain size. The rates for the shale particles were higher than those for the basaltic particles. Grain size clearly affected the shape change rates of basalt particles but not of shale particles. We interpreted these differences between rock type and grain size to be associated with particle durability, weathering mechanisms and speed, and total residence time in the channel. These findings demonstrate that image-based measurements of shape parameters in headwaters enables a detailed examination of the mechanism and rates of changes in particle shape.

    DOI: 10.5194/egusphere-2025-1080

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  • Shape of natural and manually crushed particles collected from a headwater stream in Tsugaru, Japan

    Naoya Takahashi, Daisuke Ishimura, Keitaro Yamada, Ryoga Ohta, Yuki Arai, Yuki Yamane

    2025.2

  • Late Pleistocene tephras and pollen fossils found in the vicinity of Mt. Kushigata, the Koma Mountains in central Japan Reviewed

    Ohta, Ryoga, Watanabe, Tatsuki, Kariya, Yoshihiko

    Japan Association for Quaternary Research. Dataset.   2025.2

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  • 過度な森林資源の収奪を受けた山地流域の不可逆的環境変化のモデル化:いわゆるハゲ山を捉え直す

    太田凌嘉

    GIS NEXT   71   69   2020.4

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    Authorship:Lead author   Language:Japanese  

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  • Report on participation in the 2017 International Summer School on Rockslides and Related Phenomena in the Kokomeren River Valley, Kyrgyzstan Reviewed

    Ryoga OHTA, Yoshihiko KARIYA

    J. of the Jpn. Landslide Soc.   55 ( 2 )   92 - 95   2018.3

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    Authorship:Lead author   Language:Japanese  

    DOI: 10.3313/jls.55.92

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Presentations

  • Variability of hillslope morphology in response to tectonic forcing: an example from Natsui-gawa watershed in the Abukuma massif, Fukushima Prefecture, Japan

    Ryoga Ohta

    The General Meeting of the Association of Japanese Geographers Spring 2025  2025.3 

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    Event date: 2025.3

    Language:Japanese   Presentation type:Oral presentation (general)  

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  • Three-stage evolution of particle shape in the headwaters

    Naoya TAKAHASHI, Daisuke ISHIMURA, Keitaro YAMADA, Ryoga OHTA, Yuki Arai, Yuki Yamane

    The General Meeting of the Association of Japanese Geographers Spring 2025  2025.3 

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    Event date: 2025.3

    Language:Japanese   Presentation type:Oral presentation (general)  

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  • Differences in the propagation of base-level changes on watershed denudation: an example from the Abukuma massif, Fukushima Prefecture, Japan

    Ryoga J. OHTA

    The Japanese Geomorphological Union Annual Meeting 2024  2024.11 

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    Event date: 2024.11

    Language:Japanese   Presentation type:Poster presentation  

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  • Sediment discharge and its determinants in the burnt area of wildfire: The case of Osaki peninsula, Iwate

    Hotaka Sato, Naoya Takahashi, Ryoga Ohta

    JpGU Meeting 2024  2024.5 

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    Event date: 2024.5

    Language:Japanese   Presentation type:Poster presentation  

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  • Development of fluvial terraces and moutainous hillslopes as part of the landscape evolution in the Koma Mountains, central Japan

    Ryoga Ohta, Yoshimasa Ota

    JpGU Meeting 2024  2024.5 

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    Event date: 2024.5

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  • Contrasting grain size evolution in headwaters controlled by rock strength and provenance

    Naoya Takahashi, Daisuke Ishimura, Ryoga Ohta, Yuki Arai, Yuki Yamane

    JpGU Meeting 2024  2024.5 

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    Event date: 2024.5

    Language:Japanese   Presentation type:Oral presentation (general)  

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  • Use of terrestrial cosmogenic 10Be for quantification and reconstruction of anthropogenically-accelerated hillslope erosion: as responses to the longstanding consumption of forest resources

    Ryoga Ohta, Yuki Matsushi, Hiroyuki Matsuzaki

    The 24th AMS Symposium  2024.3 

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    Event date: 2024.3

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  • Contrasting grain shape evolution in headwaters controlled by rock strength and provenance

    Naoya TAKAHASHI, Daisuke ISHIMURA, Ryoga OHTA, Yuki Arai, Yuki Yamane

    The General Meeting of the Association of Japanese Geographers, Spring 2024  2024.3 

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    Event date: 2024.3

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  • Slip-rate estimation of an active fault by using depth profiling of terrestrial cosmogenic 10Be: a case study on a middle terrace surface at Nogo along the Neodani fault, central Japan

    Yuya Ogura, Heitaro Kaneda, Ryoga Ohta, Yuki Matsushi, Hiroyuki Matsuzaki

    Japanese Society for Active Fault Studies Fall Meeting 2023  2023.11 

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    Event date: 2023.11

    Language:Japanese   Presentation type:Poster presentation  

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  • History of mass movements in a tectonically active mountainous watershed: A case study in Mt. Kushigata, Koma Moutains, central Japan

    Ryoga Ohta, Tatsuki Watanabe

    Japanese Society for Active Fault Studies Fall meeting 2023  2023.11 

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    Event date: 2023.11

    Language:Japanese   Presentation type:Poster presentation  

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  • Change in sustainability of hillslope soil and transition in watershed environment as responses to the longstanding exploitation: modelling in the Tanakami Mountains, central Japan

    Ryoga Ohta, Yuki Matsushi

    The General Meeting of the Association of Japanese Geographers Spring 2023  2023.3 

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    Event date: 2023.3

    Language:Japanese   Presentation type:Oral presentation (general)  

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  • Reconstructing anthropogenic environmental change in a mountain watershed by terrestrial cosmogenic 10Be: application of the new usage in the Tanakami Mountains, central Japan Invited

    Ryoga Ohta, Yuki Matsushi, Hiroyuki Matsuzaki

    Japan Geoscience Union Meeting 2022  2022.6 

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    Event date: 2022.5 - 2022.6

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  • Reconstructing human-induced acceleration of hillslope denudation in granite watersheds using cosmogenic nuclide: modeling in the Tanakami Mountains, central Japan

    Ryoga OHTA, Yuki MATSUSHI, Hiroyuki MATSUZAKI

    DPRI Annual meeting  2021.2 

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    Event date: 2021.2

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  • Transition of soil sustainability in granite watersheds through artificial deforestation: quantifying acceleration of hillslope erosion in the Tanakami Mountains, central Japan

    Ryoga OHTA, Yuki MATSUSHI, Hiroyuki MATSUZAKI

    JpGU-AGU Joint Meeting 2020  2020.7 

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    Event date: 2020.7

    Language:Japanese   Presentation type:Oral presentation (general)  

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  • Quantifying human-induced acceleration of hillslope denudation in granite watersheds: impacts of deforestation on soil coverage in the Tanakami Mountains, central Japan

    Ryoga OHTA, Yuki MATSUSHI, Hiroyuki MATSUZAKI

    2020.2 

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    Event date: 2020.2

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  • 人為的な森林の消失に伴う流域の斜面安定性の遷移:樹木根系の効果を考慮した土層発達モデリング

    太田凌嘉

    一般社団法人建設コンサルタンツ協会近畿支部 第52回研究発表会  2019.10 

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    Event date: 2019.10

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  • 活断層末端の活火山地域における大規模斜面崩壊の発生予測に関する研究―1858年(安政5年)立山, 鳶崩れを例としてー

    金田平太郎, 佐々木夏来, 石村大輔, 福井幸太郎, 大森貴之, 松四雄騎, 土井一生, 加納靖之, 大邑潤三, 飯島 駿, 太田凌嘉, 小倉祐弥, 渡辺 樹

    「災害の軽減に貢献するための地震火山観測研究計画(第2次)」令和4年度成果報告シンポジウム  2023.3 

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  • Reconstructing the transition of hillslope denudation in granite watersheds using cosmogenic nuclides: quantifying the anthropogenic impacts on soil coverage in the Tanakami Mountains, central Japan

    Ryoga Ohta, Yuki Matsushi, Hiroyuki Matsuzaki

    Japan Geoscience Union Meeting 2021  2021.6 

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    Language:Japanese   Presentation type:Oral presentation (general)  

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  • Adjustment timescales of channel width and hillslope angle to accelerated uplift: Insights into a basin-scale steady state

    Naoya Takahashi, J Bruce H Shyu, Yuki Matsushi, Ryoga Ohta, Shinji Toda

    Japan Geoscience Union Meeting 2021  2021.6 

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    Language:Japanese   Presentation type:Oral presentation (general)  

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  • Quantifying anthropogenic acceleration of hillslope denudation in granite watersheds: impacts of deforestation on soil coverage in the Tanakami Mountains, central Japan International conference

    Ryoga OHTA, Yuki MATSUSHI, Hiroyuki MATSUZAKI

    American Geophysical Union Fall Meeting  2019.12 

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  • Quantifying anthropogenic acceleration of hillslope destabilization by deforestation: modeling soil development incorporating tree-root reinforcement in the Tanakami Mountains, central Japan

    Ryoga OHTA, Yuki MATSUSHI, Hiroyuki MATSUZAKI

    2019 JGU 40th Anniversary Meeting  2019.11 

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  • Quantification of anthropogenic denudation caused by deforestation in mountainous watersheds: cases in Tanakami Mountains, central Japan

    Ryoga OHTA, Yuki MATSUSHI, Ken'ichirou KOSUGI, Hiroyuki MATSUZAKI

    Proceedings of the General Meeting of the Association of Japanese Geographers  2019.3 

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  • Quantitative modeling of anthropogenic irreversible transition in denudation processes and hillslope stability on mountainous watersheds: tree root reinforcement for soil development on hillslopes

    Ryoga OHTA, Yuki MATSUSHI

    2019.2 

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  • Reconstructing long term transition of denudation rates using a terrestrial cosmogenic nuclide in fluvial sediment in granite watersheds devastated by significant human impact

    Ryoga OHTA, Yuki MATSUSHI, Hiroyuki MATSUZAKI

    JpGU2018  2018.5 

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  • Reconstructing long term sediment yield from granite watersheds affected by significant human impact

    Ryoga OHTA, Yuki MATSUSHI

    2018.2 

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  • History of mass movements and paleolake formation revealed by depression-filling sediment records in a tectonically active mountainous area: a case study in Mt. Kushigata, Koma Range, central Japan International conference

    Ryoga OHTA, Yoshihiko KARIYA, Yuki MATSUSHI

    4th Slope Tectonics Conference 2017  2017.10 

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  • Development of paleolakes related to landslide activities in the late Pleistocene epoch on the eastern foot of Mount Kushigata, the Koma Mountains in central Japan International conference

    Ryoga OHTA, Yoshihiko KARIYA

    JpGU-AGU Joint Meeting 2017  2017.5 

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  • Late Pleistocene paleolakes formed on landslide blocks in the eastern foot of Mount Kushigata, the Koma Mountains in central Japan

    Ryoga OHTA, Yoshihiko KARIYA

    Proceedings of the General Meeting of the Association of Japanese Geographers  2017.3 

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  • Late Pleistocene paleolakes related to landslide activities on the eastern foot of Mount Kushigata, the Koma Mountains, central Japan

    Ryoga OHTA, Yoshihiko KARIYA

    Proceedings of the General Meeting of the Association of Japanese Geographers  2016.9 

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  • Late Pleistocene paleolakes formed by landslide activities on the eastern foot of Mt. Kushigata, the Koma Mountains, central Japan

    Ryoga OHTA, Yoshihiko KARIYA

    JpGU2016  2016.5 

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Awards

  • 宇宙線生成核種10Beを用いた深度断面法による活断層の平均変位速度推定 ―根尾谷断層,能郷地区中位段丘面を例として―

    2023.11  

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Research Projects

  • Deciphering the history of earthquake induced sediment yield by cosmogenic nuclides: Integration of tectonic and process geomorphology

    Grant number:22J01231

    2022 - 2025

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for JSPS Fellows

    Research category:Grant-in-Aid for JSPS Fellows

    Awarding organization:Japan Society for the Promotion of Science

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    Authorship:Principal investigator 

    Grant amount:\4420000 ( Direct Cost: \3400000 、 Indirect Cost:\1020000 )

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  • 山地流域における水文・地形プロセスのモデリングに基づく土砂移動現象の発生場・降雨閾値・生産土砂量の定量的評価

    2020 - 2022

    Awarding organization:Ministry of Land, Infrastructure, Transport and Tourism

    Yuki Matsushi, Taro Uchida, Yasuhiro Shuin, Yasuto Hirata Hiroyuki, Matsuzaki Ryoga Ohta

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    Authorship:Coinvestigator(s) 

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  • Modelling of irreversible environmental change in mountain watersheds caused by excessive expropriation of forest resources

    Grant number:19J22493

    2019.4 - 2022.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for JSPS Fellows

    Research category:Grant-in-Aid for JSPS Fellows

    Awarding organization:Japan Society for the Promotion of Science

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    Authorship:Principal investigator 

    Grant amount:\2500000 ( Direct Cost: \2500000 )

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  • 長期的かつ過度な人為インパクトを受けた山地における土層の生成と流出に関する調査

    2018.6 - 2019.3

    System name:平成30年度深田野外調査助成

    Awarding organization:深田地質研究所

    太田 凌嘉

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    Authorship:Principal investigator  Grant type:Competitive

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  • Study of deep water storages of watersheds under naturally forested and deforested conditions

    2017 - 2018

    System name:Grant from Research Unit for Development of Global Sustainability, Kyoto University

    Awarding organization:Research Unit for Development of Global Sustainability, Kyoto University

    Cristobal Padilla Yuki Matsushi Ryoga Ohta

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    Authorship:Coinvestigator(s) 

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  • Soil sustainability on hillslopes for forest persistence: quantification by geomorphic approach

    2017 - 2018

    System name:Grant from the Research Unit for Development of Global 651 Sustainability, Kyoto University

    Awarding organization:Research Unit for Development of Global Sustainability, Kyoto University

    Yuki Matsushi Cristobal Padilla, Ryoga Ohta

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Other research activities

  • 中学校教諭一種免許状(社会)取得

    2017.3

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  • 高等学校教諭一種免許状(地理歴史)取得

    2017.3

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  • 日本地理学会認定資格 地域調査士 取得

    2017

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  • 日本防災士機構認定資格 防災士 取得

    2015.6

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  • 測量士補

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  • GIS学術士

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Teaching Experience (researchmap)

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Media Coverage

  • 子どもウィークリー「知りたい好奇心」 Newspaper, magazine

    山梨日日新聞  山梨日日新聞・朝刊  2019.2

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  • 東北発☆未来塾 TV or radio program

    NHK  2015.3

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