著者

安井 真也 高橋 正樹 金丸 龍夫 長井 雅史

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.293-325, 2021-12-31 (Released:2022-02-22)

参考文献数

36

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The Asama-Maekake volcano has been active during the last 10,000 years. Large-scale eruptions that occurred in the 18th and 12th centuries have been well studied, whereas little information is available for older eruptions. In this paper, we aim to reconstruct the history of this volcano in detail through a combination of extensive geological survey and 14C dating. The observation and description of twenty-one trench excavations, two drilling core samples, and many outcrops enabled us to build a stratigraphy of the eruptive products in much greater detail than ever before. The trench excavation sites cover an area of nearly 180 degrees around the volcano. These sites were selected mainly in the medial area at distances between 5 and 10 km from the summit crater. Many older deposits buried by thick younger deposits were found. The pyroclastic fall deposits of this volcano vary from a thick pumice layer to pumice grains scattered in the black soil, indicating a variation in the scale of sub-plinian eruptions. More than 120 samples for 14C dating were taken from the black soil immediately beneath the pyroclastic fall deposits. Some charcoals contained in the pyroclastic flow deposits were also subjected to dating. The 14C dating results were used for the correlation of deposits of different localities and distributions of some pyroclastic fall deposits older than 2000 years were revealed. The qualitative evaluation of the number and scale of eruptions throughout history might be possible using these data. Four classes of eruptive scales are recognized in the pyroclastic fall deposits in this study. Class 1: Defined by the isopach line for 128 cm thickness being able to be drawn on the map and the area enclosed by the 64 cm isopach line being more than 25 km2. The deposits are recognized at distant locations more than 50 km from the summit crater. Class 2: Defined by that the isopach line for 64 cm thickness being able to be drawn on the map and the area enclosed by the 16 cm isopach line being more than 15 km2. Class 3: The deposit of this class is recognized as a distinct layer that continues horizontally at each locality. In most cases, the observed thickness is less than several tens of centimeters and generally no structure can be observed. Class 4: This class comprises scattered pumice grains in the soil, for which the measurement of thickness is impossible. The deposits of classes 3 and 4 are seldom found at distances farther than 15 km from the crater. Most of the pyroclastic fall deposits of the period between 9400 and 3100 cal BP are of Classes 3 and 4. On the other hand, a large-scale eruption (Class 1) occurred about 2000 years ago, generating pyroclastic fall deposits in distant areas of more than 50 km from the crater. The recurrence interval of large-scale eruptions during the last 2000 years is estimated to be about 700 years. This is less frequent than in the period prior to 2000 years ago. Therefore, a change in eruption mode occurred about 2000 years ago when eruptions became infrequent but large in scale.

著者

柳澤 妙佳 小畑 大樹 杉田 匠平 藤縄 明彦

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.83-100, 2021-06-30 (Released:2021-07-27)

参考文献数

17

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Akita-Komagatake volcano, located at 30 km west of the volcanic front in the Northeast Japan arc, has been active in the recent 100,000 years with caldera-forming eruptions occurred around 13,000 years ago. The formation history of the pre-caldera stratocone has not been fully established, though it is inevitable to grasp the whole development scenario of the volcano, and also to mitigate potential volcanic hazards in the future. We reconstruct the stratigraphy of the lavas and pyroclastics that erupted during the stratocone building stage, by combining the new field and geomorphological observations with petrographic, lithologic and geochemical data. Geomorphology involves preservation degrees of original micro-geomorphic features on their surfaces, such as lava levees and lava wrinkles. We identify 38 eruptive units that made up the stratocone, including 31 units of low-K tholeiitic (TH) as the dominant magma series, with 4 units of calc-alkaline (CA) series, and additionally 3 units of MD (medium) series that show intermediate characteristics between TH and CA. The volcanic activity of the stratocone is divided into two stages on the basis of the distinctive eruption centers and their resultant contrastive edifices. The latter stage (stage 2) can be further divided into two substages, 2-1 and 2-2, respectively, because of contrastive preservations of micro-geomorphologic features on the lava surfaces. In stage 1, fluidal lava flows, mainly basalt to basaltic andesite in compositions, were effused from the southern crater to form the southern stratocone showing a shield-like gentle slope. There are several observations that suggest dormancy and/or erosion interval might be present between the stages 1 and 2; epiclastic deposits are characteristically recognized immediately below the lavas of the stage 2, and one of the deposits directly overlies a lava flow of the stage 1. The crater moved northward and commenced discharge magmas considerably silica-rich compositions compared with those erupted in the stage 1, and built up another steeper stratocone (northern edifices). Although, the northern edifices ware mainly developed in the stage 2-1, three lava flow units display distinctively better preservation of micro-geomorphic features on their surfaces. The freshness of these topography together with some tephrochronologic data suggest that the final stage (stage 2-2) must have lasted immediately before the caldera collapse occurred ca. 13,000 years ago.

著者

馬越 孝道 清水 洋 松尾 のり道

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.5, pp.223-235, 1994-11-20 (Released:2017-03-20)

参考文献数

22

被引用文献数

1

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Fugendake, the main peak of Unzen Volcano of Kyushu Island in southwest Japan, started to erupt on November 17, 1990, after 198 years of dormancy, and lava extrusion has continued over three years since May 1991. Hypocenters of earthquakes which occurred before and during that eruption were precisely determined using P-wave arrival time data from five selected seismic stations near the focal region. The hypocenters in Chijiwa Bay are distributed in Chijiwa Caldera. Two linear arrangements of epicenters directed nearly from west to east emerged clearly in the western part of the Shimabara Peninsula, whose hypocentral depths became shallower toward the summit of Fugendake. The distribution of hypocenters is restricted by the fault systems which have been formed by the crustal movements of Unzen Graben. The stress which generates these earthquakes is dominated mainly by the north-south extension ; consistent with the regional tectonic stress. The directions of pressure axes are controlled by the magmatic pressure beneath the focal region. It is inferred from the hypocentral distribution and the orientations of pressure axes that the magma involved in the 1990-94 eruption is situated below an inclined boundary between seismic and aseismic regions in the western part of the Shimabara Peninsula. The magma ascent path is located at 13±2 km in depth beneath the western shore of the Shimabara Peninsula, becoming shollower eastward with an angle of elevation of 40〜50°.

著者

伊藤 英之 早津 賢二 鈴木 浩二

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.45, no.3, pp.181-186, 2000

参考文献数

7

著者

井村 隆介

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.37, no.5, pp.281-283, 1992-11-15 (Released:2017-03-20)

参考文献数

5

被引用文献数

3

著者

平林 順一

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.33, no.2, pp.p102-104, 1988-07

著者

宇井 忠英

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.48, no.1, pp.177-181, 2003

参考文献数

12

被引用文献数

1 3

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.app1, 2022 (Released:2023-01-30)

著者

安井 真也 金丸 龍夫 松田 ひかる

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.479-488, 2022-12-31 (Released:2023-01-30)

参考文献数

9

著者

森脇 広 永迫 俊郎 奥野 充

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.31-44, 2022-03-31 (Released:2022-04-26)

参考文献数

39

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The southwestern rim of Aira caldera, which is situated at the head of Kagoshima Bay, is critical for examining late Pleistocene and Holocene crustal movements of the caldera with respect to volcanic activity. A suite of Pleistocene and Holocene sea-level and eruption records occurs in combination in exposures on the rim, and so tectonic displacement of the caldera as well as volcanic activity in historical times are both obtainable. Using elevations of coastal landforms and deposits, and with a chronology determined via tephrochronology and archeological remnants, we examined vertical crustal movements of the Aira caldera in the late Pleistocene and Holocene, and compared these movements with historical movement in the light of concomitant volcanic activity. The main conclusions are as follows. Aira caldera has been subjected to distinct uplift, with an average rate of 0.5-0.8 mm per year over the past ~108,000 years. The uplift rate of 0.8-1.1 mm per year, from ~7000 cal BP to the present, appears to be higher than that, 0.4-0.7 mm per year from ~108,000 to ~7000 cal BP. Comparison of these late Quaternary uplift rates with those in historical time clearly suggests that volcanic activities of Aira caldera are responsible for the late Quaternary vertical movements in and around Aira caldera. The results help to evaluate future eruptions of Aira caldera, and to examine the relationships between the late Quaternary crustal movement and volcanic activities in other gigantic calderas without sea-level remnants.

著者

為 栗健 八木原 寛 筒井 智樹 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.67, no.1, pp.69-76, 2022-03-31 (Released:2022-04-26)

参考文献数

22

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We obtain a three-dimensional seismic velocity structure below the Aira caldera at a depth shallower than 15 km, southwest Japan, applying seismic tomography inversion method to analyze 14,652 P-wave onsets and 10,935 S-wave onsets of natural earthquakes observed by 45 seismic stations, and 3,121 P-wave onsets generated by artificial explosions. An anomalous zone of low S-wave velocity is discriminated at depths deeper than 12 km below the center of the Aira caldera. The S wave velocity is 18-55 % lower than the surrounding area. The volume of the anomalous zone is 139~255 km3 at shallower depths than 15 km, and the anomalous zone includes about 7 % melt (10~18 km3). Accumulation of magma in the anomalous zone activates a pressure source at the top of the zone, where velocity contrast of the S-wave is intense, and the pressure source induces inflationary ground deformation around the Aira caldera.

著者

風早 竜之介

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.347-368, 2021-12-31 (Released:2022-02-22)

参考文献数

92

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Volcanic gases are high temperature gases degassed from a magma at depths, emitting to the surface. The volcanic gases give us important clues for understanding of eruptive phenomena as their emissions are closely related to the amount of degassed magma within the volcano. The quantification of the volcanic gases is also important for environmental problems and disaster preventions because they contain toxic species. The main components of the volcanic gases are water, carbon dioxide, and sulfur dioxide (SO2). The SO2 gas has been used as an index of volcanic gas flux because SO2 is readily quantified using remote-sensing techniques based on ultraviolet (UV) spectroscopy and the atmospheric air is SO2 free. In this article, the importance of the SO2 flux and overview of current and future remote-sensing approaches from ground are discoursed. Benefits for practical operations given from the recent developments are highlighted, stressing how these brand-new techniques could be applied to help monitoring of volcanoes.

著者

地引 泰人

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.4, pp.369-374, 2021-12-31 (Released:2022-02-22)

参考文献数

21

著者

小園 誠史

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.135-146, 2021-09-30 (Released:2021-10-29)

参考文献数

16

著者

山科 健一郎

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.43, no.5, pp.385-401, 1998-10-30

被引用文献数

2

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Various suggestive documents and associated sketehes are collected for understanding the pre-eruptive and the earliest stages of the 1914 great eruption of Sakurajima volcano, southwestern Japan, in Taisho era. Based on these records, the premonitory process to the eruption was reviewed especially with respect to the occurrence of many earthquakes which resulted in repeated rock falls with dust clouds, unusual upwelling of water and hot spring, and emission of volcanic smoke in the morning of January 12. Although there are many descriptions on the beginning of the remarkable eruption, they are sometimes inconsistent with each other. In the present paper, it is proposed that the valcano started to erupt around 09 : 58 on January 12 (Japanese Standard Time) at 200 m in height in the western slope of the mountain. In several minutes, a line of craterlets was formed between 200-500 m in height in the WNW-ESE direction. The development of a subsurface fissure in this direction resulted in another outbreak in the southeastern slope probably around 10 : 05. For the better understanding of this important eruptive event, discoveries of additional references are still desired.

著者

宮城 磯治 東宮 昭彦

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.757-761, 2003-01-08 (Released:2017-03-20)

参考文献数

16

被引用文献数

3

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We developed a new thermometer that uses color of volcanic ashes. A series of heating experiments for basaltic ashes under the atmospheric condition provided a quantitative relationship among color, heating temperature, and heating duration. The higher the heating temperature, the more the redness in color of heated ash. We applied the relationship to estimate heated temperature of the ash that was underlying below or contact with a cauliflower-shaped volcanic bomb ejected from the Miyakejima volcano on 18 August, 2000. The estimated temperature was about 390℃ for the ash underlying 1 cm below the volcanic bomb, and 550℃ for the ash in contact with the bomb. Numerical heat transfer calculations for the volcanic bomb on the ash layer suggested that temperature of its center at the time of landing is about 1,000℃. This is the first concrete evidence that the bomb was essential material and that the 18 August eruption was phreatomagmatic.

著者

小山 真人 吉田 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.39, no.4, pp.177-190, 1994-09-20

被引用文献数

9

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A magma-discharge stepdiagram, which shows a relationship between time and cumulative discharge volume/mass of a volcano, is a useful tool for estimating a magma supply/discharge system beneath the volcano. We propose a model to explain the shape of the magma-discharge stepdiagram, and estimate effects of an abrupt change in crustal stress/strain field, which can modulate the shape of the stepdiagram. Using the shape of the stepdiagram, volcanoes can be classified into four types : time-predictable (TP), volume-predictable (VP), strictly-periodic (SP), and nonpredictable (NP) volcanoes. In the TP volcano, the length of a dormant period is proportional to the magma-discharge volume of the preceded eruption. In the VP volcano, the discharge volume of an eruption is proportional to the length of the preceded dormancy. In the SP volcano, both a length of a dormant period and a discharge volume of an eruption do not change. In the NP volcano, both a length of a dormant period and a discharge volume of an eruption do not have clear predictability. The predictability in the TP, VP, and SP volcanoes can be explained using a simple magma supply/discharge model beneath a volcano, assuming that ascent pressure at the top of a magma reservoir (P_m) monotonously increases in a dormant period, and that magma-discharge volume is proportional to the decrease of P_m at an eruption. Besides these two assumptions, the TP and VP volcanoes need a constant upper limit (P_u) and a constant lower limit (P_l) of P_m, respectively. The SP volcano needs constant P_u and P_l. The magma-discharge stepdiagrams of the TP, VP, and SP volcanoes can be modified by a large intrusive event, changes of physico-chemical parameters in a magma reservoir, a magma-supply rate from the lower crust or mantle, structural evolution of a magma-supply/discharge system, a small eruption which does not affect the predictability of a magma-discharge stepdiagram, and an abrupt change in a crustal stress/strain field. Such modifications spoil the predictability in the stepdiagrams and thus make the NP volcano. An abrupt change in a crustal stress/strain field causes a change in P_m and/or P_u and thus can modify a magma-discharge stepdiagram. Particularly, an increase in P_m and/or a decrease in P_u can trigger an eruption. An upward shift of a magma-discharge stepdiagram may be a key to finding such a trigger of an eruption and to estimating mechanisms of triggering.

著者

鈴木 毅彦

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.167-176, 1995

参考文献数

26

被引用文献数

4

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So-called kazanbaido which means volcanic-ash-soil in a literal translation overlies surfaces and hill slopes in most area of the Japanese island. In 1960's, the kazanbaido with massive structure and brown color was recognized as residual soil (not transported soil) which was originated from pyroclastic deposits. Recently, most studies regard the kazanbaido as soil formed through the accumulation of dispersal tephra, eolian dusts from the Asian continent and local eolian dusts. In this study, the author discusses the source of the material constructing kazanbaido on the basis of the pattern of change in its thickness (Fig. 1). The kazanbaido treated here has accumulated during the last 50,000 years in central Japan. Thickness of the kazanbaido distributed along the Japan Sea coast and in the south part of the Shizuoka Prefecture is less than 1 m. Source of the kazanbaido seems to be a lot of fine distal air-fall deposits which derived from distant volcanoes, a long-range transported eolian dust from the Asian continent, and local eolian dust from the adjacent non-vegetated area. Kazanbaido thicker than 2 m distributes in the South Kanto and North Kanto areas. Increase in the thickness of the kazanbaido in these areas is most likely caused by depositions of tephras derived from near volcanoes. Two main depositional processes of accumulation of the thick kazanbaido are as follows. One is frequent accumulation of a minor air-fall deposit associated with a small-scale eruption, which does not form stratification because of the small volume of each deposit. The other is accumulation of secondary tephras, which are derived from the slope of a volcano through wind transportation. Change in thickness in the Kanto area suggests that the former is more significant than the latter.

著者

堀田 耕平 髙橋 秀徳 本田 裕也 剣持 拓未

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.83-89, 2023-06-30 (Released:2023-07-27)

参考文献数

21

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Leveling surveys were conducted in Jigokudani valley, Tateyama volcano, since 2015. Subsidence was revealed to have started in 2017‒2018 when a new crater was formed at southwestern area of Jigokudani. Subsidence kept until 2020. During the one-year period from September 2020 to September 2021, ground of Jigokudani was revealed to have re-uplifted. We applied five types of deformation sources (Mogi-type spherical, finite spherical, penny-shaped, rectangular tensile fault and prolate spheroid sources) to the detected deformation. Using the grid search method and the weighted least squares method, we searched the optimal combination of the parameters of each model. Based on the c-AIC value, the penny-shaped deformation source was the best model among them. A penny-shaped inflation source with a radius of 375 m was located including southeastern area of Jigokudani valley where violent fumarole activities have been continued. Its depth was 50 m from the surface. The pressure change in the source of +0.8 MPa yields its volume change of +4800 m3. Inflation of the gas chamber beneath Jigokudani valley might have started due to increase in accumulation of volcanic gas/fluid or decrease in fumarolic activity.

著者

松本 恵子 コンウェイ クリス 畑 真紀 伊藤 久敏 岩橋 くるみ 片岡 香子 森田 雅明 西原 歩 三反畑 修 渡部 将太 山﨑 誠子 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.68, no.2, pp.115-123, 2023-06-30 (Released:2023-07-27)

参考文献数

7