Papers by Kazutaka Mannen
Original data of a paper entitled "History of Ancient Megathrust Earthquakes beneath Metropo... more Original data of a paper entitled "History of Ancient Megathrust Earthquakes beneath Metropolitan Tokyo Inferred from Coastal Lowland Deposits" on "Sedimentary Geology". Authored by Kazutaka Mannen, Kim Haeng Yoong, Shigeru Suzuki, Yoshiaki Matsushima, Yuki Ota, Claire L. Kain and James Goff.
Journal of Geography (Chigaku Zasshi), 2021
Since a phreatic eruption is caused by ruptures in hydrothermal systems beneath volcanoes, detect... more Since a phreatic eruption is caused by ruptures in hydrothermal systems beneath volcanoes, detecting and monitoring a hydrothermal system can play an important role in predicting such an eruption. Interferometric Synthetic Aperture Radar (InSAR) , which detects ground deformations over a large area, may be a key technology for use in various fields, as shown from the exponential growth of recent studies in terms of number and quality. The present contribution reviews surface deformations caused by the hydrothermal system of Hakone volcano, as detected by InSAR before, during, and after the 2015 eruption. The opening of the NWSE-trending crack and localized uplift in the Owakudani fumarole area were captured by InSAR analyses during the 2015 unrest at Hakone volcano. Moreover, an InSAR time series analysis showed steady subsidence on the west side of the Owakudani fumarole area. Based on models explaining these surface displacements, the shallow hydrothermal system of Hakone volcano is characterized by NW SE to WNWESE-trending crack-shaped fluid supply paths and pocket-shaped fluid reservoirs. During the 2015 and previous phreatic eruptions, it is probable that fluid was supplied using the same crack-like path, implying that fluid was repeatedly supplied using the same structure. Therefore, in order to predict the occurrence of phreatic eruptions at Hakone volcano, it is necessary to monitor volcanic activity by taking into account these structures. The activity of Hakone volcano, including formations of these NWSE to WNWESE-trending cracks, is dominated by a regional stress field. This stress field is caused by shear deformation due to plate motion occurring in this region; that is, the subducting Philippine Sea Plate, and the colliding Izu Peninsula.
Journal of Geography (Chigaku Zasshi), 2021
Hakone volcano has been in an active phase since 2001, as implied by frequent volcanic unrest eve... more Hakone volcano has been in an active phase since 2001, as implied by frequent volcanic unrest every 25 years, with each accompanied by deep inflation (610 km) , increase of deep low-frequency events (DLFEs) at a depth of ~20 km, increase of CO 2 /H 2 S ratio in fumarole gas, and surge of volcano tectonic earthquakes (VT; < 6 km deep). A series of episodes of volcanic unrest culminated in a small phreatic eruption (erupted volume; ~100 m 3) in 2015; however, lesser unrest in terms of seismic activity occurred in 2017 and 2019. Recent studies on crustal structures based on seismic tomography indicate a magma chamber 1020 km beneath the volcano, which might be connected to a large magma chamber beneath Fuji volcano, approximately 30 km NW of Hakone. Interestingly, the DLFEs beneath Hakone volcano seem to take place in a high attenuation zone that connects the magma chambers. Deep inflation beneath Hakone volcano, however, is clearly located at a shallower location than the magma chamber of Hakone. The increases of CO 2 and He within the fumarole of Hakone during its unrest may indicate degassing of magma at depth. The maximum fumarole temperature after the eruption and constraints on subsurface temperature (~200°C at 400 m deep indicated by the mineral assemblage and ~370°C at 4 km below sea level where is the lower depth limit of VT) imply a vapor-dominated hydrothermal system in the volcano from the bottom of the cap structure (~100 m deep) to a depth of possibly 24 km. Such a vapor-dominated system may allow rapid transfers of magmatic gases and their emission from the fumarole area in the very early phase of volcanic unrest, as was observed. Hakone lacks long period events (LF) and volcanic tremors, which are common at many active volcanoes. Because such events are considered to be related to fluid migration, the vapor-dominated system can be attributed to their absence in Hakone. An estimation of the water mass balance implies that the amount and rate of inflation in the hydrothermal system are comparable to those emitted from the fumarole area in pre-eruptive calm periods. Thus, continuous inflation at depth can be explained by crystal depositions from the hydro thermal fluid. The high temperature of steam emitted in the fumarole area after the eruption indicates destruction of the container of the hydrothermal system, which also caused the lower VT activity and CO 2 /H 2 S ratio during post-eruptive unrest.
Journal of Geography (Chigaku Zasshi), 2021
Journal of Geography (Chigaku Zasshi), 2021
A phreatic eruption is a phenomenon in which water near the surface expands rapidly due to magma-... more A phreatic eruption is a phenomenon in which water near the surface expands rapidly due to magma-supplied heat, ejecting the surrounding rocks. Recent studies of conceptual models, subsurface structures, pre-eruption processes, and eruption processes of phreatic eruptions are reviewed. These eruptions often occur in volcanoes with well-developed hydrothermal systems, where a low electrical resistivity layer is found near the surface using magnetotelluric surveys. The low resistivity layer indicates a low-permeability structure that acts as a pressure-confining cap on the hydrothermal system. In the brittle-ductile transition zone above deep magma, a sealing structure associated with quartz crystallization develops. Volcanoes with open conduits that connect magma reservoir and surface crater also have the potential for phreatic eruptions. A low-permeable sealing structure in the shallow part of the conduit plays an important role in eruptions of this type of volcano. Phreatic eruptions are prepared by an imbalance in the hydrothermal system, which is caused by increases of heat, volcanic gases, and fluids from the deep magma reservoir, and are triggered by depressurization of the aquifer due to the breakdown of the cap/sealing structure. In recent years, eruptive processes have been modeled using data from broadband seismograms and tiltmeters near vents. At Ontake, Hakone, and Aso volcanoes, slow crustal movements or very low-frequency earthquakes were observed just prior to phreatic eruptions. These phenomena result from crack opening due to the rapid vaporization of liquid water. Incremental seismic activities, low-frequency earthquakes, and expansion of volcanic edifice, and geochemical changes in volcanic gases and hot springs are identified as long-term eruption precursors. These precursors reflect the supply of new magma, related changes in volcanic gases, and increased fluid pressure in shallow hydrothermal systems. Several new techniques for monitoring volcanoes to detect temporal changes in resistivity, crustal deformation, and chemical composition of hot springs and groundwater have been developed for forecasting eruptions.
Japan Geoscience Union, 2015
Evening Classes; Integrated Course, Kanagawa Prefectual Mukainooka Technical High School, NPO cor... more Evening Classes; Integrated Course, Kanagawa Prefectual Mukainooka Technical High School, NPO corporation nature reproduction center toward ”the rich sea mingled with fresh water area clean, Urawahigashi high school,Saitama, Kaijo Junior and Senior High school, Faculty of Education and Human Sciences, Yokohama National University, Faculty of Education and Human Studies, Akita University, Seibu Gakuen Bunri High School, Kanto Gakuen University, J.F.Oberlin University, Saitama Municipal Sashiougi Jumior High school, Seiko Gakuin High School, Hot Springs Research Institute of Kanagawa Prefecture,Tokyo Metropolitan Ryogoku Senior Hight School, Saitama prefectural Fukaya dai-ichi High School, Tokyo Medical and Dentel University, Saitama Prefecural Kumagaya Girls’ Upper Secondary School, Kanagawa CST
Japan Geoscience Union, 2015
The purpose is geologically to resolve the occurrence timing and the accumulation process of the ... more The purpose is geologically to resolve the occurrence timing and the accumulation process of the crustal movement associated with the Kanto Earthquake repeated at the plate boundary along the Sagami Trough. Study site is the coastal lower land along Bishamon Bay which an estuary is formed in south Miura Peninsula. An evidence of four times of Kanto earthquake during approximately 1000 years was identified, and the crustal movement cycle caused by these earthquakes was estimated. (Figure 1). In the low land, the Holocene flights of marine terrace with the low cliff of 1-2m in height were authorized (National Geography Survey, 1981) . In this study, moreover, the lowest terrace was classified in five terraces from the interpretation of the aerial photographs. We named these lower terraces L1, L2, L3, L4 and L5 in the old order. The low land is raised for development now. From boring survey, the sediment mixed for abundant shell fragments and gravels in motley was founded below +2m abo...
Japan Geoscience Union, 2016
Hakone volcanic activity increased from April 2015. To monitor Hakone volcanic activity, we start... more Hakone volcanic activity increased from April 2015. To monitor Hakone volcanic activity, we started to measure seismic and pressure signals using a seismo-acoustic sensor that is a combination of a Broadband Accelerometer (Developed by Quartz Seismic Sensors, Inc., USA) and a Sensitive Microbarograph (Manufactured by Paroscientific, Inc., USA) in August. Both sensors use precise quartz crystal resonators to archive parts-per-billion resolution. The single axis accelerometer records the vertical component of ground accelerations.
Journal of Geography, 2001
Japan Geoscience Union, 2016
We monitored quantity of visible volcanic plume from Owakudani fumarolic area, Hakone volcano bef... more We monitored quantity of visible volcanic plume from Owakudani fumarolic area, Hakone volcano before and after the phreatic eruption in 2015. Quantity of volcanic plume is represented by number of white pixel in pictures taken by a time-lapse camera installed near the eruption vents. The amount of volcanic plume increased soon after the eruption in June 29 to July 1 and decreased gradually until early November; however it increased again and marked its peak in December. We also monitored water quality of downstream of the vent and volcanic gas around Owakudani area. Our monitoring shows that water temperature, its Cl content and CO2 content of volcanic gas also increased in December. Such relationship between plume quantity and water and gas chemistry could indicate that there are aseismic upwelling of geothermal water in December. SVC46-P02 Japan Geoscience Union Meeting 2016
Japan Geoscience Union, 2014
Recurrent giant earthquakes at the plate boundary along the Sagami Trough have been considered as... more Recurrent giant earthquakes at the plate boundary along the Sagami Trough have been considered as one of the greatest thread of the Tokyo Metropolitan area. At the southwestern tip of the Miura Peninsula, in south of Tokyo, the tide gauge station records the coseismic uplift amount of 1.4 m and the interseismic subsidence amount of 0.3 m in and after 1923 earthquake, respectively. It is effective to reveal evidences of the past coseismic uplift to know the future earthquake. Wave-cut benches which emerged in 1923 are widely distributed along the rocky coast. Higher wave-cut benches, good indicators of coseismic uplift prior to 1923, are also recognizable. It is, however, often difficult to spatially compare one another due to the erosion. We investigated the distribution of the tidal-flat deposits and the 1923 wave-cut benches at two small bays in the southwestern and southern parts of the Peninsula. The aggradation of the coastline associated with the 1923 uplift was identified by ...
Japan Geoscience Union, 2015
The Izu-Bonin-Marina (IBM) arc is a typical intra-oceanic arc system. The forearc is non-accretio... more The Izu-Bonin-Marina (IBM) arc is a typical intra-oceanic arc system. The forearc is non-accretionary convergent margin, where Mafic crustal rocks occurred along the inner trench slope with mantle peridotites. Mariana arc system is the southern part of the IBM arc system and forms arcuately. The trench axis of the southern Mariana trench runs across Mariana volcanic arc and backarc basin (Mariana trough) and is connected to Parece Vela Basin at the westernmost area. There have been no geological studies on the westernmost Marianas trench since Hawkins and Batiza(1977). Recently, investigations for the junction area between Mariana trench and Parece Vela Basin have been conducted using the submersible Shinkai6500 (Dive 6K1397 and 6K1398) as a part of YK14-13 cruise by the R/V Yokosuka in 2014. Shinkai6500 recovered plagioclase-bearing lherzolites and harzbergites from the tectonic ridge along the inner trench slope of the westernmost Mariana Trench. The samples show coarse grained te...
Japan Geoscience Union, 2018
Phreatic eruptions occurred in recent years in many volcanoes in Japan, for example, at Shinmoe-d... more Phreatic eruptions occurred in recent years in many volcanoes in Japan, for example, at Shinmoe-dake on October 11, 2017 and at Mt. Motoshirane on January 23, 2018. Since the eruption scale is generally small, it is difficult to detect the precursor signals relevant to phreatic eruptions. Therefore a mechanism of phreatic eruptions has not been clarified yet. However the hydrothermally altered minerals were contained in ejecta of the eruption in many cases, which suggested that the phreatic eruptions is strongly related to the hydrothermal system developed within a volcanic edifice.
Japan Geoscience Union, 2018
Japan Geoscience Union, 2014
Recurrent giant earthquakes at the plate boundary along the Sagami Trough have been considered as... more Recurrent giant earthquakes at the plate boundary along the Sagami Trough have been considered as one of the greatest thread of the Tokyo Metropolitan area. At the southwestern tip of the Miura Peninsula, in south of Tokyo, the tide gauge station records the coseismic uplift amount of 1.4 m and the interseismic subsidence amount of 0.3 m in and after 1923 earthquake, respectively. It is effective to reveal evidences of the past coseismic uplift to know the future earthquake. Wave-cut benches which emerged in 1923 are widely distributed along the rocky coast. Higher wave-cut benches, good indicators of coseismic uplift prior to 1923, are also recognizable. It is, however, often difficult to spatially compare one another due to the erosion. We investigated the distribution of the tidal-flat deposits and the 1923 wave-cut benches at two small bays in the southwestern and southern parts of the Peninsula. The aggradation of the coastline associated with the 1923 uplift was identified by ...
Since the beginning of the 21st century, volcanic unrest has occurred every 2–5 years at Hakone v... more Since the beginning of the 21st century, volcanic unrest has occurred every 2–5 years at Hakone volcano. After the 2015 eruption, unrest activity changed significantly in terms of seismicity and geochemistry. In this paper, characteristics of the post-eruptive volcanic unrest that occurred in 2017 and 2019 are described, and changes in the hydrothermal system of the volcano caused by the eruption are discussed. Like the pre- and co-eruptive unrest, each post-eruptive unrest episode was detected by deep inflation below the volcano (~ 10 km) and deep low frequency events, which can be interpreted as reflecting supply of magma or magmatic fluid from depth. The seismic activity during the post-eruptive unrest episodes also increased; however, seismic activity beneath the eruption center during the unrest episodes was significantly lower, especially in the shallow region (~2 km), while sporadic seismic swarms were observed beneath the caldera rim, ~3 km away from the center. The 2015 eru...
The Journal of the Geological Society of Japan, 2018
Earth, Planets and Space, 2018
Global navigation satellite system data from Hakone volcano, central Japan, together with GEONET ... more Global navigation satellite system data from Hakone volcano, central Japan, together with GEONET data from the Geospatial Information Authority of Japan, were used to investigate the processes associated with the volcanic activity in 2015, which culminated in a small phreatic eruption in late June 2015. Three deep and shallow sources, namely spherical, open crack, and sill, were employed to elucidate the volcanic processes using the observed GNSS displacements, and the MaGCAP-V software was used to estimate the volumetric changes of these sources. Our detailed analysis shows that a deep inflation source at 6.5 km below sea level started to inflate in late March 2015 at a rate of ~ 9.3 × 10 4 m 3 /day until mid-June. The inflation rate then slowed to ~ 2.1 × 10 4 m 3 /day and ceased at the end of August 2015. A shallow open crack at 0.8 km above sea level started to inflate in May 2015 at a rate of 1.7 × 10 3 m 3 / day. There was no significant volumetric change in the shallow sill source during the volcanic unrest, which is evident from interferometric synthetic aperture radar analysis. The inflation of the deep source continued even after the eruption without a significant slowdown in inflation rate. The inflation stopped in August 2015, approximately 1 month after the eruption ceased. This observation implies that the transportation of magmatic fluid to a deep inflation source (6.5 km) triggered the 2015 unrest. The magmatic fluid may have then migrated from the deep source to the shallow open crack. The phreatic eruption was then caused by the formation of a crack that extended to the surface. However, steam emissions from the vent area during and after the eruption were apparently insufficient to mitigate the internal pressure of the shallow open crack.
Earth, Planets and Space, 2018
We successfully monitored the ground deformation of an eruption center during the 2015 phreatic e... more We successfully monitored the ground deformation of an eruption center during the 2015 phreatic eruption of Hakone volcano, Japan, using ground-based interferometric synthetic aperture radar (GB-InSAR). GB-InSAR has been developed and applied over the past two decades and enables the frequent (< 10 min) aerial monitoring of surficial deformation of structures and slopes. We installed a GB-InSAR 4 days before the eruption of Hakone volcano on June 29, 2015, and monitored the ground deformation of an area where uplift was detected by a satellite InSAR. The ground deformation observed by the GB-InSAR began suddenly on the morning of June 29 almost coincident with the intrusion of hydrothermal fluid that was inferred by other geophysical observations. The hydrothermal crack is considered to have caused the eruption, which was known by an ash fall 5 h later. The GB-InSAR results indicated a significant uplifted area which is approximately 100 m in diameter, and new craters and fumaroles were created by the eruption in and around the area. The displacement reached up to a total of 45 mm until the evening of June 29 and continued at least until the morning of July 1. During our observation, the displacement rate decreased twice, and the timing of each decrease seemed to correspond to the formation of new conduits as implied from geophysical observations.
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Papers by Kazutaka Mannen