火山
Online ISSN : 2189-7182
Print ISSN : 0453-4360
ISSN-L : 0453-4360
52 巻, 2 号
選択された号の論文の4件中1~4を表示しています
  • 吉田 稔, 大島 峰治
    原稿種別: 論説
    2007 年 52 巻 2 号 p. 89-103
    発行日: 2007/04/27
    公開日: 2017/03/20
    ジャーナル フリー
    Fluorine (F) and chlorine (Cl) have been determined for the products of a series of large-scale pyroclastic eruptions that produced the Aira caldera at the northern end of Kagoshima bay in southern Kyushu. It started with a Plinian pumice eruption (Osumi pumice fall, 98km3) followed by the Tsumaya pyroclastic flow (13km3). After a short pose, a violent explosive eruption occurred to form the Ito pyroclastic flow (250km3) accompanied by the Aira-Tn ash fall (50km3). Pumice blocks, pumice grains, no welding matrices and welded tuffs sampled from the deposits of the Osumi pumice fall, the Tsumaya pyroclastic flow and the Ito pyroclastic flow are analyzed. Their F and Cl contents varied in the course of the eruptions. The Osumi pumice fall samples have uniform F and Cl contents and show the highest average values among those deposits. Fluorine contents of the Ito pyroclastic flow samples are distinctly lower than the Osumi pumice samples in order of grain size : fine-grained matrices > coarse-grained matrices > pumice grains > pumice blocks. The Tsumaya pyroclastic samples are divided into two groups according to their F contents. The lower-layer deposits show F contents nearly the same as those of the Osumi pumices, while the higher-layer deposits near to the Ito samples. The variation of F contents from the Osumi pumices to the Ito pyroclastic deposits is thought to be caused by the change of distribution of F between silicate melt and aqueous phases before and after the first Plinian eruption. The variation among the Ito deposits can be explained by the reaction between gases and silicates after the eruption. Chlorine contents in pumices and no welding matrices of both pyroclastic flows show wide range, but the highest values are almost the same as that of the Osumi pumices. Welded tuff samples show the lowest Cl contents and the highest F/Cl ratio. These results can be explained by release of Cl after deposition of the flows.
  • Toshiya MORI, Jun-ichi HIRABAYASHI, Kohei KAZAHAYA, Takehiko MORI, Mic ...
    原稿種別: 寄書
    2007 年 52 巻 2 号 p. 105-112
    発行日: 2007/04/27
    公開日: 2017/03/20
    ジャーナル フリー
    A compact and handy system for measuring SO2 fluxes from volcanoes is newly built using a miniature UV spectrometer. This COMPact Ultraviolet Spectrometer System (Hereafter referred as “COMPUSS”) is much smaller and lighter than a correlation spectrometer (COSPEC), which has been used for SO2 flux measurements from volcanoes over 30years. Validation of the COMPUSS was carried out comparing COMPUSS and COSPEC instruments at Sakurajima and Miyakejima volcanoes by car and heliborne traverse method, respectively. Our results show that agreement of the SO2 flux between the COSPEC and the COMPUSS data is vouched for traverse measurements. The COMPUSS has much advantage compared to the COSPEC for volcanic SO2 flux measurements, because of its portability and possibility for further improvement of the system.
  • 安田 敦, 金子 隆之, 藤井 敏嗣
    原稿種別: 寄書
    2007 年 52 巻 2 号 p. 113-120
    発行日: 2007/04/27
    公開日: 2017/03/20
    ジャーナル フリー
    Tsuya (1962) described a white pumiceous ash layer in the Hakoarezawa tunnel located at the southwest flank of Mt. Fuji, and ascribed it to an acidic magma activity of the older Fuji Volcano. We found a thin-section labeled “Hakoaresawa pumice lens 1,960m” in rock-samples left by the late Professor Hiromichi Tsuya, and analyzed it by electron microprobe. The white pumice is composed largely of flakes of colorless glass together with a few fragmented plagioclase micro-phenocrysts coated by the glass and free crystals of orthopyroxene. Chemical composition of the glass (SiO2=78.1, Al2O3=12.2, CaO=1.1, Na2O=3.7, K2O=3.3(wt%)) is identical to that of Aira-Tn (AT) ash, a widespread volcanic deposit erupted from Aira caldera about 26,000 years ago. Composition of the plagioclase is also similar to that in AT ash. Considering some other similarities between the white pumice and AT ash such as their refractive indexes of glass, we conclude that the white pumice is AT ash, and not a product of the older Fuji volcano.
  • 横尾 亮彦, 井口 正人, 石原 和弘
    原稿種別: 寄書
    2007 年 52 巻 2 号 p. 121-126
    発行日: 2007/04/27
    公開日: 2017/03/20
    ジャーナル フリー
    In June 2006, Showa crater on the southeastern flank of Minamidake, Sakurajima volcano erupted after 58 years silence. Geothermal observation has been repeated 5 times since March 2006, using an infrared thermal camera. The results of the observation were compared with the previous data. Thermal anomaly areas identified in 2006 coincide with the previous results. Increasing temperatures of the ground surface were recognized on the southeastern flank of the volcano in particular around Showa crater and fumarolic zones, over the data of 1992. In contrast, no significant change in the temperature was observed on the southern flank. These results suggest that the geothermal activity on the southeastern flank of the volcano became high prior to the 2006 eruption at Showa crater.
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