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The Walvis Ridge (''walvis'' means whale in Dutch and Afrikaans) is an aseismic ocean ridge in the southern Atlantic Ocean. More than in length, it extends from the Mid-Atlantic Ridge, near Tristan da Cunha and the Gough Islands, to the African coast (at 18°S). The Walvis Ridge is one of few examples of a hotspot seamount chain that links a flood basalt province to an active hotspot. It is also considered one of the most important hotspot tracks because the Tristan Hotspot is one of few primary or deep mantle hotspots. ==Geology== Apart from the Mid-Atlantic Ridge, the Walvis Ridge and the Rio Grande Rise are the most distinctive feature of the South Atlantic sea floor. They originated from hotspot volcanism and together they form a mirrored symmetry across the Mid-Atlantic Ridge, with the Tristan Hotspot at its centre. Two of the distinct sections in the Walvis Ridge have similar mirrored regions in the Rio Grande Rise; for example, the eastern section of the Walvis Ridge evolved in conjunction with the Torres Arch (the western end of the Rio Grande Rise, off the Brazilian coast) and, as the South Atlantic gradually opened, these structures became separated. The complex of seamounts in the western end of the Walvis Ridge, however, does not have a similar structure on the American side, but there is a Zapiola Seamount Complex south of the eastern end of the Rio Grande Rise. The formation of this mirrored structure is the result of the opening of the South Atlantic some 120 Mya and the Paraná and Etendeka continental flood basalts, the lateral-most parts of the structure, formed at the beginning of this process in areas that are now located in Brazil and Namibia.〔 The Walvis Ridge is divided into three main sections:〔 # A first long segment stretching from Africa to approximately longitude 6°E and varying in width between . # A second section, long, stretching north-south, and narrower than the first section. # A third more discontinuous section, which is marked by seamounts and connects the Walvis Ridge to the Mid-Atlantic Ridge. Cretaceous kimberlites in the central Democratic Republic of Congo and Angola align with the Walvis Ridge. The Tristan-Gough hotspot track first formed over the mantle plume that formed the Etendeka-Paraná continental flood basalts some . The eastern section of the ridge is thought to have been created in the Middle Cretaceous period, between . While the mantle plume remained large and stable, the eastern Walvis Ridge formed along with the Rio Grande Rise over the Mid-Atlantic Ridge.〔 During the Maastrichtian , the orientation of spreading changed, which is still visible in the orientation of the various sections of the Walvis Ridge.〔 The mantle plume then gradually became unstable and bifurcated to produce the two separate Tristan and Gough hotspot tracks. It finally disintegrated and formed the guyot province in the western end of the ridge.〔 Hundreds of volcanic explosions were recorded on the Walvis Ridge in 2001 and 2002. These explosions seemed to come from an unnamed seamount on the northern side of the ridge and are thought to be unrelated to the Tristan hotspot. The Ewing Seamount is part of the ridge. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Walvis Ridge」の詳細全文を読む スポンサード リンク
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