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. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.27, no.2, pp.174-175, 1982-07-01

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. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.31, no.4, pp.287-288, 1986-12-26

著者

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.30, no.1, pp.45-47, 1985-04-01

著者

久野 久

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.3, pp.123-130, 1968-12-01

被引用文献数

1

---

Andesitic and dacitic lavas form a certain kind of autobrecciated structure upon entering into the water instead of forming the pillow structure common in basaltic lavas. Such lavas consist of angular, polyhedral blocks ranging in size from a few meters to several centimeters in diameter cemented by comminuted fragments of the same material or by sediments. Matrix of palagonite is sometimes present. Individual blocks are compact and are often traversed by joints which divide them into still smaller polyhedral blocks. In blocks larger than 0.5m., which are usually angular in outline and sometimes spheroidal, closely spaced joints roughly perpendicular to the surface of the blocks are developed, indicating their quenching against the water. In the Pleistocene volcanoes of Izu Peninsula and Hakone, no such subaqueous autobrecciated lavas have been found even along the present sea coast. This fact implies that they have never been uplifted since the beginning of the Pleistocene or have been partly submerged because of the elevation of the sea level since the end of the glacial period.

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

被引用文献数

9

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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

澤田 可洋 Andal C. Marzan D.

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.25, no.4, 1980-12-01

著者

澤田 可洋

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.21, no.3, 1976-12-15

著者

宮縁 育夫 渡辺 一徳

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.45, no.1, pp.25-32, 2000-03-10

被引用文献数

3

---

Jigoku spa is located west of Ikenokubo basin of Yomineyama volcano, southwestern part of the central cones of Aso volcano. In this basin, "Ikenokubo tuff ring" and two smaller maars were developed. Two layers of ejecta, about 10^5 m^3 in bulk volume, formed by phreatic explosions were found in this area. They are very poorly sorted and mainly composed of altered fine-grained ash including lithic fragments. Kikai Akahoya ash erupted about 6,300 years BP (^<14>C) is intercalated between two layers of phreatic ejecta in thick ash layers from Nakadake, the only active central cone. Based on ^<14>C ages of buried Andisols and the succession of the deposits, the eruption ages of the two ejecta are estimated at about 10,000 years BP for older deposit and at about 4,500 years BP for younger one. Distributions of thickness and maximum grain size of the lithic fragments suggest that the both of two phreatic ejecta were exploded not from "Ikenokubo tuff ring" and two maars but from the Jigoku explosion crater in the western area. Ejecta correlative to the "Ikenokubo tuff ring" Iies under the older of the phreatic ejecta layers. Consequently, the eruption age of "Ikenokubo tuff ring" is probably older than 10,000 years BP. Frequency of phreatic explosions, Iarger than 10^5 m^3 in volume, is considered to be once in about 5,000 years. This fact is noteworthy for volcanic hazards assessment in the surrounding area of Jigoku spa and adjacent Tarutama spa.

著者

中禮 正明

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.29, no.2, 1984-07-01

著者

石川 芳治 山田 孝 川下 茂樹 松本 俊雄 高橋 努 緒続 英章

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

巻号頁・発行日

vol.1993, no.2, 1993-10-04

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火砕流の運動・堆積機構を力学的に明らかにするうえで、新しい火砕流堆積物の堆積構造並びにその物性を把握することは極めて重要となる。本調査では、1991年6月8日に雲仙普賢岳で発生した規模の大きな火砕流(堆積土砂量約350万m^3)の堆積先端部付近(国道57号直上流)において、調査トレンチを4箇所掘削し、堆積物の構造、層序、構成材料、マトリックスの粒径分布などを調べた。調査区域での火砕流本体部の堆積物の厚さは2.5&acd;3.5m程度であり、20cm&acd;1m大の安山岩の本質岩塊を含み、大礫が堆積物の表面に集積するという、逆級化構造(inverse grading)も認められる。このような堆積実態から土石流において巨礫が流れの表面に集積する現象と同じように、溶岩ドーム崩落型の比較的粗い本質岩塊を構成材料とする火砕流本体部内においても、本質岩塊同士の非弾性衝突による分散応力の効果や動的篩の効果によって、大きな粒子ほど浮上しやすくなる条件が存在するものと思われる。雲仙普賢岳で発生している火砕流の流れの状況を夜間に撮影したVTR画像からも、灼熱の本質岩塊がお互いに激しく衝突し、破砕されながらも、さらにまた衝突を繰り返している様子がよく分かる。また、火砕流本体部の下位に従来、ground-surge deposits^<1〕>と呼ばれてきたサージ堆積物が認められる場合がある。但し、この堆積物の流れ方向の分布は連続的ではなく、部分的である。このような堆積実態から火砕流の流れのモデルとしては、本体部と熱風部の境界層付近には、本体部表面と周辺の空気との剪断に起因した乱れならびに本体部から発砲されるガスの上昇によって、浮遊させられた^<2〕>細粒の火砕物が、熱風部への移行層としてのサージ状の高速流れを形成しており、緩勾配区間で本体部が減速しても、サージはそれ程減速せず本体部に先行して流下・堆積し、その後、本体部が流下するにしたがってその堆積物を埋没したものと考えられる。火砕流本体部のマトリックスは2mm以上の細砂&acd;中砂が主体であり、中央粒径は0.8&acd;2mm程度で噴煙柱崩壊型の火砕流のそれよりも粗い。空隙率は40.7%であり、一般の砂質土とほぼ同じような締まり具合を呈している。今後、火山活動が終息し、上流・中流での現地調査が可能となった時点で、流れの縦・横断方向に複数箇所、調査トレンチを掘削し、詳細な堆積構造の観察や構成材料の土質的な特性の変化(特に、流下方向の本質岩塊の粒径の変化ならびにマトリックスの粒径変化など)を明らかにすることが火砕流の運動・堆積過程を統一的に表現できる力学モデルを作成するうえで重要となる。

著者

吉川 美由紀 池辺 伸一郎 須藤 靖明 鍵山 恒臣 吉川 慎 宮本 利邦 山村 隆文 寺田 暁彦 阿蘇火山博 京大院 阿蘇市教委 南阿蘇村教委 阿蘇市 南阿蘇村

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

巻号頁・発行日

vol.2009, 2009-10-10

著者

安田 裕紀 佐藤 鋭一 和田 恵治 鈴木 桂子

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.60, no.4, pp.447-459, 2015

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Eruption interval between Hb- and Px-types pyroclastic-flows from the Ohachidaira caldera of Taisetsu volcano, central Hokkaido, Japan, was estimated from the paleomagnetic directions. Px-type pyroclastic-flow deposit rests on Hb-type one, and gravel beds are intercalated between them. Oriented 138 samples were collected from 13 sites for paleomagnetic analysis. The paleomagnetic direction of Hb-type pyroclastic-flow deposit shows a normal polarity with a westerly declination(overall mean is N=7, D=-27.1°, I=66.3°, α_<95>=2.7°, k=511.2), while that of Px-type pyroclastic-flow deposit shows a normal polarity with an easterly declination (overall mean is N=6, D=19.8°, I=67.5°, α_<95>=4.6°, k=213.8). The two paleomagnetic directions are significantly different, and the time interval between the two pyroclastic eruptions is estimated to be more than about 100±40 years based on the geomagnetic secular variation in China, Russia, Europe, North America, and Japan.

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. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.26, no.2, pp.143-144, 1981-07-01

著者

萬年 一剛 高橋 正樹 内藤 昌平

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

巻号頁・発行日

vol.2001, no.2, 2001-10-01

著者

中村 一明

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.18, no.2, 1973-08-01

著者

前田 裕太 寺川 寿子 加藤 愛太郎 山中 佳子 古本 宗充 山岡 耕春 堀川 信一郎 松廣 健二郎 奥田 隆

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

巻号頁・発行日

vol.2014, 2014-11-02

著者

及川 純 藤田 英輔 今西 祐一 山岡 耕春 井田 喜明

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

巻号頁・発行日

vol.1994, no.2, 1994-10-20

著者

長宗 留男 横山 博文 福留 篤男

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.1, pp.1-8, 1992-04-01

被引用文献数

2

---

Earthquake swarms which have frequently occurred off the east coast of the Izu Peninsula since 1978 are investigated, and the relationships between the swarms and the submarine volcanic eruption at Teisi Knoll in 1989 are discussed. The results are summarized as follows: 1) Shapes of epicentral areas of the earthquake swarms can be classified into the following two types, Type I and Type II. The former is an ellipse elongated NE-SW; the latler, an eilipse elongated approximately NW-SE. The swarms in the early years are of Type I, and those in the later stage (in particular, since 1984), for the most part, are of Type II.2) The largest earthquakes in the respective swarms for Type I are located along a straight line in the NE-SW direction, and those for Type II, along a curve line in the E-W to NW-SE directions. These two lines are probably indicative of active tectonic lines. 3) The epicentral areas for Type I and Type II, migrate periodically with a recurrece time of 6-7 years along the tectonic line in the NE-SW direction, and with a recurrence time of about 3.7 years along the tectonic line in the E-W to NW-SE directions, respectively. 4) Teisi Knoll where the submarine volcanic eruption took place on July 13, 1989, is situated in the northwestern part of the tectonic line trending E-W to NW-SE. The eruption was triggerd by the largest shock in the swarm which occurred around the northwestern end of the line.

著者

宇平 幸一 永福 順則 山本 博二 横山 博文 荒木 卓次

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.29, pp.S36-S44, 1984-12-28

被引用文献数

1

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A swarm of earthquakes, precursory indication of the eruption, began to be recorded at Miyakejima Weather Station at 1358 on 3 October, 1983, although none was recorded at any other seismic station of JMA until the onset of the eruption. On the other hand, another swarm of earthquakes that resumed after the onset of the eruption was caught by seismographs around Miyakejima. Precursory earthquakes were grouped into two types, i.e., high frequency earthquakes and low frequency ones, according as their predominant frequencies were higher than 2.5 Hz or not. It is unpromissing to try to determine hypocenters of precursory events, but, both the first motions of 5 high frequency earthquakes and the particle motions of 2 low frequency ones in the horizontal plane inidicate that their sources were located to the SW of the seismograph, probably on the island. Gradually increasing continuous tremors started immediately after the earthquake at 1522 which had a predominant frequency of about 1.4 Hz from initial motion through coda. The following continuous tremor had almost the same predominant frequency. Major eruptive activity probably began with this low frequency earthquake. The magnitudes of two large precursory earthquakes were estimated to be about 3.0 by applying the relation between the magnitudes of post-eruption earthquakes and their maximum amplitudes or duration times of vertical component at Miyakejima Weather Station. However, this estimation was not appropriate because earthquakes of such size were large enough to be recorded at seismic stations other than Miyakejima. The seismograph at the sea bottom off Omaezaki (named "TK1OBS" in the seismological bulletin of Japan Meterological Agency), about 180 km W of Miyakejima, detected post-eruption earthquakes of magnitude about larger than 2.5, but did not record any pre-eruption earthquakes. The background noise on 3-4 October had remained at a similar level of 0.02 milikine, which corresponds to the expected maximum velocity of the vertical component on TK1OBS when an earthquake of magnitude 2.4 occurs at Miyakejima. Therefore, precursory earthquakes seem to be of magnitude less than 2.4.

著者

横山 博文 藤原 善明 井上 和久 菅野 智之

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

巻号頁・発行日

vol.2014, 2014-11-02