Mud Volcano - Doro-kazan (English spelling)

Japanese: 泥火山 - どろかざん（英語表記）Mud Volcano

When high-pressure fluids containing methane and other substances are covered by sediments with low permeability, if the water pressure exceeds a certain value determined by the viscosity of the mud, the mud is pushed up and rises on the seafloor, forming a mud volcano similar to a small volcano. Sometimes there is a depression at the summit that looks just like a volcanic caldera. Since it has nothing to do with magma activity, it is technically called a mud diaper, but the name mud volcano is also often used. Colonies of Calyptogena can often be seen on the edge of the caldera where methane is seeping out. There are many mud volcanoes in the Barbados area of the western Atlantic, where a thick layer of fine mud flowing from the Orinoco River in northeastern South America has accumulated. In the eastern Mediterranean, a survey by the academic research vessel Hakuho-Maru (affiliated with the Japan Agency for Marine-Earth Science and Technology) in 2007 revealed that there are also mud volcanoes lined up in the seep area of the Greek Trench. In the Nankai Trough, there are few mud volcanoes in the eastern part (off the Tokai coast) where the sediments are coarse-grained, but there are a considerable number of mud volcanoes in the Kumano Nada Sea, away from the mouths of the Fuji River and Tenryu River, which are the mud sources.

(Kazuo Kobayashi, Professor Emeritus, University of Tokyo / 2008)

Source : "Chiezo" published by Asahi Shimbun Publications Co., Ltd. About Chiezo

Japanese:

メタンなどを含む高圧の流体が透水率の低い堆積(たいせき)物に覆われている場合に、水圧が泥の粘性によって決まるある値を超えると泥は押し上げられて、海底に盛り上がり小形の火山に似た泥火山を造る。山頂部に火山のカルデラそっくりの窪みを持つここともある。マグマ活動とは何の関係もないので厳密には泥噴出(Mud Diaper)と呼ばれるが、泥火山の名もしばしば使われている。メタンが湧出(ゆうしゅつ)するカルデラの縁にはシロウリガイの群集が見られることが多い。南アメリカ東北部のオリノコ川から流れ出た細粒の泥が厚く積もっている西大西洋バルバドス(Barbados)海域には多数の泥火山が存在する。東地中海でもギリシャ海溝の湧水域に泥火山が並んでいることが2007年の学術研究船「白鳳丸」(海洋研究開発機構所属)調査によって分かった。南海トラフでは堆積物の粒度が粗い東部(東海沖)には泥火山はほとんどないが、泥供給源である富士川、天竜川の河口から離れた熊野灘にはかなりの数の泥火山が存在する。

(小林和男東京大学名誉教授／ 2008年)

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