著者

一色 直記

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.17, no.2, pp.99, 1972

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.5, no.1, pp.61-62, 1960

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.1, no.1, 1957

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

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

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

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

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

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.

著者

中田 節也 鎌田 浩毅

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.33, no.4, pp.273-289, 1988

被引用文献数

8

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Volcanism and deposition of volcaniclastic materials within a graben in the Shimabara area, western Kyushu, started in early Pliocene and have continued up to the present. The volcanic products comprise alkalic to high-alkali tholeiitic basalts in addition to calc-alkalic andesites. The basalts are of a member of magmas erupted extensively in NW Kyushu from late Miocene to Recent. Their incompatible-element patterns in spider gram, in which the abundances of Rb, Ba, K, Nb, Zr and Y are normalized to those of MORB, are uniform independently of their eruption-ages, and show positive Ba and Nb anomalies strongly indicative of the marked affinity with ocean-island basalts. These patterns are clearly different from those of island-arc basalts which have negative Nb anomaly, as represented by the Quaternary high-alumina basalts in central Kyushu, and from those of back-arc basin basalts usually showing the same anomaly. It is concluded that basaltic magmas in NW Kyushu were derived from partial melt of fertile mantle with high Nb/Zr. Most of the andesites in the Shimabara area have phenocryst assemblages showing co-existence of magmas with different compositions. This fact and the spidergram pattern without Nb anomaly of the andesites lead us to a magmatic model; the andesite magma originated from mixing of positive-Nb-anomaly basaltic melt with negative-Nb-anomaly acidic partial melt of lower-crust materials which were presumably heated by the former melt. The graben in the Shimabara area seems to have developed in southern periphery of the region under which fertile mantle materials have been rising up from the depth and the subducted oceanic slab has not reached, like the "hot region".

著者

鎌田 浩毅 三村 弘二

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.26, no.4, pp.281-292, 1981

被引用文献数

2

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Kuju Volcano (1, 786m high) consists of dacitic lava domes and the associated non-welded pyroclastic flow deposits, Handa pyroclastic flow deposits, covering 60 km² area (Fig.2). The original vents of the pyroclastic flow deposits, whose age is estimated to be 0.04 Ma, have not been located. The volume is about 2km³. They contain pumice and accessory lithic fragments and very seldom show welding. At the upper and the basal parts of one flow unit, imbrications of pumice and lithic fragments are well developed with 10°-20°dip against the flow unit boundary (Figs. 4, 5). This dip (Table 1) is apparently not as steep as that of the other pyroclastic flow deposits. Imbrications are clearly observed at 6-12km from the center of the lava domes, while the distribution of the pyroclastic flow deposits covers 4-13km from the center (Fig. 7). The pyroclastic flows ran down 1000m in a vertical distance. The method of determining the flow direction by imbrication is very simple as shown in Fig. 6. Imbrication is most visible from the direction (a) perpendicular to the flow direction on the surface of each outcrop. The flow direction (f) is determined by the bisector (f') of the error angle 2θ formed by the two directions (b, c), between which imbrication is not observed. Data are classified into 3 ranks by the error angle θ as shown in Table 1. The flow directions at 52 outcrops (Table 2) are shown by classified arrows in Fig. 7. The estimated flow-direction patterns are largely divided into the north-flank flows and the south-flank flows (Fig. 7). The north-flank pyroclastic flow deposits flowed along the 2 km-wide major valley on ca 2°slope shown in K-L profile in Figs. 8, 10. Then it diverged to the west at the outlet of the valley, and finally collected in a small basin in the west. Such flow directions suggest that the flow was not derived from the adjacent domes D, E, F in Fig. 7. On the south flank, a fan-shaped pattern of the flow direction is generally observed. But the flows toward Aso volcano are sharply separated into two flows at the boundary between Kuju and Aso ("col" in Figs 7, 9). This is because the flow had not enough power to rush up the very gentle slope of Aso volcano. The evidence shows that the southward flow gradually bent 120°, and it rapidly went down eastward on the south flank. At Takenohata (n. in Fig. 7) this eastward flow crossed the southward flow. At this cross point, lower outcrops show eastward flow (A-B profile in Fig. 8), and higher ones show southward flow (C-D profile) as shown in Fig. 11. This means that after the eastward flow filled the old valley extending in east-west direction, the later pyroclastics flowed southward over the older deposits forming a fan-shaped deposit. Data clearly suggest that the vent for the pyroclastics is located within the circle around A, B, C lava domes, and not in the other domes. The flow directions indicated by imbrications agree with the distribution of the pyroclastic flow deposits. Pyroclastic flows follow the previous topographic relief such as valley, fan, and col. Kuju Volcano may not have emitted the flooded sheet-flows in all directions, but have emitted the tongue-shaped flows intermittently to different directions.

著者

須藤 茂 阪口 圭一 松林 修 鎌田 浩毅 加藤 完 山本 隆志

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.29, pp.S253-S265, 1984

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Temperature measurements of the lava of 1983 in Miyake-jima in the Ako district were started fifty days after the eruption and have been continued since then. The following three kinds of temperature data have been obtained (Fig. 2). 1. Temperatures at 20 cm depth along a graveled temporary road on the clinkery surface of the lava using mercury and alcohol thermometers. 2. Temperatures at 0.5 to 2.5 m depth in iron pipes inserted into the clinker layer using thermocouples and mercury thermometers. The pipe holes were distributed along the temporary road and at scattered stations on the surface of the lava. 3. We drilled a borehole (DH-1) which penetrates through 5.5 m-thick lava into the previous ground. Temperature was measured at 10 points in the hole using thermocouples. For comparison, similar measurements in the Awabe district were made in pipes with depths up to 2.5 m (Fig. 3). These pipes were buried in the holes dug into the massive part of the lava for electric poles. The temperature data at 20 cm depth and in the pipe holes (Figs. 5-10) indicate that isothermal surfaces in the clinker layer are very complicated. This complexity is explained by rising plumes of hot vapor irregularly present in the lava field. The vapor is produced by degassing process in the massive part of the lava and comes up through newly formed cooling joints. Once a cooling joint is formed, the temperature of the massive part of the lava around the joint fell rapidly because a gas plume effectively transports the heat from the massive part to the surface. But the rate of temperature decrease varies greatly from one station to another. New plumes were formed sporadically and the temperatures of the new plumes were much higher than the decreased temperatures of the older plumes. Some older plumes died out because degassing process ended or the joints were self sealed by sublimates. It is necessary to arrange a number of observation stations and to add stations timely in order to reveal a cooling history of aa lava like the lava of 1983 in Miyake-jima. Around a plume, a convection cell was identified in the clinker layer (Figs. 16-18), which is similar to a hydrothermal convection system usually found in geothermal areas. The change of the temperature-depth profile of DH-1 with time (Figs. 11, 12) clearly shows that the lava heated the underlying previous ground. The peak shape of the profile has become broader and the depth of the maximum temperature has steadily fallen. The change of the temperature-depth profile also suggests that the upper clinker layer prevented rainfall from effective cooling of the massive part of the lava for the first 250 days. During that time, raindrops were evaporated in the clinker layer and did not reach the massive part below the clinker layer. Difference of cooling rate between Awabe lava and Ako lava may be due to the difference of the thickness of the clinker layers (Figs. 15, 19).

著者

秋本 俊一 西川 正名 桂 敬 中村 保夫 久城 育夫

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 (ISSN:24330590)

巻号頁・発行日

vol.15, no.1, pp.39, 1970-04-01 (Released:2018-01-15)

著者

中田 節也

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.21, no.2, 1976

著者

中田 節也

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.31, no.2, pp.95-110, 1986

被引用文献数

6

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Eruptions of lava domes and thick lava-flows of hornblende andesites characterize the Daisen volcanic belt in Kyushu, whereas eruptions of voluminous pyroclastics and thin lava-flows of pyroxene andesites do the Kirishima volcanic belt. The hornblende andesites contain more abundant phenocrysts and have higher Fe³⁺/Fe²⁺ ratios than the pyroxene andesites. Sixty-two samples of rocks from the two volcanic belts were analyzed with X-ray fluorescence spectrometer. The hornblende andesites are lower in Fe/Mg, K/Ba and Rb/K ratios, poorer in Zr, Y, Rb and Cu contents, and richer in Nb, Sr and Ba contents than the pyroxene andesites. Along the Daisen volcanic belt, K/Rb and Ba/K ratios, and Sr and Ba contents in rocks increase eastwards. On the other hand, Fe/Mg ratio and Ti, K, P, Nb, Zr, Y, Sr, Rb, Ga and Ba contents in rocks increase northwards along the Kirishima volcanic belt. Although fractionation of hornblende and magnetite from hornblende andesite magma gives a possible explanation to the difference in major-oxide, Y and V compositions, the difference in other trace-element compositions between the hornblende and the pyroxene andesites may reflect differences in source materials. Chemical variations along the Kirishima volcanic belt may have originated either from northward increase in the degree of fractionation at higher pressures or from northward decrease in the degree of partial melting of source materials.

著者

中村 保夫 他KAIKO計画・LEG III乗船科学者一同

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.29, no.4, pp.305-306, 1984

著者

田中 康裕 古田 美佐夫 中礼 正明

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.21, no.3, pp.185-197, 1976-12-15 (Released:2018-01-15)

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The authors carried out temperature measurement of the ground surface at the Nakadake Crater of Asosan, used an infrared radiation thermometer, and compared the twice observation results at the calm period and the eruption time of the volcano. High temperature zones in the crater bottom and the crater wall were situated at the north half part of the Nakadake Crater, and anomalous high temperature zones at the eruption time extended about ten times as large as that of the calm period. Furthermore, these anomalous high temperature values at the eruption time were 10℃ to 15℃ higher than that of the calm period. These suggest that some thermally anomalous areas in the crater may change their thermal characteristics before or at the future eruptions. The thermal infrared surveys are very useful to volcano observation for the monitoring of some potentially hazardous crater, and these surveys can be done with safety and quickness.