火山.第2集
Online ISSN : 2433-0590
ISSN-L : 0453-4360
28 巻, 3 号
選択された号の論文の14件中1~14を表示しています
  • 原稿種別: 口絵写真
    1983 年 28 巻 3 号 p. App6-
    発行日: 1983/10/01
    公開日: 2018/01/15
    ジャーナル フリー
  • 森 健
    原稿種別: 論説
    1983 年 28 巻 3 号 p. 225-232
    発行日: 1983/10/01
    公開日: 2018/01/15
    ジャーナル フリー
    Standards for quantitative electron-probe analysis of geochemical samples have been evaluated in the light of recent advances in hardware technology and data reduction system. Energy dispersive type electron-probe has merits that command wide variety of standards. 200 pA electron beam scanned in a small region yields stable X-ray intensities on such weak materials as potassium dichromate, calcium carbonate and gallium phosphide. These are excellent 'standards for K, Ca and P, respectively. Energy shifts measured between metal and oxide for Al, Si and Fe are less than 1 eV. This means that the use of metals does not cause analytical errors. Wavelength dispersive electron-probe likewise can employ metal standards owing to the computer-assisted peak positionning for both standards and unknowns. Pure metals and simple oxides together cannot cover whole elements of geochemical interest. Natural minerals are complementary standards, but are inevitably heterogeneous to some extent. X-ray intensities on a spot of almost pure natural minerals measured by EDS or automated WDS combined with assumed stoichiometry give rise to independent estimates of chemical compositions. This is particularly useful for albite, jadeite, pyrite, K-feldspar and wollastonite. Thus, electron-probe analysis can now be independent of other analytical methods. Error evaluation attests that even EDS analysis can be as good as the conventional chemical analysis. The use of pure metal standards demonstrates variation of characteristic X-ray intensity in a wide energy range. When no metals are available, the compound standards can yield, by ZAF correction method, intensities for simple substances. Both sets of intensity data fit each other, and show X-ray generation-detection efficiency . This knowledge leads to quantitative analysis of elements for which no standards are available, and will in future enable entirely standardless electron-probe analysis.
  • 山岸 宏光
    原稿種別: 論説
    1983 年 28 巻 3 号 p. 233-243
    発行日: 1983/10/01
    公開日: 2018/01/15
    ジャーナル フリー
    The author has found several kinds of surface structures of the pillow lobes formed in geologic time, which are similar to those of the modern pillow lobes at recent sea bottom. They represent ropy surfaces, corrugations, spreading cracks, tensional and contraction cracks. The former three have probably formed during growing of pillow lobes, whereas the latter two after cessation of growth.
  • 日下部 実, 林 尚美, 小林 武彦
    原稿種別: 論説
    1983 年 28 巻 3 号 p. 245-261
    発行日: 1983/10/01
    公開日: 2018/01/15
    ジャーナル フリー
    Banded sulfur sediments, characterized by beautiful alternation of yellowish-white layers of fine-grained sulfur and light to dark gray clay layers, occur in the Jigokudani valley of Tateyama volcano, Japan. The sediments were deposited on the bottom of a now extinct crater lake that had been produced by phreatic explosions of the Tateyama volcano in Holocene age. Sulfur isotopic analyses imply that hydrogen sulfide of volcanic gas origin was oxidized to form colloidal sulfur in the presence of dissolved oxygen. Variation in contents of fossilized fresh water diatoms (dominated mostly by benthic species Pinnularia braunii (GRUN.) CL. var. amphicephala (A. MAYER) HUST.) and of native sulfur in the sediments suggests that lamination was caused by seasonally repetitive precipitation of the colloidal sulfur plus diatoms during circulating-oxidative periods of the lake and that of detrital materials during stagnant-reducing periods. Stratigraphic variation in the sulfur and diatom contents of the sediments may be interpreted to reflect changes in fumarolic activity and environmental conditions of the lake for a longer time scale. A sedimentation period of 3000 to 4000 years is calculated from the total thickness of the banded sulfur sediments coupled with sedimentation rates deduced from the above model. This period is in good harmony with the age of phreatic explosions (3000 to 6000 years) estimated by tephra chronology.
  • 早川 由紀夫
    原稿種別: 論説
    1983 年 28 巻 3 号 p. 263-273
    発行日: 1983/10/01
    公開日: 2018/01/15
    ジャーナル フリー
    The Chuseri pumice is a widespread Holocene dacitic tephra layer erupted from the Nakano Umi crater in the Towada caldera. The pumice is directly overlain by the Kanegasawa bedded pumice and Utarube ash. The Chuseri pumice. Kanegasawa pumice, and Utarube ash define the Chuseri tephra formation. Volumes are calculated using isopach maps to be 6.5 km^3 for the Chuseri pumice, 1.2 km3 for the Kanegasawa pumice, and 0.9 km3 for the Utarube ash. Plots of the areas enclosed by the isopleths of maximum pumice size and maximum lithic size show the Chuseri pumice to be an average plinian eruption product. The Utarube ash is an ash-fall deposit containing accretionary lapilli and is interbedded with surge deposit near source area. Grainsize characteristics of the Chuseri pumice are described. Like other plinian deposits, the Chuseri pumice does not contain an appreciable amount of fine ash (finer than 1/16mm), at least, as far as 45 km from the source vent. A new radiocarbon date (GaK-9761) on charcoal from within the Chuseri pumice deposit establishes an age for the eruption of 5,390±140 years B.P.
  • 佐藤 純, 佐藤 和郎, 高橋 春男, 木俣 賢朗
    原稿種別: 論説
    1983 年 28 巻 3 号 p. 275-287
    発行日: 1983/10/01
    公開日: 2018/01/15
    ジャーナル フリー
    Non-destructive gamma-ray spectrometry was made on the following widespread volcanic ashes for specific radioactivities of U- and Th-series nuclides and for K contents ; (1) 1978 Sakurajima ash fall samples collected at 6 different distances (4-42 km) from the crater, (2) 1982 Asama ash fall samples collected at Karuizawa (Nagano) and Tokyo, (3) Rhyolitic ash fall deposit from the N3 layer in Izu-Oshima island, (4) “AT” ash (Aira Tn volcanic ash) deposit at an outcrop near Gotemba (Shizuoka) and (5) Akahoya volcanic ash fall deposit from northern Kyushu. Detailed examination of the data for each ash fall and for some related volcanic pro-ducts showed that there was no significant difference in three ratios, Th-ser./U-ser., Th-ser./K and U-ser./K, between the ashes scattered far away in the air and such materials deposited near the crater as lavas, pyroclastic flow deposits and pumice fall deposits. As observed previously with samples occurring near their sources, these parameters tend to cluster around values characteristic of respective volcanoes.
  • 宇井 忠英, 荒牧 重雄
    原稿種別: 論説
    1983 年 28 巻 3 号 p. 289-299
    発行日: 1983/10/01
    公開日: 2018/01/15
    ジャーナル フリー
    The May 18, 1980 eruption of Mt. St. Helens gives us much information concerning identification, mode of eruption, transportation and deposition of volcanic dry avalanches. Precursor events including swarm of volcanic earthquakes, small phreatic explosions, bulging of volcanic edifice at northern part and growth of normal fault scarps at the top preceded within 2 months duration. Unstable portion of the volcanic edifice was detached 7-26 seconds after the great volcanic earthquake of M=5.1 and had collapsed towards the northern slope, filling the Toutle River valley until the area 28 km away from the source. The deposit covers an area of 60 km2. Mean thickness is 45 m (VOIGHT et al., 1981). Surface of the deposit is topographically characterised with hummockey reriefs, spiracles, natural levees and depositional ramps. Volcanic edifice exposed along the inner wall of the new crater shows fresh and extensive shattered structure. Shattered megablocks are abundant in the main depositional area. Fine-grained tuffaceous layers are found between two adjacent megablocks. Size and amount of megablocks decrease towards the distal end of the deposit. Matrix materials consisting of mixture of clasts derived from several megablocks of different lithology and pelets of soil, gravel and wood fragments captured during transportation, becomes abundant towards the downflow area. These textural evidences suggest the shattering of volcanic edifice prior to the collapse, and continuous decomposition of megablocks towards the distal end of the deposit.
  • 沢田 宗久, 行田 紀也, 長田 昇, 小山 悦郎, 辻 浩, 鍵山 恒臣, 宮崎 務
    原稿種別: 寄書
    1983 年 28 巻 3 号 p. 301-304
    発行日: 1983/10/01
    公開日: 2018/01/15
    ジャーナル フリー
  • 野津 憲治, 安孫子 勤, 脇田 宏
    原稿種別: Letter
    1983 年 28 巻 3 号 p. 305-308
    発行日: 1983/10/01
    公開日: 2018/01/15
    ジャーナル フリー
  • 関岡 満, 伊藤 芳朗, 斎藤 輝夫
    原稿種別: 寄書
    1983 年 28 巻 3 号 p. 309-311
    発行日: 1983/10/01
    公開日: 2018/01/15
    ジャーナル フリー
  • Ndontoni ZANA, 浜口 博之
    原稿種別: 寄書
    1983 年 28 巻 3 号 p. 313-316
    発行日: 1983/10/01
    公開日: 2018/01/15
    ジャーナル フリー
  • 阪口 圭一, 宇井 忠英
    原稿種別: 寄書
    1983 年 28 巻 3 号 p. 317-320
    発行日: 1983/10/01
    公開日: 2018/01/15
    ジャーナル フリー
  • 原稿種別: 訂正
    1983 年 28 巻 3 号 p. 326-
    発行日: 1983/10/01
    公開日: 2018/01/15
    ジャーナル フリー
  • 横山 泉
    原稿種別: 口絵写真解説
    1983 年 28 巻 3 号 p. 329
    発行日: 1983/10/01
    公開日: 2018/01/15
    ジャーナル フリー
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