This file was created by the TYPO3 extension publications --- Timezone: CEST Creation date: 2026-06-04 Creation time: 00:30:16 --- Number of references 51 article Yilmaz2021 The nature of sub-volcanic alteration is usually only observable after erosion and exhumation at old inactive volcanoes, via geochemical changes in hydrothermal fluids sampled at the surface, via relatively low-resolution geophysical methods or can be inferred from erupted products. These methods are spatially or temporally removed from the real subsurface and thus provide only indirect information. In contrast, the ICDP deep drilling of the Mt Unzen volcano subsurface affords a snapshot into the in situ interaction between the dacitic dykes that fed dome-forming eruptions and the sub-volcanic hydrothermal system, where the most recent lava dome eruption occurred between 1990 and 1995. Here, we analyse drill core samples from hole USDP-4, constraining their degree and type of alteration. We identify and characterize two clay alteration stages: (1) an unusual argillic alteration infill of fractured or partially dissolved plagioclase and hornblende phenocryst domains with kaolinite and Reichweite 1 illite (70)-smectite and (2) propylitic alteration of amphibole and biotite phenocrysts with the fracture-hosted precipitation of chlorite, sulfide and carbonate minerals. These observations imply that the early clay-forming fluid was acidic and probably had a magmatic component, which is indicated for the fluids related to the second chlorite-carbonate stage by our stable carbon and oxygen isotope data. The porosity in the dyke samples is dominantly fracture-hosted, and fracture-filling mineralization is common, suggesting that the dykes were fractured during magma transport, emplacement and cooling, and that subsequent permeable circulation of hydrothermal fluids led to pore clogging and potential partial sealing of the pore network on a timescale of ~ 9 years from cessation of the last eruption. These observations, in concert with evidence that intermediate, crystal-bearing magmas are susceptible to fracturing during ascent and emplacement, lead us to suggest that arc volcanoes enclosed in highly fractured country rock are susceptible to rapid hydrothermal circulation and alteration, with implications for the development of fluid flow, mineralization, stress regime and volcanic edifice structural stability. We explore these possibilities in the context of alteration at other similar volcanoes. © 2021, The Author(s). 2021 English 02588900 10.1007/s00445-021-01450-7 Bulletin of Volcanology 83 Springer Science and Business Media Deutschland GmbH Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München (LMU), Theresienstrasse 41/III, Munich, 80333, Germany; Department of Earth Sciences, Durham University, Durham, DH1 3LE, United Kingdom; Division: Engineering Geology, Technical University of Munich (TUM), Arcisstr. 21, Munich, 80333, Germany; Grant Institute, University of Edinburgh, King’s Buildings, West Mains Road, Edinburgh, EH9 3JW, United Kingdom; Department of Earth, Ocean and Ecological Sciences, University of Liverpool, 4 Brownlow Street, Liverpool, L69 3GP, United Kingdom; Department of Geosciences, Environment and Society, Université Libre de Bruxelles, Avenue Franklin Roosevelt 50, Brussels, 1050, Belgium; National Research Institute for Earth Science and Disaster Resilience, Tennodai, Tsukuba, 305-0006, Japan 5 clay mineral; dike; emplacement; hydrothermal alteration; lava dome; permeability; porosity; volcanic arc; volcanic eruption, Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-85104515398&doi=10.1007%2fs00445-021-01450-7&partnerID=40&md5=cdb1bd3d11057a3f3bd336fb82407912 cited By 5 T.I. Yilmaz F.B. Wadsworth H.A. Gilg K.-U. Hess J.E. Kendrick P.A. Wallace Y. Lavallée J. Utley J. Vasseur S. Nakada D.B. Dingwell article Cichy20111469 Isothermal decompression experiments were performed to simulate magma ascent at Unzen volcano from the depths of magma storage to shallow crustal levels, corresponding to pressure decrease from 300 to 50 MPa. A partially crystallized synthetic rhyodacitic magma (representing equilibrium conditions at 850°C and 300 MPa) was used as a starting material; this has a composition identical to the groundmass of Unzen rocks erupted in 1991-1995. Decompression rates were varied from 0·0002 to 20 MPa s-1. Experiments conducted with decompression rates ≥0·1 MPa s-1 were decompressed continuously; a multi-step decompression approach was used at decompression rates ≤0·1 MPa s-1. The experiments were fluid-saturated, either containing only water as a fluid component (H2O-bearing) or containing a water and carbon dioxide mixture (H2O + CO2; initial mole fraction of H2O in the fluid ~0·6). The experimental products of the H2O-bearing experiments consist of amphibole, pyroxenes, oxides and glass. Plagioclase microlites nucleated and grew only in experiments with the two lowest decompression rates of 0·0005 and 0·0002 MPa s-1. The length of those plagioclases is up to 200-250 μm, which is consistent with the size of plagioclase microlites observed in the natural samples. The experimental products of the H2O + CO2-bearing system are composed of pyroxenes, oxides, glass and plagioclase. Plagioclase microlites in the H2O + CO2-system were already present in the starting assemblage and grew to a maximum size of ~80 μm. Equilibrium concentrations of water in the residual glasses at the final pressure of 50 MPa are reached at decompression rates ≤1 MPa s-1 for the H2O + CO2-bearing system and ≤0·1 MPa s-1 for the H2O-bearing system. The bubble number density (BND) values range from 103·7 to 105·6 mm-3 in the H2O-bearing system and from 104·6 to 106·4 mm-3 in the H2O + CO2-bearing systems. In both systems, BND values decrease with decreasing decompression rate from 20 to 0·01 MPa s-1, and increase with decreasing decompression rates &lt; 0·01 MPa s-1, which is interpreted to reflect predominant bubble growth and bubble nucleation, respectively. The onset of crystallization, observed from changes in the chemical composition of the residual melt, occurs at decompression rates &lt; 0·1 MPa s-1. At the lowest decompression rate (0·0002 MPa s-1) the chemical composition of the residual melt in the H2O + CO2-bearing system becomes similar to the natural matrix glass composition. There is no significant variation of the microlite number density (MND) value as a function of the decompression rate. The MND values for plagioclases-only range from 105·4 to 105·7 mm-3, whereas the MND values for the other phases range from 105·3 to 105·9 mm-3. Our experimental MNDPl values are in the range of those from natural samples (105-106 mm-3). We show that the size of microlites nucleating and crystallizing during decompression (plagioclase in our experimental dataset) is useful to constrain magma ascent rates at the onset of the crystallization of the corresponding phase. Based on the size of plagioclase microlites and on the composition of the residual melts, the average magma ascent rates of Unzen magmas in the pressure range 200 to 50 MPa is estimated to be 10-50 m h-1. © The Author 2010. Published by Oxford University Press. All rights reserved. 2011 English 00223530 10.1093/petrology/egq072 Journal of Petrology 52 Oxford University Press 1469-1492 Institut Für Mineralogie, Leibniz Universität Hannover, Callinstr. 3, D-30167 Hannover, Germany 7-8 amphibole; chemical composition; decompression; glass; magma; nucleation; oxide; plagioclase; pressure; pyroxene; volcanic rock, Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-79961066913&doi=10.1093%2fpetrology%2fegq072&partnerID=40&md5=e894e4fc0ef97bbb8340310c7b5cd1f6 cited By 39 S.B. Cichy R.E. Botcharnikov F. Holtz H. Behrens article Su2010873 It has long been a dream for mankind to enter the deep Earth to sample and investigate the structures and inner geological progresses. Until now, scientific drilling has been the unique method in our understanding of the processes and structures of the Earth. This paper try to give a brief introduction of the history, the development, the mission, the structure and management, the membership, the project development scheme of International Continental Drilling Program (ICDP). Great advances have been brought about in many fields of earth sciences by continental scientific drilling in recent years. Based on the recent publications and website materials of ICDP, this paper summarize the main developments in Climate Dynamics and Global Environments, in the Study of Impact Craters, in the GeoBiospherc, in Active Volcanic Systems, in Active Faults, in Hotspot Volcanoes, in Convergent Plate Boundaries and Collision Zones, and in Natural Resources. Special introduction on the scientific results of ICDP drilling at Mt. Unzen, Japan and the Hawaii Scientific Drilling Project (HSDP) is introduced in this paper. Fascinating discoveries such as the gouge layer of San Andreas Fault and the finding of talc in cuttings of SAFOD project are also introduced in this paper. As one of the three founding members of ICDP, China has also gained a lot of developments in continental scientific drilling; typical examples are the achievements of Chinese Continental Scientific Drilling (CCSD) and the progress of Lake Qinghai Scientific Drilling Project. The preliminary progresses . of the third approved ICDP project of China -the Chinese Cretaceous Continental Scientific Drilling Project and the development of ICDP-China are also summarized in this paper. 2010 Chinese 10009515 Acta Geologica Sinica (English Edition) 84 873-886 Key Laboratory for Continental Dynamics of MLR, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China 6 active fault; climate change; collision zone; crater; deep drilling; hot spot; mantle plume; natural resource; San Andreas Fault; talc, China; Hawaii [United States]; Japan; Kyushu; Nagasaki [Kyushu]; Qinghai; Qinghai Lake; United States; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-78649844329&partnerID=40&md5=732f4e363917ab0357a84117ef5aab8b cited By 9 D. Su J. Yang article Cordonnier2009263 Transitions between effusive and explosive styles of lava dome eruptions are likely accompanied by changes in lava rheology. The common presence of crystals in dome lavas produces a complex non-Newtonian rheology. Thus models of such complex rheology are essential for volcanic eruption models. Here, we have measured the rheology of natural Unzen lavas with a compressive uniaxial press operating at stresses between 1 and 70 MPa and temperatures between 940 and 1010 °C. Crystal-rich Unzen lavas are characterised by two essential rheological features which produce non-Newtonian effects. The first is an instantaneous response of the apparent viscosity to applied stress which requires that the magma be described as a visco-elastic fluid that exhibits shear-thinning. The second effect takes the form of a time-dependence of the viscosity at moderate to high stress (≥ 10 MPa). In this regime, the apparent viscosity slowly decreases as increasing fracturing of the phenocrysts and the groundmass occurs. Fragmentation of crystals and alignment of crystal fragments are observed to produce flow banding-effects which in turn lower the apparent viscosity of natural dome lavas. Ultimately, deformation may lead to complete rupture of the lava if the stress is sufficient. Cracking thus stands as an important process in natural dome lava rheology. The ubiquitous non-Newtonian rheology of dome lavas, observed experimentally here, needs to be adequately treated in order to generate appropriate eruption models. © 2008 Elsevier B.V. All rights reserved. 2009 English 0012821X 10.1016/j.epsl.2009.01.014 Earth and Planetary Science Letters 279 263-272 Ludwig-Maximilians Universität, Theresienstrasse 41 /III, D-80333 Munich, Germany 3-4 brittle; ductile; flow banding; lava; magma; non-Newtonian rheology; Unzen; visco-elastic, Cements; Crystals; Domes; Elasticity; Non Newtonian flow; Plasticity; Rheology; Volcanic rocks; Volcanoes, Viscosity, cracking; crystal structure; deformation; fragmentation; lava dome; magma; phenocryst; rheology; stress; viscoelasticity; volcanic eruption; volcanic rock, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-60949113083&doi=10.1016%2fj.epsl.2009.01.014&partnerID=40&md5=ade738563fb955a325c3a7494e85ff54 cited By 91 B. Cordonnier K.-U. Hess Y. Lavallée D.B. Dingwell article Watanabe200882 Permeability measurement was made on five rock samples from USDP-4 cores. Rock samples were collected from the conduit zone and its country rock. One sample (C14-1-1) is considered as a part of the feeder dyke for the 1991-1995 eruption. The transient pulse method was employed under confining pressure up to 50 MPa. Compressional wave velocity was measured along with permeability. The measured permeability ranges from 10- 19 to 10- 17 m2 at the atmospheric pressure, and is as low as that reported for tight rocks such as granite. The permeability decreases with increasing confining pressure, while the compressional wave velocity increases. Assuming that pores are parallel elliptical tubes, the pressure dependence of permeability requires aspect ratio of 10- 4-10- 2 at the atmospheric pressure. The pore aperture is estimated to be less than 1 μm. The estimated aspect ratio and pore aperture suggest that connectivity of pores is maintained by narrow cracks. The existence of cracks is supported by the pressure dependence of compressional wave velocity. Narrow cracks (&lt; 1 μm) are observed in dyke samples, and they must have been created after solidification. Dyke samples do not provide us information of pore structures during degassing, since exsolved gas has mostly escaped and pores governing the gas permeable flow should have been lost. Both dyke and country rock samples provide us information of materials around ascending magma. Although the measured small-scale permeability cannot be directly applied to geological-scale processes, it gives constrains on studies of large-scale permeability. © 2008 Elsevier B.V. All rights reserved. 2008 English 03770273 10.1016/j.jvolgeores.2008.03.021 Journal of Volcanology and Geothermal Research 175 82-90 Department of Earth Sciences, University of Toyama, Gofuku 3190, Toyama, 930-8555, Japan; Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-0032, Japan 1-2 Capillarity; Liquids; Rocks; Solids, Compressional wave velocities; Confining pressures; crack; Drill holes; drilled core; permeability; Permeability measurements; pore structure; Rock samples; Transient pulse; Unzen volcano, Rock drilling, atmospheric pressure; country rock; crack; degassing; dike; drilling; gas flow; granite; permeability; solidification; volcanic eruption; wave velocity, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-50049093966&doi=10.1016%2fj.jvolgeores.2008.03.021&partnerID=40&md5=8678980b0549b4ed3eb0490147613467 cited By 12 T. Watanabe Y. Shimizu S. Noguchi S. Nakada article Vetere2008208 The viscosity of an iron-bearing melt with composition similar to Unzen andesite was determined experimentally in the high (109-1010.5 Pa s) and low (5-1000 Pa s) viscosity range using a parallel plate viscometer and the falling sphere method, respectively. Falling sphere experiments were carried out in an internally heated argon pressure vessel and in a piston cylinder apparatus at 1323 to 1573 K and 200 to 2000 MPa. Creep experiments were performed in the temperature range of 747-845 K at 300 MPa. The water content of the melt varies from nominally dry to 6.2 wt.% H2O. The Fe2+/Fetot ratio was determined for each sample in the quenched glass using a colorimetric method. Pressure has minor influence on the viscosity compared with the effect of temperature, water content (main compositional parameter controlling the viscosity) or with the Fe2+/Fetot ratio (especially important at low water content of the melt). Based on our new viscosity data and literature data with measured Fe2+/Fetot ratio we propose a new empirical equation to estimate the viscosity η (in Pa s) of andesitic melts as a function of temperature T (in K), water content w (in wt.%) and Fe2+/Fetot ratio. The derived relationship reproduces the experimental data (87 in total) in the viscosity range from 100.5 to 1013 Pa s with a 1σ standard deviation of 0.17 log units. However, application of this calculation model is limited to Fe2+/Fetot Fetot &gt; 0.3 and to temperatures above Tg. Moreover, in the high viscosity range the variation of viscosity with water content is constrained only by few experimental data and needs verification by additional measurements. The viscosity data are used to interpret mixing processes in the Unzen magma chamber prior to 1991-1995 eruption. We demonstrate that the viscosities of the rhyolite and andesite melts from the two end-member magmas are nearly identical prior and during mixing, enabling efficient magma mixing. © 2008 Elsevier B.V. All rights reserved. 2008 English 03770273 10.1016/j.jvolgeores.2008.03.028 Journal of Volcanology and Geothermal Research 175 208-217 Institut für Mineralogie, Universität Hannover, Callinstr. 3, D-30167 Hannover, Germany; Istituto Nazionale di Geofisica e Vulcanologia (INGV), via di Vigna Murata 605, I-00143 Roma, Italy; Poliklinik für Zahnärztliche Prothetik, Medizinische Hochschule, Carl-Neuberg-Str. 1, D-30625 Hannover, Germany 1-2 Igneous rocks; Iron; Mixing; Viscometers; Viscosity, andesite melt; dissolved water; magma mixing; redox state of iron; Unzen, Hydrodynamics, andesite; magma chamber; redox conditions; rhyolite; viscosity; volcanic eruption; water content, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-50049129893&doi=10.1016%2fj.jvolgeores.2008.03.028&partnerID=40&md5=1320cb47ad39728dcba2974e0b6c8387 cited By 37 F. Vetere H. Behrens J.A. Schuessler F. Holtz V. Misiti L. Borchers article Suto200820 The Unzen Scientific Drilling Project was initiated in 1999 to investigate a magma conduit that had recently fed a volcanic eruption. The conduit hole, USDP-4, was drilled to 810 m in 2003. In 2004, the hole was extended with intention of reaching the conduit at a drilled depth of about 2000 m. This objective was achieved, and the final measured depth of USDP-4 was 1995.75 m. A new temperature memory gauge for rotary drilling application was designed and developed for the project in order to measure borehole temperatures as often as possible in the expected high temperature environment near the conduit. Temperature ratings of the tool are up to 250 °C with dewar. A total of 10 surveys were conducted at depths of 1555-1995.75 m. This tool was used in six surveys, and borehole temperature data was successfully obtained from all surveys. Based on the measured temperatures, it is apparent that the thermal energy potential of the conduit regime (i.e. thermal supply from conduit) is not large compared to that of most known geothermal systems. Formation temperatures along the conduit hole were estimated from measured temperatures by using a borehole temperature simulator, which we developed and subsequently modified. According to the simulation, the maximum in the formation temperature profile is located at a depth of about 1970 m, and its temperature was about 170 °C before the drilling operation started. This maximum approximately coincides with the center of the conduit, but is surprisingly low for a system that ceased eruption only 9 years before the temperature survey. © 2008 Elsevier B.V. 2008 English 03770273 10.1016/j.jvolgeores.2008.03.034 Journal of Volcanology and Geothermal Research 175 20-27 Graduate School of Environmental Studies, Tohoku University, Japan; Geothermal Engineering Co., Ltd., Japan; Ichinoseki National College of Technology, Japan; Sandia National Laboratory, United States 1-2 Drilling; Estimation; Gages; Geothermal energy; Geothermal fields; Surveys; Volcanoes, Bore hole; borehole temperature; Drilling operations; Energy potential; formation temperature; Geothermal systems; High-temperature environments; Measured depth; Rotary drilling; temperature memory gauge; temperature simulation; temperature survey; volcanic conduit; Volcanic eruptions, Boreholes, borehole logging; drilling; gauge; geothermal system; magma; temperature profile; volcanic eruption, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-50049118836&doi=10.1016%2fj.jvolgeores.2008.03.034&partnerID=40&md5=9aa671f719a411e6d732acdb380e9446 cited By 8 Y. Suto S. Sakuma H. Takahashi N. Hatakeyama J. Henfling article Botcharnikov2008168 The compositions of homogenized melt inclusions trapped in plagioclase (Pl) microphenocrysts (40-200 μm length) from mafic enclaves within dacitic rocks erupted at Unzen volcano in 1991-95 were investigated. The SiO2 contents of the melt inclusions vary from 58 to 70 wt.% and Pl anorthite content is An50-70. The stability fields (in terms of temperature and water activity) of natural Pl and coexisting melts from the melt inclusions were estimated from data of phase equilibria experiments performed with a synthetic andesite composition at T = 900-1140 °C, P = 200 MPa, log fO2 = NNO-2-NNO, and water activity of about 0-1. This composition is representative of the average composition of mafic enclaves from the 1991-95 eruption and nearly identical to the composition of andesitic lavas from 1663 Unzen eruption. The temperatures and H2O melt concentrations, calculated using the compositions of coexisting Pl and melt inclusions, provide an estimation of the conditions of andesitic magma evolution within the mafic enclaves prior to eruption. The formation of melt inclusions in plagioclase microphenocrysts occurred at a maximum temperature of ~ 1010 ± 35 °C for a melt containing 2 wt.% H2O and a minimum temperature of ∼ 945 °C ± 30 °C for a melt with ∼ 4 wt.% dissolved H2O. The compositional range of the melt inclusions indicates that the composition of the mafic enclave was not significantly contaminated by the host magma when inclusions were formed. The difference between concentrations of dissolved S (up to 0.06 wt.%) and Cl (up to 0.05 wt.%) in melt inclusions in Pl of mafic enclaves and concentrations of S (&lt; 0.005 wt.%) and Cl (0.05-0.11 wt.%) in melt inclusions in phenocrysts of the dacitic magma clearly implies that two distinct sources for S and Cl in the 1991-95 eruption of Unzen volcano need to be considered. Sulfur degassing was generated by a release of fluids from the high-temperature andesitic magma whereas Cl was degassed from the low-temperature silicic magma. The combination of data from melt inclusions and phase equilibria experiments indicates that the mafic end-member magma at Unzen was already partially crystallized and contained significant proportions (20 to 40 wt.%) of Pl and orthopyroxene (Opx) when melt inclusions started to form. Since clinopyroxene (Cpx) and magnetite (Mt) crystallize after Pl and Opx, the temperatures derived for the mafic end-member magma from coexisting Opx-Cpx and Ilm-Mt pairs do not represent temperatures near to the liquidus. Assuming that the injected mafic magma was nearly aphyric, its initial temperature might have been higher than estimated in previous studies. © 2008 Elsevier B.V. All rights reserved. 2008 English 03770273 10.1016/j.jvolgeores.2008.03.026 Journal of Volcanology and Geothermal Research 175 168-180 Institut für Mineralogie, Leibniz Universität Hannover, Callinstr. 3, 30167 Hannover, Germany; Department of Earth and Planetary Science, Kobe University, Kobe, 657-8501, Japan 1-2 Chemical engineering; Feldspar; Landforms; Silicate minerals; Silicon compounds; Volcanic rocks; Volcanoes, andesite; experiment; magma mixing; melt inclusions; storage conditions; Unzen volcano; volatiles, Phase equilibria, andesite; clinopyroxene; magma; magnetite; melt inclusion; phase equilibrium; volatile element; volcanic eruption, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-42549100320&doi=10.1016%2fj.jvolgeores.2008.03.026&partnerID=40&md5=bf71003951e7904107b86f41469ef4a9 cited By 25 R.E. Botcharnikov F. Holtz R.R. Almeev H. Sato H. Behrens article Tretner200828 During the Unzen conduit drilling project USDP-4, the gas phase dissolved in the drill mud was continuously analyzed. Starting from the volcano's north flank an almost complete gas profile was achieved to the final depth of 1995.75 m in July 2004. Limitations were given due to the extremely difficult drilling conditions. The highly fractured rock formation led to loss of drill mud circulation in the shallow parts of the drill hole. Significant fluid inflow horizons did not occur above 800 m (drill string length). Starting from that depth on, invading fluids were detected with the real-time gas monitoring system. Major variations in the mud gas composition occurred only below a depth of 1000 m. Of major importance are fluid inflow zones with high 3He/4He at depths of 1555 m (7.3 RA), 1755.5 m (7.48 RA) and 1977.4 m (6.21 RA). These values indicate a significant influence of fluids with mantle signature. Furthermore, enhanced methane, radon and helium concentrations were also detected at specific depth. These detected major fluid- and gas inflow horizons may be able to explain magmatic degassing processes, related to the Unzen's eruption mechanism. This is generally true for the main fluid inflow zones and especially for the detected inflows at 1555 m, 1755.5 m and 1977.4 m. Furthermore, a correlation between lithology and gas composition was observed. Higher H2S concentrations were detected while drilling in pyrite-rich rocks. Cracks and fissures as well as lithological changes are often correlated with increasing amounts of gas. Trends with depth, from a minor to a more magmatic influenced regime were observed together with a change in hydrothermal alteration of the surrounding rock. This corresponds with the magmatic conduit zone which was penetrated at a depth of 1600 m, and supports the model of a high influence of hydrothermal fluid, accelerating cooling and mineral alteration. © 2008 Elsevier B.V. All rights reserved. 2008 English 03770273 10.1016/j.jvolgeores.2008.03.031 Journal of Volcanology and Geothermal Research 175 28-34 GeoForschungsZentrum Potsdam (GFZ), Potsdam, Germany; Volcano Research Center, Earthquake Research Institute, University of Tokyo, Japan; Shimabara Observatory, Institute of Seismology and Volcanology, Kyushu University, Shimabara, Japan 1-2 Dissolution; Drilling; Drills; Gas detectors; Gases; Landforms; Mud logging; Volcanoes; Well drilling, conduit drilling; continuous gas monitoring; Drill holes; Drill strings; Fractured rocks; Gas compositions; Gas monitoring; Gas-phase; He isotopes; Mud circulation; Unzen; USDP-4, Natural gas well drilling, cooling; degassing; drilling; helium isotope; hydrothermal alteration; hydrothermal fluid; mineral alteration; real time; volcanic eruption; well logging, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-50049109149&doi=10.1016%2fj.jvolgeores.2008.03.031&partnerID=40&md5=dfc3904dc57a51d009d6f0a452a97f08 cited By 14 A. Tretner M. Zimmer J. Erzinger S. Nakada M. Saito article Ikeda200813 The objective of the Unzen Scientific Drilling Project (USDP) is not only to reveal the structure and eruption history of the Unzen volcano but also to clarify the ascent and degassing mechanisms of the magma conduit. Conduit drilling (USDP-4) was conducted in 2004, which targeted the magma conduit for the 1990-95 eruption. The total drilled length of USDP-4 was 1995.75 m. Geophysical well logging, including resistivity, gamma-ray, spontaneous potential, sonic-wave velocity, density, neutron porosity, and Fullbore Formation MicroImager (FMI), was conducted at each drilling stage. Variations in the physical properties of the rocks were revealed by the well-log data, which correlated with not only large-scale formation boundaries but also small-scale changes in lithology. Such variations were evident in the lava dike, pyroclastic rocks, and breccias over depth intervals ranging from 1 to 40 m. These data support previous models for structure of the lava conduit, in that they indicate the existence of alternating layers of high-resistivity and high P-wave velocity rocks corresponding to the lava dikes, in proximity to narrower zones exhibiting high porosity, low resistivity, and low P-wave velocity. These narrow, low-porosity zones are presumably higher in permeability than the adjacent rocks and may form preferential conduits for degassing during magma ascent. © 2008 Elsevier B.V. 2008 English 03770273 10.1016/j.jvolgeores.2008.03.036 Journal of Volcanology and Geothermal Research 175 13-19 Faculty of Science, Hokkaido University, North-10 West-8, Kita-ku, Sapporo, Hokkaido, 060-0810, Japan; Japan Metals and Chemicals Co., Ltd., 101-1 Ukai Takizawa-mura, Iwate, 020-0172, Japan; National Research Institute for Earth Science and Disaster Prevention, 3-1 Tennodai, Tsukuba, Ibaraki, 305-0006, Japan; U.S. Geological Survey, 345 Middlefield Rd, Menlo Park, CA 94025, United States 1-2 Acoustic logging; Acoustic wave velocity; Degassing; Drilling; Forestry; Gamma rays; Harvesting; Human computer interaction; Hydraulic structures; Levees; Lithology; Logging (forestry); Neutron logging; Oil well logging; Porosity; Rock drilling; Rocks; Scale (deposits); Spontaneous potential logging; Structural geology, Alternating layers; Conduit structure; Data support; High porosity; Log data; Low resistivity; Magma ascent; Neutron porosity; P-wave velocities; Physical Properties; Pyroclastic rocks; Rock properties; Scale formation; Scientific drilling; Spontaneous potential; Unzen volcano; Wave velocities; Well logging, Well drilling, degassing; drilling; lava; lithology; magma; permeability; rock property; volcanic eruption; wave velocity; well logging, Corrosion; Degassing; Deposits; Drilling; Hydraulic Structures; Logging; Porosity; Velocity, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-50049126633&doi=10.1016%2fj.jvolgeores.2008.03.036&partnerID=40&md5=288963c217fb5646821f0fd13ee360e3 cited By 18 R. Ikeda T. Kajiwara K. Omura S. Hickman article Fujimitsu200835 Drilling of the volcanic conduit in the Unzen Scientific Drilling Project (USDP) was completed in 2004. Some conduit materials of the 1990-95 eruption were encountered at the bottom of Well USDP-4 (150 m below sea level), and a bottom temperature of about 200 °C was estimated using logging data, although before drilling a temperature of about 700 °C had been inferred. Accordingly, conduit cooling from the initial temperature (850 °C) to the estimated temperature (about 200 °C) was evaluated by numerical simulation. The drilling provides constraints for the numerical model. The drilling indicates that the N-S width of the conduit of the latest eruption is 20 to 30 m and that it occupies a zone of about 300 m, which includes conduits of past eruptions. The process of cooling in the conduit, from an initial temperature of 850 °C in 1995 (the end of the eruption) to 200 °C in 2004 (completion of the conduit drilling), was replicated in models with permeabilities of 1 and 10 mdarcys. This result demonstrates that a highly permeable volcanic body surrounding a small conduit is required to explain the estimated bottom temperature. Our study also aimed to use a numerical simulation to construct a comprehensive hydrothermal model beneath Unzen Volcano. There are four large geothermal systems in the Shimabara Peninsula (Obama hot springs, Unzen fumarolic field, Shimabara hot springs and the West Unzen High Temperature Body [WUHTB]). Three pressure sources ("Sources A", "B" and "C" from shallow to the deep) were determined by geodetic data during the 1990-95 eruption. Source C is located at about 8 km deep at WUHTB, and is considered to be a magma body. We attempted to explain the existence of the four geothermal systems from the large-scale structures (the topography of the Shimabara Peninsula and Unzen Graben) and the various heat sources. We first set a heat source around Source C and changed its position and size. This numerical model produced the upflow zones at the Obama and Shimabara hot springs and WUHTB; however, the Unzen fumarolic field became a recharge area. This result indicates that another heat source is required to explain the Unzen fumarolic field and that two heat sources beneath WUHTB and the Unzen fumarolic field are involved in the formation of the four hydrothermal systems in the Shimabara Peninsula. © 2008 Elsevier B.V. All rights reserved. 2008 English 03770273 10.1016/j.jvolgeores.2008.03.032 Journal of Volcanology and Geothermal Research 175 35-44 Faculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan; Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan 1-2 Computer simulation; Cooling; Drilling; Estimation; Geothermal fields; Geothermal prospecting; Geothermal springs; Geothermal wells; Hot springs; Landforms; Numerical methods; Oceanography; Offshore oil well production; Offshore oil wells; Oil well logging; Sea level; Springs (components); Temperature; Volcanic rocks; Volcanoes; Water levels; Well logging, Bottom temperature; Fumarolic field; Geodetic data; geothermal fluid; Geothermal systems; heat source; Heat sourcing; High temperature; Hydro-thermal systems; hydrothermal system; Initial temperature; Large-scale structures; Logging data; numerical model; Numerical modelling; Numerical simulations; Recharge area; Shimabara Peninsula; Unzen Volcano; Volcanic conduits, Well drilling, heat source; hydrothermal fluid; hydrothermal system; magma; numerical model; thermal spring; volcanic eruption, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Shimabara Peninsula; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-50049122949&doi=10.1016%2fj.jvolgeores.2008.03.032&partnerID=40&md5=8bb420787441578149fd894cb91982b9 cited By 7 Y. Fujimitsu S. Ehara R. Oki R. Kanou article Noguchi200871 Groundmass textural and compositional analyses of the drilled dacite dykes of the Unzen Scientific Drilling Project (USDP-4) identify the feeder dyke of the 1990-1995 eruption and elucidate the crystallization process of dykes at depth. In the drilling depth range of 1582-1996 m ("conduit zone"), four dacite dykes were recognized. The groundmasses of all but one of these dykes have textures ranging from cryptocrystalline to microcrystalline aggregate of crystals &lt; 10 μm across forming an equigranular mosaic of plagioclase, alkali feldspar, quartz, and pyrite. The samples include a small number of coarser-grained plagioclase microlites (20 μm to 0.3 mm long). The compositions of groundmass consisting only of grains &lt; 10 μm plotted at the lower pressure (&lt; 50 MPa) ternary minimum in the Qz'-Ab'-Or' system suggests that the crystallization of plagioclase, alkali feldspar, and quartz took place nearly simultaneously. The compositions of coarser plagioclase microlites and groundmass, the plagioclase microlite textures, and the phenocryst assemblages show significant differences from historical lavas exposed in the summit area. This implies the possibility that most of the dacite dykes are not feeder dykes for the lavas at the summit and remained beneath the surface, perhaps because of high viscosity associated with high SiO2. One sample C14-1-1 collected 1977 m, has a texture, composition, and phenocryst assemblage nearly identical to that of the dome lava of the 1990-1995 eruption, differing only in the presence of hydrothermal alternation. At this time we cannot definitely conclude that C14-1-1 was the feeder dyke for the 1990-1995 eruption until we can elucidate the time scale and the conditions governing hydrothermal alternation. © 2008 Elsevier B.V. All rights reserved. 2008 English 03770273 10.1016/j.jvolgeores.2008.03.037 Journal of Volcanology and Geothermal Research 175 71-81 Department of Earth and Planetary Sciences, Graduate School of Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan; Volcano Research Center, Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan; Technology and Research Center, Japan Oil, Gas and Metals National Corporation, 1-2-2, Hamada, Mihama-ku, Chiba, 261-0025, Japan 1-2 Crystallization; Crystallography; Drilling; Feeding; Feldspar; Metallic glass; Nanocrystalline alloys; Oxide minerals; Pyrites; Quartz; Silicon compounds; Textures, Alkali feldspar; annealing; Compositional analysis; conduit drilling; Crystallization processes; dacite dyke; Drilling depth; groundmass texture; hydrothermal alteration; Lower pressures; Microlite; Microlites; Unzen, Silicate minerals, crystallization; dacite; dike; drilling; hydrothermal alteration; lava dome; volcanic eruption, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-50049114104&doi=10.1016%2fj.jvolgeores.2008.03.037&partnerID=40&md5=b8a4a26bc098dbe5beef3221f26ada07 cited By 20 S. Noguchi A. Toramaru S. Nakada article Scheu2008110 Protracted dome-building eruptions may be profitably investigated using laboratory-based experiments. Density distribution studies on the pyroclastic flow deposits of Unzen 1990-1995 allow us to apply the results of experimental investigations on Unzen samples to the interpretation of the last eruption of Unzen. Here, primary laboratory experiments have focused on several aspects of the degassing (permeability) and the fragmentation behavior (threshold, speed, and efficiency). Those investigations have been flanked by analyses of flexural strength, fracture toughness, and seismic velocities, to provide new insights into eruption related processes. Here we present a review of these results and their application to the eruption dynamics of Unzen Volcano. We propose that efforts be made to incorporate routinely such comprehensive experimental analyses into the response to emerging volcanic crises in future. © 2008 Elsevier B.V. All rights reserved. 2008 English 03770273 10.1016/j.jvolgeores.2008.03.023 Journal of Volcanology and Geothermal Research 175 110-119 Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, 113-0023 Tokyo, Japan; Department of Earth and Environmental Sciences, University of Munich, Theresienstr. 41 /III, 80333 Munich, Germany; Centro de Vulcanologia e Avaliação de Riscos Geológicos, Universidade dos Açores, 9501 - 801 Ponta Delgada, Açores, Portugal; Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS81RJ, United Kingdom 1-2 Degassing; Experiments; Fracture fixation; Landforms; Volcanic rocks; Volcanoes, block-and-ash flow; Density distributions; elastic wave velocities; Eruption dynamics; Experimental investigations; Flexural strength; fragmentation behavior; Laboratory experiments; permeability; porosity; Pyroclastic flow deposits; Seismic velocities; Unzen; volcanology, Fracture toughness, ash flow; degassing; fracture toughness; permeability; porosity; seismic velocity; volcanic eruption; volcanology, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-50049132862&doi=10.1016%2fj.jvolgeores.2008.03.023&partnerID=40&md5=f2cd89c93fc0f6dd8a406594c6c29ef5 cited By 36 B. Scheu U. Kueppers S. Mueller O. Spieler D.B. Dingwell article Sakuma20081 Borehole USDP-4 was drilled into the Unzen volcanic conduit 9 years after its last eruption. The sub-surface mechanism of eruption at Unzen Volcano was investigated by taking cores and by geophysical logging. The drilling operations were carried out in 2003-04, as a joint research program sponsored by the Japanese Government and the International Continental Scientific Drilling Program (ICDP). Borehole USDP-4 was a directional 6-1/4 in. (158.8 mm) borehole drilled from a site located on the northern slope of the volcano at 840 m above sea level, and was designed to penetrate into the conduit at sea level with a final deviation angle of over 70° from vertical and a borehole depth of 1800 m. An igneous dyke with a high likelihood of being the Unzen conduit was encountered at 1996 m depth and core samples were taken from that location. Chemical analysis of drill cores confirmed the identification of the conduit. Geophysical logging, including recording of gamma ray, resistivity, self-potential, density, neutron porosity, sonic velocity, and temperature suggested an alternation of dykes and flows in rock penetrated during the drilling, and in-hole pictures confirmed the lithologic identifications. Although borehole collapse and high temperature had been expected in the conduit, the actual drilling and logging into the conduit experienced no gas or fluid kick, and the measured temperatures within the dyke were below 200 °C. © 2008 Elsevier B.V. All rights reserved. 2008 English 03770273 10.1016/j.jvolgeores.2008.03.039 Journal of Volcanology and Geothermal Research 175 1-12 Japan Metals and Chemicals Co., Ltd. (Japan), 101-1 Hosoyachi, Ukai, Takizawa, Iwate, 020-0172, Japan; Volcano Research Center, Earthquake Research Institute, University of Tokyo (Japan), 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan; National Institute of Advanced Industrial Science and Technology (Japan), Central 7, Tsukuba, Ibaraki, 305-8567, Japan; Institute of Seismology and Volcanology, Kyushu University (Japan), 2-5643-29 Shin'yama, Shimabara, Nagasaki, 855-0843, Japan 1-2 Acoustic logging; Core drilling; Drilling; Forestry; Gamma rays; Geophysics; Harvesting; Ionizing radiation; Landforms; Logging (forestry); Neutron logging; Oceanography; Offshore oil wells; Rock drilling; Sea level; Volcanic rocks; Volcanoes; Water levels, Bore hole; Chemical-; Deviation angles; Drilling operations; extended reach borehole; Geophysical logging; High temperature; Neutron porosity; Research programs; scientific drilling; Self-potential; Sonic velocity; spot coring; Surface mechanism; tough logging; volcanic conduit; Volcanic conduits, Boreholes, borehole logging; chemical analysis; dike; geophysical survey; volcanic eruption, Drilling; Forestry; Gamma Rays; Harvesting; Ionizing Radiation; Logging; Oceanography; Volcanism; Water, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-50049107821&doi=10.1016%2fj.jvolgeores.2008.03.039&partnerID=40&md5=b969afce5b6898cd3ae0762f6c1bcc69 cited By 33 S. Sakuma T. Kajiwara S. Nakada K. Uto H. Shimizu article Almberg200860 Core samples from the conduit of Unzen Volcano, obtained only 9 years after cessation of the 1991-1995 eruption, exhibit important differences in physical characteristics and mineralogy, and subtle differences in bulk chemistry from erupted samples. These differences in the conduit samples reflect emplacement under a confining pressure where about half of the original magmatic water was retained in the melt phase, maintenance at hypersolidus temperature for some unknown but significant time span, and subsequent subsolidus hydrothermal alteration. In contrast, magma that extruded as lava underwent decompression to 1 atm with nearly complete loss of magmatic water and cooling at a sufficiently rapid rate to produce glass. The resulting hypabyssal texture of the conduit samples, while clearly distinct from eruptive rocks, is also distinct from plutonic suites. Given the already low temperature of the conduit (less than 200 °C, [Nakada, S., Uto, K., Yoshimoto, M., Eichelberger, J.C., Shimizu, H., 2005. Scientific Results of Conduit Drilling in the Unzen Scientific Drilling Project (USDP), Sci. Drill., 1, 18-22]) when it was sampled by drilling, this texture must have developed within a decade, and perhaps within a much shorter time, after emplacement. The fact that all trace-element concentrations of the conduit and the last-emplaced lava of the spine, 1300 m above it, are identical to within analytical uncertainty provides strong evidence that both were produced during the same eruption sequence. Changes in conduit magma that occurred between emplacement and cooling to the solidus were collapse of vesicles from less than or equal to the equilibrium value of about 50 vol.% to about 0.1 vol.%; continued resorption of quartz and reaction of biotite phenocrysts due to heating of magma prior to ascent by intruding mafic magma; breakdown of hornblende; and micro-crystallization of rhyolitic melt to feldspar and quartz. Subsolidus changes were deposition of calcite and pyrite, growth of sericite in anorthite-rich zones of plagioclase, and development of montmorillonite as an alteration product. Significant changes in bulk composition were depletion of Mg, Fe and Na and enrichment in C and S. These changes were due mainly to the breakdown of hornblende and plagioclase, and addition of carbonate and pyrite, respectively. The identical concentrations of REEs in the conduit and surface lava are consistent with low water to rock ratios during alteration. This suggests to us that despite convective hydrothermal removal of heat from the conduit, chemical open-system effects were limited to early loss of magmatic water and later addition of magmatic CO2 and SO2 and/or H2S streaming up the conduit from deeper levels. © 2008 Elsevier B.V. 2008 English 03770273 10.1016/j.jvolgeores.2008.03.020 Journal of Volcanology and Geothermal Research 175 60-70 University of Alaska Fairbanks Geophysical Institute, Fairbanks, AK 99775, United States; Michigan State University, Department of Geological Sciences, East Lansing, MI 48824, United States 1-2 Calcite; Carbonate minerals; Clay minerals; Cooling; Crystallography; Dewatering; Drilling; Feldspar; Heating; Landforms; Lithology; Metallic glass; Mica; Mineralogy; Minerals; Ore deposit geology; Oxide minerals; Physical chemistry; Product development; Pyrites; Quartz; Rate constants; Silicate minerals; Sodium; Sulfate minerals; Textures; Trace elements; Volcanic rocks; Volcanoes, Analytical uncertainties; Bulk compositions; Chemical-; Confining pressures; crystallization texture; decompression experiments; Element concentrations; Equilibrium value; Hydrothermal alterations; Low temperature; Magmatic water; Melt phase; phase equilibria; Physical characteristics; Plutonic suites; Pressure-temperature-time paths; Rapid rate; Rhyolitic; Scientific results; Sericite; Subsolidus; System effects; Time span; Unzen; vesicularity, Cooling water, confining pressure; drilling; emplacement; hydrothermal alteration; igneous intrusion; lava; magmatic differentiation; phase equilibrium; trace element; volcanic eruption, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-50049092347&doi=10.1016%2fj.jvolgeores.2008.03.020&partnerID=40&md5=fdb618dad80322b624d97b564553927c cited By 8 L.D. Almberg J.F. Larsen J.C. Eichelberger T.A. Vogel L.C. Patino article Goto200845 Article 2008 10.1016/j.jvolgeores.2008.03.041 Journal of Volcanology and Geothermal Research 175 45 – 59 1-2 https://www.scopus.com/inward/record.uri?eid=2-s2.0-50049084633&doi=10.1016%2fj.jvolgeores.2008.03.041&partnerID=40&md5=22dcd014d57a931402c62ceae8882d2f Cited by: 39 Yoshihiko Goto Setsuya Nakada Masaru Kurokawa Taketo Shimano Takeshi Sugimoto Sumio Sakuma Hideo Hoshizumi Mitsuhiro Yoshimoto Kozo Uto article Nakada200637 To understand the structure and growth history of Unzen Volcano in Japan and to clarify the eruption mechanisms of SiO 2-rich viscous magmas, the Unzen Scientific Drilling Project (USDP), a six-year program consisting of two phases, began in April 1999. In the first phase, two holes were drilled into the volcano's flank (USDP-1 and -2 wells). In the second phase, drilling penetrated the magma conduit that fed a lava dome at the summit during the 1991-95 eruption. Through directional drilling, samples of the lava dike believed to have fed the 1991-95 eruption were recovered. The lava dike sample was unexpectedly altered, suggesting that circulation of hydrothermal fluids rapidly cools the conduit region of even very active volcanoes. It is likely that seismic signals monitored before the emergence of lava dome reflected fracturing of the country rocks, caused by veining as volatiles escaped predominantly upward, not outward, from the rising magma. 2006 English 09693769 Geodrilling International 37-39 Earthquake Research Institute, University of Tokyo, Tokyo, Japan; Geological Survey of Japan, Japan; Japan Metals and Chemicals Co., Japan; Geophysical Institute, University of Alaska, Fairbanks, AK, United States; Institute of Seismology and Volcanology, Kyushu University, Higashi-ku, Fukuoka, Japan 120 drilling https://www.scopus.com/inward/record.uri?eid=2-s2.0-33645349337&partnerID=40&md5=b496f9f7581e2ef1fe66dd7ed94e0461 cited By 0 S. Nakada K. Uto S. Sakuma J. Eichelberger H. Shimizu article Scheu2006175 Knowledge of the dynamics of magma fragmentation is necessary for a better understanding of the explosive behaviour of silicic volcanoes. Here we have measured the fragmentation speed and the fragmentation threshold of five dacitic samples (6.7-53.5 vol% open porosity) from Unzen volcano, Kyushu, Japan. The measurements were carried out using a shock-tube-based fragmentation apparatus modified after Alidibirov and Dingwell (1996a,b). The results of the experimental work confirm the dominant influence of porosity on fragmentation dynamics. The velocity of the fragmentation front increases and the value of the fragmentation threshold decreases with increasing porosity. Further, we observe that the fragmentation speed is strongly influenced by the initial pressure difference and the texture of the dacite. At an initial pressure difference of 30 MPa, the fragmentation speed varies from 34 m/s for the least porous sample to 100 m/s for the most porous sample. These results are evaluated by applying them to the 1990-1995 eruptive activity of Unzen volcano. Emplacements of layered lava dome lobes, Merapi-type pyroclastic flows and minor explosive events dominated this eruption. The influence of the fragmentation dynamics on dome collapse and Vulcanian events is discussed. © Springer-Verlag 2006. 2006 English 02588900 10.1007/s00445-006-0066-5 Bulletin of Volcanology 69 175-187 Earth and Environmental Sciences, University of Munich, Theresienstr. 41/III, 80333 Munich, Germany; Earthquake Research Institute, University of Tokyo, 113-0032 Tokyo, Japan 2 explosive volcanism; fragmentation; lava dome; volcanology, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-33747341625&doi=10.1007%2fs00445-006-0066-5&partnerID=40&md5=13bb4a97d81c1abde8e643116bff9669 cited By 51 B. Scheu O. Spieler D.B. Dingwell article Browne2006301 Mafic to intermediate enclaves are evenly distributed throughout the dacitic 1991-1995 lava sequence of Unzen volcano, Japan, representing hundreds of mafic recharge events over the life of the volcano. This study documents the morphological, textural, chemical, and petrological characteristics of the enclaves and coexisting silicic host lavas. The eruptive products described in this study appear to be general products of magma mingling, as the same textural types are seen at many other volcanoes. Two types of magmatic enclaves, referred to as Porphyritic and Equigranular, are easily distinguished texturally. Porphyritic enclaves display a wide range in composition from basalt to andesite, are glass-rich, spherical and porphyritic, and contain large, resorbed, plagioclase phenocrysts in a matrix of acicular crystals and glass. Equigranular enclaves are andesitic, non-porphyritic, and consist of tabular, medium-grained microphenocrysts in a matrix glass that is in equilibrium with the host dacite magma. Porphyritic enclaves are produced when intruding basaltic magma engulfs melt and phenocrysts of resident silicic magma at their mutual interface. Equigranular enclaves are a product of a more prolonged mixing and gradual crystallization at a slower cooling rate within the interior of the mafic intrusion. © The Author 2005. Published by Oxford University Press. All rights reserved. 2006 English 00223530 10.1093/petrology/egi076 Journal of Petrology 47 301-328 University of Alaska Fairbanks, Geophysical Institute, Fairbanks, AK 99775, United States; Michigan State University, Department of Geological Sciences, East Lansing, MI 48824, United States; Geological Survey of Japan, Higashi 1-1-3, Tsukuba, Ibaraki 305-8567, Japan; California State University, Department of Geological Sciences, Fullerton, CA 92834, United States 2 enclave; mafic rock; magmatism; petrogenesis, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-31544433943&doi=10.1093%2fpetrology%2fegi076&partnerID=40&md5=cbcec4529d6996b61df9f7ae1a8db2a3 cited By 73 B.L. Browne J.C. Eichelberger L.C. Patino T.A. Vogel J. Dehn K. Uto H. Hoshizumi article Fujimitsu2006373 The Unzen Scientific Drilling Project (USDP) had been conducted by the Science and Technology Agency (FY1999-2000) and the Ministry of Education, Culture, Sports, Science and Technology, Japan (FY2001-2004). In this project, one of the objectives of our study was to construct a comprehensive hydrothermal model of beneath Unzen Volcano by using a numerical simulation. Four large geothermal systems are known in the Shimabara Peninsula (Obama hot springs, Unzen fumarolic field, Shimabara hot springs and the West Unzen High Temperature Body [WUHTB]). Three pressure source locations (“Sources A”, “B” and “C” from shallow to the deep) were determined by geodetic data during the 1990-95 eruption. Source C is located at about 8 km deep at WUHTB, and is considered to be a magma reservoir. We attempted to explain the existence mechanism of the four geothermal systems from the large-scale structures (the topography of the Shimabara Peninsula and Unzen Graben) and the various heat sources. We first set a heat source around Source C and changed its position and size. This numerical model produced the upflow zones at the Obama and Shimabara hot springs and WUHTB; however the Unzen fumarolic field became a recharge area. This result indicated that it would be difficult to develop the Unzen fumarolic field only by Source C ; therefore, we set another heat source just beneath the fumarolic field. Consequently, two heat sources beneath WUHTB and the Unzen fumarolic field are involved in the formation of the four hydrothermal systems in the Shimabara Peninsula. Especially, the heat source beneath the Unzen fumarolic field is essential to generate heat discharges at the fumarolic field. © 2006, THE GEOTHERMAL RESEARCH SOCIETY OF JAPAN. All rights reserved. 2006 English 03886735 10.11367/grsj1979.28.373 Journal of the Geothermal Research Society of Japan 28 373-382 Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan, Japan; Department of Earth Resources Engineering, Graduate School of Engineering, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan, Japan 4 https://www.scopus.com/inward/record.uri?eid=2-s2.0-77955844565&doi=10.11367%2fgrsj1979.28.373&partnerID=40&md5=e57ea16723d655398f4a93ae010435cd cited By 2 Y. Fujimitsu S. Ehara R. Oki article Browne2006103 Textural and geochemical characteristics of plagioclase phenocrysts from the eruptive products of Mount Unzen (SW Japan) record repeated intrusions of basaltic magma into a dacitic host magma chamber over the lifetime of the volcano. An important aspect of this mixing style is the exchange of phenocrysts between the intruding basalt magma and host dacite magma, and the effect that this wide-reaching mixing style has on the mineralogical diversity of the erupted products. Plagioclase phenocrysts that originally crystallized from the host dacite magma are identified by oscillatory zoning patterns, low An content cores (An45 to An60), and low Sr / Ba ratios. Host-derived plagioclase phenocrysts are engulfed during intrusion of basaltic magma, evidenced by their presence in basaltic to andesitic enclaves. In response to changes in temperature and composition of the surrounding melt, the engulfed plagioclases develop resorption zones, which are composed of a densely packed network of micron-sized glass inclusions and high An content plagioclase (An72-An92) with high Sr / Ba ratios that match those of plagioclase microphenocrysts inherent to the enclave-forming magma. Over time, host-derived plagioclase phenocrysts that were once engulfed during replenishment events are recycled back to the host as enclaves disaggregate (e.g.[ Clynne, M.A., 1989. The disaggregation of quenched magmatic inclusions contributes to chemical diversity in silicic lavas of Lassen Peak, California. Bull New Mexico Bureau of Mines and Mineral Resources, 131: 54]). An eruption of andesite lava with no enclaves, something particularly unique for Unzen, occurred in 1663. Similar to enclaves, all plagioclase phenocrysts in this lava flow are surrounded by resorption zones suggesting that the 1663 lava may represent a magma that was erupted after thoroughly mixing with the intruding basaltic. Using experimentally calibrated crystallization rates, we estimate that phenocrysts exist in the Unzen chamber a minimum of 0.5-3 months between the time of their encounter with a basaltic intrusion and eruption. © 2006 Elsevier B.V. All rights reserved. 2006 English 03770273 10.1016/j.jvolgeores.2005.09.022 Journal of Volcanology and Geothermal Research 154 103-116 University of Alaska Fairbanks Geophysical Institute, Fairbanks, AK 99775, United States; Michigan State University, Department of Geological Sciences, East Lansing, MI 48824, United States; Geological Survey of Japan, Higashi 1-1-3, Tsukuba, 305-8567, Japan 1-2 Crystallization; Geochemistry; Laser ablation; Mineralogy; Trace elements, Enclaves; Magma mixing; Plagioclase; Unzen volcano, Volcanoes, andesite; lava flow; magma; phenocryst; plagioclase; volcanic eruption, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-33646866594&doi=10.1016%2fj.jvolgeores.2005.09.022&partnerID=40&md5=4bb74c469245b9eb1704d4599b5f7811 cited By 92 B.L. Browne J.C. Eichelberger L.C. Patino T.A. Vogel K. Uto H. Hoshizumi article Scheu2006136 Laboratory measurements of elastic properties of volcanic rocks are crucial for the modelling of volcano seismic activity. Compared to the large database reported in the literature for sedimentary, igneous and metamorphic rocks, the data set for volcanic rocks is limited and mostly restricted to basalts. Data for more silica-rich rocks are sparse. In particular, velocity data for silica-rich volcanic rocks measured at elevated temperature are lacking. We measured the elastic P- and S-wave velocities and the velocity anisotropy of porous dacitic rocks from Unzen Volcano, Japan, exhibiting an open porosity of 3.3 to 24.3 vol.%. The measurements were done at temperatures of up to 600 °C and confining pressures of 100 MPa, corresponding to depths of ∼ 3000-4000 m. Samples with even higher porosities failed at the required pressures. The measurements were carried out in a cubic multi-anvil pressure apparatus, using the pulse transmission technique. In contrast to low-porosity magmatic and metamorphic rocks, the seismic velocities of the investigated volcanic rocks increased and the velocity anisotropies decreased with increasing temperature, due to further sample compaction. There is a close relationship between velocity, density and porosity. The higher the density (and the lower the porosity) the higher are the P- and S-wave velocities. These results can contribute to a better understanding of the propagation of seismic energy through the volcanic edifice. © 2005 Elsevier B.V. All rights reserved. 2006 English 03770273 10.1016/j.jvolgeores.2005.08.007 Journal of Volcanology and Geothermal Research 153 136-147 Department of Earth and Environmental Sciences, University of Munich, Theresienstr. 41 /III, 80333 Munich, Germany; Institut für Geowissenschaften der Universität Kiel, Olshausenstr. 40-60, 24098 Kiel, Germany 1-2 SPEC. ISS. Anisotropy; High temperature effects; Metamorphic rocks; Porosity; Seismology; Volcanic rocks; Volcanoes, Pulse transmission technique; Silica-rich rocks; Volcano seismic activity, Elastic waves, dacite; elasticity; high temperature; P-wave; S-wave; seismic anisotropy; seismology; volcanic rock; volcanology, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano https://www.scopus.com/inward/record.uri?eid=2-s2.0-33747799611&doi=10.1016%2fj.jvolgeores.2005.08.007&partnerID=40&md5=7bde461b30d7402c9e5ff902a61c1c31 cited By 29 B. Scheu H. Kern O. Spieler D.B. Dingwell article nakada2005scientific 2005 Scientific drilling 1 18--22 Setsuya Nakada Kozo Uto Sumio Sakuma John C Eichelberger Hiroshi Shimizu article Uto200513 The subsurface structure and magma ascending mechanism of Unzen Volcano was investigated by Unzen Scientific Drilling project (USDP) not only by scientific drillings but also related by geophysical and geochemical studies. A hole was drilled to reach the conduit of the Heisei eruption inorder to clarify the ascending and degassing process of magma and to understand the mechanism of an eruption. There was a conduit zone near the area right under Mt.Fugen at around the sea level, where old and new conduits including the Heisei conduit were concentrated within approximately 500 meters. The temperature in the conduit zone was approximately 200°C, lower than expected before the drilling resulted from quick cooling due to hydrothermal activities. 2005 English 1346602X AIST Today (International Edition) 13 Institute of Geology and Geoinformation, Japan 16 https://www.scopus.com/inward/record.uri?eid=2-s2.0-23944450912&partnerID=40&md5=27f47bfbec8a680ae952631be388fa1a cited By 0 K. Uto article Okubo2005743 On September 18, 2002, we conducted a high-resolution, low-altitude helicopter-bome aeromagnetic survey at two flight altitudes, using spiral trajectories for the first time, over Unzen Volcano in the framework of the Unzen Scientific Drilling Project (USDP). This study obtained more detailed and new information than the previous aeromagnetic studies in Unzen volcano about the geological features, for understanding the history and eruption mechanism of the Unzen volcano. Therefore, we conducted a magnetization intensity mapping on the volcano, on the assumption that the magnetic anomalies are caused by the terrain magnetized in the same direction as the present Earth's magnetic field and the magnetization intensity varies only laterally. This map shows good agreement with the geologic features, especially the hydrothermal alteration zone and the collapsed pyroclastic deposits. In addition, even in the area covered by lavas, the magnetization intensities show various values corresponding to each eruption event. It may be considered that the differences in magnetic properties reflect different oxygen fugacity in rocks during their cooling time period. Local magnetization lows on Heisei-Shinzan suggest that the Heisei lava produced by the 1991-1995 eruption has not yet been cooled enough. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB. 2005 English 13438832 10.1186/BF03351853 Earth, Planets and Space 57 Springer Berlin 743-753 Disaster Prevention Research Institute, Kyoto University, Kyoto 611-0011, Japan; Institute for Geothermal Sciences, Graduate School of Science, Kyoto University, Kumamoto 869-1404, Japan; Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, Nagasaki 855-0843, Japan 8 aeromagnetic survey; cooling; lava flow; magnetic intensity; volcano, Asia; Eastern Hemisphere; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano; World https://www.scopus.com/inward/record.uri?eid=2-s2.0-26844491999&doi=10.1186%2fBF03351853&partnerID=40&md5=30b161c808706502b238ac7a832836ac cited By 5 A. Okubo Y. Tanaka M. Utsugi N. Kitada H. Shimizu T. Matsushima article Holtz2005319 Crystallization experiments were conducted on dry glasses from the Unzen 1992 dacite at 100 300 MPa, 775-875°C, various water activities, and fO2 buffered by the Ni-NiO buffer. The compositions of the experimental products and natural phases are used to constrain the temperature and water contents of the low-temperature and high-temperature magmas prior to the magma mixing event leading to the 1991-1995 eruption. A temperature of 1050 ± 75°C is determined for the high-temperature magma based on two-pyroxene thermometry. The investigation of glass inclusions suggests that the water content of the rhyolitic low-temperature magma could be as high as 8 wt % H2O. The phase relations at 300 MPa and in the temperature range 870-900°C, which are conditions assumed to be representative of the main magma chamber after mixing, show that the main phenocrysts (orthopyroxene, plagioclase, hornblende) coexist only at reduced water activity; the water content of the post-mixing dacitic melt is estimated to be 6 ± 1 wt % H2O. Quartz and biotite, also present as phenocrysts in the dacite, are observed only at low temperature (below 800-775°C). It is concluded that the erupted dacitic magma resulted from the mixing of c. 35 wt % of an almost aphyric pyroxene-bearing andesitic magma (1050 ± 75°C; 4 ± 1 wt % H2O in the melt) with 65 wt % of a phenocryst-rich low-temperature magma (760-780°C) in which the melt phase was rhyolitic, containing up to 8 ± 1 wt % H2O. The proportions of rhyolitic melt and phenocrysts in the low-temperature magma are estimated to be 65% and 35%, respectively. It is emphasized that the strong variations of phenocryst compositions, especially plagioclase, can be explained only if there were variations of temperature and /or water activity (in time and/or space) in the low-temperature magma. © Oxford University Press; all rights reserved. Article 2005 English 00223530 10.1093/petrology/egh077 Journal of Petrology 46 319 – 337 2 Asia; Eastern Hemisphere; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano; World; dacite; magma chemistry; petrology; volcanic rock https://www.scopus.com/inward/record.uri?eid=2-s2.0-13344259964&doi=10.1093%2fpetrology%2fegh077&partnerID=40&md5=2202f170708ef9f84f90fbef82e75543 Cited by: 129; All Open Access, Bronze Open Access François Holtz Hiroaki Sato Jared Lewis Harald Behrens Setsuya Nakada article Sato2005339 High-temperature-pressure experiments were carried out to determine the chlorine-hydroxyl exchange partition coefficient between hornblende and melt in the 1992 Unzen dacite. Cl in hornblende and melt was analyzed by electron microprobe, whereas OH in hornblende and melt was calculated assuming anion stoichiometry of hornblende and utilizing the dissociation reaction constant for H2O + O = 2(OH) in water-saturated melt, respectively. The partition coefficient strongly depends on the Mg/(Mg + Fe) ratio of hornblende, and is expressed as In K1 = (Cl/OH)hb/(Cl/OH)melt = 2· 37 - 4·6[Mg/(Mg + Fe)]hb at 2-3kbar and 800-850°C. The twofold variation in Cl content in the oscillatory zoned cores of hornblende phenocrysts in the 1991-1995 dacite cannot be explained by the dependence of the Cl/OH partition coefficient on the Mg/(Mg + Fe) hb ratio, and requires c. 80% variation of the Cl/OH ratio of the coexisting melt. Available experimental data at 200 MPa on Cl/OH fractionation between fluid and melt suggest that c. 1· 2-1·8 wt % degassing of water from the magma can explain the required 80% variation in the Cl/OH ratio of the melt. The negative correlation between Al content and Mg/(Mg + Fe) ratio in the oscillatory zoned cores of the hornblende phenocrysts is consistent with repeated influx and convective degassing of the fluid phase in the magma chamber. © Oxford University Press 2004; All rights reserved. Article 2005 English 00223530 10.1093/petrology/egh078 Journal of Petrology 46 339 – 354 2 Asia; Eastern Hemisphere; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano; World; dacite; magma chemistry; petrology; volcanic rock https://www.scopus.com/inward/record.uri?eid=2-s2.0-13344285318&doi=10.1093%2fpetrology%2fegh078&partnerID=40&md5=9bc0a3728bae5dba836b69b79f9b863f Cited by: 70; All Open Access, Bronze Open Access, Green Open Access Hiroaki Sato François Holtz Harald Behrens Roman Botcharnikov Setsuya Nakada article Xu2004560 Soil samples were collected from the upper layers of two Unzen volcano Scientific Drilling Project boreholes and dated by radiocarbon using accelerator mass spectrometry (AMS). The humic soils underlying volcanic related lahar flow deposits at a depth of 56.42 m of the USDP-1 borehole gave a 14C age of 18.8 kaBP, suggesting that the accumulation of the lahar flow deposits was caused by the Kureishibaru pyroclastic eruption (19 kaBP) dated at the surface. The humic soils underlying a pyroclastic flow deposit at depths of 71.60-71.90 m of the USDP-2 borehole gave 14C ages of 27.5 and 29.3 kaBP at the top and bottom layers, respectively. This reveals that the initial activity of Fugendake volcano occurred around 27 kaBP and the collapse of Myokendake volcano around 29 kaBP. © 2004 Elsevier B.V. All rights reserved. 2004 English 0168583X 10.1016/j.nimb.2004.04.104 Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms 223-224 560-567 JNC, Tono Geoscience Center, 959-31 Jorinji, Toki, Gifu 509-5102, Japan; Scottish Univ. Environ. Res. Centre, Scottish Enterprise Technology Park, East Kilbride G75 0QF, United Kingdom; Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, Ibaraki 305-8567, Japan; IDEP, Tono Res. Inst. of Earthquake Sci., 1-47 Yamanouchi, Mizunami, Gifu 509-6132, Japan SPEC. ISS. Boreholes; Carbon; Deposits; Geochronology; Leveling (machinery); Mass spectrometry; Project management; Radioactive elements; Stratigraphy; Volcanoes, Accelerator mass spectrometry (AMS); Pyroclastic eruption; Soil carbon fraction; Unzen volcano, Soils https://www.scopus.com/inward/record.uri?eid=2-s2.0-3943106776&doi=10.1016%2fj.nimb.2004.04.104&partnerID=40&md5=0325a5f97dd37af1578d249fdea5e10b cited By 8 S. Xu H. Hoshizumi Y. Ochiai H. Aoki K. Uto article Nakada200414 Article 2004 English 00168556 Geotimes 49 14 – 15 3 https://www.scopus.com/inward/record.uri?eid=2-s2.0-34447269564&partnerID=40&md5=85473aab8f6a1656514531e93f878510 Cited by: 5 Setsuya Nakada John Eichelberger conference Saito2002633 The International Scientific Drilling Project to drill into the recently erupted magma conduit was initiated in 1999, at the Unzen Volcano, Japan. Since then, two flank core holes and a pilot hole, with a total length of 2.5 km, were drilled successfully. Borehole temperatures were measured using existing Sandia CTDL (Core Tube Data Logger) while coring. The conduit hole, with a very high angle and with about a 1700m-drilled length, is planned to be drilled beginning in January 2003. To identify conduit position and to assure drilling safety, temperature measurements are planned during conduit drilling operations. New memory tools, with 250 °C temperature rating, and possibly 500 °C with MR dewar, are planned to be designed and fabricated to satisfy the project requirements. 2002 English 01935933 Transactions - Geothermal Resources Council 633-637 Boreholes; Project management; Underground temperature measurement; Volcanoes, Memory tools, Rock drilling https://www.scopus.com/inward/record.uri?eid=2-s2.0-0242409780&partnerID=40&md5=cbcd5d237bd7458dbb01854417b0be1a cited By 1 S. Saito J. Henfling article Nakamura20009 The purpose of this study is to learn how to consider setting the borehole and arrangement of the measuring instruments for seismic tomography. For this purpose we made an underground structure model of Unzen Volcano based on the results of previous studies, and simulated the seismic tomography identifying this model with the true structure because one of some plans in "Scientific drilling project at Unzen Volcano" is seismic tomography by using a borehole approaching conduit" We located sources and receivers along the borehole and at the surface, and calculated synthetic seismograms at the receiver positions by a 2-D finite difference method. We measured the first P arrival time in the synthetic seismograms, and constructed the observational equation for seismic tomography. We investigated the solution of this equation by the Singular Value Decomposition (SVD) technique. We found we can consider borehole location and arrangement of sources and receivers through such a simulation by Singular values and eigenvalue that got in this way. 2000 Japanese 13480545 Science Reports of the Kyushu University, Department of Earth and Planetary Sciences 21 9-18 1 array; crosshole seismic method; seismic tomography https://www.scopus.com/inward/record.uri?eid=2-s2.0-13844276804&partnerID=40&md5=9d0974859a0f4531f0e6f1b20fd7f528 cited By 0 M. Nakamura T. Hayashida H. Takenaka H. Shimizu S. Suzuki article Kagiyama199935 The resistivity structure of Unzen Volcano has been revealed by extensive magnetotelluric surveys since the first eruption on November 17, 1990. This structure comprises a highly resistive surface layer, a low-resistive second layer at several hundred meters depth, interpreted as a water-saturated layer, a resistive third layer, and a low-resistive fourth layer at 10 km depth, possibly related to the deep magmatic activity. The structure has influenced the volcanic activity of Unzen. This activity was characterized by a series of dramatic changes in eruption type: a minor phreatic eruption on November 17, 1990; phreatic eruptions after February 12, 1991, preceded by several weeks of volcanic tremor; phreatomagmatic eruptions after April 9, and dome effusion beginning May 19, 1991. This paper presents a hypothesis in which the top of the magma column rose about 20 m/day, reached the base of the water-saturated layer at the end of January, 1991, and approached the upper boundary of this layer on April 9. Thus, the temporal change of eruption type and associated phenomena are systematically explained by an interaction between magma and groundwater contained in the saturated layer. Article 1999 English 03770273 10.1016/S0377-0273(98)00120-6 Journal of Volcanology and Geothermal Research 89 35 – 42 1-4 Japan; magmatism; phreatomagmatism; resistivity; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032819102&doi=10.1016%2fS0377-0273%2898%2900120-6&partnerID=40&md5=a5a70f37b9fab80c5f52696ffe614999 Cited by: 58 T. Kagiyama H. Utada T. Yamamoto article Yamashina199973 Using a pair of old and new photographs taken at the same location, a method named as a time-differential stereoscopy is successfully applied to detect visually the deformation at Unzen volcano, Japan. On September 6, 1992, gradual movement of a lava lobe was visible in a stereo image as relief surrounded by immobile areas. In this case, accelerated movement of a lava block was detected immediately before the time of its collapse, which resulted in the occurrence of a pyroclastic flow. In November 1994, growth of a lava spine was also measured with time-differential stereoscopy. A possible fluctuation of the growth rate might have correlated with an abnormal oscillation of tilt, with a period of about 40 h. This convenient photographic method is recommended for various occasions to detect volcanic and any other deformations as a supplement to precise instrumental measurements. Article 1999 English 03770273 10.1016/S0377-0273(98)00124-3 Journal of Volcanology and Geothermal Research 89 73 – 80 1-4 Japan; crustal deformation; lava flow; stereo image; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032876063&doi=10.1016%2fS0377-0273%2898%2900124-3&partnerID=40&md5=bfd71a350c11e740723e77dd2671ceaa Cited by: 22 Ken'Ichiro Yamashina Takeshi Matsushima Shiro Ohmi article Chen1999243 The magma generation at Unzen volcano may be considered as the product of crustal material mixed with mantle magma accompanied by fractional crystallization (AFC). The magma in the Unzen volcano is estimated to consist of about 50-80% of residual magma (F) and about 30-70% assimilated crustal material (A) relative to the original magma. Concerning the 1991-1995 eruption, it is estimated that the magma formed as the result of mixing of about 50-60% crustal material and about 55-65% of residual magma. An alternative magma eruption model for the 1991-1995 eruption is proposed here. In the early stage, the isotopic characteristics of 1991 eruption are defined by AFC process in the deeper magma chamber. Later, the magma ascended through the conduit and quiescently stayed for a long time in a shallow reservoir before eruption. The minerals continuously crystallized as phenocrysts especially at the chilled top and outer margin in the shallow chamber. The crystallized phenocryst mush was reworked into the central part of the magma chamber by means of magma convection and rapid magma ascent. Therefore, the reaction between phenocrysts and melt occurs only in internal chemical disequilibrium in the magma chamber. In contrast, the isotopic compositions of the original magma shall be little influenced by the above processes throughout its eruptive history. The 1991-1995 eruptive rocks of the Unzen volcano show their characteristics in Sr and Nd isotopic values independent of their two previous eruptions. However, the isotopic values of early eruptive product could represent the original magma value. This result also supports the previous work of Chen et al. (1993) [Chen, C.H., DePaolo, D.J., Nakada, S., Shieh, Y.N., 1993. Relationship between eruption volume and neodymium isotopic composition at Unzen volcano. Nature 362, 831-834], that suggested the εNd of early or precursory eruptive products could be a qualitative indicator of the maximum size of a continuing or impending eruption. Article 1999 English 03770273 10.1016/S0377-0273(99)00002-5 Journal of Volcanology and Geothermal Research 89 243 – 253 1-4 Japan; isotopic analysis; magma chemistry; phenocryst; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032819439&doi=10.1016%2fS0377-0273%2899%2900002-5&partnerID=40&md5=94ddac5b1070c812d614c2ae71119b38 Cited by: 20 Chang-Hwa Chen Setsuya Nakada Yuch-Ning Shieh Donald J. DePaolo article Fujii1999159 Large-scale collapse of a dacite dome in the late afternoon of 15 September 1991 generated a series of pyroclastic-flow events at Unzen Volcano. Pyroclastic flows with a volume of 1 X 106 m3 (as DRE) descended the northeastern slope of the volcano, changing their courses to the southeast due to topographic control. After they exited a narrow gorge, an ash-cloud surge rushed straight ahead, detaching the main body of the flow that turned and followed the topographic lows to the east. The surge swept the Kita-Kamikoba area, which had been devastated by the previous pyroclastic-flow events, and transported a car as far as 120 m. Following detachment, the surge lost its force after it moved several hundred meters, but maintained a high temperature. The deposits consist of a bottom layer of better-sorted ash (unit 1), a thick layer of block and ash (unit 2), and a thin top layer of fall-out ash (unit 3). Unit 2 overlies unit 1 with an erosional contact. The upper part of unit 2 grades into better-sorted ash. At distal block-and-ash flow deposits, the bottom part of unit 2 also consists of better-sorted ash, and the contact with the unit 1 deposits becomes ambiguous. Video footage of cascading pyroclastic flows during the 1991-1995 eruption, traveling over surfaces without any topographic barriers, revealed that lobes of ash cloud protruded intermittently from the moving head and sides, and that these lobes surged ahead on the ground surface. This fact, together with the inspection by helicopter shortly after the events, suggests that the protruded lobes consisted of better-sorted ash, and resulted in the deposits of unit 1. The highest ash-cloud plume at the Oshigadani valley exit, and the thickest deposition of fall-out ash over Kita-Kamikoba and Ohnokoba, indicate that abundant ash was also produced when the flow passed through a narrow gorge. In the model presented here, the ash clouds from the pyroclastic flows were composed of a basal turbulent current of high concentration (main body), an overriding and intermediate fluidization zone, and an overlying dilute cloud. Release of pressurized gas in lava block pores, due to collisions among blocks and the resulting upward current, caused a zone of fluidization just above the main body. The mixture of gas and ash sorted in the fluidization zone moved ahead and to the side of the main body as a gravitational current, where the ash was deposited as surge deposits. The main body, which had high internal friction and shear near its base, then overran the surge deposits, partially eroding them. When the upward current of gas (fluidization) waned, better-sorted ash suspended in the fluidization zone was deposited on block-and-ash deposits. In the distal places of block-and-ash deposits, unit 2 probably was deposited in non-turbulent fashion without any erosion of the underlying layer (unit 1). Article 1999 English 03770273 10.1016/S0377-0273(98)00130-9 Journal of Volcanology and Geothermal Research 89 159 – 172 1-4 Japan; ash flow; pyroclastic flow; volcanic ash; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032840272&doi=10.1016%2fS0377-0273%2898%2900130-9&partnerID=40&md5=de8bba4cdb31ef25adbb1bb33d1f6dd3 Cited by: 75 Toshitsugu Fujii Setsuya Nakada article Jousset1999255 Usu volcano (Hokkaido, Japan) is a dacitic volcano, known for its high production rate of lava domes and crypto-domes. It is thus a good target to study processes of volcanic dome evolution (upheaval and/or relaxation). We carried out repeated GPS and microgravity surveys on the three most recent domes of Mt. Usu (1910: Meiji Shinzan; 1943-1945: Showa-Shinzan and 1977-1982: Usu-Shinzan). The repeat period was 1 to 2 months and extended from October 1996 to June 1997. We also compare new data with results from former studies. More than 20 years after the start of Usu-Shinzan dome growth, there is still subsidence at a maximum rate of about 7 to 8 cm/year. The reasons for this subsidence are discussed. Repeated gravity surveys revealed an increase of gravity on the domes (about 60 ± 10 microgal/year for Usu-Shinzan, about 15 microgal at Showa-Shinzan and 10 to 20 microgal for Meiji-shinzan); this gravity increase exceeds that expected due to subsidence. We discuss and interpret the excess gravity change in terms of a density increase in the edifice, caused by a combination of processes (contraction of the edifice, water level change, devesiculisation, cooling and magma intrusion). Quantification of these processes at Usu volcano may help to understand the processes of evolution at domes on other volcanoes such as Merapi (Indonesia), Unzen (Japan) or Montserrat (West Indies). Article 1999 English 03770273 10.1016/S0377-0273(99)00003-7 Journal of Volcanology and Geothermal Research 89 255 – 273 1-4 Japan; crustal deformation; gravity anomaly; lava dome; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032842082&doi=10.1016%2fS0377-0273%2899%2900003-7&partnerID=40&md5=c15bf281c2d8ee51355a006c36b3ddc1 Cited by: 22 Philippe Jousset Hiromu Okada article Nakada1999173 Effusive eruption of dacite magma (2.1 X 108 m3) during 1991-1995 formed a lava dome at the summit of Unzen Volcano, Japan. The effusion rate was highest at the beginning, 4.0 X 105 m3/day (4.6 m3/s), and decreased roughly with time, to almost zero before this pattern was repeated with a second pulse of magma supply. The whole-rock chemistry of lavas shows significant variation attributable to variations in phenocryst abundance; the more mafic, the more abundant the phenocrysts. The pattern of chemical variation with time shows some difference from that of the effusion rate. All phenocrysts in dacite (plagioclase, hornblende, biotite, quartz and magnetite) show evidence of disequilibrium with melt. Although a glomerophyric aggregation of phenocrysts suggests coexistence with each other, phenocrysts are isotopically heterogeneous from species to species. The calculated initial melt composition was rhyodacite, and was nearly constant throughout the activity. In contrast, the bulk phenocryst population is andesite. A model explaining the textures and the isotopic heterogeneity is the capture of diorite fragments (or xenocrysts) by parental rhyodacite magma. It is suggested that, when effusion rate was high, less viscous crystal-poor magma exited from the reservoir. Groundmass glass and plagioclase microlite rims show temporal chemical variations correlating with the effusion rate; the higher the effusion rate, the more evolved the compositions. Groundmass crystallinity increased with decreasing effusion rate; from 33% to 50%. Textures in dome lavas suggest that groundmass crystallization had been mostly completed when magma reached the conduit top. The Fe-Ti oxide temperature (880-780°C) was low when the crystallinity was high. Micropumice erupted before dome growth provided a sample recording magmatic foam in the conduit. Porosity of dome lavas was lower at lower effusion rates. Collapse of foam magma and simultaneous escape of volatiles through the conduit top were probably responsible for the accompanying low-frequency earthquakes. Phenocrysts were broken and the breakdown rims on hornblende phenocrysts were torn off during collapse and successive compaction. When effusion waned, degassing and the resultant crystallization proceeded more completely, so that the magma became too viscous to flow in the conduit top and behaved as a plug, resulting in a temporary halt of effusion. In turn, groundmass crystallization in magma below the plug increased excess pressure in the upper parts of conduit due to slow cooling. The plug was scavenged when rising excess pressure overcame its effective strength. Then, the second pulse of magma supply began. Strong endogenous growth and extrusion of a lava spine in the later stage probably occurred for the same reason. Article 1999 English 03770273 10.1016/S0377-0273(98)00131-0 Journal of Volcanology and Geothermal Research 89 173 – 196 1-4 Japan; dacite; petrology; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032818582&doi=10.1016%2fS0377-0273%2898%2900131-0&partnerID=40&md5=e81ae59e4f174edcd0f3bc72bff8c315 Cited by: 178 Setsuya Nakada Yoshinobu Motomura article Venezky1999213 A dacitic magma (64.5 wt.% SiO2), a mixture of phenocryst-rich rhyodacite and an aphyric mafic magma, was erupted during the recent 1991-1995 Mount Unzen eruptive cycle. The experimental and analytical results of this study reveal additional details about conditions in the premixing and postmixing magmas, and the nature of the mixing process. The preeruption rhyodacitic magma was at a temperature of 790 ± 20°C according to Fe-Ti oxide phenocryst cores, and at a depth of 6 to 7 km (160 MPa) according to Al-in-hornblende geobarometry. The mafic magma that mixed with the rhyodacite is found as andesitic (54 to 62 wt.% SiO2) enclaves in the erupted magma and was essentially aphyric when intruded. Phase equilibria indicate that an aphyric andesite at 160 MPa is >1030°C (H2O-saturated) and possibly as high as 1130°C (2 wt.% H2O). The composition of the rhyodacite which was mixed with the andesite is estimated to lie between 67 and 69 wt.% SiO2. Using these compositions and temperatures, the temperature of the Unzen magma after mixing is estimated to be at least 850°to 870°C. The groundmass Fe-Ti oxide microphenocrysts and those in pargasite-bearing reaction zones around biotite phenocrysts both give 890 ± 20°C temperatures; the oxide-oxide contacts give temperatures of 910 ± 20°C. The 900 ± 30°C postmixing temperatures are consistent with phase-equilibria experiments which show that the magma was not above 930°C at 160 MPa. Our Fe-Ti oxide reequilibration experiments suggest that the mixing of the two magmas began within a few weeks of the eruption, which is a shorter time than is calculated using available diffusion data. There is also evidence that some mixing took place much closer to the time of extrusion based on the presence of unrimmed biotite phenocrysts in the magma. Article 1999 English 03770273 10.1016/S0377-0273(98)00133-4 Journal of Volcanology and Geothermal Research 89 213 – 230 1-4 Japan; dacite; geobarometry; magma chemistry; petrology; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032856599&doi=10.1016%2fS0377-0273%2898%2900133-4&partnerID=40&md5=09f16d72165e8c1aba8c5c851cd1cff8 Cited by: 171 Dina Y. Venezky Malcolm J. Rutherford article Nakada19991 Following 198 years of dormancy, a small phreatic eruption started at the summit of Unzen Volcano (Mt. Fugen) in November 1990. A swarm of volcano-tectonic (VT) earthquakes had begun below the western flank of the volcano a year before this eruption, and isolated tremor occurred below the summit shortly before it. The focus of VT events had migrated eastward to the summit and became shallower. Following a period of phreatic activity, phreatomagmatic eruptions began in February 1991, became larger with time, and developed into a dacite dome eruption in May 1991 that lasted approximately 4 years. The emergence of the dome followed inflation, demagnetization and a swarm of high-frequency (HF) earthquakes in the crater area. After the dome appeared, activity of the VT earthquakes and the summit HF events was replaced largely by low-frequency (LF) earthquakes. Magma was discharged nearly continuously through the period of dome growth, and the rate decreased roughly with time. The lava dome grew in an unstable form on the shoulder of Mt. Fugen, with repeating partial collapses. The growth was exogenous when the lava effusion rate was high, and endogenous when low. A total of 13 lobes grew as a result of exogenous growth. Vigorous swarms of LF earthquakes occurred just prior to each lobe extrusion. Endogenous growth was accompanied by strong deformation of the crater floor and HF and LF earthquakes. By repeated exogenous and endogenous growth, a large dome was formed over the crater. Pyroclastic flows frequently descended to the northeast, east, and southeast, and their deposits extensively covered the eastern slope and flank of Mt. Fugen. Major pyroclastic flows took place when the lava effusion rate was high. Small vulcanian explosions were limited in the initial stage of dome growth. One of them occurred following collapse of the dome. The total volume of magma erupted was 2.1 x 108 m3 (dense-rock-equivalent); about a half of this volume remained as a lava dome at the summit (1.2 km long, 0.8 km wide and 230-540 m high). The eruption finished with extrusion of a spin endogenous dome top. Several monitoring results convinced us that the eruption had come to an end: the minimal levels of both seismicity and rockfalls, no discharge of magma, the minimal SO2 flux, and cessation of subsidence of the western flank of the volcano. The dome started slow deformation and cooling after the halt of magma effusion in February 1995. Article 1999 English 03770273 10.1016/S0377-0273(98)00118-8 Journal of Volcanology and Geothermal Research 89 1 – 22 1-4 Japan; earthquake; lava dome; pyroclastic flow; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032840270&doi=10.1016%2fS0377-0273%2898%2900118-8&partnerID=40&md5=f1d1e57c93d8235872c64299815a2925 Cited by: 274 Setsuya Nakada Hiroshi Shimizu Kazuya Ohta article Miller1999275 Holocene eruptions from Mount Dutton, a small Late Quaternary volcano near the tip of the Alaska Peninsula, bear strong physical and petrologic similarities to the 1990-1995 Unzen Fugendake eruption in Japan. The volcano had a protracted phase of effusive calcalkaline andesitic (54-59 wt.% SiO2) cone-building in the late Pleistocene followed by an abrupt switch to more silicic (~ 65 wt.% SiO2) lavas, emplaced as a central summit cluster of steep-sided domes beginning in the early Holocene. The flanks of the volcano are mantled by pyroclastic flows, debris flows, and talus formed as a result of gravitational dome collapse. Disequilibrium mineral assemblages, including coexisting quartz and olivine in eruptive episodes ranging from the initial cone-building basaltic andesite lavas to the latest Holocene dacite domes, suggest extensive magma mixing. In addition, up to meter-sized, pillow-like cognate mafic enclaves of hornblende + plagioclase + glass are common in the latest of the summit dacite domes. Mineralogical evidence and bulk chemical data indicate the enclaves represent a high-alumina basalt parent with variable and subordinate reservoir contaminant, and the host lava is reservoir magma with variable and subordinate basaltic contaminant. Mount Dutton's history and petrology can be interpreted as reflecting the monotonous repetitive intrusion of mantle-derived mafic magma into a silicic crystal-rich crustal reservoir. During the Holocene, these injections resulted in the extrusion of partially crystallized, viscous, 'sticky' central domes which typically failed by collapse resulting in small volume Merapi-type flowage deposits. We speculate that slow introduction of mafic magma into the silicic chamber leads both to enclave formation and to the effusive eruption style. Mount Dutton volcano experienced severe shallow earthquake swarms in 1984, 1988, and to a lesser extent in 1991; although none of these swarms resulted in an eruption, their epicenter distribution and volcanic-tectonic character indicate they recorded the movement of magma at shallow depth beneath the volcano. The lessons of Unzen and Montserrat suggest that, despite limited tephra production, these small volcanic centers with central dome complexes present a serious hazard to life and property. Article 1999 English 03770273 10.1016/S0377-0273(99)00004-9 Journal of Volcanology and Geothermal Research 89 275 – 301 1-4 Japan; United States; Holocene; lava dome; magma chemistry; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032867234&doi=10.1016%2fS0377-0273%2899%2900004-9&partnerID=40&md5=3651f2866a2b829449ec6df9e86dd861 Cited by: 36 T.P. Miller D.G. Chertkoff J.C. Eichelberger M.L. Coombs article Yamashina199965 Ground temperature associated with eruptive activity of Unzen Volcano, southwestern Japan, was observed in a cave about 680 m west of the central vent. Based on the data during 1991-1996, eliminating the effects of seasonal change, the temperature rose to the highest level probably around the first half of 1992. Hereafter the temperature decreased gradually year by year at least up to the autumn of 1996, beyond the level recovered at the beginning of the lava extrusion in May 1991. Although it is not necessarily conclusive, the present observation suggests a possible rise in ground temperature prior to the commencement of the first phreatic eruption in November 1990. If so, a careful observation may help to predict future eruptions by detecting a precursory rise of the ground temperature in this volcano. Article 1999 English 03770273 10.1016/S0377-0273(98)00123-1 Journal of Volcanology and Geothermal Research 89 65 – 71 1-4 Japan; prediction; surface temperature; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032817285&doi=10.1016%2fS0377-0273%2898%2900123-1&partnerID=40&md5=7422e1107518bda6bb31ee9593982175 Cited by: 4 Ken'Ichiro Yamashina Takeshi Matsushima article Kaneko199957 We analyse shortwave infrared thermal data of the phase 1 eruption of Unzen Volcano (Japan) extracted from eight nighttime Thematic Mapper (TM) images taken from the Landsat 5 satellite between October 1991 and November 1992. We identify two discrete regions of the dome that were heated to high temperature by the ongoing eruptive activity; a fumarolically heated region and an area associated with the effusion of new lava. We concentrate analysis on the fumarolically heated region and investigate the relationships between parameters derived from the infrared radiance data and the nature of the fumarolic gas and magma fluxes. Temporal variations in the parameters derived from the radiance data closely follow those observed in the measured rate of magma effusion. The positive correlation observed between the fumarolically driven shortwave infrared flux and the magma discharge rate (r2 = 0.64) indicates that degassing occurred efficiently and in proportion to the amount of magma supplied. Over our monitoring period, the data suggest that gas accumulation within the edifice did not occur, this conclusion agreeing with a previous finding obtained using correlation spectrometer (COSPEC) analysis of SO2 flux rates. A positive correlation (r2 = 0.56) was also found between the mean radiance of the pixels in the fumarolically heated region and the overall size of that region. This suggests a potential mechanism whereby, when gas pressure within the edifice increased, excess gas escaped through additional pathways to the surface as well through an increased flux at the main fumarolic vents. Article 1999 English 03770273 10.1016/S0377-0273(98)00122-X Journal of Volcanology and Geothermal Research 89 57 – 64 1-4 Japan; fumarole; Landsat thematic mapper; magma; volcanic eruption; volcanic gas https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032839903&doi=10.1016%2fS0377-0273%2898%2900122-X&partnerID=40&md5=8c1be40d02eabeff2a12d67b21b535cf Cited by: 29 Takayuki Kaneko Martin J. Wooster article Watanabe1999113 Fugen-dake, the main peak of Unzen volcano, began to erupt on 17 November 1990 after 198 years of dormancy. Following a period of steam-dominated tephra eruptions, a new lava dome appeared at the bottom of Jigokuato Crater in the summit region on 20 May 1991. Non-hydrated vesiculated glass was detected in the precursory tephra eruptions, beginning 12 February 1991. Determination of whether glass pyroclasts are hydrated or not appears to be an effective means of ascertaining whether the tephra contains juvenile material from ascending magma. The detection of juvenile pyroclasts at Fugen-dake more than 3 months before the appearance of the lava dome suggests that monitoring of early tephra emissions is an effective way to help forecast impending magmatic eruptions. Article 1999 English 03770273 10.1016/S0377-0273(98)00127-9 Journal of Volcanology and Geothermal Research 89 113 – 121 1-4 Japan; lava dome; magma chemistry; volcanic eruption; volcanic glass https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032838558&doi=10.1016%2fS0377-0273%2898%2900127-9&partnerID=40&md5=ff2da1b9b40b686b38fb17451dd7c79d Cited by: 23 Koichiro Watanabe Tohru Danhara Kazunori Watanabe Kunihisa Terai Tohru Yamashita article Sato1999197 Pargasite commonly occurs in the dacitic groundmass of the 1991-1995 eruption products of Unzen volcano. We described the occurrence and chemical compositions of amphibole in the dacite, and also carried out melting experiments to determine the low-pressure stability limit of amphibole in the dacite. The 1991-1995 ejecta of the Unzen volcano show petrographic evidence of magma mixing, such as reverse compositional zoning of plagioclase and amphibole phenocrysts, and we used a groundmass separate as a starting material for the experiments. Reversed experiments show that the maximum temperature for the crystallization of amphibole is 930°C at 196 MPa, 900°C at 98 MPa, and 820°C at 49 MPa. Compared with the experimental results on the Mount St. Helens dacite, present experiments on the Unzen dacitic groundmass show that amphibole is stable to pressures ca. 50 MPa lower at 850°C. Available Fe-Ti oxide thermometry indicates the crystallization temperature of the groundmass of the Unzen dacite to be 880 ± 30°C, suggesting that the groundmass pargasite crystallized at > 70 MPa, corresponding to a depth of more than 3 km in the conduit. The chlorine content of the groundmass pargasite is much lower than that of phenocrystic magnesiohornblende in the 1991-1995 dacite of Unzen volcano, indicating that vesiculation/degassing of magma took place before the crystallization of the groundmass pargasite. The present study shows that the magma was water oversaturated and that the degassing of magma along with magma mixing caused crystallization of the groundmass amphibole at depths of more than 3 km in the conduit. Article 1999 English 03770273 10.1016/S0377-0273(98)00132-2 Journal of Volcanology and Geothermal Research 89 197 – 212 1-4 Japan; crystallization; dacite; pargasite; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032868174&doi=10.1016%2fS0377-0273%2898%2900132-2&partnerID=40&md5=4300f1c3eb73e4dcd09f8f4d02da4295 Cited by: 73 Hiroaki Sato Setsuya Nakada Toshitsugu Fujii Michihiko Nakamura Keiko Suzuki-Kamata article Nishi199923 Global positioning system (GPS) measurements made around Unzendake volcano, Kyushu, Japan, since January 1991 have detected ground deformation caused by magma intrusion and lava discharge. In the intermittent phreatic and phreatomagmatic eruption stage, the ground was inflating. After growth of the lava dome and following frequent pyroclastic flows at Unzendake volcano, the ground began deflating. These ground deformations are explained by the inflation and deflation of a Mogi's source model (a point source model) located about 6 km west of the active crater at a depth of 11 km, at an aseismic region. The observed horizontal displacement vectors pointed radially away from the estimated pressure source during inflation and pointed to the pressure source during deflation. The horizontal displacements at the reference GPS station calculated from contraction of the estimated pressure source coincide well with the actual horizontal displacements observed from other GPS baseline systems. These observations validate our estimates for the pressure source. Based on the relation between the deformation volume of the ground surface and the discharged volume of the lava, it is estimated that during the eruption there was magma supply from the deeper portion as well as magma discharge at the crater. Magma is estimated to be supplied to the reservoir at an average rate of 1.1 x 105 m3/day; magma intrusion began in December 1989 at the latest and continued for 1.9 x 103 days. Article 1999 English 03770273 10.1016/S0377-0273(98)00119-X Journal of Volcanology and Geothermal Research 89 23 – 34 1-4 Japan; crustal deformation; GPS; ground motion; lava flow; magmatism; volcanic earthquake; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032840563&doi=10.1016%2fS0377-0273%2898%2900119-X&partnerID=40&md5=f84c7b3e30c9c82e47dcb474eed16107 Cited by: 38 K. Nishi H. Ono H. Mori article Hoshizumi199981 During the past 500 thousand years, Unzen volcano, an active composite volcano in the Southwest Japan Arc, has erupted lavas and pyroclastic materials of andesite to dacite composition and has developed a volcanotectonic graben. The volcano can be divided into the Older and the Younger Unzen volcanoes. The exposed rocks of the Older Unzen volcano are composed of thick lava flows and pyroclastic deposits dated around 200-300 ka. Drill cores recovered from the basal part of the Older Unzen volcano are dated at 400-500 ka. The volcanic rocks of the Older Unzen exceed 120 km3 in volume. The Younger Unzen volcano is composed of lava domes and pyroclastic deposits, mostly younger than 100 ka. This younger volcanic edifice comprises Nodake, Myokendake, Fugendake, and Mayuyama volcanoes. Nodake, Myokendake and Fugendake volcanoes are 100-70 ka, 30-20 ka, and <20 ka, respectively. Mayuyama volcano formed huge lava domes on the eastern flank of the Unzen composite volcano about 4000 years ago. Total eruptive volume of the Younger Unzen volcano is about 8 km3, and the eruptive production rate is one order of magnitude smaller than that of the Older Unzen volcano. Article 1999 English 03770273 10.1016/S0377-0273(98)00125-5 Journal of Volcanology and Geothermal Research 89 81 – 94 1-4 Japan; historical perspective; lava dome; pyroclastic flow; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032842080&doi=10.1016%2fS0377-0273%2898%2900125-5&partnerID=40&md5=a9881a8328525b14c0957e14da29d627 Cited by: 75 Hideo Hoshizumi Kozo Uto Kazunori Watanabe article Ui1999123 Processes generating block and ash flows by gravitational dome collapse (Merapi-type pyroclastic flow) were observed in detail during the 1990-1995 eruption of Unzen volcano, Japan. Two different types were identified by analysis of video records and observations during helicopter flights. Most of the block and ash flows erupted during the 1991-1993 exogenous dome growth stage initially involved crack propagation due to cooling and flowage of the dome lava lobes. The mass around the crack became unstable, locally decreasing in tensile strength. Finally, a slab separated from the lobe front, fragmented progressively from the base to the top within a few seconds, and became a block and ash flow. Rock falls immediately followed, in response to local instability of the lobe front. Clasts in these rock falls fragmented and merged with the preceding flow. In contrast, block and ash flows during the endogenous dome growth stage in 1994 were generated due to local bulge of the dome. Unstable lava blocks collapsed and subsequently fragmented to produce block and ash flows. Article 1999 English 03770273 10.1016/S0377-0273(98)00128-0 Journal of Volcanology and Geothermal Research 89 123 – 137 1-4 Japan; ash flow; lava dome; volcanic ash; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032865221&doi=10.1016%2fS0377-0273%2898%2900128-0&partnerID=40&md5=b24563729f0b63a2d9d96184149ca11d Cited by: 92 Tadahide Ui Norimichi Matsuwo Mari Sumita Akihiko Fujinawa article Yamashina199943 Tilt observations at FG1 station located about 680 m west of the central crater of Unzen volcano, southwestern Japan, revealed details about the process of magma ascent during the mid-May 1991 crisis, just before the appearance of a lava dome. Crustal deformations measured during this period can be interpreted by a combination of upward growth of a buried magma column and lateral intrusion of a dike, modeled by a vertical line source and a planer tensile dislocation in an elastic half space. Marked change in tilt was observed at first in the EW direction at FG1 during May 11-14, suggesting the ascent of a magma column with a diameter of about 40 m from about 300 m to 160 m in depth beneath the central crater. After the interruption of the rise of the magma column, magma began to intrude laterally as a dike on May 15 toward approximately the N80°W direction. This resulted in a large tilt change essentially in the NS component at FG1. The horizontal extent of the dike might have exceeded 400 m in a few days with a thickness of about 6 m. On May 17, the magma column started to rise again, probably because the impediment to magma ascent was fractured by the growth of the dike. The top of the magma column finally reached to the crater bottom probably on May 19, and a new lava dome was actually observed on May 20. After which, the remarkable upward tilt to the south at FG1 due to the dike intrusion decreased rapidly. The deformation after May 20 can be interpreted by a gradual increase in the thickness of the dike up to 13 m by the end of May 1991. Although large errors are inevitable in estimated values because of a lack of sufficient data, the present results confirm the importance of making continuous observations of crustal deformation near the summit areas of active volcanoes in order to clarify the underground processes of magma movement leading to eruptions. Article 1999 English 03770273 10.1016/S0377-0273(98)00121-8 Journal of Volcanology and Geothermal Research 89 43 – 55 1-4 Japan; crustal deformation; dacite; lava dome; tilt; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032817016&doi=10.1016%2fS0377-0273%2898%2900121-8&partnerID=40&md5=57109987da8a64a63b068a28099e6f1d Cited by: 22 Ken'Ichiro Yamashina Hiroshi Shimizu article Watanabe199995 Fugen-dake, the main peak of Unzen Volcano, began a new eruption sequence on November 17, 1990. On May 20, 1991, a new lava dome appeared near the eastern edge of the Fugen-dake summit. Small-scale, 104-106 m3 in volume, Merapi-type block and ash flows were frequently generated from the growing lava dome during May-June, 1991. These pyroclastic flows were accompanied by co-ignimbrite ash plumes that deposited ash-fall deposits downwind of the volcano. Three examples of co-ignimbrite ash-fall deposits from Unzen pyroclastic flows are described. The volume of fall deposits was estimated to be about 30% by volume of the collapsed portions of the dome that formed pyroclastic flows. This proportion is smaller than that described for other larger co-ignimbrite ash-fall deposits from other volcanoes. Grain size distributions of the Unzen co-ignimbrite ash-fall deposits are bi-modal or tri-modal. Most ashes are finer than 4 phi and two modes were observed at around 4-7 phi and 9 phi. They are composed mainly of groundmass fragments. Fractions of another mode at around 2 phi are rich in crystals derived from dome lava. Some of the fine ash component fell as accretionary lapilli from the co-ignimbrite ash cloud indicating either moisture or electrostatic aggregation. We believe that the co-ignimbrite ash of Unzen block and ash flows were formed by the mechanical fracturing of the cooling lava blocks as they collapsed and moved down the slope. These ashes were entrained into the convective plumes generated off the tops of the moving flows. Article 1999 English 03770273 10.1016/S0377-0273(98)00126-7 Journal of Volcanology and Geothermal Research 89 95 – 112 1-4 Japan; ash flow; ignimbrite; pyroclastic flow; volcanic ash; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032840564&doi=10.1016%2fS0377-0273%2898%2900126-7&partnerID=40&md5=fd9ef553e578da73aa28de610fa49b33 Cited by: 30 Kazunori Watanabe Koji Ono Keiichi Sakaguchi Akira Takada Hideo Hoshizumi article Yoshida1999303 In explosive magma eruptions, magma ascends through a conduit as a Poiseuille flow at depth, and gas exsolves gradually and expands as the pressure decreases (bubbly flow regime). When the volume fraction of gas becomes sufficiently large, liquid or solid parts of magma fragment into droplets or ashes, and the flow dynamics becomes governed by the gas phase (gas-ash flow regime). We propose a new flow regime, which we call fractured-turbulent flow regime, between the bubbly flow regime and the gas-ash flow regime. In the new regime, both liquid magma and gas are continuous phases. The high connectivity of the two phases allows the relative velocity between them to increase significantly. We present one sample calculation, which displays basically explosive characteristics, but has three features distinct from previous models. The explosive characteristics are manifested as the fragmentation of the magma and the high speed jet that issues from the vent. The first distinct feature is a nearly lithostatic pressure distribution, which results from the increase of the height of the fragmentation surface. The second one is the atmospheric pressure at the vent; the flow is not choked. The third one is that the relative velocity between the gas and the ash is large at the vent despite the large interaction force between the two phases. The large relative velocity is established in the fractured-turbulent regime, and is maintained in the subsequent gas-ash flow regime. Article 1999 English 03770273 10.1016/S0377-0273(99)00005-0 Journal of Volcanology and Geothermal Research 89 303 – 315 1-4 explosive volcanism; magmatism; two phase flow; volcanic eruption https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032839904&doi=10.1016%2fS0377-0273%2899%2900005-0&partnerID=40&md5=ff9a8c04920b1996658931e8c7f701c7 Cited by: 32 Shigeo Yoshida Takehiro Koyaguchi article Kusakabe1999231 Water contents and hydrogen isotopic ratios were determined for blocks from pyroclastic flow deposits, and bread-crust bombs and blocks from the 1991 Vulcanian eruptions of Unzen volcano, Japan. Groundmass water contents and δD values of samples were calculated by subtracting the contribution of major hydrous minerals (hornblende and biotite) from the bulk rock analyses, and range from 0.1 to 0.5 wt.% and -83 to -49‰, respectively. The samples do not show a systematic H2O-δD relationship, although the block samples tend to have lower δD values than the bomb samples. The non-systematic H2O-δD relationship is likely a result of near surface, kinetically-controlled gas loss. High viscosity of this magma would hinder attainment of hydrogen isotopic equilibrium between exsolved vapor and melt in the final degassing stage. The near surface degassing, however, was accompanied by kinetic fractionation resulting in enrichment of deuterium in the final products as exemplified by bread-crust bombs with high H2O-low δD margins and low H2O-high δD cores. Relatively high δD values of the blocks and bombs as well as high temperature volcanic gas (-30 to -35‰) suggest a closed system degassing of an initial water-rich magma (H2O = 6 wt.%) until its water content was reduced to 0.5 wt.%. The pre-eruptive δD value (-46‰) was estimated from the volcanic gas data and D/H analysis of hornblende phenocrysts coupled with assumed isotopic equilibration in the initial hydrous magma. Article 1999 English 03770273 10.1016/S0377-0273(98)00134-6 Journal of Volcanology and Geothermal Research 89 231 – 242 1-4 Japan; degassing; hydrogen isotope; igneous geochemistry; volcanic eruption; water content https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032842081&doi=10.1016%2fS0377-0273%2898%2900134-6&partnerID=40&md5=f23056aa528d17e3e2f1f083eb093004 Cited by: 32 Minoru Kusakabe Hiroaki Sato Setsuya Nakada Toshihiro Kitamura