著者

井村 隆介 小林 哲夫

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.36, no.2, pp.135-148, 1991-07-15 (Released:2017-03-20)

被引用文献数

8

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This paper presents results of geologic investigation of the eruptive activity in the last 300 years of Shinmoedake, an active volcano in the Kirishima Volcano Group. The recent activity of this volcano is divided into four eruptive episodes : the 1716-1717, 1771-1772, 1822 and 1959 episodes. The most important activity occurred in 1716-1717. During the 1716-1717 eruption, fallout deposits, pyroclastic flows and mudflows were widely dispersed around the volcano. The products of this episode show that the eruption progressed with time from phreatic to magmatic. These field data are in good agreement with historic records of eruptive activity. According to the historic records, the eruptive activity lasted from 11 March, 1716 to 19 September, 1717. The 1771-1772 and 1822 activities produced base surges, pyroclastic flows, fallout tephra and mudflows that were confined to the slope and eastern base of the volcano, but historic records do not reveal the details of these eruptions. The field evidence shows the same phreatic to magmatic sequence as the 1716-1717 activity. However, the eruptions of both episodes were on a smaller scale than the 1716-1717 eruption. The 1959 activity was well described. This episode produced minor gray silty to sandy lithic fallout tephra indicating that only phreatic activity occurred. The fallout was distributed northeast of the vent. In conclusion, the field evidence and historical records show that each eruptive episode of the current activity of Shinmoedake progressed from phreatic to magmatic. The eruptions are frequently accompanied by pyroclastic flows and mudflows.

著者

西川 空良 浜本 未希 本田 明紗海 図子田 和典 清藤 大河

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.99-104, 2023-06-30 (Released:2023-07-27)

参考文献数

12

著者

鈴木 隆介

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.13, no.2, pp.95-108, 1968

被引用文献数

1

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One of the fundamental differences between volcanic cone and non-volcanic mountains such as folded mountains is that the latter itself is a part of the earth's crust, while the former is taken as a heavy load which is laid upon the pre-existing earth's crust within a short geological time and is durable for several tens of thousands of years. In this respect, a volcanic cone resembles an ice sheet, a huge building and a large dam. It is, therefore, postulated that volcanic cone settles down by its own weight. From this point of view, characteristics of the subsidence of some strato-volcanic cones in Japan and Indonesia (Table 1) are comprehensively discussed in this paper. The results are summarized as follows. The settlement of volcanic cone causes various deformations at the foot of volcanic cone such as ring fault, thrust and the circular anticlinally uplifted ridge, all of which tend to encircle the volcanic cone settled. Based on the modes of these deformations at the foot, the settlement of volcanic cone is classified into three types ; 1) fault type, 2) fold type, and 3) mixed type. They are schematically shown in Fig. 5. Which type among the three takes place seems to depend on the nature of the basal rocks beneath the volcanic cone (Table 1 and Fig. 5). The fault type occurs in the case where Pliocene sedimentary rocks are thinner than about two hundreds meters in thickness and also most of the basal rocks are composed of Tertiary sedimentary rocks older than Pliocene. On the contrary, in the case where Pliocene sedimentary rocks are thicker, generally several hundreds to thousands meters, the fold type or the mixed type results. Magnitude of settlement is of order of one to two hundreds of meters in the depth settled. Rate of settlement of Iizuna volcano, which belongs to the fold type, is estimated to be of order of about four millimeters per year. Distance from the center of volcanic cone to the circular deformed feature (D), which is thought to show the magnitude of deformation originated by the settlement, is proportional to the relative height of volcanic cone (H), which can be taken as the substitute for the weight of volcanic cone (Fig. 6). Such relationship between D and H is also found in the case of guyot, which is surrounded by circular moat or ridge (Fig. 5), but not found in the case of collapse calderas as shown in Fig. 6.

著者

及川 輝樹 池上 郁彦 渡部 将太

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.3, pp.171-187, 2023-09-30 (Released:2023-11-02)

参考文献数

73

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Submarine volcanic eruptions produce a large amount of drifting pumice around the globe at a frequency of once every several to ten years. However, there is little knowledge about what kind of eruptions produce them. Document records of large amounts of pumice washed ashore in the Nansei Islands in southwest Japan are summarized in this article, along with an assessment of their source volcanoes and eruption frequency and style. A large amount of drifting pumice has washed ashore on the Nansei Islands eight times (1778 or 1779, 1905, 1914, 1915, 1924, 1934, 1986, 2021) since the 18th century, seven of which were after the 20th century, at a frequency of several times every 100 years. This frequency is not remarkably low compared to other natural hazard events. The eruptions that provided the source of these drifting pumice were the Fukutoku-Oka-no-Ba 1904‒1905 and 1914 eruptions, the Myojin-Shou 1915 eruption, Submarine Volcano NNE of Iriomotejima 1924 eruption, the Showa Iwo-jima 1934 eruption and the Fukutoku-Oka-no-Ba 1986 and 2021 eruptions. In the 8 recorded volcanic eruptions, including the uncertain ones, 6 were due to submarine volcanic eruptions in the southern part of the Izu-Bonin Arc. It took 2 to 6 months (mostly 2 to 4 months) for drifting pumice to reach the shores of the Nansei Islands from the Izu-Bonin Arc. The eruption styles that generated a large amount of drifting pumice can be divided into three cases. (1) An eruption that ejects a large amount of pumice from the seafloor to the sea surface and causes a steam-based volcanic plume to rise at the center of the eruption. They often occur from vents with seafloor depths of several hundred meters (Submarine Volcano NNE of Iriomotejima 1924 and Showa Iwo-jima 1934), but they also occur in shallower waters (Myojin-Shou 1915). (2) An eruption that occurs in shallow water (<50 m), with repetitive Surtseyan eruption activity that forms islands composed of large amounts of pyroclastic material, while at the same time producing large amounts of drifting pumice (Fukutoku-Oka-no-Ba 1904‒1905, 1914 and 1986). (3) An eruption that occurs in shallow water (<50 m) and produces a volcanic plume reaching the stratosphere. This style of eruption forms an island and generates a large amount of pyroclastic material, including drifting pumice (Fukutoku-Oka-no-Ba 2021).

著者

木尾 竜也 成尾 英仁 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.67, no.3, pp.401-408, 2022-09-30 (Released:2022-10-27)

参考文献数

12

著者

小野 晃司 渡辺 一徳 星住 英夫 高田 英樹 池辺 伸一郎

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.40, no.3, pp.133-151, 1995

参考文献数

41

被引用文献数

21

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We describe in this paper the character of ash eruption of Nakadake volcano presently going on and maintain that the products of the volcano during the recent geologic past are the main constituents of ashy soils distributed around, especially to the east of, the volcano. Nakadake volcano, the only active central cone of Aso caldera, mainly discharges black, sandy essential ash of basaltic andesite during its active period. The ash is the most voluminous constituent of the products of Nakadake through its activity of recent more than 20,000 years. We call ash eruption for the activity which discharges dominantly ash. The ash is divided into three groups : block-type ash, splash-type ash, and free crystals. The block-type ash, most common, is polyhedral surrounded by a few flat planes. It is formed by brittle fracturing of semi-solid top part of the magma column. While, the splash-type ash, discharged only during the very active phase in active periods, is derived from liquid magma which underlies the semi-solid top of the column. The ash is transported by gas stream from the magma in a quasi-steady state or intermittently, and is distributed around Nakadake volcano in a near-circular pattern by a low eruption column usually less than 1,000 m in height. Long-term thickness contours of the ashy soil from Nakadake volcano in three time intervals, separated by the present earth surface and three ash or pumice layers, of recent more than 20,000 years also show near-circular pattern but a little elongated to the east. 'Loam beds', mainly composed of decomposed and argillized volcanic ash, are said to be formed by accumulation of aeolian dusts during periods of no eruption in volcanic districts. But, loam beds (Akaboku) and black humic soils (Kuroboku) distributed around Aso volcano are composed mainly of primary fall-out deposits of ash or pumice along with aeolian dusts. Ash eruption of Nakadake mostly produces sandy ash rather continuously without long time break but in small rate of discharge. A correlation of detailed columnar sections eastwards of Nakadake crater shows most single strata of ashy soils, light brown- to black-colored, thin according to the increase of distance from the source crater. The ash, especially very fine ash distributed in the distal area, easily decompose and lose primary stratification to form a massive layer which is hardly discernible from aeolian loam beds by their close resemblance. Not only fine ash layers but Plinian pumice fall layers form 'loam' beds which are not distinguishable with adjacent aeolian beds by further decomposition. The thickness contours of the Kanto loam elongate and thin eastward from Fuji volcano over the Kanto plain. The thickness of loam beds changes regionally, thicker in volcanic areas and thinner in non-volcanic areas. These facts suggest contributions of primary pyroclastic falls for thickening of 'loam beds'

著者

井村 隆介 小林 哲夫

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.36, no.2, pp.135-148, 1991

被引用文献数

16

---

This paper presents results of geologic investigation of the eruptive activity in the last 300 years of Shinmoedake, an active volcano in the Kirishima Volcano Group. The recent activity of this volcano is divided into four eruptive episodes : the 1716-1717, 1771-1772, 1822 and 1959 episodes. The most important activity occurred in 1716-1717. During the 1716-1717 eruption, fallout deposits, pyroclastic flows and mudflows were widely dispersed around the volcano. The products of this episode show that the eruption progressed with time from phreatic to magmatic. These field data are in good agreement with historic records of eruptive activity. According to the historic records, the eruptive activity lasted from 11 March, 1716 to 19 September, 1717. The 1771-1772 and 1822 activities produced base surges, pyroclastic flows, fallout tephra and mudflows that were confined to the slope and eastern base of the volcano, but historic records do not reveal the details of these eruptions. The field evidence shows the same phreatic to magmatic sequence as the 1716-1717 activity. However, the eruptions of both episodes were on a smaller scale than the 1716-1717 eruption. The 1959 activity was well described. This episode produced minor gray silty to sandy lithic fallout tephra indicating that only phreatic activity occurred. The fallout was distributed northeast of the vent. In conclusion, the field evidence and historical records show that each eruptive episode of the current activity of Shinmoedake progressed from phreatic to magmatic. The eruptions are frequently accompanied by pyroclastic flows and mudflows.

著者

筒井 正明 小林 哲夫

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.67, no.1, pp.21-30, 2022-03-31 (Released:2022-04-26)

参考文献数

37

---

Ohatayama and Ohataike are adjacent volcanoes aligned in NE-SW direction at the northeastern portion of Kirishima Volcano Group, Kyushu, Japan. Ohatayama volcano has three small craters around the summit area, and Ohataike has a summit crater lake with a diameter of 400 m. Both volcanoes are composed mainly of tephra fall deposits by plinian or sub-plinian eruptions, with intercalations of pyroclastic flow deposits. The main volcanic edifice of the highest point of Ohatayama volcano was formed at least 22 cal ka BP. Tsukiyama were formed earlier than the highest point, and there is a possibility that they can be separated from the highest point. The triangulation point of Ohatayama volcano started its activities on the highest point somewhere around 17-11 cal ka BP, and forming craters A and B. Ohataike volcano was formed by erupting again around 17-11 cal ka BP, after the main volcanic edifice was formed during around 22-17 cal ka BP on the northeast side of the triangulation point. This was followed by four different modes of eruption at Ohatayama C crater in the following order: a phreatic eruption (Oy-4) in 7.6 cal ka BP, Ohatayama lava emission, magmatic and phreatic eruptions (Oy-3) in 7.1 cal ka BP, magmatic and phreatic eruptions (Oy-2) in 6.8 cal ka BP, and lastly, phreatic eruption (Oy-1) in 6.5 cal ka BP. Although no volcanic activity occurred from Ohataike volcano since 11 cal ka BP, foamy volcanic gas is currently being detected on the surface of the crater lake.

著者

石橋 秀巳 岩橋 くるみ 安田 敦 諏訪 由起子 長崎 志保 外西 奈津美

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.2, pp.119-129, 2021-06-30 (Released:2021-07-27)

参考文献数

51

---

Recent studies proposed empirical equations describing the relations between amphibole single-phase chemistry and the pressure-temperature-compositional conditions of the coexisting melt. These methods are called amphibole single-phase thermometer, barometer, and melt-chemometer, and have been used in the previous ten years to investigate magma reservoir processes of subduction-related volcanoes. Here, the three methods are briefly introduced with their reliabilities. Then, we review the applications of these methods to clarify magma reservoir processes, chiefly using as examples three volcanoes of Kyushu, i.e. the Tsurumi-dake, Aso and Unzen volcanoes. The pressure-temperature-SiO2 content conditions of the melts estimated from amphiboles enable us to determine physicochemical conditions of the end-member melts of magma mixing, even for cases in which the mixed melt is perfectly homogenized and/or the end-member melt is chemically similar to the mixed melt. We could further identify a phenocryst mineral-melt disequilibrium in a magma, which is usually difficult to recognize from petrography and is a potential factor of misinterpretation for magma reservoir processes, based on the results. Furthermore, the estimated pressures constrain the depth conditions of magma plumbing systems, which can be cross-checked by the results of geophysical observations. These results demonstrate the usefulness of the methods for investigating magma reservoir processes.

著者

早川 由紀夫 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.403-407, 1998-10-30

被引用文献数

14 12

著者

西村 太志

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.64, no.2, pp.53-61, 2019-06-30 (Released:2019-07-06)

参考文献数

14

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Eruptive activities of volcanoes are examined by using a global data catalog of volcanoes provided from Smithsonian Institution. Yearly numbers of volcanic eruptions with a volcanic explosivity index (VEI) larger than or equal to 2 are almost constant from 1900, and the frequency distribution of the magnitude of volcanic eruptions obeys a power law in the range of VEI≥2. About 10 to 30% of volcanic eruptions with VEI≤2 end within one day, and 8 to 15% continue for more than 1 year. On the other hand, a few percentages of large eruptions with VEI≥3 end for a few days, and 25-30% continue for more than 1 year. Once an eruption occurs, the occurrence possibility of new eruptions at volcanoes locating within a 100km distance increases about 30% for 0.2 year. When the volcanoes locating at a region with a radius of 200km are examined together, yearly numbers of eruptions per volcano fluctuate within a factor of three for a few tens of years at more than about 90% of the regions. Frequency distribution of the yearly number of eruptions follows an exponential decay, which suggests an existence of a characteristic frequency of the eruptive activity on the globe. These averaged features of eruptive activities at volcanoes around the world can be used to give some basic characteristics of the occurrence of new eruptions.

著者

池辺 伸一郎 藤岡 美寿夫

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.46, no.4, pp.147-163, 2001

参考文献数

28

被引用文献数

1 2

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Yunotani spa is located to the west part of the Central cones of Aso Volcano. Since the 14th Century, many people have been visiting this hot spring. A few explosions were referred in an old document "Nagano-ke-nikki; Diary of Nagano family". However, the details of these events are not yet clear. We have found a set of historical records on the explosion called "Yunotani Catastrophe" that took place at the solfatara of Yunotani spa in July 6, 1816. These records, two drawings and five reports on the explosion, describe the events and damages in detail. A lot of "hot-mud" with many blocks were ejected from two vents, and destroyed 12 bathrooms and injured one person in the area about 100 m from the vents. Judging from the descriptions and occurrences of the hydrothermally altered ejecta around the vents, it can be said that this event was caused by steam explosions from the solfatara. By the revelation of these records, it became clear that an explosion occurred not only at Naka-dake but also in the area outside of Naka-dake in the historic age. This fact is important for the prevention of volcanic disaster in Aso Volcano.

著者

宮城 磯治 前嶋 美紀

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.57, no.1, pp.45-50, 2012-03-30 (Released:2017-03-20)

参考文献数

13

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For better estimation of the temperature of red-hot volcanic ejecta from their images taken by online digital cameras at night, we studied the applicability of a new pyrometer to the images. Our pyrometer applies the theory of black-body radiation to the color of red-hot object. We examined the color of red-hot volcanic ejecta, a heated basaltic rock with known temperature, and infra-red LEDs. Because of the sensitivity to infra-red ray, a digital camera Nikon D40 can visualize hot basalt specimen at temperatures much lower (ca. 370℃) than the naked eyes (500~550℃). As a side-effect of this capability, color data of the hot basalt discord from the isothermal color lines calculated from the black-body radiation and the CIE colorimetric system. Night photographs taken by the online digital camera aimed at the explosive ash eruptions of Asama volcano (2 a.m. 2 Sep., 2009) indicated that the color of red-hot volcanic ejecta was disturbed by the influence of infra-red ray in the same manner as observed on the heated basalt specimen in the laboratory. As a result, the temperature of the volcanic ejecta would be much lower than their appearance in digital images (e.g., 1000℃) but higher than the detection limit (370℃). Comparison of the color of red-hot volcanic ejecta and isothermal color lines revealed that some of the volcanic ejecta fell along the 600℃ isotherm line of the black-body radiation, which suggests that volcanic cloud reduces the influence of infra-red ray. The estimated temperature (600℃) is consistent with those deduced from petrological observation and thermodynamic computation (600〜700℃). We conclude that color analysis of the images of red-hot ejecta taken by online digital cameras are useful in temperature evaluation when images suffer less influence of infra-red ray.

著者

星住 英夫 宮縁 育夫 宮城 磯治 下司 信夫 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.1, pp.91-112, 2022-03-31 (Released:2022-04-26)

参考文献数

71

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Aso volcano produced four huge ignimbrite-forming eruptions named Aso-1, 2, 3 and 4 in ascending order, among which Aso-4 is considered the largest eruption in Japan in the last 1 million years. This paper describes the tephra sequence between the Aso-4 and Aso-3 eruptions (Aso-4/3 tephra group). The reconstruction of the eruptive history for Aso-4/3 tephra group presented here provides a valuable contribution to the understanding of caldera volcanism by outlining the preparatory processes of a catastrophic ignimbrite eruption. The eruption sequence of the Aso-4/3 tephra group, which is composed of at least 37 units of pumice-fall, scoria-fall, and ash-fall deposits, is divided into five stages. Stage 1 is characterized by the eruption of mafic scoria (VEI 3-4) during 133-114.1 ka, after the eruption of Aso-3. Stage 2 is characterized by the frequent eruptions of mafic scoria and ash (VEI 3-4) during 114.1-108.4 ka. The magma composition became more felsic during explosive eruptions (VEI 3-4) from 108.4-104.7 ka (Stage 3). During the most active stage from 104.7-97.7 ka (Stage 4), voluminous felsic pumice-falls erupted (VEI 4-5). The ABCD tephra (97.7 ka) is the largest plinian pumice-fall deposit of Aso volcano. Stage 5 (97.7-88 ka) is a relatively dormant period, during which only a biotite dacite pumice-fall was deposited (VEI 4). The low number of eruptions during stage 5 suggests that the magma supply rate decreased during the 10 thousand years that preceded the Aso-4 ignimbrite eruption. The estimated total tephra volume for the Aso-4/3 tephra group is 23 km3, which corresponds to 10 km3 in dense rock equivalent (DRE). The estimated the long-range tephra discharge rate (0.23 km3 DRE/ky) is similar to that in the post-caldera stage of Aso-4 (0.2 km3 DRE/ky).

著者

金田 泰明 長谷川 健

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.1, pp.1-19, 2022-03-31 (Released:2022-04-26)

参考文献数

46

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Nigorikawa volcano in southwestern Hokkaido, Japan, has a small caldera approximately 2 km in diameter. We carried out geologic, petrologic, and paleomagnetic studies of pyroclastic deposits on Nigorikawa volcano to reveal its eruption sequence and geologic history with high resolution. Nigorikawa pyroclastic deposits are divided into two eruption stages (1 and 2) separated by a paleosol layer 14C-dated at 12,901-12,750 calendar years. This suggests a ca. 1000 year hiatus between the Syn-caldera-forming eruption (Stage 1) and post-caldera activity (Stage 2). Stage 1 is composed of 7 units (Ng-1~Ng-7, in ascending stratigraphic order), while Stage 2 (Ng-8) is represented by a small (>0.01 km3) pyroclastic flow deposit. The minimum total volume of the whole units (Ng-1 - Ng-8) is estimated to be 8.2 km3. Ng-1 consists of a lower (Ng-1 a) 0.11 km3 ash unit and an upper (Ng-1b) 0.53 km3 ash and pumiceous fall deposit, respectively. Ng-2 is a small (<0.02 km3) pyroclastic flow deposit narrowly distributed in the northeast of the volcano. Ng-3 (0.02 km3) and Ng-5 (0.07 km3) are respectively sub-Plinian to Plinian pumice falls, that sandwich the Ng-4 (0.01 km3) intra-Plinian flow deposit. Ng-6 is a climactic ignimbrite (7.35 km3) further divided into Ng-6 a (lower) and -6b (upper) units based on the existence of a lithic concentration zone (LCZ) between the 2 units. In addition, co-ignimbrite ash (Ng-6c) widely covers the eastern distal area of the volcano. Ng-7 is a lithic-dominated pyroclastic surge deposit (0.07 km3) characterized by cross/parallel laminations. Ng-1 and Ng-7 commonly contain silty ash and blocky glass shards with moss-like morphology suggesting that they were formed by magma-water interaction (phreatomagmatic eruption) that occurred at the initiation and termination of Stage 1. Ng-8 (Stage 2) is a newly discovered eruption unit. Paleomagnetic features demonstrate that Ng-8 is a lateral flow deposit that was emplaced at a high (350-400 °C) temperature. Stage 2 can be stratigraphically and chronologically correlated with the post-caldera activity of the volcano that generated (1) tephra in the caldera-lake (lacustrine) deposits and (2) intrusive rocks (lava and dykes) through the caldera-fill deposits, both of which are described in borehole samples by previous work. Amphibole andesite lava fragments showing oxidization coating and having slightly different chemistry than co-existing juvenile pumice are generally included in all Nigorikawa pyroclastic deposits. We speculate that the older edifice of the andesitic lava dome (1.7 km3) existed before the Nigorikawa caldera formed.

著者

筒井 智樹 為栗 健 井口 正人

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.66, no.2, pp.71-81, 2021-06-30 (Released:2021-07-27)

参考文献数

24

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A seismic reflector at 13.6 km beneath western Aira Caldera, northmost part of Kagoshima Bay, Kyushu, Japan is discussed through later phase analysis of controlled source seismograms obtained in the experiment in 2008. A prominent seismic later phase appears at 8.3 s in travel time on the seismograms in northeastern Sakurajima Volcano for ray paths across western Aira Caldera in the seismic experiment in 2008. Back-azimuth of the later phase orientates center of western Aira Caldera and apparent velocity of 3.7 km/s is measured in the seismic array at northern Sakurajima Volcano. The later phase is inferred as P-SV converted reflection at 13.6 km depth from its travel time and a corresponding reflector located in the east off Osakigahana point, western part of Aira Caldera. Negative impedance contrast at the reflector is inferred from negative polarity of the onset of the later phase. Some clear later phases after S arrival, which appears in seismograms of natural earthquakes through trans-caldera ray paths, can be explained as SS reflection at the reflector. The reflector inferred as top surface of a possible magma reservoir of Aira Caldera, from its negative polarity and its location at depth of the west of known pressure source from preceding geodetic surveys.

著者

西村 太志 石橋 秀巳 森 俊哉 地引 泰人 中道 治久 齋藤 武士 嶋野 岳人 吉村 俊平 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.3, pp.133-134, 2021-09-30 (Released:2021-10-29)

著者

石原 和弘 小林 哲夫

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:04534360)

巻号頁・発行日

vol.33, no.3, pp.269-271, 1988-10-31

被引用文献数

2

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

参考文献数

74

被引用文献数

9

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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

田島 靖久 松尾 雄一 庄司 達弥 小林 哲夫

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.59, no.2, pp.55-75, 2014-06-30 (Released:2017-03-20)

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The Kirishima volcanoes located in southern Kyushu are comprised of more than 20 volcanic edifices. The volcanoes occupy an elliptical area of approximately 330km2 with the WNW-ESE direction. Among the different types of volcanic edifices, the typical ones are compound maars and lava flows in Ebinokogen. We studied the volcanic history of Ebinokogen by geological examination of tephra layers and lava flows. After the Karakunidake-Kobayashi plinian eruption, seven tephra were formed in this area. We determined the ages of those tephra and two lava flows. The magmatic eruptions, produced Tamakino B tephra, occurred after Karakunidake-Kobayashi tephra eruption. The first activity in Ebinokogen from about 9.0 cal ka BP generated Fudoike lava flow, and Fudoike-Tamakino A tephra erupted from Fudoike crater. Karakunidake north-Ebino D tephra was generated from the northwest flank of Karakunidake at 4.3 cal ka BP, with debris avalanche and lahars. Phreatic Fudoike-Ebino C tephra erupted from the Fudoike crater at 1.6 cal ka BP. Ioyama-Ebino B tephra eruption started from around the 16th to 17th century with lava flow. Phreatic Ioyama east-Ebino A tephra erupted from Ioyama east crater in 1768 AD. The Ebinokogen area is one of the active regions of Kirishima volcanoes explicated by geophysical observations. Our results indicate cyclical tephra depositions mainly produced by small magmatic and strong phreatic eruptions in this area after the Karakunidake-Kobayashi pyroclastic eruption. Furthermore, the vent locations were found to migrate with each eruption.