著者

久野 久

出版者

特定非営利活動法人 日本火山学会

雑誌

火山.第2集

巻号頁・発行日

vol.2, no.2, pp.59-62, 1957

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Human remains of Middle Zyomon (Jomon) age (about 4500 years old) have been found between a tuff layer and a lava flow exposed at Tatunokuti on the western coast of O-sima, Izu, south-southwest of Tokyo. These rocks were formed during the period of pre-caldera or Somma lava activity. As the surface of the tuff layer had been subjected to weathering and stream erosion before the remains were laid down, the volcano appears to have been dormant or at least weakly active for some time before the pre-historic men lived at this place. The time interval between this stage and the close of the Somma lava activity is estimated as at least 1000 years, and probably about 2000 years . Therefore the formation of the summit caldera may be dated as 3000 or 2000 years old.

著者

久野 久

出版者

特定非営利活動法人 日本火山学会

雑誌

火山.第2集

巻号頁・発行日

vol.7, no.2, pp.110-111, 1962

著者

中村 一明

出版者

特定非営利活動法人 日本火山学会

雑誌

火山.第2集 (ISSN:24330590)

巻号頁・発行日

vol.20, no.TOKUBE, pp.229-240, 1975-12-25 (Released:2018-01-15)

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Volcanoes are generally classified into monogenetic and polygenetic types. Monogenetic volcanoes erupt only once to form smaller volcanoes, such as maars, pyroclastic cones and lava domes. Polygenetic volcanoes erupt repeatedly from the same general vents (summit or main crater) for up to 105 years to form larger volcanoes such as strato-volcanoes (composite volcanoes of Macdonald, 1972) and shield volcanoes of Hawaiian type. Monogenetic volcanoes tend to occur in clusters as flank and post-caldera cones. Some of the clusters are however, independent of polygenetic volcanoes and appear to be equivalent to them. The essential part of the conduit of a monogenetic volcano is inferred to be a simple dike, intruded into a newly formed crack, whereas a long endured pipe-shaped conduit may exist under a polygenetic volcano. The common occurrence of xenoliths in the eruptive products of monogenetic volcanoes may be related to this difference. Various lines of evidence, indicating the existence, depth, shape, volume and internal structure, of magma reservoirs are tabulated. A shallow magma reservoir appears to exist beneath polygenetic volcanoes with one to one correspondence, which is not the case for monogenetic volcanoes. Most flank volcanoes are monogenetic, thus indicating dikes within the polygenetic volcanic edifice. Dike formation is understood as a magma version of hydraulic fracturing. For the dike to intrude and propagate, would require either the increase of differential stress due to a decrease of minimum compression or increase of pore pressure over the sum of the minimum compression and the tensile strength of the rocks. Earthquakes are understood as the generation of elastic waves associated with an acute release of tectonic stress due to faulting. Accumulation of tectonic stress and strain prior to earthquakes is, then, a necessary part of earthquake phenomena in a broad sense, as well as their release after the event. Based on the above-stated understanding, possible mechanical correlations between volcanic eruptions and earthquake occurrences have been studied. Contractional strain around the magma reservoir can cause the squeezing up of magma within an open conduit causing a summit eruption on the one hand, and dike formation resulting in a flank eruption through the increase of pore pressure, on the other. Second boiling triggered by both the magmatic pressure decrease caused by dilatational strain and the dynamic excitation due to seismic waves might have the same effect as contraction. Decrease of minimum compression causing the increase of differential stress leading to dike formation will also contribute to the liklihood of flank eruptions. Both volcanic eruptions and earthquake occurrences can precede each other depending on geographical location in terms of faulting-related stress-strain changes which are calculated by the fault model of earthquakes. Actual possible examples of volcanic eruptions and earthquakes which are allegedly mechanically related are given. In order to demonstrate which mechanism is responsible for the correlation of the two phenomena, continuous strain measurement on and around volcanoes is necessary together with the observation of changes in the level of magma in crater bottoms.

著者

岡田 弘

出版者

特定非営利活動法人 日本火山学会

雑誌

火山.第2集

巻号頁・発行日

vol.27, no.4, pp.340-341, 1982

著者

三反畑 修 綿田 辰吾 佐竹 健治 金森 博雄 Luis Rivera Zhongwen Zhan

出版者

特定非営利活動法人 日本火山学会

雑誌

日本火山学会講演予稿集 (ISSN:24335320)

巻号頁・発行日

vol.2020, pp.6, 2020

著者

藤井 直之

出版者

特定非営利活動法人 日本火山学会

雑誌

火山.第2集 (ISSN:04534360)

巻号頁・発行日

vol.29, no.2, pp.95-107, 1984

被引用文献数

1

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ペルー・チリ海溝に沿ってのプレートの沈み込む角度は, 約30度であるが, その上面が深さ100kmのところで水平になっている部分がある.現在の活火山のギャップは, まさに水平なスラブがあるところと一致している.そして, これら両者は2~3百万年前から出現したと考えられる.沈み込んだスラブが, 30度の傾きをもったまま, さらに深部まで続く領域と水平になっている領域との違いは, その上部のマントル・ウェッジ部の構造-特に温度構造-を決定的に違わせている.一般に島弧の火山活動は, (1)沈み込むスラブがもたらす含水鉱物からの脱水反応によるH₂Oの供給と, (2) H₂Oが供給されれば溶融相が形成される状態(Potential melting状態)が必要条件と考えられる.したがって, 深さ100kmで水平に"沈み込む"スラブは, (2)の条件を満たさない温度構造を形成していると考えられる.ナスカ海嶺とペルー・チリ海溝との会合点以北に分布する活火山のギャップの領域では, 下部地殻も上部マントルも部分溶融の状態にないらしい.地殻熱流量のデータは不十分ではあるが, これと矛盾していない.一方, 南部ペルー(及び北部チリ)においては, 重力異常などから推定される地殻の厚さが60km以上の部分(アルティプラーノ)に活火山が存在する.そこでは30度の角度で沈み込むスラブ, 厚い地殻, 地殻熱流量が90mW/m²以上であることなどから, 深さ50km以深のガブロ質の組成をもった地殻は, 少くとも部分溶融の状態にあると結論できる.このようにして推定された温度構造から考えると, 中部アンデスにおける現在の火山活動は, 下部地殻の部分溶融状態と密接な関係にあるといえよう.

著者

植田 義夫 小野寺 建英 大谷 康弘 鈴木 晃

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.46, no.4, pp.175-185, 2001-08-30 (Released:2017-03-20)

参考文献数

31

被引用文献数

2

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The Myojin-sho volcano is one of the active submarine volcanos in the northern part of the Izu-Ogasawara arc about 400 km south of Tokyo. This volcano is a somma edifice of the Myojin-sho caldera, 6.5 km×8 km in diameter and 1000 m deep. The topography, seismic profiler, magnetic and gravity surveys around the Myojin-sho caldera were conducted by the Hydrographic Department, Japan (JHD) in 1998 and 1999. The geophysical structures of the caldera were derived, and the possible cause of the caldera formation is discussed. The residual gravity anomalies were calculated from the observed free-air anomalies by subtracting the gravity effect of 2-layer subbottom model structure, which amounts to 10 m Gals in a localized zone from the caldera to the northern somma. Bouguer gravity anomalies with the assumed density of 2.0 and 2.4 g/cm3 also show the positive anomaly over the same zone, which is accompanied by the acoustic and magnetic basement depression. Moreover, it seems that the sediment volume nearby Myojin-sho caldera cannot compensate the volume loss of caldera (20 to 41 km3). These features insist that the Myojin-sho caldera is caused by the collapse of the pre-caldera edifice rather than the explosion. The origin of the high gravity caldera may be ascribed to the magma pocket causing the depression, instead of the high density erupted material filling the caldera floor. The magnetization intensity of 4.8-5.3 A/m at the Myojin-sho volcano is derived from the magnetic anomaly, which may claim that the Myojin-sho volcano consists of andesitic to basaltic rock rather than dacitic rock. On the other hand, magnetization of the central cone of Takane-sho volcano is estimated to be 1.1-1.9 A/m, which is consistent with the fact that dacite pumices were sampled.

著者

須藤 靖明 筒井 智樹 中坊 真 吉川 美由紀 吉川 慎 井上 寛之

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.51, no.5, pp.291-309, 2006-10-31 (Released:2017-03-20)

参考文献数

55

被引用文献数

3

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So far the ground deformation associated with a magma supply system of Aso Volcano had not been discussed because any clear signals in ground deformations and volcanic earthquake activity had been hardly observed near the Nakadake active crater during its activity enhancement cycles. In this article, however, the deflation source and magma supply system is investigated by the long-term geodetic surveys. The secular subsidence is observed in the Kusasenri area about 3km west of the Nakadake active crater from the 1951’s levelling survey in compiled levelling surveys along the Bouchuu-line since 1937. While the ground deformation near the active crater has been obscure. The source of this deflation near the Kusasenri area is estimated on the basis of the spherical pressure source model through the non-linear least square method with using recent survey data which include the Bouchuu-line and an extended survey route. The deflation source is located beneath the Kusasenri area at about 5km depth. However, recent volume changes at the spherical deflation source are smaller than before 1959. The location of the deflation source coincides with the low P- and S-wave velocity body in the 3D seismic velocity structure. This fact supports a hypothesis that the low seismic wave velocity body represents a magma reservoir. Therefore this magma reservoir beneath the Kusasenri area must be connected to the Nakadake active crater. We inferred a rigid conduit in the magma supply system from the obscure ground deformation in the vicinity of the Nakadake crater.

著者

茂木 昭夫 土出 昌一

出版者

特定非営利活動法人 日本火山学会

雑誌

火山.第2集 (ISSN:24330590)

巻号頁・発行日

vol.23, no.1, pp.91-100, 1978-04-15 (Released:2018-01-15)

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The Hydrographic Department of Maritime Safety Agency has been conducting surveillance and investigation about the activity of submarine volcanoes in the adjacent seas of Japan. There are three active submarine volcanoes belonging to Middle Mariana ridge; Fukutoku oka-no-ba about 4 miles mrtheastward, Minami-Hiyosi Kaizan about 50 miles south-south eastward and Fukuzin Kaizan about 180 miles southeastward from Minami-Io Sima Is. respectively. Discolored water around them is found at irregular intervals, which should be caused by submarine volcanic eruption. The Hydrographic Department conducts to research their activity using remote sensing techniques such as aerial photogrammetry, multiband photographs and thermal camera by an airplane. A survey ship also is used to research bathymetry, geological structure, geomagnetism and gravity in the submarine volcanic areas at the rest time of the volcanic activity. In this paper, wedescribe about the system of surveillance and investigation to them together with the record of recent submarine volcanic eruptions in the adjacent seas of Japan.

著者

北原糸子

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.43, no.5, pp.297-321, 1998

参考文献数

64

被引用文献数

1

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The purpose of this paper is to give an analysis of the spreading of disaster information in the case of 1888 A.D. eruption of Bandai Volcano. A socio-historical approach focusing on newspaper articles, magazines, and other printed matters is adopted to analyze the disaster process. The 1888 eruption of Bandai Volcano was the first experience of a great natural disaster for the Meiji government, which was just under the process of developing the modern nation. The social structure of information in the transit time and its relation to the modernization process in the educational field of physical geography, will be discussed. The newspaper articles about the Bandai Eruption can be characterized into the following three stages in chronological order; l) Reports on the outbreak of the disaster, the initial damage, and the dispatch of the government officials for investigations of the volcano. 2) Further reports on the damage and the donation campaign raised by the newspapers. 3) More on donation campaigns for much more donations among the general public. These three stages clearly show that the social background had changed from the pre-modern society. Having gone through the contemporary understandings about volcanic eruptions and earthquakes with the age of Bandai eruption, and taking the modernization of educational system into consideration, the following reasons for the changes can be pointed out; (a) After the Meiji Restoration accompanied with the so-called "Scientific Revolution" of Japan, the young generation raised under the modern educational system had more scientific attitude to natural phenomena than those of previous generations. (b) The combined effect of the traditional system of charity activities and the new type of donation which was raised by newspapers and other media, such as disaster photographs or charity performances were quite effective in helping the people struck with the disaster under the conditions of the insufficient governmental relief.

著者

渡辺 一徳 本田 圭一 原 浩太郎 宮縁 育夫

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.66, no.1, pp.21-34, 2021-03-31 (Released:2021-03-25)

参考文献数

36

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Aso Volcano in central Kyushu, SW Japan, is one of the largest caldera volcanoes in the world. Aso caldera, 25 km north-south and 18 km east-west, was formed by four gigantic ignimbrite eruptions: Aso-1 (270 ka), Aso-2 (140 ka), Aso-3 (120 ka) and Aso-4 (90 ka). The only outlet of the caldera, named as Tateno gorge, is located at the western edge of the caldera. Since the gorge’s formation history remains poorly studied, a detailed geologic study has been conducted to clarify the stratigraphic relationships between lavas and Aso ignimbrites, and evaluate the formation age of the gorge. The gorge walls are composed mainly of pre-Aso volcanic rocks (0.8-0.4 Ma), and densely welded Aso-2 pyroclastic flow deposits occur on both northern and southern walls of the gorge. Andesitic lava flows (Hokamaki lava) are found between the Aso-1 and Aso-2 ignimbrites in the gorge, and the lavas show potassium-rich characteristics that are indicative of the whole-rock chemistry of magmatic products from Aso Volcano. Additionally, welded Aso-1 blocks were observed in the gravel beds (lahar deposits) underlying the Hokamaki lava from borehole cores. The evidences suggest that the origin of Tateno gorge, which was draining a pre-existing caldera, formed after the Aso-1 ignimbrite eruption (270 ka), and thereafter Hokamaki lavas and the Aso-2 pyroclastic flows (140 ka) passed through the gorge.

著者

山岡 耕春 井田 喜明 山科 健一郎 渡辺 秀文

出版者

特定非営利活動法人 日本火山学会

雑誌

火山.第2集 (ISSN:04534360)

巻号頁・発行日

vol.34, no.4, pp.263-274, 1989

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Mt. Mihara of Izu-Oshima Volcano exploded on November 16, 1987 after one year's rest of its eruptivity. The eruption followed an intensive activity of earthquakes at the summit which began in January 1987. We studied the earthquakes and their mechanisms with a closely installed seismograph network around the summit. We found that most of the earthquakes occurred very narrow portion just below the summit crater with radius of 300 m. Their focal depths are shallower than 100 m above sea level. Most of the focal mechanisms are of normal types. The seismic activity ceased after this event. These facts show that the earthquakes were caused by small break of the bottom of the crater which was filled with the lava of the 1986 eruption, probably due to the load of the lava. The event on November 16 was the final break of the bottom which supported the load of the lava above it. The explosion on November 16 was caused by the sudden fall of both the bottom and the lava above it. The pressurized gas in the cavity below the bottom moved explosively upward in exchange of the falling body.

著者

荒川 洋二 関 琢磨 新村 太郎 大鹿 淳也 森 康 池端 慶

出版者

特定非営利活動法人 日本火山学会

雑誌

日本火山学会講演予稿集 2016 (ISSN:24335320)

巻号頁・発行日

pp.148, 2016 (Released:2017-02-07)

著者

長橋 良隆 小林 聡子 奥平 敬元 吉川 周作 吉田 武義 里口 保文

出版者

特定非営利活動法人 日本火山学会

雑誌

日本火山学会講演予稿集 (ISSN:24335320)

巻号頁・発行日

vol.2006, 2006

著者

萬年 一剛 安藤 伸 伊藤 順一

出版者

特定非営利活動法人 日本火山学会

雑誌

日本火山学会講演予稿集 2011 (ISSN:24335320)

巻号頁・発行日

pp.159, 2011-10-02 (Released:2017-02-10)

著者

山科 健一郎

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.44, no.2, pp.71-82, 1999-04-30 (Released:2017-03-20)

参考文献数

79

被引用文献数

2

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Associated with the 1914 great eruption at Sakurajima volcano, southwestern Japan, the maximum height of volcanic cloud is discussed based on collected documents, sketches and photographs in those days. A series of photographs up to around 10 : 40 on January 12 (in Japanese Standard Time) represents that the volcanic cloud height attained to 7,000 to 8,000 m above sea level. After then, it proved that several documents reported the height to be 9,500-15,000 m, or even more than 18,000 m a.s.l, although it is difficult to obtain reliable evidences. Considering these reports and other observations from a distance, the height of 15,000 m is tentatively proposed here as a possible maximum value. According to an empirical relation, an eruption rate of small pyroclastic materials is suggested as, roughly speaking, 5,000 tons per second or 20 millions of tons per hour, if the volcanic cloud was 15,000 m in height.

著者

佐藤 博明 嶋野 岳人 石橋 秀巳

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.60, no.2, pp.257-263, 2015-06-30 (Released:2017-03-20)

著者

町田 洋 新井 房夫

出版者

特定非営利活動法人 日本火山学会

雑誌

火山.第2集

巻号頁・発行日

vol.28, no.2, 1983

被引用文献数

3

著者

浜口 博之 Mahinda KASEREKA Mifundu WAFULA

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.48, no.1, pp.191-193, 2003-03-18 (Released:2017-03-20)

参考文献数

4

著者

佐藤 純 中村 利廣 菅原 伸一 高橋 春男 佐藤 和郎

出版者

特定非営利活動法人 日本火山学会

雑誌

火山.第2集 (ISSN:24330590)

巻号頁・発行日

vol.34, no.1, pp.19-39, 1989-04-10 (Released:2018-01-15)

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Chemical analysis for major and minor elements was performed on the pumice fall deposit, essential blocks from the two pyroclastic flow deposits and the lava flow, erupted in succession during the 1783 (Temmei) volcanic activity on Mt. Asama. The pumice samples representing a vertical column exhibit no remarkable trend of chemical variation with time. The analytical results for the lava flow show small spatial variation in K, Mg, Sr and some other elements. Further inspection of the data for all the samples indicates that Fe, Na, Ti, Sr, Cu, Co and Ni tend to increase with time throughout the whole eruptive sequence. A plot of Sr/(SiO2 + K2O) vs. (Fe2O*3+K2O)/(SiO2+K2O) illustrates that the erupting magma became progressively more mafic and more enriched in Sr during the activity. This type of plot, combined with the spatial distribution of certain elements superimposed on the distribution pattern of the lava flow, reveals that, during the lava eruption, the composition of erupting magma still shifted to slightly mafic.