著者
宮縁 育夫 杉山 真二 佐々木 尚子
出版者
公益社団法人 東京地学協会
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.119, no.1, pp.17-32, 2010-02-15 (Released:2010-05-21)
参考文献数
51
被引用文献数
10 11

Holocene environmental changes and vegetation history are constructed using phytolith and macroscopic-charcoal analyses of a 23-m-deep drilling core obtained at the Senchomuta marsh in Asodani Valley, northern part of Aso caldera, SW Japan. An intra-caldera lake existed in the Asodani Valley prior to approximately 9 cal ka (calibrated 14C age). Multiple large flood events occurred during the period 8.9-8.1 cal ka and emplaced thick sandy deposits in the valley basin. Thereafter, the center of the Asodani Valley (northern part of caldera floor) changed to swampy and fluvial environments. sasa (cool-temperature dwarf bamboo) grasslands and/or forests with understory sasa covered slopes of the Asodani Valley basin between 11 and 9 cal ka. sasa phytoliths significantly increased at ca. 7.3-6.5 cal ka, but thereafter decreased. Miscanthus (Japanese pampas grass) grasslands existed continuously on the slopes. Macroscopic-charcoal particles were abundant during the last 6000 years, and the peak (6.1 cal ka) amount of charcoal particles is consistent with that of Miscanthus phytoliths. This indicates that the existence of Miscanthus grassland might be related to fire events. Inside the Asodani Valley, Phragmites (reed) became established continuously along the shore of the intra-caldera lake (prior to ca. 9 cal ka) and in subsequent marshes. Gramineae phytoliths were detected predominately through all horizons of the drilling core, whereas a small amount of arboreal phytolith was observed at most horizons. We, therefore, believe that forests existed on steep slopes such as the caldera wall where human impacts were small, although sasa and Miscanthus grasslands were maintained by human activity outside Aso caldera.
著者
宮縁 育夫 星住 英夫 高田 英樹 渡辺 一徳 徐 勝
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.2, pp.195-214, 2003-05-20
被引用文献数
12

Aso central cones located within Aso caldera, central Kyushu, southwestern Japan, initiated their activity soon after the formation of the caldera (ca. 90 ka). The cones have produced voluminous airfall tephra layers and lava flows. Most of the tephra layers distributed in and around Aso caldera are andesite to basaltic-andesite scoria-fall and ash-fall deposits. Their stratigraphy is very complicated because it is difficult to distinguish between scoria-fall layers in the field. However, dacite to rhyolite pumice-fall deposits from some central cones interbedded between the tephra layers are very useful to correlate stratigraphic units at separated localities. Therefore, we used the pumice-fall deposits in order to construct the tephrostratigraphy and eruptive history of Aso central cones during the past 90,000 years. Thirty-six pumice-fall deposits were identified including eleven major key beds. In ascending order they are Nojiri pumice (NjP), Ogashiwa pumice (OgP), Yamasaki pumice 5 (YmP5), Sasakura pumice 2 (SsP2) and 1 (SsP1), Aso central cone pumice 6 to 3 (ACP6-ACP3), Kusasenrigahama pumice (Kpfa) and Aso central cone pumice 1 (ACP1). Phenocrystic minerals of most pumice are plagioclase, ortho- and clino- pyroxene and magnetite, but NjP, ACP5, ACP3 and ACP1 include biotite, and NjP and SsP2 contains hornblende phenocrysts. On the basis of several ^<14>C ages of buried soils just below pumice (above Kpfa) and stratigraphic position eruption ages for the eleven major pumice are estimated as follows: NjP (85 ka), OgP (80 ka), YmP5 (69 ka), SsP2 (57 ka), SsP1 (56 ka), ACP6 (52 ka), ACP5 (45 ka), ACP4 (40 ka), ACP3 (39 ka), Kpfa (31 ka) and ACP1 (4ka). During the past 90,000 years Aso central cones produced pumice-fall deposits at an interval of about 2,500 years. Many of the sources of the pumice appear now buried under the present Aso central cones.
著者
阿部 和時 黒川 潮 浅野 志穂 岡本 隆 松山 康治 落合 博貴 寺嶋 智巳 島田 和則 野口 宏典 大丸 裕武 宮縁 育夫 小川 泰浩
出版者
日本緑化工学会
雑誌
日本緑化工学会誌 (ISSN:09167439)
巻号頁・発行日
vol.28, no.1, pp.91-96, 2002-08-31
被引用文献数
6 4

2000年6月から始まった三宅島の火山活動による多量の降灰で雄山山腹の植生は壊滅的被害を受けた。この影響で泥流災害が島全域で発生し,現在も危険性は非常に高い状態にあると考えられる。本研究では,このような火山降灰地帯が形成された直後の激しい土壌侵食の実態を実証的に明らかにすることを目的とした土壌侵食の発生状況は降灰による森林被害の程度と相関性があると推察されるので,空中写真による森林被害区分を行い,それぞれの区分において現地水路侵食実験で侵食特性を検討した。その結果,降灰が堆積し形成された地表面は流速が20〜35cm/secと早く,浸透性が低いこと,しかし流出土砂量は降灰層中に枝葉が混入した地区よりも少ないこと等が示された。このデータをもとに汎用土壌侵食式(USLE)によって相対的な面状侵食の危険度を,火口を中心とした14.5km^2の範囲について示した。
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

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.