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Masato Koyama

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Papers by Masato Koyama

Research paper thumbnail of Three-dimensional density tomography determined from multi-directional muography of the Omuroyama scoria cone, Higashi–Izu monogenetic volcano field, Japan

Bulletin of Volcanology, Sep 20, 2022

Scoria cone is one of the basic forms of volcanoes, and clarifying its detailed internal structur... more Scoria cone is one of the basic forms of volcanoes, and clarifying its detailed internal structure and magma movement during its formation is important for understanding the nature of eruptions and also for volcanic disaster mitigation. We conducted a multi-directional muographic survey of the Omuroyama scoria cone, Japan, in order to determine the three-dimensional density structure of the scoria cone. We used a nuclear emulsion detector optimized for multi-directional muography that was installed at 11 sites around the volcano. Muon tracks recorded on emulsion films were read with a high-speed automated readout system. We obtained the three-dimensional density structure by applying a linear inversion to the muographic images, and evaluated the uncertainties. High-density zones were detected in scoria cone. Based on these observations and detailed topographic and geological constraints, we infer that high-density zones are the central, highly welded vent of the scoria cone, three-directional radial dikes extending from the central vent, respectively. We also infer that an E-W-trending dike fed a small lava flow, and that a SSE-NNW-trending dike caused a small flank eruption and produced a crater on the flank of the cone. Our results visualize the three-dimensional internal structure of volcanoes with novel resolution, and thereby demonstrate that the formation process of volcanoes can be discussed in detail. Since it has been difficult to directly detect such clear visualization of the internal structures and eruptive processes in the past, multi-directional muography has resulted in providing one hope for understanding volcanic activity.

Research paper thumbnail of How do we treat debris avalanches on the disaster mitigation plan for Fuji Volcano

Japan Geoscience Union, Mar 14, 2018

Research paper thumbnail of Reevaluation of the West Sagami Bay Fracture and Seismotectonics in and around the Northwestern Sagami Bay, Japan

Journal of Geography, 1995

Research paper thumbnail of Evolution of Oceanic Island Arc-Geology of the Izu-Bonin island and approach from the samples and data of the ODP Leg 126

Journal of Geography, 1991

Research paper thumbnail of Reexamination of the eruption types and their origin for Izu Oshima Volcano

Japan Geoscience Union, 2017

The origin of the eruption types of Izu Oshima Volcano, Japan, was reexamined mainly by geologica... more The origin of the eruption types of Izu Oshima Volcano, Japan, was reexamined mainly by geological and historical data. We once revealed the detailed synand post-caldera eruptive history of Izu Oshima Volcano by tephra and loess stratigraphy (Koyama and Hayakawa, 1996, J.Geogr.). Twenty-four tephra layers, which overlie the slope outside the caldera, show that 24 explosive eruptions occurred for the past 1500 years. Reexamining the relationship between the level of magma head and the period of ash spouting in the final stage of each eruption, we reclassified all the eruptions including effusive/small ones of Izu Oshima Volcano into five types: 1) effusive eruption with small-middle discharge mass of magma, occurred repeatedly during 1876-1974: a period of high magma head 2) explosive eruption with middle discharge mass of magma, associated with deposition of ash falls outside the caldera but with no dike intrusion (5 eruptions) 3) explosive eruption with middle discharge mass of mag...

Research paper thumbnail of How should geoparks contribute to disaster mitigation in each local society

The American Journal of Gastroenterology, 2016

Research paper thumbnail of Research of paleo-earthquakes and paleo-tsunami deposits from the coastal lowland of the southern Izu Peninsula, central Japan

Research paper thumbnail of The 2011 Great East Japan Earthquake and its Influence to the Tokai District

Research paper thumbnail of Tectonic Evolution of the Philippine Sea Plate Based on Paleomagnetic Results

Journal of Geography (Chigaku Zasshi), 1991

Research paper thumbnail of Mechanical Coupling Between Volcanic Unrests and Large Earthquakes: A Review of Examples and Mechanisms

Journal of Geography (Chigaku Zasshi), 2002

Research paper thumbnail of Knowledge Structure and Estimate Method of Formative Processes of Geologic Terrane and Its Bearing Mineral Resources

Research paper thumbnail of Syn- and Post-caldera Eruptive History of Izu Oshima Volcano based on Tephra and Loess Stratigraphy

Journal of Geography (Chigaku Zasshi), 1996

Research paper thumbnail of A Beginner's Guide to “Shiryo” (historical documents) Seismology and Volcanology

Journal of Geography (Chigaku Zasshi), 1999

Research paper thumbnail of Evolution of Oceanic Island Arc-Geology of the Izu-Bonin island and approach from the samples and data of the ODP Leg 126

Journal of Geography (Chigaku Zasshi), 1991

Research paper thumbnail of Drilling across the Izu-Bonin arc. Results of ODP Leg 126 cruise

Journal of Geography (Chigaku Zasshi), 1989

Research paper thumbnail of Izu-Bonin Arc and Philippine Sea

Journal of Geography (Chigaku Zasshi), 1991

Research paper thumbnail of A Rule-based Expert System for Geological Study and Education

Research paper thumbnail of Pre-20th Century of Earthquake Swarms and Volcanic Activity in the Higashi Izu Monogenetic Volcano Field, Based on Historical Documents

The Quaternary Research (Daiyonki-Kenkyu)

Higashi-Izu monogenetic volcano group exist in the Izu Peninsula?: Relationships between late Qua... more Higashi-Izu monogenetic volcano group exist in the Izu Peninsula?: Relationships between late Quaternary volcanism and tectonics on the northern tip of the Izu-Bonin arc. Jour. Phys. Earth, 39, 391-420.

Research paper thumbnail of What Happened on the Northern Tip of the Izu-Bonin Arc during 15-10Ma?

Journal of Geography (Chigaku Zasshi)

What Happened on the Northern Tip of the Izu-Bonin Arc during 15-10 Ma ?

Research paper thumbnail of Historical Seismology of Next Generation. A Review of Historical Seismology in Japan. Analyses and proposals for next stage of study of historical documents

Journal of Geography (Chigaku Zasshi)

Research paper thumbnail of Three-dimensional density tomography determined from multi-directional muography of the Omuroyama scoria cone, Higashi–Izu monogenetic volcano field, Japan

Bulletin of Volcanology, Sep 20, 2022

Scoria cone is one of the basic forms of volcanoes, and clarifying its detailed internal structur... more Scoria cone is one of the basic forms of volcanoes, and clarifying its detailed internal structure and magma movement during its formation is important for understanding the nature of eruptions and also for volcanic disaster mitigation. We conducted a multi-directional muographic survey of the Omuroyama scoria cone, Japan, in order to determine the three-dimensional density structure of the scoria cone. We used a nuclear emulsion detector optimized for multi-directional muography that was installed at 11 sites around the volcano. Muon tracks recorded on emulsion films were read with a high-speed automated readout system. We obtained the three-dimensional density structure by applying a linear inversion to the muographic images, and evaluated the uncertainties. High-density zones were detected in scoria cone. Based on these observations and detailed topographic and geological constraints, we infer that high-density zones are the central, highly welded vent of the scoria cone, three-directional radial dikes extending from the central vent, respectively. We also infer that an E-W-trending dike fed a small lava flow, and that a SSE-NNW-trending dike caused a small flank eruption and produced a crater on the flank of the cone. Our results visualize the three-dimensional internal structure of volcanoes with novel resolution, and thereby demonstrate that the formation process of volcanoes can be discussed in detail. Since it has been difficult to directly detect such clear visualization of the internal structures and eruptive processes in the past, multi-directional muography has resulted in providing one hope for understanding volcanic activity.

Research paper thumbnail of How do we treat debris avalanches on the disaster mitigation plan for Fuji Volcano

Japan Geoscience Union, Mar 14, 2018

Research paper thumbnail of Reevaluation of the West Sagami Bay Fracture and Seismotectonics in and around the Northwestern Sagami Bay, Japan

Journal of Geography, 1995

Research paper thumbnail of Evolution of Oceanic Island Arc-Geology of the Izu-Bonin island and approach from the samples and data of the ODP Leg 126

Journal of Geography, 1991

Research paper thumbnail of Reexamination of the eruption types and their origin for Izu Oshima Volcano

Japan Geoscience Union, 2017

The origin of the eruption types of Izu Oshima Volcano, Japan, was reexamined mainly by geologica... more The origin of the eruption types of Izu Oshima Volcano, Japan, was reexamined mainly by geological and historical data. We once revealed the detailed synand post-caldera eruptive history of Izu Oshima Volcano by tephra and loess stratigraphy (Koyama and Hayakawa, 1996, J.Geogr.). Twenty-four tephra layers, which overlie the slope outside the caldera, show that 24 explosive eruptions occurred for the past 1500 years. Reexamining the relationship between the level of magma head and the period of ash spouting in the final stage of each eruption, we reclassified all the eruptions including effusive/small ones of Izu Oshima Volcano into five types: 1) effusive eruption with small-middle discharge mass of magma, occurred repeatedly during 1876-1974: a period of high magma head 2) explosive eruption with middle discharge mass of magma, associated with deposition of ash falls outside the caldera but with no dike intrusion (5 eruptions) 3) explosive eruption with middle discharge mass of mag...

Research paper thumbnail of How should geoparks contribute to disaster mitigation in each local society

The American Journal of Gastroenterology, 2016

Research paper thumbnail of Research of paleo-earthquakes and paleo-tsunami deposits from the coastal lowland of the southern Izu Peninsula, central Japan

Research paper thumbnail of The 2011 Great East Japan Earthquake and its Influence to the Tokai District

Research paper thumbnail of Tectonic Evolution of the Philippine Sea Plate Based on Paleomagnetic Results

Journal of Geography (Chigaku Zasshi), 1991

Research paper thumbnail of Mechanical Coupling Between Volcanic Unrests and Large Earthquakes: A Review of Examples and Mechanisms

Journal of Geography (Chigaku Zasshi), 2002

Research paper thumbnail of Knowledge Structure and Estimate Method of Formative Processes of Geologic Terrane and Its Bearing Mineral Resources

Research paper thumbnail of Syn- and Post-caldera Eruptive History of Izu Oshima Volcano based on Tephra and Loess Stratigraphy

Journal of Geography (Chigaku Zasshi), 1996

Research paper thumbnail of A Beginner's Guide to “Shiryo” (historical documents) Seismology and Volcanology

Journal of Geography (Chigaku Zasshi), 1999

Research paper thumbnail of Evolution of Oceanic Island Arc-Geology of the Izu-Bonin island and approach from the samples and data of the ODP Leg 126

Journal of Geography (Chigaku Zasshi), 1991

Research paper thumbnail of Drilling across the Izu-Bonin arc. Results of ODP Leg 126 cruise

Journal of Geography (Chigaku Zasshi), 1989

Research paper thumbnail of Izu-Bonin Arc and Philippine Sea

Journal of Geography (Chigaku Zasshi), 1991

Research paper thumbnail of A Rule-based Expert System for Geological Study and Education

Research paper thumbnail of Pre-20th Century of Earthquake Swarms and Volcanic Activity in the Higashi Izu Monogenetic Volcano Field, Based on Historical Documents

The Quaternary Research (Daiyonki-Kenkyu)

Higashi-Izu monogenetic volcano group exist in the Izu Peninsula?: Relationships between late Qua... more Higashi-Izu monogenetic volcano group exist in the Izu Peninsula?: Relationships between late Quaternary volcanism and tectonics on the northern tip of the Izu-Bonin arc. Jour. Phys. Earth, 39, 391-420.

Research paper thumbnail of What Happened on the Northern Tip of the Izu-Bonin Arc during 15-10Ma?

Journal of Geography (Chigaku Zasshi)

What Happened on the Northern Tip of the Izu-Bonin Arc during 15-10 Ma ?

Research paper thumbnail of Historical Seismology of Next Generation. A Review of Historical Seismology in Japan. Analyses and proposals for next stage of study of historical documents

Journal of Geography (Chigaku Zasshi)

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