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

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

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.2010, 2010-10-09

著者

直江 寛明 木下 紀正 池辺 伸一郎

出版者

社団法人日本気象学会

雑誌

天気 (ISSN:05460921)

巻号頁・発行日

vol.40, no.9, pp.671-679, 1993-09-30

被引用文献数

6

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阿蘇火山博物館で測定している大気中の二酸化硫黄濃度が30ppbを越えた高濃度事象を対象に, 気象データと衛星画像や桜島噴煙の地上観測などのデータを用いて発生源の推定を行い, 特徴的な事例について気象条件との関連性について解析した.上層が東風系のとき, 阿蘇火山からの直接的な影響がみられ, 数百ppbに達する高濃度が長時間にわたってしばしば観測された.桜島は常時多量の噴煙と火山ガスを放出していて, 上層で南風系が卓越しているとき, 150km離れた測定点で30ppb以上, 時には100ppbを越える高濃度が検出された.二酸化硫黄濃度の日変化で特に高濃度が観測されるのは, 夜間に地表で放射冷却による接地逆転層が形成され阿蘇中岳火口からの火山ガスによる局所的な汚染濃度が極度に高められるとき, 及び九州が移動性高気圧の後面に位置し, 安定した大気中を桜島からの火山ガスが移流して混合層内の汚染濃度が高められたときと考えられる.

著者

吉川 美由紀 池辺 伸一郎 佐藤 よしみ 中山 亜紀 村山 美由紀 小出 哲也

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.2006, 2006-10-23

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

須藤 靖明 池辺 伸一郎

出版者

京都大学防災研究所

雑誌

京都大学防災研究所年報. B = Disaster Prevention Research Institute Annuals. B (ISSN:0386412X)

巻号頁・発行日

vol.44, no.B-1, pp.345-352, 2001-04-01

著者

宮縁 育夫 池辺 伸一郎 渡辺 一徳

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.2005, 2005-10-05

著者

宮縁 育夫 池辺 伸一郎 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.50, no.4, pp.227-241, 2005-08-31

被引用文献数

6

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Ash emissions occurred from a hot water pool of one of the craters of Nakadake, the only active central cone of Aso Volcano, southwestern Japan, on July 10, 2003 and January 14, 2004. The former ash was dispersed throughout an area extending 14km east-northeast of the vent, whereas the latter ash extended 8km to the east-southeast. Based on isopleth maps, the total weight of ash discharged by each event was 41tons and 32tons, respectively. Both ash-fall deposits were composed of fine-grained (<1mm) glass shards, crystals and lithic fragments, and contained neither lapilli nor blocks. Some glass shards appear fresh and are probably juvenile material. We therefore believe that these phenomena represent non-explosive gas-and-ash emissions through the hot water pool. The ash particles emitted from the hot water pool of the Nakadake crater were aggregated at a size of 1-3mm and deposited because of a high content of water. The ash-fall deposits in proximal areas (<1.5km from the crater) were finer grained and more poorly sorted than in distal areas (>5km). Moreover, the deposit volume obtained from actual data in the proximal area was much larger than the volume extrapolated only from the isopleth data of the distal deposits. These phenomena suggest that the proximal deposits were emplaced mainly by another fine-grain-rich column different from the main ash plume that extended to distal areas, or that some parts of the column detached from the main plume that emplaced the proximal deposits.