著者
室生団体研究グループ 八尾 昭 茅原 芳正 別所 孝範 鎌田 浩毅 山本 俊哉 渕上 芳孝 石井 久夫 森山 義博 西尾 明保 寺戸 真 八尾 昭
出版者
地学団体研究会
雑誌
地球科学 (ISSN:03666611)
巻号頁・発行日
vol.62, no.2, pp.97-108, 2008
参考文献数
52
被引用文献数
2

中新世の室生火砕流堆積物は近畿地方,紀伊半島中央部に分布し,その面積は1.9×10^2km^2に達する.室生火砕流堆積物は基底相と主部相に区分できる.基底相は層厚50m未満で異質岩片を含む溶結した火砕流堆積物と火山豆石を含む降下火山灰,火砕サージ堆積物で構成される.主部相はさらに下部にはさまれる層厚30m未満の斜方輝石を含むデイサイト質火山礫凝灰岩と上部の層厚400mを超える膨大な黒雲母流紋岩質火山礫凝灰岩に分けられる.主部相の基質はほとんどが溶結した結晶凝灰岩である.基底相には中礫大未満のチャート,砂岩,頁岩などの岩片が含まれており,室生火砕流堆積物を供給した地域の基盤岩を構成していた.室生火砕流堆積物は以前から中期中新世の熊野・大峯酸性岩類など大規模な珪長質火成岩が分布する南方から供給されたと推定されていた.異質岩片のチャートにペルム紀〜ジュラ紀の放散虫化石が含まれ,その給源火山の一部は秩父帯にあった可能性がある.秩父帯では半円形の断裂に沿って火砕岩岩脈群が貫入する大台コールドロンが存在しており,膨大な火砕流を噴出したことが推定される.
著者
鎌田 浩毅 宇都 浩三 内海 茂
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.33, no.4, pp.305-320, 1988-12-28
被引用文献数
4

中部九州,豊肥火山地域中央部の涌蓋(わいた)山地域には,輝石安山岩質の溶岩流の上に角閃石安山岩質の溶岩流と溶岩円頂丘から成る火山群が形成されている.涌蓋山地域は,耶馬渓(やばけい)火砕流の噴出に伴って形成された猪牟田(ししむた)カルデラの南西縁に位置する.涌蓋山地域に分布する火山岩の地質層序をたて,火山岩のK-Ar年代測定を行なった.涌蓋山地域の火山岩はそれぞれ噴出中心の異なる単成火山群の特徴をもち,猪牟田カルデラの後カルデラ火山活動の産物と考えられる.これらの火山活動は,耶馬渓火砕流噴出直後の1Maから0.3Maまで継続したことが判明した.また火山岩の噴出量と噴出岩石の組成変化を検討した結果,火山活動は0.7Ma付近を境とし,1回の噴出量の多い輝石安山岩質の活動から,噴出量の少ない角閃石安山岩質の活動へと変化したことが判明した.このことは猪牟田カルデラ直下のマグマ溜りの温度が時間とともに低下したことを示唆する.涌蓋山地域の火山活動は0.7 Ma 付近を境として総噴出量が減少し,火山体の形態も溶岩台地卓越型から少数の成層火山体を伴った溶岩円頂丘卓越型へと変化した.涌蓋山地域の火山岩の変化は豊肥火山地域全体のテクトニクスの変化を反映すると考えられる.
著者
中田 節也 鎌田 浩毅
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.33, no.4, pp.273-289, 1988
被引用文献数
8

Volcanism and deposition of volcaniclastic materials within a graben in the Shimabara area, western Kyushu, started in early Pliocene and have continued up to the present. The volcanic products comprise alkalic to high-alkali tholeiitic basalts in addition to calc-alkalic andesites. The basalts are of a member of magmas erupted extensively in NW Kyushu from late Miocene to Recent. Their incompatible-element patterns in spider gram, in which the abundances of Rb, Ba, K, Nb, Zr and Y are normalized to those of MORB, are uniform independently of their eruption-ages, and show positive Ba and Nb anomalies strongly indicative of the marked affinity with ocean-island basalts. These patterns are clearly different from those of island-arc basalts which have negative Nb anomaly, as represented by the Quaternary high-alumina basalts in central Kyushu, and from those of back-arc basin basalts usually showing the same anomaly. It is concluded that basaltic magmas in NW Kyushu were derived from partial melt of fertile mantle with high Nb/Zr. Most of the andesites in the Shimabara area have phenocryst assemblages showing co-existence of magmas with different compositions. This fact and the spidergram pattern without Nb anomaly of the andesites lead us to a magmatic model; the andesite magma originated from mixing of positive-Nb-anomaly basaltic melt with negative-Nb-anomaly acidic partial melt of lower-crust materials which were presumably heated by the former melt. The graben in the Shimabara area seems to have developed in southern periphery of the region under which fertile mantle materials have been rising up from the depth and the subducted oceanic slab has not reached, like the "hot region".
著者
陶山 淳治 石井 吉徳 山口 靖 鎌田 浩毅 長谷 絋和 小川 克郎
出版者
一般社団法人 日本リモートセンシング学会
雑誌
日本リモートセンシング学会誌 (ISSN:02897911)
巻号頁・発行日
vol.2, no.4, pp.57-65_9, 1982

This paper reviews the method and results of the airborne SAR survey which was conducted by NEDO (New Energy Development Organization) as a part of the Nation-Wide Geothermal Survey Project. The whole Japanese Islands except IzuOgasawara Islands were covered by non-stereo/west-look SAR images. In addition to this, main geothermal area was covered by non-stereo/northlook images and Izu peninsula was covered by stereo/north and west-look images. The SAR holographic date was processed through an optical correlator to present the mosaic image of scale 1 : 200, 000. The geological and geothermal interpretation of the images are now under progress.<BR>This paper presents several SAR images as well as maps produced from SAR images. Some technical problems arisen during the data acquisition (flight) are also presented.
著者
綿貫 陽子 鎌田 浩毅 味喜 大介 石原 和弘
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.6, pp.513-518, 2003
参考文献数
16
被引用文献数
1

During the Taisho Eruption (1914-1915) of Sakurajima Volcano, the Secondary Lava Flows drained out from the front of the primary lava flows after a certain pause from their settlement. We investigate distribution, timing and conditions of the effusion of the Secondary Lava Flows which have not been clarified yet. We define the features of the Secondary Lava Flows by means of geomorphological interpretation using aerial photographs and field survey. More than 200 landscape photographs, which were taken at the time of the Taisho Eruption, indicate that the earliest Secondary Lava Flows effused on 14 February 1914; this date was several months earlier than those previously considered. The effusing of the Secondary Lava Flows did not occur as a single event but as several events in different areas. Based on volumetric estimation of the individual Secondary Lava Flows, the volume of the Secondary Lava Flows tend to have increased as time passed after the eruption. The Secondary Lava Flows effused from the underlying tip of river valleys.
著者
鎌田 浩毅 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.第2集 (ISSN:04534360)
巻号頁・発行日
vol.26, no.4, pp.281-292, 1981
被引用文献数
2

Kuju Volcano (1, 786m high) consists of dacitic lava domes and the associated non-welded pyroclastic flow deposits, Handa pyroclastic flow deposits, covering 60 km<sup>2</sup> area (Fig.2). The original vents of the pyroclastic flow deposits, whose age is estimated to be 0.04 Ma, have not been located. The volume is about 2km<sup>3</sup>. They contain pumice and accessory lithic fragments and very seldom show welding. At the upper and the basal parts of one flow unit, imbrications of pumice and lithic fragments are well developed with 10°-20°dip against the flow unit boundary (Figs. 4, 5). This dip (Table 1) is apparently not as steep as that of the other pyroclastic flow deposits. Imbrications are clearly observed at 6-12km from the center of the lava domes, while the distribution of the pyroclastic flow deposits covers 4-13km from the center (Fig. 7). The pyroclastic flows ran down 1000m in a vertical distance. The method of determining the flow direction by imbrication is very simple as shown in Fig. 6. Imbrication is most visible from the direction (a) perpendicular to the flow direction on the surface of each outcrop. The flow direction (f) is determined by the bisector (f') of the error angle 2θ formed by the two directions (b, c), between which imbrication is not observed. Data are classified into 3 ranks by the error angle θ as shown in Table 1. The flow directions at 52 outcrops (Table 2) are shown by classified arrows in Fig. 7. The estimated flow-direction patterns are largely divided into the north-flank flows and the south-flank flows (Fig. 7). The north-flank pyroclastic flow deposits flowed along the 2 km-wide major valley on ca 2°slope shown in K-L profile in Figs. 8, 10. Then it diverged to the west at the outlet of the valley, and finally collected in a small basin in the west. Such flow directions suggest that the flow was not derived from the adjacent domes D, E, F in Fig. 7. On the south flank, a fan-shaped pattern of the flow direction is generally observed. But the flows toward Aso volcano are sharply separated into two flows at the boundary between Kuju and Aso ("col" in Figs 7, 9). This is because the flow had not enough power to rush up the very gentle slope of Aso volcano. The evidence shows that the southward flow gradually bent 120°, and it rapidly went down eastward on the south flank. At Takenohata (n. in Fig. 7) this eastward flow crossed the southward flow. At this cross point, lower outcrops show eastward flow (A-B profile in Fig. 8), and higher ones show southward flow (C-D profile) as shown in Fig. 11. This means that after the eastward flow filled the old valley extending in east-west direction, the later pyroclastics flowed southward over the older deposits forming a fan-shaped deposit. Data clearly suggest that the vent for the pyroclastics is located within the circle around A, B, C lava domes, and not in the other domes. The flow directions indicated by imbrications agree with the distribution of the pyroclastic flow deposits. Pyroclastic flows follow the previous topographic relief such as valley, fan, and col. Kuju Volcano may not have emitted the flooded sheet-flows in all directions, but have emitted the tongue-shaped flows intermittently to different directions.