著者

加藤 祐三

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.33, no.1, pp.21-30, 1988-04-01 (Released:2018-01-15)

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Since the late of May, 1986, many pumices have drifted to the Ryukyu Islands. These pumices are characterized by their size, color and components. The pumices vary in size: some are about 5 mm and the maximum size is about 20 cm. Most of these pumices are gray and a few of them are drak- or light-gray. The pumices contain several percent of essential black xenolithes which vary in size from 1 mm to 5 mm and rarely 2 cm. The rock name of pumices is olivine-augite-bearing trachyte and that of xenolithes is forsterite chromian diopside trachybasalt. These characteristics of the pumices correspond with those of pumices erupted from Fukutoku-oka-no-ba in the north of the Mariana Islands in January 18-21, 1986. Moreover, the chemical composition of host pumice (free from xenolith), bulk composition (including xenolith) and mineral chemistry of phenocryst also correspond with those of the pumices effused from Fukutoku-oka-no-ba. Based on these facts, it is evident that the pumices drifted to the Ryukyu Islands had their origins in Fukutoku-oka-no-ba. Judging from the data concerning the current and wind around the area through Fukutoku-oka-no-ba toward the Ryukyu Islands, it is confirmed that the pumices reached the Ryukyu Islands from Fukutoku-oka-no-ba after four months under the effect of current and wind which run both to the direction of west.

著者

早川 由紀夫

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.28, no.1, pp.25-40, 1983-04-01 (Released:2018-01-15)

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The Hachinohe ash is a widespread pyroclastic-fall deposit erupted from the Towada caldera about 13, 000 years B. P. Along the dispersal axis, the thickness is 150cm 50km away from source, and the estimated volume is 14km3 It is composed of alternating beds of fine ash (65%) and pumice lapilli (35%). No erosional break is observed and the contacts between beds are gradational. The fine ash beds have two components : a dominate component of grain-supported accretionary lapilli and a subordinate component of fine ash-coated pumice; an ash matrix is lacking. The maximum grain size of accretionary lapilli does not decrease systematically away from source. The size population of constituent ash particles shows a small degree of fractionation with distance from source; the grain size class 1mm to 1/4mm increases while the class finer than 1/16mm decreases. Pumice beds are composed primarily of sub-angular to sub-rounded pumice fragments coated with fine ash and a subordinate amount of lithic fragments and accretionary lapilli. Maximum pumice size and maximum lithic size systematically decrease away from source. The beds show bimodal grain size distributions and contain more than 10 weight percent fine ash. An individual fine ash particle has too low a terminal velocity to fall out as a separate grain near the source area. It is certain that, throughout the Hachinohe ash eruption, fine ash continued to fall in the form of accretionary lapilli and/or attached to pumice fragments. The fine grained nature and wide dispersal indicate that the Hachinohe ash is representative of the phreatoplinian deposit formed by the interaction of water and silicic magma during explosive eruptions. At times when the proportion of erupted magma to lake water gaining access to the vent became sufficiently high, violet eruptions took place and deposited pumice fragments and accretionary lapilli simultaneously at the same place. Examples of phreatoplinian deposits are also reported from the Kutcharo and Hakone calderas, in addition to two other deposits from the Towada caldera. Such deposits are used as a possible indicator of source environment.

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.25, no.4, pp.255-269, 1980-12-01 (Released:2018-01-15)

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Rift zones are characteristic features of Hawaiian volcanoes. They are long narrow zones of flank fissure eruptions but are distinct from ordinary flank eruption sites on stratovolcanoes in that eruptions, and therefore dike intrusions, occur repeatedly at the same general place for a long time and thus cause a considerable amount of lateral spreading. This spreading should somehow be accomodated. Moreover, the stress field should remain the same after accomodation in order for a new dike to intrude in the same orientation. The current spreading episode in Iceland (BJORNSSON et al., 1979) between North American and European plates revealed that the sequence of events in the spreading process is similar to that observed for Hawaiian volcanic activities. This implies that the process of plate separation and accretion is nothing but the activity of rift zones. Constructional plate boundaries may be regarded as composed of a chain of rift zones and associated feeding polygenetic centers. Room necessary for repeated dike intrusion is supplied in the case of spreading centers, by the lateral motion (separation) of lithosphere over asthenosphere. In the case of Hawaii, sliding of the volcanic edifice over a deep sea sediment layer may be the analogous mechanism such as appears to have occurred during the 1975 Kalapana earthquake, as studied by ANDO (1979) and FURUMOTO and KOVACH (1979). Kalapana earthquake had been anticipated by SWANSON et al. (1976) as one of the repeated steps as the east rift zone has continuously dilated. Thus, the primary cause for the long, well developed rift zones of Hawaiian volcanoes may be in the existence of thick enough oceanic sediments serving as a potential sliding plane beneath the volcanic edifices. Lack of rift zones in Galapagos shields which grew over the young ocean floor with rough topography is consistent with this view.

著者

荒牧 重雄

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.8, no.3, pp.110-113, 1963-12-25 (Released:2018-01-15)

著者

早川 由紀夫 荒牧 重雄 高田 亮 浅岡 伸之 金子 隆之 津久井 雅志 岸 智 山下 茂 野原 状 平田 由紀子 小山 真人 白尾 元理 川辺 禎久

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 (ISSN:24330590)

巻号頁・発行日

vol.32, no.3, pp.259-262, 1987-10-15 (Released:2018-01-15)

著者

金 允圭 吉田 武義 李 大声

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.31, no.2, pp.144-145, 1986-07-01 (Released:2018-02-13)

著者

巽 好幸 柵山 雅則 福山 博之 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.27, no.1, pp.45-65, 1982-04-30 (Released:2018-01-15)

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The compositions of the primary tholeiitic, high-alumina and alkali-olivine basalt magmas (THB, HAB and AOB magmas, respectively) which are derived directly from the upper mantle beneath the volcanic arcs, are obtained by calculating the average compositions of liquid in equilibrium with the mantle peridotite, which can produce basalts in NE Japan arc through olivine maximum fractionation. Anhydrous high-pressure melting experiments on these three basalts indicate that the AOB and HAB magmas coexist with olivine, orthopyroxene and clinopyroxene at 1360℃ and 17.5 kbar and at 1340℃ and 15 kbar, respectively. The THB magma, on the other hand, coexists with olivine and orthopyroxene at 1320℃ and 11 kbar. The volcanic arc magmas are believed to contain significant amounts of water which affect the P-T conditions of the phase equilibria at high temperatures and pressures. However, the detailed petrographic studies on the rock suites in volcanic arcs revealed that the island arc primary basalt magmas contain water not more than 3 wt.% at generation in the upper mantle. Combining this with the experimental results, the THB, HAB and AOB magmas are suggested to segregate from the mantle at temperatures of about 1300℃ and at pressures of 11 kbar (THB), 16 kbar (HAB) and 20 kbar (AOB), respectively. As the temperatures of segregation of the magmas given above are too high for a stable mantle geotherm, the mantle diapir is the most probable mechanism for magma generation under the volcanic arcs. Due to the heat of formation of liquid in the diapir, the temperature of the diapiric mantle must be higher at deeper levels. The required temperature of the upper mantle is 1400℃ at a certain depth between the descending slab and depth of approximately 70km.

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.17, no.1, pp.33, 1972-06-01 (Released:2018-01-15)

著者

関谷 慱

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.12, no.2, pp.90, 1967-08-01 (Released:2018-01-15)

著者

荒牧 重雄 藤井 敏嗣

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.33, no.SPCL, pp.S297-S306, 1988-06-30 (Released:2018-01-15)

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Detailed characterization of the whole rock composition of the ejecta of the 1986-1987 eruption of Izu-Oshima volcano by the XRF technique (FUJII et al., 1988) clearly indicates that the ejecta from the central crater of Miharayama (Crater A) are different from those erupted from the fissures (Fissures B and C) on the caldera floor and on the outer slope of the main stratovolcano. This suggests that the conduits which led the A and B, C magmas to the surface were separated physically from each other down to a certain depth. The ejecta from A crater resemble closely to those erupted during the past 1300 years (Y magmas) while the ejecta from B and C fissures are unique in composition among the Izu-Oshima magmas. The A and Y magmas are Fe-enriched island arc type tholeiites that must have been derived from the primary tholeiite magmas through crystal fractionation of olivine, pyroxenes and plagioclase. The B and C magmas can be derived simply through crystal fractionation of A or Y magmas leading to Fe-enriched basaltic andesites, andesites and dacites. This strongly suggests that an isolated pocket of magma starting with a composition of Y underwent strong fractionation to produce volatile enriched ferroandesitic magma. This body of magma was probably activated by the sudden depressurization caused by shattering and fissuring of the crust to form a 1500 m high fire fountains and to produce a sub-Plinian scoria fall deposit. The vent of A crater must have been stable at least during the last 1300 years and directly, or through the subsidiary magma chamber(s), connected to the main chamber above the Moho, where an extensive crystal fractionation has been taking place to produce Y magma from the parent tholeiitic magma. Marked ground depression and extension and migration of seismicity observed during the eruption suggest a possibility that a substantial amount of additional magma was intruded to form a NW-SE trending dike during the peak phase of the eruption. This is in harmony with the Nakamura’s model of the volcano with the NW-SE trending dike swarm which is controlled by the regional compressional stress field. However, gravity and some other grophysical data suggest that the deformation could have been the result of underground cracking without magma injection. Our model is not conclusive on this matter and the expectation that this eruption will eventually lead to the large-scale activity that has been recurring in every 130±50 years is yet to be tested.

著者

宇井 忠英 柴橋 敬一

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.20, no.2, pp.51-64, 1975-08-01 (Released:2018-01-15)

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Volcanic activity at the snow-capped summit of Mt. Chokai was first noticed by the captain of scheduled airline on March 1, 1974. The activity began with swarm of volcanic earthquakes, succeeded by fumarolic activity and finally explosion took place and a few craters were formed at eastern (late February-early March) and western (late April) foot of 1801 lava dome (Shinzan). The ejecta were exclusively fine-grained air-fall ash and accidental blocks. The blocks, formed the mud flow mixed with melted snow, rushed down the slope of volcanic edifice. Essential materials, such as bombs, air-fall scoria, or lava flows were not erupted. Rapid melting of snow was supposed to have been triggered by the formation of fumaroles caused by ascent of hot magma and associated juvenile gas. Thermal energy consumed for melting and evaporating snow is calculated as 3×1021 ergs. Total volume of mud-flow deposit is around 3×104 cubic meters, and that of air-fall ash is an order of 105 cubic meters. The entire area which showed thermal activity is approximately 700×200 meters, elongated in east-west direction. Distribution of earthquake foci was also trending east-west just passing the prehistoric summit and parasitic vents. Direction of vent alignments is the same for the most volcanoes in northeastern Japan, and is supposed to reflect regional stress field.

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

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

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

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

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.

著者

川本 竜彦

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.35, no.1, pp.41-56, 1990-04-14 (Released:2018-01-15)

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The Kannabe monogenetic volcano group is situated in the back-arc region of southwest Japan and is composed of six scoria cones (Nishiki, Yamanomiya, Buri, Otsukue, Kiyotaki and Kannabe) and one scoria bed (Nishibashi-kita). Stratigraphic relationships between various groups of ejecta are inferred from the tephrochronology of fall scoriae and widespread tephra. With the exception of Yamanomiya and Kiyotaki, the volcanic activity began with the formation of scoriae and ended with a phase of lava flow extrusion. No such lava flows are developed in either Yamanomiya or Kiyotaki. The volcanic activity of the Kannabe volcano group mainly took place prior to 21,000-22,000 y. B. P. with the exception of the Kannabe scoria cone itself, which was active before 6,000-6,500 y. B. P. In the vicinity of the Yamanomiya scoria cone, a new debris avalanche deposit has been discovered. This consists mainly of blocks of the Yamanomiya scoria cone, which preserve their original stratification defined by preferential alignment of scoriae and spatters.

著者

水田 敏夫 小畑 正明 江上 桂子

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.35, no.2, pp.249-262, 1990-07-02 (Released:2018-01-15)

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Morphology, abundance and vertical distribution of vesicles were studied in a thick (40-60 m) andesitic lava flow, that lies in the underground of Kumamoto City. The vesicles are frozen bubbles that were fomed in the molten lavas at the time of its eruption. The lava can be divided into three zones: (1) an upper vesicular zone (2) a middle non-vesicular and compact zone and (3) a lower, thinner vesicular zone. The vesicles in the upper zone are elongated vertically, probably due to bouyancy-driven ascent of the bubbles, and those in the lower zone are flattened and elongated horizontally, that may be ascribed to a viscous shear flow at the bottom of the lava flow. Size distribution of the vesicles typically display nearly the log-normal distribution. Abundance, the mean size and the number density of the vesicles are greater in the upper zone than in the lower zone. Such vesicle distribution pattern is consistent to the hypothesis that the lava originally contained abundant bubbles when it was poured on the ground and then the bubbles started to ascent in the lava. Vesicles in the lower zone were the bubbles trapped by the advancing cooling front from the bottom surface of the lava. Bubbles that have escaped from the cold trap below have been accumulated in the upper zone and have been frozen in the lava upon cooling from the top surface. Mass balance calculation, however, indicates that much of the bubbles that were originally present in the lava, have been escaped through the lava surface. A dynamic cooling model was, therefore, proposed, that is to say, in the presence of surface flow in the lave during its cooling, impermeable lava crusts may not be maimtained so that gas bubbles may leak out of the lava into the air.

著者

岩崎 岩次 小沢 竹二郎 平山 光衞 鎌田 政明

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.3, no.2, pp.165, 1959-02-20 (Released:2018-01-15)

著者

小林 哲夫 早川 由紀夫 荒牧 重雄

出版者

The Volcanological Society of Japan

雑誌

火山.第2集 (ISSN:24330590)

巻号頁・発行日

vol.28, no.2, pp.129-139, 1983-07-01 (Released:2018-01-15)

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大隅降下軽石堆積物は, 約22, 000年前に鹿児島湾最奥部で起こった一連の巨大噴火の最初期のプリニアン噴火の産物である.灰白色の軽石と遊離結晶および少量の石質岩片からなる本堆積物は, 全層にわたってほぼ均質な見かけを呈するが, 多くの場合, 上方に向かって粒径がやや大きくなる逆級化層理を示す.層厚分布図(Fig.3)と3種の粒径分布図(軽石の平均最大粒径・石質岩片の平均最大粒径・堆積物の中央粒径;Figs.5, 6, 7)は, いずれも本堆積物の噴出火口が姶良カルデラの南縁, 現在桜島火山の位置する地点付近にあったことを示している.分布軸は火口からN120°E方向に伸びるが, 分布軸から60 km以上離れた地点にも厚く堆積している.又, 堆積物は分布軸の逆方向すなわち風上側にも20 km以上追跡できる.分布軸上で火口から30 km離れた地点での層厚は10 mに達するが, 40 km地点より遠方は海域のため層厚値は得られない.そのため噴出量の見積もりには多くの困難が伴うが, すでに知られている他のプリニアン軽石堆積物の層厚-面積曲線(Fig.4)にあてはめて計算すると, 総体積98 km3(総重量7×1016g)が得られ, 本堆積物は支笏-1軽石堆積物(116 km3)に次ぐ最大規模のプリニアン軽石堆積物であることがわかる.3種の粒径分布図から得られる粒径-面積曲線(Fig.8)は, 噴出速度・噴煙柱の高さ・噴出率などで示される噴火の「強さ」を比較する上で有効である.それにより, 大隅降下軽石噴火の「強さ」はけっして例外的なものではなく, プリニアン噴火の平均あるいはそれをやや上回る程度であったことが判明した.