著者

伊藤 英之 早津 賢二 鈴木 浩二

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.45, no.3, pp.181-186, 2000

参考文献数

7

著者

早津 賢二

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.102, no.5, pp.611-613, 1993-10-25 (Released:2009-11-12)

参考文献数

10

著者

早津 賢二 清水 智 板谷 徹丸

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.103, no.3, pp.207-220, 1994-06-25 (Released:2009-11-12)

参考文献数

52

被引用文献数

6 8

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The Myoko volcano group, consisting of five stratovolcanoes, Myoko, Kurohime, Iizuna, Yakeyama and Madarao, is situated in the northern part of central Japan. Twenty one volcanic rocks from the early stage of volcanic successions of Myoko (5 samples), Kurohime (4 samples), Iizuna (9 samples) and Madarao (3 samples) were dated with K-Ar methods. On the basis of previously well studied geology and petrology of the volcano group and chronology of marker tephra layers in this area together with newly obtained K-Ar ages, volcanic history of the Myoko volcano group was discussed in detail. The results confirmed the genetical story of the volcanoes by Hayatsu (1985), i. e., the Myoko volcano has grown by four stages of active volcanisms with three distinctive pauses and each stage has a chemical fractionation trend from basalt to dacite through andesite during a volcanism, and other volcanoes were also in the same story though number of stages was variable : three for Kurohime and two for Iizuna and Madarao, and the fractionation trend was little changeable. This paper calls this type of volcano “poly-generation volcano”.Growth mechanism of the poly-generation volcano was also revealed in detail : life span of each generation, that is time span of each stage of activity, is nearly constant, 20-50 kyrs though some exceptions but total amount of volcanic ejecta decreases with time, e. g., 40-20-7-5 km3 for Myoko, and pause period between any two active volcanic stages decreases with time from 100-160 kyrs of early pause to ca. 10 kyrs of late one.This poly-generation volcano is common in Japan and should be studied in further detail from view points of igenous petrology and tectonics of magmatism as well as geothermal energy and volcanic hazards.

著者

早津 賢二

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.26, no.3, pp.91-103, 1972

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The Myoko Volcano Group, consisting of Yakeyama, Myoko, Kurohime, lizuna, Madarao and Sadoyama Volcanoes, is situated in the boundary area between Nagano and Niigata Prefectures, Central Japan. Most of the volcanoes are distributed along the anticlinal or synclinal axes of basal Neogene strata. Except for Sado-yama and Madarao Volcanoes, the volcanic cones are arranged in a north-south trend with each nearly equal interval (about 8 km), and generally the age of each volcano tends to become younger northward. The rocks of this Volcano Group, characterized by hornblende andesite, are in striking contrast to those of sothern part of Fuji Volcanic Zone. They also differ from the basement volcanic rocks with biotite phenocrysts. Both Myoko and Kurohime Volcanoes are double stratovolcanoes of the latest stage of the Quaternary. Their activities may be divided into four stages; the older stratovolcano, the younger stratovocano, the caldera and the central cone stages. Myoko Volcano is constructed by a large amount of lava flow, pyroclastic flow, pyroclastic fall and mud flow. The rocks are characterized by common occurrence of hornblende and/or olivine phenocrysts, and by larger petrographical variation. On the other hand, in Kurohime Volcano, lava flows are predominant overwhelmingly, and pyroclastics are subordinate. Most of the rocks are augitehypersthene andesites, and the petrographical nature is rather uniform.

著者

早津 賢二

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.101, no.1, pp.59-70, 1992-02-25 (Released:2010-10-13)

参考文献数

18

被引用文献数

3 3

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Myoko volcano, situated in the northern part of Central Japan, is one of the composit stratovolcanoes whose life histories have been studied in detail. In this paper, ten volcanic ash layers belonging to the central cone stage of Myoko volcano are described, and more detailed volcanic history of the central cone stage is compiled in connection with the informations already known.The result are summarized as follows:(1) The central cone stage started ca. 5, 800 years ago. The central cone, Mt. Myoko, was almost built at the early time of the stage.(2) The youngest magmatic eruption of Myoko volcano took place ca. 4, 200 years ago, and produced pyroclastic flows and pyroclastic surges.(3) The youngest steam explosion of Myoko that was confirmed took place ca. 3, 000 years ago, and produced small pyroclastic surges.(4) For 1, 600 years between 5, 800 and 4, 200 years ago, a series of eruption whose ejecta were kept as an obvious stratum at the foot of Myoko volcano took place at the average rate of once for 200 or 300 years. After the violent eruption of ca. 4, 200 years ago, Myoko rapidly became less active, and the eruption in the similar scale took place only once or twice for ca. 4, 200 years up to the present.(5) The central cone stage was dominated mainly by the activity of dacitic magma, and coincided with the time when pyroclastic flows and pyroclastic surges were apt to be produced by explosive eruptions.

著者

早津 賢二

出版者

日本第四紀学会

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.14, no.1, pp.1-13, 1975-04-30 (Released:2009-08-21)

参考文献数

24

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The Myoko volcano, one of the stratovolcanoes in the northern part of the Fossa Magna, Central Japan, has the complicated history (Table 1).The last activity of the Myoko volcano is called the IV stage, and is divided into precaldera, caldera, and central cone substages. The strata formed during this stage are collectively called the Myokosan group which consists of lavas, pyroclastic flow deposits, pyroclastic fall deposits, volcanic mud flow deposits, and lake deposits. They are described in detail and their stratigraphic relations are tabulated in Table 2 and Fig. 4.The rocks of the essential eruptives are basalt, pyroxene andesite and hornblende andesite. They change from basalt to pyroxene andesite and hornblende andesite keeping step with the eruptive order. Quantitatively, the hornblende andesite is predominant.

著者

早津 賢二

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.32, no.1, pp.77-80, 1987-04-30

被引用文献数

1