Ridge - Kairei (English spelling)

Japanese: 海嶺 - かいれい（英語表記）ridge

A long, narrow undersea mountain range with steep slopes on both sides. Its length ranges from several hundred to 20,000 km. It is divided into mid-oceanic ridges, where hydrothermal vents and shallow earthquakes along the mountain ridges prove the formation of the ocean floor, and those with various other causes. The topography of mid-oceanic ridges is almost symmetrical on either side of the ridge, and the water depth increases roughly in proportion to the square root of the age of the ocean floor. The mid-ocean ridge of the Indian Ocean branches into three at the Rodrigues Ridge triple junction near 25 degrees south latitude and 68 degrees east longitude, forming an inverted Y shape. The water depth at the top is usually about 2,500 m, but near the summit, basaltic pillow lava that erupted on the ocean floor is exposed, and the base is covered with sediments. There are many other ridges around Japan that were formed when island arcs were left behind and sunk due to the expansion of the ocean floor and ocean basins. A chain of islands and seamounts that is thought to be the result of plate movement on a hotspot, such as the Hawaiian Ridge, can also be called a ridge. Other examples include the Zenisu Ridge and the Okushiri Ridge, which are thought to be the result of the seafloor rising near a convergent plate boundary.

(Kazuo Kobayashi, Professor Emeritus, University of Tokyo / 2007)

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

Japanese:

両側に急斜面を持ち、細長く連なる海底の大山脈。延長は数百〜2万km。山稜沿いの熱水噴出や、浅い地震の列の存在が海底の生成を証拠立てる大洋中央海嶺(mid‐oceanic ridge)と、それ以外の多様な成因を持つものに分かれる。大洋中央海嶺の地形は、稜線を挟みほぼ対称で、水深は海底の生成年代の平方根に、おおむね比例して増す。インド洋の中央海嶺は南緯25度東経68度付近のロドリゲス海嶺三重点で3つに枝分かれして、逆Y字型をしている。頂の水深はたいてい約2500mだが、山頂付近は海底に噴出した玄武岩質の枕状(まくらじょう)溶岩が露出し、麓の部分は堆積物で覆われている。他に、海洋底や海盆の拡大で島弧が取り残され、沈没してできた海嶺が、日本周辺に数多くある。ハワイ海嶺のように、ホットスポット上のプレート運動の跡とされる島と海山の列も海嶺と呼ばれる場合がある。プレート収束境界付近で海底が盛り上がったと思われる銭洲海嶺、奥尻海嶺などの例もある。

(小林和男東京大学名誉教授／ 2007年)

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