火山.第2集
Online ISSN : 2433-0590
ISSN-L : 0453-4360
最新号
選択された号の論文の9件中1~9を表示しています
  • 原稿種別: 口絵写真
    1990 年 35 巻 4 号 p. App2-
    発行日: 1990/12/28
    公開日: 2018/01/15
    ジャーナル フリー
  • 原稿種別: 口絵写真
    1990 年 35 巻 4 号 p. App3-
    発行日: 1990/12/28
    公開日: 2018/01/15
    ジャーナル フリー
  • 加藤 完, 高橋 誠, 安藤 直行
    原稿種別: 論説
    1990 年 35 巻 4 号 p. 351-358
    発行日: 1990/12/28
    公開日: 2018/01/15
    ジャーナル フリー
    A rapid rise of groundwater tempemture by up to 20℃, observed at the Koshimizu and Otsu wells in Motomachi area after the 1986 fissure eruption of Izu-Oshima Volcano, was most likely induced by invasion of thermal water into a shallow aquifer lying below the Motomachi area. In order to locate a site of the thermal water invasion, measurements on groundwater temperature and soil air chemistry in the area were carrid out. The highest temperature was found at the Koshimizu well. The highest H2 and CO2 concentrations in soil air were also found near the Koshimizu well. These findings may indicate that the thermal water has invaded into a shallow aquifer in the vicinity of the Koshimizu well.
  • 菅 香世子, 藤岡 換太郎
    原稿種別: 論説
    1990 年 35 巻 4 号 p. 359-374
    発行日: 1990/12/28
    公開日: 2018/01/15
    ジャーナル フリー
    Amounts ofvo1canic materials along northern Izu-Bonin Arc were calculated based on the topographic maps (Latitude 30°40’ N to 35°00’ N) for the first time. The method of the volume calculation is as follows; First, all of the seamounts and knolls are picked up from the topographic maps with careful examination by using topographic cross sections as well as seismic profiles across them as for the submarine area. Subaerial volcanoes were treated by using topographic maps as well as topographic cross sections of them. We regarded individual volcanoes as a come or elliptical cone, then calculated their volumes and summed them up. The characteristic features of the volume are as follows. (1) Volume of volcanic matedal across northern Izu-Bonin Arc has maximum just on the volcanic front but it decreases toward backarc side. This feature is quite similar to that of Northeast Japan or other arcs. However, the volume of volcanic material increases again Nishi shichito Ridge (backarc echelon ridges), which have large seamoumts with comparable size to volcanoes on the volcanic front. These seamounts are thought to be Tertiary volcanoes. (2) The volume of volcanic material along the volcanic front increases northward from near Aogashima. This pattermn is concordant with existence of thick continental crusts surrounded by 1000 m depth of contour line. This suggests that the volume of volcanic material on the volcanic front has close relationship to the growth of the arc. (3) On the volcanic front, edifice of large basaltic stratovolcano is clearly different from that of an acidic submarine volcano or caldera. The former is three or four times as large as the latter. (4) Volume of volcanoes on the volcaic front of Izu-Bonin Arc is larger than those on the backarc region except volcanoes on the Nishi shichito Ridge. Volume of volcanic material along the arc shows minimum values at some places, where spacing of volcanoes along the volcanic front of the Arc are much wider compared to the other place. These results concern the volume of volcanic material offer prime role of understanding how island arcs develop and what is the essential factor to constract them.
  • 岡崎 紀俊, 田中 和夫, 三品 正明
    原稿種別: 論説
    1990 年 35 巻 4 号 p. 375-388
    発行日: 1990/12/28
    公開日: 2018/01/15
    ジャーナル フリー
    Surveys of magnetic total intensity and gravity were conducted to reveal the underground structure of Medake, one of the central cones in the cadera of Akita-Komaga-take Volcano, from which about 1.42 million m3 of lavas flowed in the period of 1970-1971 eruption. Magnetic and gravity anomalies obtained show some characteristic features suggesting the subsurface structure. Long wave length magnetic anomalies show that Me-dake is composed of uniformly magnetized volcanic rocks, lavas and scoriae, On the other hand, short ones found at the summit of Me-dake indicate there is a body with reversal or weaker magnetization than the surroundings. The distribution of the Bouguer anomalies is characterized by a narrow area of higher values of anomalies at the summit and a trend of higher values in northwest of Me-dake and lower ones in southeast. The latter suggests the basement structure of the caldera. The former implies an exislence of more dense intrusive rocks under the ground surface. Both centers of short wave length magnetic anomaly and of the narrow area of higher value of gravity locate at the same place about 100 m northeast of the 1970 crater on the summit. Judging from the topographic features, this place is one of the old craters. To interpret magnetic and gravity anomalies, numerical analyses for demagnetization model and for more dense intrusion model with various shapes were carried out independently. Finally, magnetic anomalies can be expained by a demagnetized vertical pentagonal prism, of which size is 80 m in N-S, 150 m in E-W and 300 m in thickness and of which top is at the depth of 5-10 m. Gravity anomalies can be interpreted by a more dense vertical rectanglar prism, of which size is 30 m×110 m×300 m and the top is at 15 m deep. The zones of high ground temperature and fumaroles are found at the surroundings of the 1970 crater and the area of the higher gravity anomalies. The fumarolic area preceding the 1970 eruption was found at north of the crater. We can infer the processes of the 1970 eruption by using the interpreting subsurface model of Me-dake and the distribution of fumaroles. At the first stage of eruptive activity in 1970, magma intruded into northeast of the 1970 crater. At the second, most of magma passed through the vent conncted with the crater and flowed out. Small quantity of magma remained in the narrow part at northeast of the crater make the present magnetic and gravity anomalies and fumaroles.
  • 竹下 壽, 應地 善雄, 沢井 長雄, 英彦山団研グループ
    原稿種別: 寄書
    1990 年 35 巻 4 号 p. 389-392
    発行日: 1990/12/28
    公開日: 2018/01/15
    ジャーナル フリー
  • 横山 泉
    原稿種別: 解説・紹介
    1990 年 35 巻 4 号 p. 393-394
    発行日: 1990/12/28
    公開日: 2018/01/15
    ジャーナル フリー
  • 岩森 光, 寅丸 敦志, 荒井 章司, 古山 勝彦, 隅田 まり, 守屋 以智雄
    原稿種別: 解説・紹介
    1990 年 35 巻 4 号 p. 395-398
    発行日: 1990/12/28
    公開日: 2018/01/15
    ジャーナル フリー
  • 宇井 忠英
    原稿種別: 口絵写真解説
    1990 年 35 巻 4 号 p. 425-426
    発行日: 1990/12/28
    公開日: 2018/01/15
    ジャーナル フリー
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