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

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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

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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

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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

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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

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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

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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.

著者

草野 有紀 及川 輝樹 石塚 吉浩

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.4, pp.327-346, 2021-12-31 (Released:2022-02-22)

参考文献数

54

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Nikko-Shirane Volcano located on the border of Gunma and Tochigi prefectures had the largest eruption on the historic records in AD 1649. We reconstructed the eruption event based on the geological mapping of the pyroclastic fall deposit and craters at the summit, 14C dating of soil underlying the pyroclastic fall deposit and interpretation of historic records. The pyroclastic fall deposit is observed in a 10×6 km area around Nikko-Shirane Volcano and thickens to the summit of Mt. Shirane. The pyroclastic fall deposit is preserved at>4 km east from the summit and observed 5-8 cm thick around Lake Yunoko and 20 cm thick in maximum around the southern part of Senjogahara. Based on the historic records of the 1649 eruption, the craters with about 220 m in long axis diameter and 30 m deep located next to a small shrine at the summit were opened. Thus, the 1649 eruption is considered to occur at the summit of Mt. Shirane and pyroclastic materials fell east to southeast ward. The total mass of pyroclastic fall deposit is estimated at 2×107-3×107 m3 which is a digit larger than the previous report, and it is comparable to Volcanic Explosive Index=3 and Magnitude=3.4-3.6. The pyroclastic material contains essential vesicular vitreous particles consisting 1-48 % (mean 19 %) of component in 250-2000 μm fraction. Combination of the essential particles in the 1649 pyroclastic materials suggests that a magmatic eruption was occurred during the 1649 eruption. The essential particles are concentrated in three principal distribution axes of the pyroclastic fall deposit extending to the east, southeast and west. However, the pyroclastic fall deposit is composed of a lot of fine particles, indicating that the 1649 eruption would be possible of a phreatomagmatic eruption triggered by magma intrusion to an aquifer below the volcanic body. Around the time of the eruption, lahar occurred at the western valley of Mt. Shirane and flowed through Ohirogawara to the Nigamatazawa River.

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.323-347, 1998-10-30 (Released:2017-03-20)

参考文献数

74

被引用文献数

5

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All available historical documents, which reeord abnormal phenomena relating (or possibly relating) to the activity of Fuji Volcano, Japan, were re-examined and classified aceording to the reliability of each document. Comparisons of the reliable descriptions with geologic evidence were executed and several new correlations between historical records and eruptive deposits are proposed. Volcanic activity of Fuji Volcano was in high-level from the 9th to I Ith century; in this period at least 7 reliable and 5 possible eruptions occurred. Although only 2 reliable and 1 possible eruption records exist from the 12th to the early 17th century, this low-level activity may be apparent because of lack of enough historical records. After the middle 17th century, enough historical records suggest that the activity is generally low except for the 1707 eruption, which is one of the most voluminous and explosive eruptions in the history of Fuji Volcano. At least thirteen large earthquakes (M 8 and possible M 8 class) have occurred near Fuji Volcano (in east Nankai and Sagami Troughs) since the 9th century. Eleven of these 13 earthquakes were accompanied with volcanic events (eruption, rumbling, or change in geothermal activity) of Fuji Volcano before and/or after each earthquake (in ±25 years).

著者

津久井 雅志

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 2017 (ISSN:24335320)

巻号頁・発行日

pp.68, 2017 (Released:2018-02-01)

著者

宮縁 育夫 星住 英夫 渡辺 一徳

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.49, no.2, pp.51-64, 2004-05-20 (Released:2017-03-20)

参考文献数

33

被引用文献数

5

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The stratigraphy and chronology of late-Pleistocene (after deposition of AT ash) tephra layers erupted from post-caldera central cones of Aso Volcano, SW Japan, are evaluated through study of the thick tephra sequence preserved mainly atop the pyroclastic-flow plateau east of the caldera. Twenty andesite to basaltic-andesite scoria-fall deposits (YmS20-YmS1 in ascending order) and two pumice-fall deposits (NbP2 and NbP1) were identified as maker beds for the interval ca. 29-13ka (calibrated 14C age). The tephra layers were produced mostly by scoria and ash eruptions of Nakadake, the only active post-caldera central cone, and their bulk volumes calculated from isopach maps range from 0.01 to 0.9km3. The radiocarbon ages of buried soils just below individual tephra layers reveal that YmS20 to YmS15 were erupted at ca. 22-21 ka and YmS20 to Ym-S1 at ca. 18-16ka. Total tephra volume during 29-13ka is estimated at about 1.3km3 (DRE). Production of tephra was mainly concentrated in two periods : 22-21 ka (0.8km3) and 18-16ka (0.5km3).

著者

栗谷 豪

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.3, pp.147-156, 2021-09-30 (Released:2021-10-29)

参考文献数

35

著者

長谷川 健 柴田 翔平 小林 哲夫 望月 伸竜 中川 光弘 岸本 博志

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.66, no.3, pp.187-210, 2021-09-30 (Released:2021-10-29)

参考文献数

57

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Based on detailed fieldwork, petrological and paleomagnetic investigations, we present a revised stratigraphy of deposits from the 7.6 ka eruption at Mashu volcano and the formation process of its summit caldera, eastern Hokkaido, Japan. As previously described, the eruption products consist of an initial phreatomagmatic unit (Ma-j) and the overlying three pumice-fall layers (Ma-i, -h, and -g), which are in turn overlain by pyroclastic-flow deposits (Ma-f). In the present study, we divide Ma-f into 4 subunits: Ma-f1/2, Ma-fAc, Ma-f3a and Ma-f3b in descending order. Ma-f3b is a valley-ponding, pumice-flow deposit with limited distribution. Ma-f3a comprises clast-supported facies (fines-depleted ignimbrite: FDI) and matrix-supported (normal ignimbrite) facies, the two changing across topography. The FDI is characterized by a gray, fines-depleted, lithic-breccia-rich layer with materials incorporated from the substrate. Impact sag structures from large (>50 cm) dacite ballistic blocks were recognized at the base of the Ma-f3a within 10 km from the source. Ma-fAc is a minor eruption unit consisting of accretionary lapilli. Ma-f1/2 is a most voluminous (8.8 km3), widely distributed and weakly stratified ignimbrite. Both Ma-f3a and Ma-f1/2 can be classified as “low aspect ratio ignimbrite (LARI)”. Dacite lithic fragments are ubiquitously observed throughout the sequence and are not considered to be juvenile; they have distinctly different chemical compositions from the pumice fragments in the early pumice-fall (Ma-g~Ma-i) and pyroclastic-flow (Ma-f3b) deposits, but those of pumice clasts in the late pyroclastic-flow units (Ma-f3a and Ma-f2) lie between the two on a FeO*/MgO vs. SiO2 diagram. The 7.6 ka caldera-forming eruption of the Mashu volcano was initiated by Plinian fall (Ma-j~-g), and then, a small-volume high aspect ratio ignimbrite (Ma-f3b) was deposited by a valley-confined pyroclastic flow that was generated by partial column collapse. After that, a violent pyroclastic flow was generated probably during a strong explosion of a dacite lava edifice on the summit of Mashu volcano. This flow emplaced Ma-f3a. The caldera collapse that followed the explosion generated a climactic pyroclastic flow that emplaced Ma-f1/2. Ma-f3a flow was extremely fast. Ma-f1/2 flow was related to sustained flow due to low settling velocity and high discharge volume. These are supported by field observations and numerical simulation that shows the ability of the flow to surmount high topographic obstacles and spread widely. The 7.6 ka caldera-forming process of Mashu volcano was driven not only by subsidence of roof block but also by violent explosions.

著者

湯浅 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.40, no.4, pp.277-284, 1995-09-20 (Released:2017-03-20)

参考文献数

29

被引用文献数

1

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Many caldera volcanoes occur in the northern part of the Izu-Ogasawara Arc. These submarine calderas produced a large amount of pumice and show high gravity anomalies in the central parts along with small amplitude of magnetic anomalies on the volcanic edifices. They have no equivalent in the usual classification of on-land calderas as far as known. Elsewhere I proposed that the submarine "calderas" associated with pumice in the arc were pumice cones which were difficult to form under subaerial conditions but easy under subaqueous conditions. The Myojin Knoll is one of the typical pumice cones with calderas in the arc. It is located between Aogashima Island and Myojinsho Reef. The size of the knoll is about 18 km in diameter at the base and 950 m in height. The knoll has caldera structure on its summit. The nearly circular caldera rim is 5-7 km in diameter. The caldera floor is about 1400 m deep and 5-6 km across. A central cone rises from the floor. Relief of the caldera wall is about 700-900 m with the inner slope being at about 20-30°. The submersible study by Shinkai 2000 reported here shows that the top of knoll is constructed mainly of stratified pumice deposits underlain by rhyolitic lava. These rocks have characteristic chemical compositions with high SiO2 (more than 71 wt%) and low K2O (less than 0.86 wt%), and show similar range to the rocks from Aogashima Rift volcanoes to the west of the knoll rather than those from adjacent Myojinsho Reef Volcano. The eruption under the deep water conditions caused the deposition of pumice near the crater. The repetition of such eruptions formed the submarine pumice volcano. Acid volcanism under subaqueous conditions in the northern part of the arc formed the volcanoes with pumice cones and calderas.

著者

松本 弥禄 石﨑 泰男

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 2019 (ISSN:24335320)

巻号頁・発行日

pp.165, 2019 (Released:2020-04-13)

著者

片山 郁夫

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.61, no.1, pp.69-77, 2016-03-31 (Released:2017-03-20)

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Water plays an important role for magma genesis and frictional properties; consequently, water circulation systems contribute to the variation of magmatic and seismic activity at subduction zones. Although subducting plate transports a large amount of water, most of water is released into the mantle via dehydration reactions at elevated temperature during subduction. Aqueous fluids released from the subducting plate then migrate along the plate boundary due to permeability anisotropy developed in the highly sheared serpentinite. Based on laboratory data, we estimated the fluid migration velocity to be〜7cm/year, which is close to the descending plate velocity, suggesting that polarity of water migration can be different in subduction systems. In northeast Japan, fluid migration velocity is slower than the subduction velocity, and hence water is transported downward into the deeper portions trapped by the mantle corner flow. In contrast, in southwest Japan where the fluid velocity is higher than the subduction velocity, water could be returned to the shallow regions along the subducting plate interface. This model can explain the seismic low velocity anomalies and geochemical signatures in these regions, in which the hydration of the plate interface is observed in shallow mantle wedge in southwest Japan, but is limited to the deeper parts of the mantle in northeast Japan. Water transported to deep levels could contribute to the active arc volcanism in northeast Japan, whereas water circulating at shallow levels in southwest Japan could trigger slow earthquakes due to fluid pressure build-up at the plate boundary.

著者

木下 貴裕 神田 径 高倉 伸一 関 香織 松永 康生 木下 雄介 相澤 広記

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.2017, pp.181, 2017

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.