著者
小林 淳 青木 かおり 村田 昌則 西澤 文勝 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.65, no.2, pp.21-40, 2020-06-30 (Released:2020-07-06)
参考文献数
35

This study established tephrostratigraphy and clarified the eruption history of Niijima volcano (Izu Islands, Japan) after the Miyatsukayama event (12.8-8.5calka) through geological survey around the central and northern parts of Niijima island, and Shikinejima and Jinaijima islands. Detailed explanation is summarized below. The Miyatsukayama eruptive event started at the north of Akazakinomine lava dome (central part of Niijima island) at 12.8calka. The series of eruptions formed Miyatsukayama lava dome, and produced Nj-MtG tephra (12.8-8.5calka) and K tephra (ca. 8.5calka). In particular, the first pyroclastic density current covered the Akazakinomine lava dome thickly, accompanying fallout deposits (Nj-Mt tephra) which were widely distributed in the northern part of Izu Islands. Subsequently, the Shikinejima event ejecting Nj-Sk tephra occurred at ca. 8calka. At ca. 7.5calka, H(s) tephra was produced by the eruption near Shikinejima island, and H(n) tephra was produced by the Niijimayama event. During the Miyatsukayama-nanbu event (ca. 5.5calka) producing Nj-Mt(s) tephra, pyroclastic density currents erupted from the southern part of Miyatsukayama lava dome, buried depressions on the Miyatsukayakma lava dome and formed horizontal and flat surface. The erupted pyroclastic material covered the Akazakinomine lava dome widely and formed pyroclastic cones and lava domes near the source. After that, the Wakago event (Ni-Wg tephra), the D tephra event and the Kudamaki-Atchiyama event (Nj-KdAt) erupted basaltic magma at ca. 3.6calka, ca. 1.6calka and AD 856-857, respectively. Several decades after the Kudamaki-Atchiyama event, the Mukaiyama event (Nj-My) occurred at the southern part of Niijima island in AD 886-887. The Mukaiyama event is the largest eruption during the last 12.8 kys. At Niijima Volcano, eruptions with the magnitude equivalent to the Mukaiyama event (>0.1DREkm3) have occurred every thousand years since the Miyatsukayama event, and the large area of the island was covered with pyroclastic density currents at each eruption.
著者
西村 裕一 荒牧 重雄
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.44, no.1, pp.41-43, 1999-03-05 (Released:2017-03-20)
参考文献数
3
被引用文献数
1
著者
早川 由紀夫 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.36, no.1, pp.25-35, 1991-04-15 (Released:2017-03-20)
被引用文献数
1

The eruptive history of Aso volcano for the past 80,000 years is revealed by tephrochronology and loess-chronometry. Around the Aso caldera is a thick accumulation of loess, which is intercalated with numerous Aso tephra layers of limited dispersal as well as three widespread tephra layers of known age that are good marker horizons ; the Akahoya ash (6.3 ka), the Aira-Tn ash (22 ka), and the Aso-4 ignimbrite (70 ka). Loess-chronometry is based on the assumption that, in the Aso region, the accumulation rate of loess has been constant as 12 cm/ky from 80 ka to the present. Most of tephra layers after the caldera-forming Aso-4 eruption are composed of volcanic sand or scoria lapilli of basaltic andesite composition. However the 27 ka Kusasenri dacite (SiO2 = 67%) pumice is a conspicuous exception. The large volume of 5.85 km3 (bulk) and wide dispersal of this pumice suggests that it is a product of plinian eruption. From October 5 to the end of November 1989, the Nakadake crater of Aso volcano was in eruption. Ash was uninterruptedly emitted from a 500-1,000 m high eruption column coming out of the crater. The average discharge rate of ash was 5 × 107 kg/day. The total mass of ash discharged during the two months reached 3 × 109 kg. The penultimate eruption in recent history was June-August 1979, when 7.5 × 109 kg of ash was discharged. Outside the Aso caldera, the thickness of the 1989 ash is less than 1 cm. It is almost impossible to detect an old ash layer of thickness about 1 cm in a loess cross section, suggesting that sedimentary records 10 km away from a volcano are insufficient to reconstruct past eruptions smaller than 1010 kg. Eruptions smaller than 1010 kg can be determined only from proximal deposits. The history of eruptions of Aso volcano over the last few thousand years is tentatively determined from cross sections 2-4 km west of the Nakadake crater. After a 580-1,250 year dormant period, Aso volcano became active about 1,780 years ago. From then, small eruptions each with 109-1010 kg ash discharge have been repeated 48-88 times up to the present. The duration of each eruption was a few months, and the dormant interval between eruptions averaged 20-37 years.
著者
横尾 亮彦 市原 美恵 谷口 宏充
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.49, no.5, pp.299-304, 2004-10-29 (Released:2017-03-20)
参考文献数
24
被引用文献数
1

Izu-Oshima volcano, one of the most active volcanoes in Japan, started a series of emotions on Nov. 15, 1986. One of the characters of the e ructions is the small-scale explosions with flashing arcs, which were the visualized shock waves as a phase change of H2O in the air. occurred at the summit lava-lake. The flashing arcs, seen on the movie, show several characteristics; 1) they spread and propagate semi-spherically, and 2) the launching of semi-spherical ballistics follows the flashing arcs. Analysis of the movie indicates that the velocities of flashing arcs were 300-440 m/s and their sources were located almost on the surface of the lava-lake. We paid attention to the ballistics in the light of scaling laws, which were established from field explosion experiments, so that we were able to estimate explosion energy as about 8×109J. Additionally, assuming that the flashing arcs were produced by an explosion, such as a bursting of pressurized-bubbles, we could get information of their condition, a relationship between inner-pressure and the size.
著者
菅 香世子 小林 勝己 印牧 もとこ 宮原 智哉 遠藤 邦彦
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.37, no.2, pp.71-83, 1992
参考文献数
21
被引用文献数
4

Kozushima consists of rhyolitic monogenetic volcanoes (lava domes and thick lava flows), and is located on Zenisu Ridge, northern part of Izu-Bonin Arc. Activities of the momogenetic volcanoes were accompanied with pyroclastic flows and surges. But their succession and stratigraphy are not well known. We tried to discuss them based on observation in construction field of Kozushima Airport and its neighborhood in southern part of the island. Three pyroclastic surge deposits were confirmed on thick lava flow which was fomed tens of thousands years ago. They are, Chichibuyama pyroclastic-surge deposit-B which was older than 22,000 y.B.P., Chichibuyama pyroclaslic-surge deposit-A which erupted 21,000-19,000y.B.P. and Tenjosan pyroclastic-surge deposit which was fomed 838 A.D. in ascending order. Two regional ash-fall deposits which originated from gigantic eruptions in Southern Kyushu and several ash-fall deposits from another islands were interbeded with them. Thus, only three pyroclastic surge deposits have come to deposit in southern part of Kozushima while tens of thousands years. It does not mean that only three eruptions occurred in Kozushima the while, but suggests that most eruptions could not bring pyroclasic materials on the thick lava flow whose height is 100-300 m in southern part of Kozushima except above mentioned three eruptions. Most pyroclastic flows and surges were strongly controled by topography in Kozushima, but some were not. That might be caused by the difference of eruption energy or eruption types.
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.Special, pp.S1-S15, 1995-12-25 (Released:2017-03-20)

Age of a tephra can be determined by simple stratigraphy, if adequate number of time-markers are provided. Eleven master tephras are chosen as the time-markers for the last one million years. They are Kikai-Akahoya (7.330 ka), Aira-Tanzawa (26.00 ka), Daisen-Kurayoshi (50.00 ka), Aso-4 (87.00 ka), Ata-Torihama (250.0 ka), Kakuto (340.0 ka), Suiendani-TE5 (420.0 ka), Kobayashi-Sakura (540.0 ka), Kaisyo-Toriitoge (650.0 ka), Shishimuta-Azuki (870.0 ka), and Shishimuta-Pink (1000 ka). The present earth surface and Bruhnes/Matuyama boundary (780.0 ka) play a same role as master tephras. Ages of some master tephras are assigned rather arbitrarily, however, it is productive to affix them once to a specific value. A tephra sandwiched between two master tephras is afforded its age by interpolating the thicknesses of loess between them. This technique, loess-chronometry, has the advantage of ability to measure an interval of tens to thousands years in the geologic past, over radiometric dating. More than 900 tephras are presently recorded and linked each other in a computer database including name, source volcano, age, magnitude, stratigraphy, and remarks. An updated version is listed in WWW at "http://www.la.gunma-u.ac.jp/〜hayakawa/English.html".
著者
石崎 泰男 森田 考美 鳥山 光
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.62, no.3, pp.95-116, 2017-09-30 (Released:2017-10-11)
参考文献数
32

The ca. 17 cal. ka BP eruption at Nantai Volcano, NE Japan, initially produced widespread Plinian fallout deposit (Nantai-Imaichi Tephra:Nt-I) and two overlying associated scoria flow deposits, i.e., dacitic pyroclast-rich, Shizu Scoria Flow Deposit (SZ) and andesitic pyroclast-rich, Takanosu Scoria Flow Deposit (TKS). A∼2.8m thick outcrop of the Nt-I at Nikko City, 7.5km ESE of the volcano, consists of a basal phreatic fall bed (∼2cm thick) and eleven overlying fall units (units 1-11 in ascending stratigraphic order) defined by componentry, size grading, and chemical composition of the pyroclasts. The total lack of clear boundary structures between each unit suggests that the Nt-I was generated by the pyroclasts falling from continuous eruptive column. Grain size analyses of the Nt-I shows that column height rapidly increased and reached its climax soon after the eruption began, and then oscillated slightly and declined until the end of the Plinian phase. The composition of the pyroclasts shows that the Nt-I resulted from the tapping of a stratified magma chamber, in which dacitic magma capped hybrid andesitic magma. Light-colored, microlite-free, dacitic pumice (DWP) predominates from unit 1 through unit 9. In contrast, moderately vesicular andesitic scoria (AGS) is a major constituent of units 10 and 11. Microlite-rich dacitic obsidian (DOB) is present from unit 1 through unit 3, but was not observed above unit 3. Microlite-rich dacitic scoria (DBS) is present from unit 1 through unit 8, and coexists with DOB in single pyroclast. A plausible explanation for the common eruption of a small amount of microlite-rich pyroclasts along with the predominant DWP is that the microlite-rich pyroclasts represent fragments of the degassed margins of the conduit through which the dacitic magma rose. As the eruption advanced, the passageway may have widened, and the microlite-rich magma along the conduit wall was eroded and ejected along with the DWP. The density of the DWP remained constant from unit 1 through unit 8, and then increased at unit 9. The incorporation of slightly denser, dacitic pyroclast into the column is likely to have destabilized the eruption column. The destabilization caused partial collapse of the column and generated the intra-Plinian Shizu Scoria Flow Deposit, whose particle density is similar to that of unit 9. In contrast, the ejection of dense AGS combined with the incorporation of dense lithics into the eruption column is likely to have destabilized the column, and triggered total column collapse that formed the post-Plinian Takanosu Scoria Flow Deposit.
著者
三村 弘二
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.47, no.4, pp.217-225, 2002-09-17 (Released:2017-03-20)
参考文献数
19
被引用文献数
2

Nekoma Volcano, situated between Bandai Volcano and the Aizu Basin in northeast Japan, is a composite volcano of andesite to dacite with a total eruption volume of 16 km3. A horseshoe-shaped caldera a few km in radius was formed at the top of the volcano, and the volcanic activity is divisible into the Old Nekoma Volcano established before the caldera forming event from ca. 1 Ma to 0.6 Ma and the New Nekoma Volcano established after the caldera forming event after ca. 0.5 Ma. Old Nekoma Volcano is subdivided into Oguninuma north lava, Hayama lavas, Hagidaira pyroclastic flow (block and ash flow) deposit, Main cone lavas, Oguniyama lavas and Ougigamine lavas, in ascending stratigraphic order. They formed a flat cone-shaped volcano. All but the Ougigamine lavas were produced by summit eruptions and the Ougigamine lavas formed monogenetic volcanoes from several vents on the western flank. New Nekoma Volcano, erupted after Oshizawa debris avalanche deposit, which related to the caldera forming event, is composed of Nekomagatake lavas and 1349 m lavas occurred at the horseshoe-shaped caldera margin.
著者
山﨑 誠子 星住 英夫 松本 哲一
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.61, no.3, pp.519-531, 2016-09-30 (Released:2016-11-08)
参考文献数
33

Unspiked K-Ar dating procedure enables the correction for mass fractionated initial 40Ar/36Ar ratios, and has been successfully applied to young volcanic samples, especially younger than 0.5 Ma. We reconstructed the growth history of western to central part of Kuju Volcanic Group based on the unspiked K-Ar age data. The unspiked K-Ar ages for the small andesitic-dacitic volcanoes of Stage 1 (Kutsukakesan Volcano, Iozan Lava, Kuroiwasan Volcano, Narukoyama Volcano) provided with two age group of ca. 160-150 and ca. 90-80 ka, suggesting that Stage 1 may be divided into at least two sub-stages. During Stage 3 after the largest eruption associated with Handa pyroclastic flow deposit, some lava domes and stratovolcanoes in the central part (Ogigahana Volcano, Nakadake Volcano and Mimatayama Volcano) were built up from ca. 54 to 34 ka, which is older than the previous interpretation.Based on these K-Ar ages and estimated volume for each volcanic unit, we calculated the magma discharge rate during each volcanic stage and the whole period of the volcano history. The calculated magma discharge rate for Stage 1, 3 and 4 are 0.09, 0.12, 0.18 km3/ky, respectively, showing that the activity has slightly increased. The rate of 0.12 km3/ky for the whole period is similar to that for Aso and Unzen volcanoes lie to the west of this volcano.
著者
松本 亜希子 中川 光弘 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.61, no.3, pp.545-558, 2016-09-30 (Released:2016-11-08)
参考文献数
38

On the 24th July, 2012, a large scale explosion occurred at Minamidake Summit crater of Sakurajima volcano, for the first time in last 1.5 years. This eruption is characterized by a clear, large preceding inflation ca.22 hours before the eruption. The juvenile glass particles in the volcanic ash of this eruption have less amount of microlite than those of Showa crater. The crystal size of microlite is also smaller. In contrast, their microlite number densities (MND) of plagioclase and pyroxenes are similar to those of Showa crater. According to the results of the decompression experiments by previous studies, the variations of crystallinity of microlite with the constant MND can be explained by the difference in the length of the duration for decompression, and/or the duration until the quench after the decompression. Considering these results, the juveniles of the summit eruption are derived from the eruption induced by relatively rapid decompression with rapid quench, and the juveniles from Showa crater are the products of the eruptions accompanied with the relatively slower decompression and/or the longer annealing after decompression. Therefore, it is interpreted that the 24th July, 2012 eruption was caused by rapid magma ascent with much shorter stagnation in the conduit. In contrast, the eruptions at Showa crater might have been induced by slower magma ascent and/or longer stagnation at a shallower depth of the conduit. This interpretation agrees with the data of geophysical observations. On matrix glass chemistry, juveniles of this summit eruption show the distinct trend from those of Showa crater. This feature can be produced by the difference in mode of microlite, which are crystallized during magma ascent. Accordingly, it is possible to evaluate the difference in magma ascent process, using the matrix glass chemistry.
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
火山 (ISSN:04534360)
巻号頁・発行日
vol.56, no.2, pp.89-94, 2011-06-30

Old historical documents on 1779 AD An'ei eruption of Sakurajima, southwest Japan were collected from distal places as well as those from neighboring area of the volcano. These records revealed that the ash-fall front traveled to the northeast at about 50-100km/h, reached as far as Tohoku district 1200km from Sakurajima, and covered area of ca. 2.33×10^5km^2. Investigation of old documents helped to improve understanding of behavior of the volcano and environmental effects at the time of infrequent and great eruption. The wide distribution of ash-fall in 1779 Sakurajima eruption suggests that there is a high potential that ash discharged by future eruption of Sakurajima may cover down through the mainland of Japan. We should keep in mind both physical and economical effects of ash-fall in assessing the activity and making the scenario of an eruption.
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
被引用文献数
4

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
林 信太郎
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.4, pp.207-212, 1998
参考文献数
19
被引用文献数
1

Kampu volcano is a small stratovolcano situated at the central part of Oga Peninsula, Akita Prefecture. In 1810, an earthquake as large as M 6.5 occurred near this volcano. Yoshimasa Satake, the lord of the Akita clan, wrote two official reports to the Tokugawa shogunate. They included eruption records of Kampu volcano: "Yamayake" and "Yamayakekuzure". These words were usually used for the eruption during Edo period and mean that the mountain was firing. Several reliable documents, which was written at Oga Peninsula included no eruption record. In addition, there is no eruption record in the note of Yoshimasa Satake, which is thought to have used for making the two official reports. It is concluded that the eruption descriptions of 1810 Kampu is false and created by Yoshimasa Satake at Akita clan office at Edo (Tokyo). The false eruption might have been created to make the exaggerated damage report of earthquake.
著者
高橋 正樹
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.207-218, 1994-09-20
被引用文献数
4

Late Quaternary poly genetic volcanoes in Japanese islands can be classified into two types : P-type and O-type. The vent of the P-type (parallel types) aligns in parallel with the orientation of regional σ_<Hmax>, while the vent alignment of the O-type (oblique type) is normal or highly oblique to it. The P-type consists of three sub-types based on the kind of associated active faults : PN (with normal faults), PS (with strike-slip faults), and PR (with reverse faults). Most of the O-type are constructed on the mountain range which is bounded on both side with reverse faults ; its vent alignment is probably controlled by the local extensional stress field in the mountain mass caused by the gravity tectonics. Thin sheet-like magma chambers are estimated to be present beneath the O-type volcanoes ; the arrangement of maximum principal stress axis producing reverse faults (σ_v=σ_3) favors the formation of sheet-like magma chambers. The eruption rate of the O-type is generally small because of the complexity of its magma plumbing system.
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.58, no.1, pp.103-114, 2013-03-29

桜島火山の噴火活動について見通しを得るため,北部鹿児島湾とほぼ位置が重なる姶良カルデラの周りの地殻変動について,特に水準点2474番と2480番の相対的な高さの変化に注目して検討を加えた.この区間では,これまで注目されることがほとんどなかったが,1914年の桜島火山の大きな噴火に先立って明瞭な膨張が生じていたであろうことが確かめられた.これにより,大きな噴火に先立って姶良カルデラ地下に蓄えられたマグマの1914年時点の限界量が推測される.1914年の噴火によって姶良カルデラでは顕著な収縮が生じたが,その後膨張が進んで1900年(大噴火まで14年)の水準を超え,1970年代初め頃には1914年の限界値にかなり近づいたと考えられる.桜島では,1970年代から80年代にかけて爆発的活動が活発に続いた.この期間,姶良カルデラの膨張は停滞およびやや後退していたが,桜島の爆発的な活動が低下すると再び変動が進み始めた.近年,ここで推測された1914年の限界値にさらに近づきつつあり,大きな噴火の可能性があり得ることを示している.一方,姶良カルデラ地下のマグマ量の増減と桜島からの噴出物量の収支については課題があり,今後の検討に委ねられる.