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The geology of Ascension Island is the geologically young, exposed part of a large volcano, 80 kilometers west of the Mid-Atlantic Ridge. The island formed within the last six to seven million years and is primarily mafic rock with some felsic rock. [1] [2] Physical map of Ascension Island
The Azores High also known as North Atlantic (Subtropical) High/Anticyclone or the Bermuda-Azores High, is a large subtropical semi-permanent centre of high atmospheric pressure typically found south of the Azores in the Atlantic Ocean, at the Horse latitudes. It forms one pole of the North Atlantic oscillation, the other being the Icelandic Low.
The latitudinal movement of the subtropical ridge is strongly correlated with the progression of the monsoon trough or Intertropical Convergence Zone. Most tropical cyclones form on the side of the subtropical ridge closer to the equator, then move poleward past the ridge axis before recurving into the main belt of the Westerlies. [10]
The archipelago lies on the lateral branch of the Mid-Atlantic Ridge near the junction of three major tectonic plates; the North American Plate, the Eurasian Plate and the African Plate. [3] This unique location causes the area to have ridge-hotspot interaction with a variation of volcanic processes.
A relief map of the Azores Triple Fault region and southern bathymetric zone. The hydrothermal vents and seamounts of the Azores (Portuguese: fontes hidrotermais e montes submarinos dos Açores) are a series of Atlantic seamounts and hydrothermal vents that are part of the Mid-Atlantic Ridge system, giving rise to the archipelago and bathymetric region of the Azores.
The Mid-Atlantic Ridge is a mid-ocean ridge (a divergent or constructive plate boundary) located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. In the North Atlantic, the ridge separates the North American from the Eurasian plate and the African plate , north and south of the Azores triple junction .
In contrast, if formed by past above-water volcanism, they are known as a seamount chain. The largest and best known undersea mountain range is a mid-ocean ridge, the Mid-Atlantic Ridge . [ 1 ] It has been observed that, "similar to those on land, the undersea mountain ranges are the loci of frequent volcanic and earthquake activity".
It is believed that the massif was formed underneath the nearby Mid-Atlantic Ridge but was pulled from under the ridge during the movement of the plates, about 1.5 to 2 million years ago. Geologic studies of the massif have indicated that it is not composed of the black basalt typical of the ocean floor but rather of dense green peridotite ...