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Yokoyama, I.
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- PublicationOpen AccessFormation processes of the 1909 Tarumai and the 1944 Usu lava domesin Hokkaido, Japan(2004)
; ;Yokoyama, I.; Higashi 1-17-7-1304, Kunitachi, Tokyo, JapanThe formation of the two particular lava domes in Hokkaido, Japan is described and interpreted mainly from geophysical viewpoints. The 1909 eruption of Tarumai volcano was not violent but produced a lava dome over four days. The growth rate of the dome is discussed under the assumption that the lava flow was viscous and plastic fluid during its effusion. By Hagen-Poiseuille’s Law, the length of the conduit of the lava dome is rather ambiguously determined as a function of viscosity of the magma and diameter of the conduit. The 1944 Usu dome extruded as a parasitic cone of Usu volcano, not in the crater, but in a flat cornfield at the foot of the volcano. From the beginning to the end for more than 17 months, seismometric and geodetic observations of the dome activity were carried out by several pioneering geophysicists. Utilizing their data, pseudo growth curves of the dome at each stage can be drawn. The lava ascended rather uniformly, causing uplift of the ground surface until half-solidified lava reached the surface six months after the deformation began. Thereafter, the lava dome added lateral displacements and finally achieved its onion structure. These two lava domes are of contrasting character, one is andesitic and formed quickly while the other is dacitic and formed slowly, but both of them behaved as viscous and plastic flows during effusion. It is concluded that both the lava domes formed by uplift of magma forced to flow through the conduits, analogous to squeezing toothpaste out of a tube.172 337 - PublicationOpen AccessAnomalous crustal movements with low seismic efficiency - Campi Flegrei, Italy and some examples in Japan(2002)
; ; ;Yokoyama, I.; Higashi 1-17-7-1304, Kunitachi, Tokyo, Japan ;Nazzaro, A.; Viale Italia 419, Avellino, Italy; Campi Flegrei is a unique volcanic region located near Naples, Italy. Anomalous crustal movements at Pozzuoli in Campi Flegrei have been documented since the Roman period. The movements were gradual and have continued to the present, occasionally accompanying swarms of local earthquakes and volcanic eruptions. Generally the movements proceed with low seismicity. After the 1538 eruption of Monte Nuovo, Pozzuoli had subsided monotonously, but it changed to uplift abruptly in 1969. The uplift accelerated in 1983 and 1984 reaching more than 2 m, and thereafter began to subside. Many discussions of this event have been published. In Japan, we have examples of deformations similar to those at Campi Flegrei, mainly in volcanic areas, and rarely in non-volcanic areas. The former includes Iwojima, Miyakejima and Aira caldera while the latter is represented by Cape Omaezaki. Iwojima is a volcano island, and its secular uplifts since the 18th century are recognized as an unusual event. Miyakejima volcano and Aira caldera exhibited anomalous movements with low seismicity after their eruptions. Cape Omaezaki is not situated in volcanic zone but near a subduction zone, and gradually and continuously subsides as a precursor to a large earthquake. In such cases as Campi Flegrei and the Japanese localities, we would question whether the deformations are accompanied by normal seismicity or low seismicity. To examine quantitatively the relationship between seismicity and related deformation, seismic efficiency is generally useful. The crustal deformations in all the regions cited above are characterized by exceptionally low seismic efficiencies. In the present paper, the deformations at Pozzuoli and Iwojima are mainly described and a comparative discussion among these and other localities in Japan is supplemented. It is concluded that such anomalous phenomena in volcanic areas are attributable to peculiar rheological aspects of the material composing the local upper crust, and the deformation in a non-volcanic area is of tectonic origin.193 613 - PublicationOpen AccessThe largest magnitudes of earthquakes associated with some historical volcanic eruptions and their volcanological significance(2001-10)
; ;Yokoyama, I.; Higashi 1-17-7-1304, Kunitachi, Tokyo, JapanWe know several reports of earthquake swarms associated with volcanic eruptions in the 19th century or older periods when seismographs were not yet available. Even if we have no seismographs, the largest magnitudes of earthquakes can be estimated by the maximum distances of perceptibility which are determined by reports of felt shocks or by records of earthquake movements at various distances from the origins. For example, the largest magnitudes of the earthquake swarms associated with the 1815 eruption of Tambora is estimated at 7 by the reports of felt shocks from three sites and that of the 1883 eruption of Krakatau is estimated at 5 by examination of magnetograms in place of seismograms. The magnitude of the 7 class is exceptionally large as volcanic origin, but we know a few examples besides Tambora. The magnitude 5 of the Krakatau eruption is rather small contrary to our expectation, and implies that crustal stresses had not accumulated much at the Krakatau area to cause larger earthquakes. The earthquake magnitudes associated with volcanic eruptions are not necessarily proportional to explosion magnitudes or volume of volcanic ejecta, and may have a volcanological significance. Such volcanic earthquakes may be closely related to readjustments of tectonic stresses caused by magma movements or phase transitions of magmatic material beneath and around volcanoes, and may be called magmatotectonic earthquakes.186 553 - PublicationRestrictedCommon geophysical characteristics of Campi Flegrei, Rabaul and Usu: Three volcanic events(2011)
; ; ;Berrino, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Yokoyama, I.; Volcanogenic deformations during periods of unrest are related to volcanic seismicity in various ways. Magmas or geothermal fluids intrude beneath volcanoes and cause deformations at the surface gradually or rapidly. Mechanical energies of the intrusions are converted to deformation energy, earthquakes, and also explosions under certain circumstances. Partition among the three kinds of energies provides information of the internal processes and yields a clue to their origin. From the above standpoint, deformations accompanying seismicity at Campi Flegrei, Rabaul and Usu are discussed with the aid of published data. To quantitatively correlate the deformations and the seismicity, we discuss the time-derivatives of uplift and release of seismic energy, which are energetically interrelated. The correlation between them is moderate at Campi Flegrei, somewhat higher at Rabaul and high at Usu, but the data sets are not always equal in quality. The deformation volumes are also different among the three volcanoes. In order to standardize the volumes, seismic energies released by unit volume of each deformation are compared. The specific seismic energy is found to increase from Campi Flegrei through Rabaul to Usu. Such different behavior in seismodeformations among the three volcanoes is interpreted as differences in the mechanism of volcanic activity, and in physical properties of the mediums involved.222 31 - PublicationOpen AccessCommon geophysical characteristics of Campi Flegrei, Rabaul and Usu: Three volcanic events(2011)
; ; ;Berrino, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Yokoyama, I.; Usu Volcano Observatory Hokkaido University Japan; Volcanogenic deformations during periods of unrest are related to volcanic seismicity in various ways. Magmas or geothermal fluids intrude beneath volcanoes and cause deformations at the surface gradually or rapidly. Mechanical energies of the intrusions are converted to deformation energy, earthquakes, and also explosions under certain circumstances. Partition among the three kinds of energies provides information of the internal processes and yields a clue to their origin. From the above standpoint, deformations accompanying seismicity at Campi Flegrei, Rabaul and Usu are discussed with the aid of published data. To quantitatively correlate the deformations and the seismicity, we discuss the time-derivatives of uplift and release of seismic energy, which are energetically interrelated. The correlation between them is moderate at Campi Flegrei, somewhat higher at Rabaul and high at Usu, but the data sets are not always equal in quality. The deformation volumes are also different among the three volcanoes. In order to standardize the volumes, seismic energies released by unit volume of each deformation are compared. The specific seismic energy is found to increase from Campi Flegrei through Rabaul to Usu. Such different behavior in seismodeformations among the three volcanoes is interpreted as differences in the mechanism of volcanic activity, and in physical properties of the mediums involved.215 161 - PublicationOpen AccessGrowth rates of lava domes with respect to viscosity of magmas(2005-12)
; ;Yokoyama, I.; Higashi 1-17-7-1304, Kunitachi, Tokyo 186-0002 JapanIn the discussion of lava dome formation, viscosity of magma plays an important role. Measurements of viscosity of magmas in field and laboratory are briefly summarized. The types of lava dome emplacements are classified into two, squeeze- and spine-type, by kinetic processes. The squeeze-type is the formation of a dome as a result of squeezes of magma through conduits and the latter is solidified magma forced to ascend by underlying fluid magma. An important parameter in the formation of such lava domes is their growth rates. Lava domes of squeeze-type are governed by the Hagen-Poiseuille Law which involves their viscosoties and other eruption parameters. At present, the real viscosity of magmas at the site of lava dome is still inaccessible. In order to avoid uncertainty in viscosity of magmas, a conception of «macroscopic viscosity» is proposed, which involves effects of chemical components, mainly SiO2 and volatile material, crystals and temperature, and their changes with time. Lava dome formations during the 20th century are briefly examined and their growth rates are estimated. The relationship between the growth rates and the SiO2 content of the magma is statistically studied, and the macroscopic viscosity is empirically expressed as a function of SiO2 content. The linearity between the two parameters is reasonably interpreted. This means that formation processes of lava domes are dominantly controlled by macroscopic viscosity of magma.261 923 - PublicationRestrictedThe MU-RAY project: Summary of the round-table discussions(2010)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Beauducel, F.; Institut de Physique du Globe, Paris, (IPGP), France ;Bross, A.; Fermi National Accelerator Laboratory (FNAL), Batavia, IL, USA ;Buontempo, S.; Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Napoli, Italy ;D’Auria, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;D´eclais, Y.; Institut de Physique Nucleaire de Lyon (IPNL), France ;De Lellis, G.; Universit`a di Napoli “Federico II” (UniNA), Italy;Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Napoli, Italy ;Festa, G.; Universit`a di Napoli “Federico II” (UniNA), Italy ;Gasparini, P.; Universit`a di Napoli “Federico II” (UniNA), Italy;Consorzio Analisi e Monitoraggio Rischi Ambientali (AMRA), Napoli, Italy ;Gibert, D.; Institut de Physique du Globe, Paris, (IPGP), France ;Hoshina, K.; University of Wisconsin, Madison, USA ;Iacobucci, G.; Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Napoli, Italy ;Lesparre, N.; Institut de Physique du Globe, Paris, (IPGP), France ;Macedonio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Marotta, A.; Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Napoli, Italy ;Marteau, J; Institut de Physique Nucl´eaire de Lyon (IPNL), France ;Martini, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Miele, G.; Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Napoli, Italy; Universit`a di Napoli “Federico II” (UniNA), Italy ;Migliozzi, P.; Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Napoli, Italy ;Moura, C. A.; Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Napoli, Italy ;Orazi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Pla-Dalmau, A.; Fermi National Accelerator Laboratory (FNAL), Batavia, IL, USA ;Pisanti, O.; Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Napoli, Italy; Università di Napoli “Federico II” (UniNA), Italy ;Pastor, S.; Instituto de F´ısica Corpuscular (CSIC-Universitat de Val`encia), Spain ;Peluso, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Rubinov, P.; Fermi National Accelerator Laboratory (FNAL), Batavia, IL, USA ;Scarpato, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Sekhniaidze, G.; Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Napoli, Italy ;Strolin, P.; Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Napoli, Italy; Università di Napoli “Federico II” (UniNA), Italy ;Taira, H.; Earthquake Research Institute (ERI), University of Tokyo, Japan ;Tanaka, M.; Institute of Particle and Nuclear Studies, KEK, Japan ;Tanaka, H. K. M.; Earthquake Research Institute (ERI), University of Tokyo, Japan ;Tarantola, A.; Institut de Physique du Globe, Paris, (IPGP), France ;Uchida, T.; Department of Physics, University of Tokyo, Japan ;Vassallo, M.; Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Napoli, Italy; Consorzio Analisi e Monitoraggio Rischi Ambientali (AMRA), Napoli, Italy ;Yokoyama, I.; Usu Volcano Laboratory, Hokkaido University, Japan ;Zollo, A.; Università di Napoli “Federico II” (UniNA), Italy; ;; ; ; ; ; ; ; ; ;; ; ;; ; ; ; ;; ;; ; ; ;; ; ;; ; ;; ; ; ; The MU-RAY project has the challenging aim of performing muon radiography of the summit cone of Mt. Vesuvius. The muon telescopes developed for this purpose will be available for the radiography of other volcanoes, in particular Stromboli. The scientific goals, the strategy for their implementation and the baseline detector design are discussed in detail. A tentative time schedule for the project is drawn.318 35