Heat Flow Observations in and around Wakamiko Crater in Kagoshima Bay, Kyushu, Japan

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  • FUJINO Keiko
    Department of Earth Resources Engineering, Graduate School of Engineering, Kyushu University
  • YAMANAKA Toshiro
    Graduate School of Natural Science and Technology, Okayama University
  • EHARA Sachio
    Institute for Geothermal Information
  • FUJIMITSU Yasuhiro
    Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University

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  • 鹿児島湾若尊火口と周辺での熱流量分布
  • カゴシマワン ワカソンカコウ ト シュウヘン デ ノ ネツ リュウリョウ ブンプ

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Abstract

Hydrothermal activities are observed in Wakamiko Crater in Aira Caldera, south Kyushu, Japan. Wakamiko Crater is an active volcano that was formed by a big explosive eruption of Aira Caldera ca. 25 ka. Although Wakamiko Crater is characterized by many submarine active hydrothermal activities, its subsurface geothermal structures have not been clarified. Generally, it is difficult to obtain reliable heat flow values in shallow sea areas where the bottom water temperature is not stable and sedimentation rate is high. Hence, annual bottom sea water temperature variations were measured in order to correct the observed heat flow and the effect of the sedimentation rate.We observed under ground temperature at 95 points and determined marine surface heat flows at 44 points on between 2005 and 2009 in and around Wakamiko Crater. Hydrothermal site with hydrothermally alteredwhite patch or chimneys were found at 4 points in the crater. These results present that extremely high heat flow values (several hundred to 104 mW/m2) were observed near submarine hydrothermal sites, and these high values gradually decrease from the center of the Wakamiko Crater to the surrounding area. Heat flow values ranging 80to 100 mW/m2 around Wakamiko Crater represent the background heat flow values in south Kyushu. We also detected 51 nonlinear temperature profiles around Wakamiko Crater, which suggest water migration around the crater.

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