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)

---

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.

著者

小山 真人 井村 隆介 石橋 克彦

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.43, no.4, pp.205, 1998-08-31 (Released:2017-03-20)

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.36, no.3, pp.357-370, 1991-10-15 (Released:2017-03-20)

被引用文献数

2

---

The recent progress of physical volcanology is reviewed focusing on studies on volcaniclastic flows and their deposits. Pyroclastic flows are high-particle-concentration, laminar currents with gas as a continuous phase. Pyroclastic surges are low-particle-concentration, turbulent currents with gas as a continuous phase. Lahars are flows of debris with liquid water as a continuous phase. Debris avalanches are catastrophic landslides in which a continuous phase is absent or plays no role for the motion. Owing to the upward gas flow, fluidization processes operate in pyroclastic flows. Flow behavior and resultant deposits are remarkably different depending the degree of fluidization, because it effectively reduces the yield strength of the flow. However, the distance traveled is slightly affected by the degree of fluidization. It is determined mainly by the mass incorporated at the source or by the velocity acquired when it wes initiated.

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.177-190, 1995-07-31 (Released:2017-03-20)

参考文献数

47

被引用文献数

13

---

Loam is an international scientific term, however, it has been used in a peculiar way in Japan. Japanese loam is a massive, brown, weathered rock unit composed of silt, clay, sand and occasional lapilli. It extensively covers coastal terraces, river terraces, ignimbrite plateaus and other uplands around volcanoes. Loam is not a product of soil forming process operated beneath the earth surface against rock bodies ; but it is a sediment accumulated slowly on the earth surface. Small-magnitude volcanic eruptions play a very minor role for the sedimentation. An eolian reworking process of pre-existing fine-grained deposits by the wind plays a major role. This is proved by following facts : 1) loam has accumulated even during the time when no ash-fall was observed ; 2) a volcano infrequently erupts explosively and the intensity of ash fallout is far lower than the sedimentation rate of loam ; it is about 0.1 mm/year ; 3) loam is hardly thickening toward a volcano. Very small particles carried from continental China by the westerlies at a high altitude are contained in loam, however, in the area around volcanoes their contribution is little for the formation of loam compared with eolian dust carried from nearby bare grounds by local winds at a low altitude. Loam does not accumulate all the year round. Just before and during fresh verdure, occasional strong winds pick up fine particles into the air from a bare ground which is dried up by a high-angle sunlight and high-temperatures. Eventually fine particles will settle down in vegetation. The most favorable season for loam deposition is April to May, in which more than half of an annual amount is achieved. It is convenient and practical to define a single eruption by a tephra layer which is not interbedded with loam. The thickness of loam can be used for the quantitative measurement of geologic time intervals, in years to thousands years, on certain conditions. Lithology of Japanese loam and the mechanism of sedimentation are identical to those of loess in other areas, such as China, northern Europe, northern America and New Zealand. There is no reason to hesitate to designate Japanese loam loess.

著者

上木 賢太 原口 悟 吉田 健太 桑谷 立 浜田 盛久 Iona McINTOSH 宮崎 隆 羽生 毅

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.1, pp.3-21, 2023-03-31 (Released:2023-03-31)

参考文献数

60

---

Kikai caldera, a submarine caldera to the south of Kyushu, is the source of the youngest caldera-forming supereruption during the Holocene (i.e., the Kikai-Akahoya eruption at 7.3 ka). During its volcanic history, the Kikai caldera has experienced at least three caldera-forming supereruptions (i.e., the Kikai-Akahoya, Kikai-Tozurahara and Koabi eruptions). To better understand the processes of submarine caldera-forming supereruptions and the evolution of the large felsic magma bodies from which they derive, we have constructed a geochemical database for the eruption products of the Kikai Caldera, including proximal deposits and distal tephras (https://doi.org/10.6084/m9.figshare.20066630). We compiled geochemical data reported in various papers and proceedings from both domestic Japanese and international journals. The new database, comprising 413 individual samples from 59 publications, contains all available major- and trace-element concentrations, isotopic ratios, analytical methods, geographical coordinates (latitude, longitude, and altitude) of sampling points, age data, refractive index, and geological and petrological information. The database is freely available to the public online. Based on the constructed database, we review the current geochemical understanding of Kikai caldera magmatism and discuss geochemical characteristics of magmas from the Kikai caldera. The difference in magma composition between the two recent caldera-forming supereruptions (the Kikai-Akahoya eruption at 7.3 ka and the Kikai-Tozurahara eruption at 95 ka) is clearly seen in the compiled data. Moreover, we find that the distal tephra represents a more SiO2-rich magma composition than that of the proximal deposits, especially in the case of the Kikai-Akahoya eruption.

著者

竹内 晋吾

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.501-511, 2022-12-31 (Released:2023-01-30)

参考文献数

41

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

---

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

---

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

---

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 林 信太郎 三浦 光世 内柴 良和

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 2006 (ISSN:24335320)

巻号頁・発行日

pp.111, 2006-10-23 (Released:2017-02-10)

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

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

---

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

田中 智 白井 慶 白石 浩章 山田 哲哉 早川 雅彦 後藤 健 山田 竜平 及川 純 村上 英記 佐伯 和人 井口 正人

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.73, 2019 (Released:2020-04-13)

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

---

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

---

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