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 (ISSN:04534360)

巻号頁・発行日

vol.38, no.6, pp.223-226, 1993-12-20

被引用文献数

4 9

著者

津金 達郎 牧野 州明 三宅 康幸 高橋 康

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.1, pp.49-61, 2006-02-28

被引用文献数

4

---

The September 2004 eruptions of Asama volcano, central Japan, ejected essential materials such as pumice with bread crust on September 1st and scoria on September 23rd. The textural and chemical analyses on the materials reveal the crystallization processes in a deep magma chamber and a shallow vent. Two distinct stages of crystallization can be recognized in size distributions and morphology of plagioclase phenocryst and microlite both in the pumice and scoria. First stage (range I ): In a deep magma chamber, pyroxene phenocryst began to crystallize out at 1150℃, and then pyroxene and plagioclase continued to nucleate and grow slowly. Second stage (range II) is divided into two sub-stages for pyroxene or three (range IIa-c) for plagioclase. II a: Magma left the chamber and rose slowly through the vent with ever increasing nucleation rate. II b-c: In a shallow vent beneath the crater, numerous plagioclase microlites like swallow-tailed shape precipitated rapidly under a high undercooling condition induced by decompression. Plagioclase microlite in the pumice and scoria developed a characteristic population density like a bell with a peak at the grain size of 0.003mm, which is interpreted to reflect a decrease in nucleation rate of plagioclase, in response to crystallization and establishment of equilibrium during the time duration when the magma stayed in the vent. Magmatic temperatures estimated from plagioclase-glass equilibrium decreased to 850℃ before the September 1st eruption. The similarity in crystal size distribution of the pumice and scoria implies that they had a common ascent history, although groundmass in the scoria has lower crystallinity than that in the pumice, suggesting that the magma of the Sept. 23rd eruption stood lower in the magma column than the Sept. 1st magma.

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:04534360)

巻号頁・発行日

vol.16, no.2, pp.63-71, 1971

被引用文献数

1 11

---

A model is presented which explains the temporal relation between an eruption and a succeeding earthquake, taking a basaltic stratovolcano, Izu-Oshima volcano, as an example. In the model, volcano is assumed to consist of an underground reservoir and a long pipe connecting the reservoir to the surface. As the compressional crustal strain is gradually stored toward the earthquakes to occur, the volcano, located near the potential fault, is also deformed and contracts to some degree. Then the magma in the reservoir is squeezed up through the pipe. The rise of the magmatic head above a certain level in the pipe causes an eruption, which, once started, may proceed as a self-moving machine. Later, when the earthquake occurs, the strain that squeezed up the magma is released. And the head of the magma falls off resulting in the end of the eruption, in case it has still continued. The bottom of the summit crater of Oshima volcano showed remarkable rise and fall in this century amounting to some 400 meters. The bottom can be regarded as the head of the magma column, since red hot glow was frequently observed during the period. There were two maxima of the height of the bottom, January 1923 and June 1951. Shortly after each of the maxima, occurred great earthquakes with magnitude larger than 8, September 1923 and November 1953 along the Sagami trough which runs some 20km northeast of the volcano toward northwest, branching off from the Japan trench. The area including the volcano has been under compressional tectonic stress with the maximum pressure axis in a horizontal N30°W direction, during at least these hundreds of thousand years. On the other hand, recent fault-model studies of the 1923 earthquake indicate that the fault trace of the earthquake almost coincides with the Sagami trough and that the slip vector of the southwestern block, in which the volcano is located, is toward northwest almost horizontal with slight down going component. This tectonic situation implies that the strain which had been accumulated prior to the occurrence of the great earthquakes along the Sagami trough was caused by the same origin, probably the motion of the Philippine sea plate against the Japanese plate, with what has produced the compressive stress field of the volcanic area. The model appears to be successfully applied for the interpretation of the relation between the eruption of Akita-Komagatake volcano which started on September 17, 1970 and the October 16 earthquake with the magnitude of 6.2 at the epicentral distance of 55km. The frequency of explosion discontinuously dropped down to one half or lower level, three days after the earthquake together with the cessation of Strombolian type of eruption. The preliminary mechanism study of the earthquake showed that there is some component of thrust motion indicating the accumulation of contractional strain prior to the earthquake. The volcano to which the proposed model is applied is thus able to be regarded as a sensitive natural indicator of tectonic crustal strain, and also at the same time as being in a near critical condition ready to erupt.

著者

中禮 正明 福井 敬一 清野 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:04534360)

巻号頁・発行日

vol.31, no.1, pp.63-64, 1986-04-30

著者

山岡 耕春

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.39, no.4, pp.141-153, 1994-09-20

被引用文献数

2 3

---

Relations between activity of volcanic earthquakes in Izu-Oshima volcano and stress and/or strain state around it are investigated. In this paper three kinds of relations are examined during and after the 1986 eruption of Izu-Oshima volcano : (1) How did big earthquakes affect on the volcanic activity of Izu-Oshima? (2) How did the pressure decrease of magma reservoir induce earthquakes around it. (3) How did the dike intrusion induce big earthquakes. The results are as follows : (1) Nine earthquakes of M>5.0 occurred from 1987 through 1990 within the epicentral distance of 100 km from Izu-Oshima volcano. They gave influences on the activity of volcanic earthquakes and/or volcanic tremor when they exerted normal strain of over 10^<-8> on the vertical plane trending N30W. (2) Swarm-like seismic activity in north and western part of Izu-Oshima volcano during the summit eruption is interpreted as an induced swarm due to pressure decrease of magma reservoir. The earthquake swarms occurred both sides of the magma reservoir whose location is estimated from the data of crustal movement. The location of two-lobed earthquake swarm is well explained by a simple model ; infinite two-dimensional elastic medium under differential stress with a circular hole. (3) Large earthquakes accompanied the dike intrusion of 1986 eruption of Izu-Oshima. Two biggest earthquakes occurred at both ends of the dike. A M 5.1 event occurred at the northwestern end and M 6.0 occurred at the southeastern end. Both events may played a role to stop the further propagation of dike intrusion.

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:04534360)

巻号頁・発行日

vol.14, no.1, pp.8-20, 1969

被引用文献数

2

---

Examples are presented in which arrangement of lateral and post-caldera cones indicates the probable regional stress field in the late Quaternary. Izu-Oshima, Hakone and Fuji are among the larger stratovolcanoes to the southwest of Tokyo, the former two having collapse calderas on their summit. Parasitic and post-caldera cones and craters of the three volcanoes are following a trend of similar direction, some of them being produced by fissure eruptions on their flank. The zones trend in the direction of about N 35° W at Fuji, N 45° W at Hakone and N 30° W at Oshima. Dikes are also found in these zones running mostly parallel to them. The trend of fissures of fissure eruptions on the flanks of Fuji and Oshima is also similar to the zones of recent activity. Because sites of flank eruption are regarded as points where radially formed dikes around the central magma column have penetrated the flank, the above described distribution of craters in these volcanoes would indicate a concentration of radial dikes in a specific direction at the three adjacent volcanoes. Considering that dikes are fossil tension cracks formed perpendicularly to the axis of the minimum principal compressional stress, the concentration of parasitic craters can be explained by the stress field caused by the pressure increase in the magma column superimposed on the preexisting regional field with the maximum principal stress axis in a NW direction. The nearly identical, preexisting stress field in the three adjacent volcanoes suggests that the field is part of a more regional one including the area of the volcanoes. This suggestion is strongly supported by the presence of active, conjugate strike-slip faults in the same general area, i.e. on the Izu-peninsula. The maximum compressonal axis indicated by the faults is again in a direction of about N 30° W and oriented horizontally. The last movement of the fault system was observed in 1930, at the time of the Kita-Izu earthquake, whose magnitude was 7.0.

著者

小野 晃司 渡辺 一徳 星住 英夫

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.40, no.3, pp.212-213, 1995-07-31

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 (ISSN:04534360)

巻号頁・発行日

vol.40, no.3, pp.211-212, 1995-07-31

著者

日下部 実 荒牧 重雄 金成 誠一 大隅 多加志

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 (ISSN:04534360)

巻号頁・発行日

vol.32, no.4, 1987-12-28

著者

横山 泉

出版者

The Volcanological Society of Japan

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.58, no.1, pp.77-90, 2013-03-29 (Released:2017-03-20)

参考文献数

34

---

桜島火山は歴史時代において,数度にわたり大噴火が起こり,溶岩流出と地盤の変動が記録されている.それらの中で,1914年噴火は当時の水準で種々の定量的観測がなされている.ここでは特にこの噴火によって生じた沈降の回復を詳論した.水準測量の結果は1916年の発表以来,しばしば議論されているが,姶良カルデラ周辺の沈降の中心は,海域のためもあり,その位置の決定には任意性がある.今回,噴火直後の三角測量の結果をも参考にして,従来より広範囲の沈降について,その中心の位置を桜島の北岸辺に決めた.そして,1914年噴火に伴った大規模の沈降の回復をB.M.2474を例にとり解析した.その際,活動的なこの地域で変動の基準を決めることは極めて難しい.本来は歪みなしの状態(No-strain level)を基準とすべきであるが,ここでは全く便宜上,1914年噴火に先立つ1892年(水準測量の開始)を基準(Reference level)にした.従来,観測を重ねることにより,漸近的に,歪みなしの状態を決められるであろう.結論として,その永年変化は地盤の粘弾性的回復と桜島直下の圧力源の増強との2要素で説明される.1914年噴火直後から粘弾性的回復が進行した(遅延時間は約16.6年).平行して,次第に圧力源へマグマが蓄積するに従って,約20年を経て,その効果が沈降回復へ寄与している.2000年現在は,沈降歪みは既に1892年の基準まで回復して,それにマグマ圧の効果が蓄積している状態である.この議論に付随して,姶良カルデラ地域の地殻上部の粘性を求めた.このような火山地域における粘弾性的地殻変動の他の例として,1983年三宅火山噴火後の沈降を論じ,上記と同じ桁の粘性値を得た.

著者

長谷川 健 松本 恵子 橋本 武志 畑 真紀 岩橋 くるみ 無盡 真弓 村松 弾 大橋 正俊 三反畑 修 嶋野 岳人 田中 良 安田 裕紀

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.68, no.2, pp.105-113, 2023-06-30 (Released:2023-07-27)

参考文献数

10

著者

岡田 里奈 近藤 美左紀 梅田 浩司 古澤 明 天野 格

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.68, no.2, pp.91-98, 2023-06-30 (Released:2023-07-27)

参考文献数

25

---

The Zenikame-Menagawa tephra (Z-M) has been reported from distal terrestrial settings in the southern Hokkaido, with those erupted from Zenikame volcano, and provides an important stratigraphic marker for paleoenvironmental reconstructions of marine isotope stage 3 (MIS 3). We use both major element (EPMA) and trace element (LA-ICP-MS) analyses on proximal and distal Z-M shards to make the correlations to explosive eruptive events. Proximal stratigraphic succession is divided into deposits of two main eruptive phases with pyroclastic fall (Z-Mpfa) followed by pyroclastic flow (Z-Mpfl). The Z-Mpfl and Z-Mpfl deposits are geochemically distinct and thus their origins can be different. Considering geochemical characteristics of glass shards, the distal Z-M in the Tokachi district, located about 200 km west of the source volcano, can be identified as ash fall deposits associated with the Z-Mpfl eruption.

著者

田城 陽菜 八木原 寛

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.68, no.2, pp.75-82, 2023-06-30 (Released:2023-07-27)

参考文献数

14

---

We investigated temporal changes in the peak frequency of harmonic tremors accompanied by eruptions at the Showa crater of the Sakurajima volcano from January 1 to September 30, 2015. The peak frequency characteristics of harmonic tremors at the summit crater of Minamidake from 1982 to 2002 were also compared. We calculated the running spectrum of the harmonic tremors of eruptions at the Showa crater and detected their peak frequency based on the findings of Maryanto et al. (2008) by modifying the parameters. Based on the value of peak frequency and associated temporal changes, we classified harmonic tremors at the Showa crater into the following three types: nearly constant (NC), positive gliding (PG), negative gliding (NG), and others. A sharp transition, with abrupt peak frequency of the harmonic tremor changes over a brief period, was also observed at the Showa crater. Assuming that the fundamental frequency corresponds to changes in the length of the gas pocket, the length of the gas pocket was estimated to change from 110 m to 220 m at the Showa crater. Compared with the features of peak frequencies of harmonic tremors at the summit crater of Minamidake (Maryanto et al., 2008), those at the Showa crater present three differences: 1) Compared with HTB of the summit crater of Minamidake (Maryanto et al., 2008), Depending on the event, NC values had different frequency bands at the Showa crater. HTBs occur several hours after swarms of B-type earthquakes and their peak frequencies remained within a certain range (Maryanto et al., 2008). 2) The increase in f0 of PG at the Showa crater was smaller than that of HTE at the summit crater of Minamidake. HTEs occur several minutes after an eruption, as well as accompanying remarkably strong eruptions and their peak frequencies showed a gradual increase (Maryanto et al., 2008). 3) NG and sharp transitions were only recognized in harmonic tremors during volcanic activity at the Showa crater.

著者

井口 正人 為栗 健 平林 順一 中道 治久

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.64, no.2, pp.33-51, 2019-06-30 (Released:2019-07-06)

参考文献数

50

---

In order to find an empirical event branch logic from abnormal phenomena to following volcanic activity for forecasting scale and type of eruption, the magma intrusion rate prior to eruptions of Sakurajima volcano is examined using ground deformation mostly from observation data and partially based on legends, for eruptions after the 20th century: the 1914 eruption starting with plinian eruption followed by effusion of lava, the 1946 eruptions with lava effusion, eruptions at the summit crater of Minamidake during the period from 1955 to 2005, and vulcanian eruptions at Showa crater east of the summit from 2006 to 2017. Prior to the 1914 eruption, it is estimated that the magma intrusion rate attained a level of approximately 108m3/day and was on the order of 106m3/day during the effusion of lava in the 1946 eruption. During the eruptive period of Minamidake summit crater, three types of eruption occurred: vulcanian eruption, strombolian/lava fountain and continuous emission of volcanic ash. In cases of intrusion of magma forming a new conduit, the intrusion rate immediately before the 1914 eruption exceeded 108m3/day, but only 106m3/day in the dyke-forming event of August 15, 2015. Magma intrusion rate into a pre-existing conduit prior to eruptions at Minamidake summit crater are ordered as follows: vulcanian eruption (1×105 to 8×105m3/day)>continuous emission of volcanic ash (approximately 1×105m3/day)>strombolian/lava fountain (0.2×105 to 2×105m3/day). The magma intrusion rate prior to vulcanian eruptions at Showa crater is smaller (approximately 104m3/day) than for eruptions at Minamidake summit crater. However, the rate reached an order of 105m3/day prior to lava fountain on August 22, 2017. Magma intrusion rates well correspond to the scale and type of eruption. In the case of magma intrusion under detection, the change of volcanic gas and increase in the heat discharge rate are available for the empirical event branch logic.

著者

吉田 明夫 細野 耕司

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.47, no.6, pp.727-738, 2003-01-08 (Released:2017-03-20)

参考文献数

28

---

We investigated how the intermediate-depth seismicity changes with depth in the Pacific slab beneath Hokhaido and the Kanto district using JMA data since Oct. 1997. We found that seismicity in the upper seismic plane decreases noticeably at about the depth of 100 km and on its deeper side both in Hokkaido and the Kanto district. In Hokkaido the volcanic front is located nearly above the line where the seismicity in the upper seismic plane starts to decrease (the D line). This feature is the same as that seen in the Tohoku district (Hosono and Yoshida, 200la). In the Kanto region, however, the D line is located several tens km to the east of the volcanic front, the cause of which may be attributed to the subduction of the Philippine Sea plate above the Pacific plate. We think the noticeable decrease of seismicity in the upper seismic plane at about the depth of 100 km which is commonly observed in the Pacific slab beneath Japan and the correspondence between the location of the D Iine and the volcanic front in Hokkaido and the Tohoku district indicate that the decrease of seismicity in the upper seismic plane may be related to the genetic process of magmatic bodies in the subduction zone.

著者

橋本 武志

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.67, no.4, pp.489-500, 2022-12-31 (Released:2023-01-30)

参考文献数

18

著者

高橋 良 伊藤 久敏

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.65, no.3, pp.69-82, 2020-09-30 (Released:2020-10-13)

参考文献数

32

被引用文献数

1

---

We detected thick pumice layers by observations of cuttings taken from a 1,000 m deep hot spring well at the central Hakodate City, southwestern Hokkaido. In this study, we perform petrological investigations and U-Pb dating for these pumice layers and compare them with the eruptive products from the Quaternary volcanoes at the southern Oshima Peninsula. The pumice layers can be divided into several porphyritic pumice (depth 570-420 m, 310-283 m and 261-66 m) and aphyric pumice (depth 950-660 m, 420-380 m, 343-310 m and 283-261 m) layers. The porphyritic pumice is rich in plagioclase and hornblende phenocrysts and occasionally contains minor amounts of orthopyroxene, clinopyroxene, biotite, quartz and cummingtonite phenocrysts. The U-Pb ages of the lowermost and uppermost parts of the porphyritic pumice layers are 0.93±0.04 Ma and 0.81±0.06 Ma, respectively. Although lithic-rich part is partly observed, these pumice layers mostly consist of pumice clasts. In addition, pumices show variously welded textures at several depths. These features suggest that the thick pumice layers resulted from repeated pyroclastic flows and that reworked deposits are limited. This indicates that the source of the pumice layers should be located adjacent to Hakodate City, whereas the petrological features and U-Pb age of the pumice layers are inconsistent with the known eruptive products of the Quaternary volcanoes at the southern Oshima Peninsula. Therefore, our results indicate that unknown pumice eruptions repeatedly occurred around this area during 0.9-0.8 Ma. Although any pumice eruptions have not been detected in Hakodateyama volcano (1.5 km SW of the hot spring well), the eruption ages and mineral assemblage of the porphyritic pumice are similar to the lavas of the volcano, implying that the source of the pumices was Hakodateyama volcano or its adjacent area.

著者

奥野 充 井口 正人 三好 雅也 三浦 大助 小林 淳 橋本 武志 大場 武 佐藤 鋭一 宝田 晋治

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.67, no.3, pp.251-254, 2022-09-30 (Released:2022-10-27)

参考文献数

18

著者

鈴木 由希

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.67, no.2, pp.233-244, 2022-06-30 (Released:2022-07-28)

参考文献数

27

著者

小山 真人

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.349-371, 1998-10-30 (Released:2017-03-20)

参考文献数

53

被引用文献数

2

---

Reevaluation of places, type, magnitude, and influences of the 800-802 A.D. eruption (Enryaku eruption) of Fuji Volcano, Japan, was made through tephrochronology and analyses of historical records. The Nishi Kofuji fissure on the northeastern slope is newly recognized as a crater of the 802 A.D. flank eruption. The Nishi Kofuji fissure ejected fallout scoria toward ENE and lava flows, which can be correlated with Takamarubi and Hinokimarubi 11 Lavas on the northeastern foot. The Tenjinyama-lgatonoyama fissure on the northwestern slope probably erupted during the Enryaku eruption and ejected fallout scoria and lava fiows. A series of historical documents and paintings (Miyashita documents), which are unauthorized, personal records and are regarded to be unreliable by many historians, includes many detailed descriptions of paleogeogra-phy around Fuji Volcano and of the Enryaku eruption. Although some of the descriptions were exaggerated and conflict with geological observations, some of them are concordant with geologic data. The Enryaku eruption probably gave serious damages to ancient traffic routes particularly on the northwestern-northeastern foot of Fuji Volcano. The Gotenba area, which is located on the eastern foot, was also damaged by thin ash-fall and probably by lahars. This caused a temporal, southward relocation of the offical trafiic route, which had passed through the Gotenba area.