Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

The physical processes that operate within, and beneath, a volcano control the frequency, duration, location and size of volcanic eruptions. Volcanotectonics focuses on such processes, combining techniques, data, and ideas from structural geology, tectonics, volcano deformation, physical volcanology, seismology, petrology, rock and fracture mechanics and classical physics. A central aim of volcanotectonics is to provide sufficient understanding of the internal processes in volcanoes so that, when combined with monitoring data, reliable forecasting of eruptions, vertical (caldera) and lateral (landslide) collapses and related events becomes possible. To gain such an understanding requires knowledge of the material properties of the magma and the crustal rocks, as well as the associated stress fields, and their evolution. The local stress field depends on the properties of the layers that constitute the volcano and, in particular, the geometric development of its shallow magma chamber. During this decade an increasing use of data from InSAR, pixel offset and structure-from-motion, as well as dense, portable seismic networks will provide further details on the mechanisms of volcanic unrest, magma-chamber rupture, the propagation of magma-filled fractures (dikes, inclined sheets and sills) and lateral and vertical collapse. Additionally, more use will be made of accurate quantitative data from fossil and active volcanoes, combined with realistic numerical, analytical and machine-learning studies, so as to provide reliable models on volcano behaviour and eruption forecasting.

DOI： 10.1007/s00445-022-01582-4

researchmap

Other Link： https://link.springer.com/article/10.1007/s00445-022-01582-4/fulltext.html

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.jvolgeores.2022.107582

researchmap

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

DOI： 10.1007/s00445-021-01451-6

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jvolgeores.2021.107267

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-020-01222-1

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41598-020-66226-z

Language：Japanese  

DOI： 10.18940/kazan.65.2_59

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s00445-020-01384-6

Language：Others   Publishing type：Research paper (scientific journal)  

© 2020, The Author(s). We present petrological evidence of the shallow magmatic processes that may have supplied heat and gas to the eruption of Mount Ontake, Japan, on 27 September 2014, which resulted in 63 fatalities. Ash from the eruption comprises primarily hydrothermally altered, white-toned rock fragments. However, the ash contains trace amounts (< 0.7 wt&#37;) of vitreous less-altered particles (LAPs), which are only altered on their surfaces, suggesting rapid ascent through the hydrothermal system. The LAPs are classified into two categories: “glassy” and “crystalline.” Glassy LAPs comprise high-silica rhyolitic glass (74–83 wt&#37; SiO2) with rounded quartz, chalcedony-free vesicles, and reversely zoned plagioclase (cores = 47 mol&#37; An; rims = 70 mol&#37; An), indicating magma re-heating. Crystalline LAPs have a groundmass-like texture that suggests eutectic crystallization at shallow depths. Thermodynamic calculations indicate that the pre-eruptive temperatures of the glassy and crystalline LAPs were 700–1300 °C and ~ 700 °C, respectively, and that the storage depth was < 4 km (pressure < 100 MPa). The observed petrological features suggest that the LAPs were sourced from a magma recently intruded at shallow depths. Although crustal deformation (i.e., the volume change associated with magmatic intrusion) was insignificant prior to the 2014 eruption, a clear signature of crustal deformation was observed in 2007, the source of which was located 3 km below the summit. We suggest that the magma that was intruded 3 km below the summit in 2007 supplied the heat and gas for the 2014 phreatic eruption.

DOI： 10.1007/s00445-020-1358-x

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.5194/sd-26-29-2019

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

DOI： 10.1016/j.quaint.2018.12.023

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.epsl.2019.01.038

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-018-0881-x

Language：Others  

Pyroclastic density currents associated with the 2015 phreatomagmatic eruption of the Kuchinoerabujima volcano

DOI： 10.1186/s40623-018-0881-x

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

DOI： 10.1016/j.epsl.2018.03.023

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s00445-018-1215-3

Language：English  

Salt shell fallout during the ash eruption at the Nakadake crater, Aso volcano, Japan: evidence of an undergrounds hydrothermal system surrounding the erupting vent

DOI： 10.1186/s40623-018-0798-4

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

DOI： 10.1016/j.jvolgeores.2017.09.015

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

DOI： 10.1007/s00445-017-1154-4

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

DOI： 10.1007/s00445-017-1153-5

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

DOI： 10.1007/s00445-017-1112-1

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

DOI： 10.1002/2016GC006712

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

DOI： 10.1007/s00445-017-1105-0

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

DOI： 10.1186/s40623-016-0548-4

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

DOI： 10.1186/s40623-016-0511-4

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

DOI： 10.1016/j.jvolgeores.2016.07.005

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

DOI： 10.3389/feart.2016.00099

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

DOI： 10.1016/j.jvolgeores.2016.06.020

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

DOI： 10.1007/s00445-016-1057-9

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

DOI： 10.1016/j.jvolgeores.2015.10.005

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

DOI： 10.1016/j.epsl.2015.08.004

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

DOI： 10.1111/iar.12073

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

DOI： 10.1016/j.jvolgeores.2014.08.006

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

DOI： 10.3389/feart.2014.00013

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

DOI： 10.1016/j.epsl.2014.03.059

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

DOI： 10.1007/s00445-014-0797-7

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

DOI： 10.1007/s00445-013-0750-1

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

DOI： 10.1016/j.jvolgeores.2013.05.010

Language：English  

Preface

DOI： 10.5047/eps.2013.06.002

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

DOI： 10.1002/grl.50284

Language：Others   Publishing type：Research paper (other academic)  

DOI： 10.1002/2013EO020010

Language：English   Publishing type：Research paper (other academic)  

DOI： 10.1016/j.nimb.2012.05.015

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

DOI： 10.1016/j.jsg.2012.10.004

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

DOI： 10.1007/s00445-012-0617-x

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

DOI： 10.1029/2012JB009229

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

DOI： 10.1016/j.jvolgeores.2012.03.003

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

DOI： 10.1016/j.jvolgeores.2012.02.004

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

DOI： 10.1016/j.jvolgeores.2010.11.012

Language：Japanese  

DOI： 10.5026/jgeography.120.1

Language：Japanese  

DOI： 10.5026/jgeography.119.959

Language：Japanese  

DOI： 10.5026/jgeography.119.187

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

DOI： 10.1130/G30350.1

Language：Japanese  

DOI： 10.5026/jgeography.118.1021

Language：Japanese  

A large pyroclastic eruption occurred around 7.3 ka from the Kikai caldera about 30 km north of Yakushima Island. Its pyroclastic flow and fall deposits covered the entire area of Yakushima Island and may have influenced the evolution of unique floras and faunas of Yakushima Island.  Detailed field survey revealed that the Koya pyroclastic flow deposit spread from NW to SE, covering almost the entire area of Yakushima. A part of the southern coastal area remained from the pyroclastic flow due to local alignment of topographic ridges and valleys, which acted as barriers to the pyroclastic flows. Possible tsunami deposits associated with the Kikai-Akahoya eruption were discovered in the area below ca. 50 m above sea level along the northern coasts of Yakushima and Kuchinoerabujima Islands.

DOI： 10.5026/jgeography.118.1254

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

DOI： 10.1016/j.epsl.2009.01.027

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

DOI： 10.1016/j.jvolgeores.2008.04.013

Language：Japanese  

&emsp;A strong earthquake of M7.2 (M_W6.7-6.9) occurred on 14 June 2008 in the north-central part of Northeastern Japan. It was named the Iwate-Miyagi Nairiku Earthquake in 2008. Several seismic models show a 25-30km long reverse fault in the NNE-SSW direction and a westward inclination. Although some geological thrusts with a similar trend are known, as shown in Fig. 1, none of them has been recognized as an active fault. Surface faults associated with the earthquake were found at several points along the geological thrusts. The quake induced many mass-movements in the mountainous and hilly area, which is composed mostly of Neogene to Pleistocene volcaniclastic rocks (Fig. 1), near the seismic fault and particularly on the western side (upper block). Most of the damage caused by the earthquake was closely connected to mass-movements. &emsp;A large-scale block glide amounting to about 7&times;10⁷m³ in the volume of dislocated mass (Figs. 2, 3) occurred in the northern half of the pre-existing landslide area composed of poorly-consolidated pyroclastic flow deposits with a welded cap around 5Ma (Np3 in Fig. 1). The almost horizontal slip surface of the glide is considered to have been formed in the underlying lacustrine beds. A large collapse, occurring at a slope on which snow remained on Kurikoma Volcano, composed of Quaternary andesitic lavas and pyroclastics (Qm2 in Fig. 1), formed a debris flow (Fig. 4) which buried a lodge at Komanoyu Spa. Many landslides checked river channels. One of them was observed at Ogawara, where a slide of a spur composed of Pleistocene pyroclastic deposits checked the Ichihasama River (Fig. 5). The collapse of Matsurube Bridge, a three-span 95 m-long bridge over a tributary of the Iwai River, was also entirely caused by a landslide at the north-facing slope of a narrow ridge (Fig. 6). A surface fault appeared in rice fields at Mochikorobashi on the side of a tributary of the Koromo River (Fig. 7). The trace of the water's edge and lines of planted rice indicate a co-seismic uplift and a right-lateral offset with a clockwise turn of the trend (Fig. 8).

DOI： 10.5026/jgeography.117.697

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

DOI： 10.1029/2007JB005325

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

DOI： 10.1016/j.jvolgeores.2008.01.001

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

DOI： 10.1029/2007JB005325

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

DOI： 10.1029/2007GL031551

Language：English  

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

DOI： 10.1016/j.epsl.2007.03.019

Language：English  

Implication of the temporal sulphur isotopic variation during the 2000 eruption of Miyakejima Volcano, Japan
The variation of sulphur isotopic composition during the 2000 eruption of the Miyakejima Volcano was examined in order to monitor the temporal change of the volcanic activity. The delta S-34 values of water-soluble sulphate leached from volcanic ash effused during intermittent eruptions from July to September 2005 range from +5 to +11 parts per thousand with a fluctuation of ca 3 parts per thousand within a single eruption. The delta S-34 value of sulphuric acid mist collected with 'Cu-metal trap' placed on the flank of the volcano from December 2000 to January 2001 is +6.2 parts per thousand. These sulphur isotopic compositions of sulphate, which were isotopically equilibrated in the subvolcanic hydrothermal system, indicate that the temperature of the hydrothermal system beneath the caldera increased after the period of intermittent phreatic and phreatomagmatic eruptions. Then, the delta S-34 value of sulphuric acid trapped from January to March 2001 was +9.0 parts per thousand and the delta S-34 value of water-soluble sulphate on volcanic ash emitted with minor eruption in May 2001 was +11.0 parts per thousand, suggesting a decrease in temperature of the subvolcanic hydrothermal system.

DOI： 10.1111/j.1440-1738.2007.00549.x

Language：Japanese  

DOI： 10.5026/jgeography.116.1

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

DOI： 10.1016/j.jvolgeores.2004.11.002

Language：Japanese  

設楽火山岩体の一部を構成する大峠火山岩体の形成過程は,コールドロン形成期の火砕噴火のステージと,後コールドロン期の岩脈・シート群の貫入のステージに分けられる後コールドロン期における貫入岩体の形成は,大峠コーンシート群の形成から設楽中央岩脈群の形成に漸移し,ほぼ同時期に大峠ストック群が形成された大峠火山岩体は主にアルカリ苦鉄質岩からなり,少量のカルクアルカリ質デイサイトを伴う全岩組成の時間変化は,後コールドロン期の初期に発生した浅部のマグマ溜りへの未分化な苦鉄質マグマの再供給によって後コールドロン期の貫入岩体が形成されたことを示唆する

DOI： 10.5575/geosoc.109.580

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

DOI： 10.1007/s00445-001-0184-z

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

DOI： 10.1016/S0377-0273(00)00271-7

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

DOI： 10.1016/S0377-0273(99)00188-2

Language：English  

DOI： 10.1111/j.1751-3928.1999.tb00035.x

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

2014年6月3日に西之島火山で噴出した降下火砕物について岩石学的特徴を明らかにするとともに,マグマ脱ガス量を見積もった.降下火砕物の全岩化学組成と鉱物組み合わせは1973-74年噴火噴出物と同様であり,2014年噴火は1973-74年噴火と同様な化学的特徴を持つマグマによって引き起こされたと考えられる.メルト包有物分析と火山ガス観測による二酸化硫黄放出率から見積もられた2014年1月末のマグマ脱ガス率は地形変化から見積もられる溶岩噴出率と同程度である.

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

The Miyakejima volcano repeats small ash eruptions from the degassing vent opening inside the A.D. 2000 caldera. The juvenile glassy fragments in the tephra indicate that the basaltic magmas with primitive composition are ascending in the open conduit and degassing at the shallow depth. We examined the representative 12 tephra samples erupted between October 2001 and July 2010, and found the juvenile glassy fragments with basaltic character. Their fresh surfaces and free from alteration or weathering indicate that these glassy grains are juvenile materials. The glassy fragments occupy less than 1 vol.&#37; of the tephra, that mainly consists of the fragments of lavas and pyroclastics derived from the previous edifice. The juvenile fragments consist of volcanic glass with pale-brownish color and euhedral crystals of plagioclase, clinopyroxene and olivine up to several tens micrometers across. Larger crystals of plagioclase and olivines more than 100 micrometers are also contained as microphenocryst. The range of the Fo contents of the olivine microphenocrysts in the glassy fragments is 73-83, which is higher than that of the phenocryst olivine in the basaltic bombs erupted during the August 18, 2000 eruption and similar to that of the olivine phenocrysts derived from the primitive basaltic magma, indicating that the continuous degassing since the A.D. 2000 eruption has been driven by the basaltic magmas with primitive character. The low sulfur and chlorine contents in the groundmass glass indicate the degassing under low pressure.

Language：English  

&emsp;This article provides an overview of papers collected in the special issue titled &ldquo;Geotectonic Evolution of the Japanese Islands under New Paradigms of the Next Generation (Part I-III)&rdquo; for international readers. Research on the geologic evolution of the Japanese Islands started from the geotectonic subdivision with definitions of elements and boundaries in the late 19th century. Traditionally, some remarkable faults, such as Median Tectonic Line (MTL), Fossa magna, and Tanakura Tectonic Line (TTL), were regarded as the most important; however, these apparent features were in fact formed during the Miocene opening of the Japan Sea, whereas the major structures of Japan were made by the Pacific-type orogenies throughout the Phanerozoic after the initiation of subduction at 520 Ma (the Cambrian). &emsp;Marine geophysicists have realized that the formation of accretionary complex (AC) along modern active subduction zones is rather exceptional; instead, tectonic erosion takes place dominantly. The estimated addition rate of juvenile arc crust (composed of tonalite&ndash;tronjemite&ndash;granodiorite suite; TTG) is negative at present for the entire globe, i.e., the total volume of the continental crust is currently decreasing. This indicates that tectonic erosion must also have occurred effectively in the past, and that its geological remnants need to be investigated carefully. A possible proxy geologic body for ancient tectonic erosion is a serpentinite m&eacute;lange, which often includes calc-alkaline volcanics and coeval high-P/T blueschists within serpentinite matrices as shown in the geology of Japan. The large-scale shortening of a fore-arc crust can occur solely due to tectonic erosion, which may involve more than 150 km-wide areas of missing rocks between volcanic arc and trench. The sporadic occurrence of tectonic blocks of older (520-150 Ma)TTG rocks in serpentinite m&eacute;lange indicates that four arc crusts, out of the five made by Pacific-type orogeny in Japan during the past 500 million years, have already been consumed. &emsp;The Pacific-type orogeny was revisited after recent critical discoveries of; (1) orogenic core of high-P/T regional metamorphic belt as a thin (< 2 km) solid high-T intrusion, bounded on the top and bottom by a paired fault; (2) rapid increase of 200-300 km-wide TTG belt formed by slab-melting; (3) these culminated with an approaching mid-oceanic ridge, associated with large-scale tectonic erosion; and (4) formation of an AC after ridge subduction and doming up of a sandwiched set of high-P belt and accretionary belt below and above. The Pacific-type orogeny has been ignored since the &ldquo;terrane plague&rdquo;; however, Pacific-type orogeny dominated to increase the TTG crust leading to the births of continents and supercontinent by 1.8 Ga. The extensive tectonic erosion and arc subduction through time, suggesting 10 times more TTG materials, enriched with radiogenic elements, floated at the bottom of the mantle transition zone, which generated heat to warm up the mantle up to 200 K within 100 million years in the Archean, and to 100 K in the Phanerozoic. Subducted TTG and presence of second continents in the mid-mantle may explain more general aspects of mantle dynamics, and the concept may become a frontier of solid Earth science in the 21st century. &emsp;From the viewpoint of the history of science, the previous geological studies in Japan since the Meiji Era are also summarized briefly, with special reference to the orogeny, tectonics, and geotectonic subdivision of the Japanese Islands.

DOI： 10.5026/jgeography.119.947

Language：Japanese  

Language：Japanese  

A phreatic eruption occurred on August 22, 2008 from Shinmoedake Volcano, one of the members of Kirishima volcanic group, Kyushu, southwestern Japan. Some explosive craters and eruption fissures aligning in E-W direction for 800 meters were formed inside the summit crater and the western flank of Shinmoedake Volcano. These craters produced clay-rich tephra, consisting of non-juvenile lithic fragments with various degree of hydrothermal alteration. Ballistic blocks distribute in an area within 800 meters from the main crater. The total volume of the tephra produced this eruption is evaluated as 2×10^8kg. Distribution of the tephra indicates that the main source of the tephra is S-17 crater, which is the largest crater located at the center of the crater chain. More than 70&#37; of the tephra deposit inside the area within 1km from the craters, suggesting the low height of the eruption cloud. Absence of the juvenile materials suggests that this eruption was phreatic caused by a rapid release of steam from the hydrothermal system beneath Shinmoedake Volcano.

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

DOI： 10.5026/jgeography.117.1

Language：Japanese  

&amp;emsp;A large number of intraplate volcanoes erupted two to several hundred kilometers off the fast-spreading East Pacific Rise (EPR). These volcanoes consist of large lava fields, monogenetic volcanoes, and linear chains of monogenetic volcanoes and volcanic ridges. Large lava fields of 7-26 km³ in volume are known at 8&amp;deg;N, 14&amp;deg;S, and 16&amp;deg;S within 2-19 km from the rise axis and from the top 75-100 m of ODP Site 1256 on the 15 Ma Cocos plate. Monogenetic volcanoes form within &amp;sim;20 km from the rise axis or on the basement < 200 kyr, and are evenly distributed over the rise axis. Linearly aligned volcanoes and volcanic ridges occur farther from the rise axis than large lava fields and monogenetic volcanoes, and run subparallel to the direction of the Pacific plate motion. The Sojourn Ridge, the largest volcanic ridge, extends up to 440 km in length and is several hundred cubic kilometers in volume. Eruptive ages along a volcanic ridge and a volcano chain contradict the hot-spot origin of these volcanic features. Negative free-air and residual mantle Bouguer anomalies correlate well with the linearly aligned volcanoes and volcanic ridges, suggesting excess magma supply beneath the volcanic edifices. Seismic experiments show volcanic ridges have no keel below the Moho, indicating compensation of surface loading by plate flexure and underplating. &amp;emsp;Whole rock compositions of off-ridge volcanoes have a much wider spectrum than the adjacent axial lavas, spanning from depleted NMORB through TMORB to isotopically fertile EMORB. Some off-ridge lavas could be produced by the fractional crystallization of the same parent magma as the adjacent axial lavas. However, most off-ridge lavas originate from different parent magmas than the neighboring axial lavas. Some TMORB magmas including the 14&amp;deg;S large lava field are the mixing product of the NMORB and EMORB magmas. Copious differentiated lavas of the large lava fields require a large magma chamber as a the site for crystallization differentiation and magma mixing. The lava geochemistry of off-ridge volcanoes strongly suggests the presence of a magma source that is independent of the axial magma plumbing system. &amp;emsp;Seismic tomography and seafloor compliance measurements beneath the northern EPR indicate that the presence of melt across the rise axis is restricted in a narrow zone &amp;sim;4 km in width through the crust, but has a 10-14 km wide distribution in the uppermost mantle. Broad distribution, volume, and geochemistry of off-ridge monogenetic volcanoes and large lava fields strongly suggest that the off-ridge volcanoes originated from the Moho transition zone (MTZ). The MTZ is formed by a reaction between the uprising magma and the host mantle peridotite, leaving replacive dunite that experienced variable depletion and enrichment processes. Passive asthenospheric upwelling beneath the fast-spreading ridges produces a broad partial melt zone, through which magma ascends and accumulates beneath the off-ridge lithosphere. More depleted off-ridge magmas than axial magmas differentiate and mix with residual magmas in the MTZ, and react with variably enriched, impregnated dunite, resulting in variety of off-ridge lava compositions. &amp;emsp;Small clusters of volcanoes and linear volcano chains are created by partial melting in asthenospheric return flows or local instability of the thermal boundary layer beneath the cooling lithosphere. Linear volcano chains will develop into long and robust volcanic ridges extending several hundred kilometers in length.

DOI： 10.5026/jgeography.117.190

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Volcanic history of Kuchinoerabujima Volcano in the last 30,000 years is reconstructed based on tephra stratigraphy. Kuchinoerabujima is a volcanic island which is a cluster of at least nine volcanic edifices; Gokyo, Jyogahana, Ban-yagamine, Takadomori, Noike, Kashimine, Hachikubo, Furutake and Shintake. Eruptions within the last 30,000 years occurred from Noike, Hachikubo, Furutake and Shintake volcanoes. Two major pumice and scoria eruptions occurred between 15 and 11 ka after an inactive period since ca. 30ka. NoikeYumugi tephra (15-14ka, DRE>0.06km^3), erupted from the summit of Noike Volcano, consists of Yumugi pumice fall deposit and Nemachi pyroclastic flow deposit. Furutake-Megasaki tephra (12-11 ka, DRE ca. 0.8km^3) erupted from Furutake Volcano and consists of Furutake agglutinate, Furutake scoria flow deposit and Megasaki scoria fall deposits. Volcanic edifice of Older Furutake was built during the 12-11 ka eruption. Eruption style changed around 10ka, after the collapse of Older Furutake Volcano. Activities of Yougner Furutake and Shintake Volcanoes are characterized with effusion of lava flow and no major pumice eruption is recognized. Lithic tephra erupted from Younger Furutake and Shitake Volcanoes within the last 10,000 indicates repetitive Vulcanian-type and phreatomagmatic eruptions. All historical eruptions since 1841 occurred at and around Shintake crater and were Vulcanian-type explosions with emission of magmatic materials and phreatic explosions.

Language：Japanese  

Language：Japanese  

Erupted magma of the 2000 eruption of the Miyakejima volcano changed from basaltic andesite to basalt during the caldera formation, from aphyric basaltic andesite with SiO_2=54 wt.&#37; to plagioclase-phyric basalt with SiO_2=51.5 wt.&#37;. Whole-rock compositions of the basaltic andesite of the June and July eruptions are plotted on the extension of the temporal variation of the previous eruptive materials, suggesting that the andesitic magma erupted in June and July eruptions were driven from the magma system worked for the last 500 years. Petrological character of the basalt in the eruptive materials of August, by contrast, is different from the previous lavas of the Miyakejima volcano. This shows that a new basaltic magma ascended to the shallow magma system after the caldera collapse. Identical ratio of the incompatible elements among the eruptive materials of the 2000 eruption and the recent eruptions suggests that they were driven from a common parental magma.

Language：English  

噴火中の火山で, どのような地形変化が起きているかを知ることは, 活動状況を把握するうえで, 最も重要な点の一つである. しかし, 我が国のような湿潤な気候帯では, しばしば, 山頂部が雲に覆われ観測できない事態が起きる. このような場合, 合成開ロレーダー(SAR)は, 昼夜, 天候, 噴煙等に左右されないため, 火山の地形変化の監視に有効であると考えられる. しかし, SAR 画像は, 独自の歪みをもっため,地形図との対応関係を知るのが容易でないなどの問題がある.本論は,RADARSATSAR 画像をGround Control Points (GCP) を用いたマッチングにより地形図上に重ね合わせ, 2000年7月に噴火を開始した三宅島陥没カルデラ縁の拡大状況の推定を行った. この際フォアショートニングによる歪みを抑えるため, カルデラ縁に近い場所にGCPを設定した. 得られた結果を空中写真等からの推定と比較すると,両者のずれは大きい部分でも1OOm程度であり, 比較的良く一致していることがわかった. このことから, RADARSATSAR 画像は, 緊急時にカルデラ縁の位置を推定するといった用途には十分利用できると考えられる.