The Online Encyclopedia and Dictionary






East Pacific Rise

The East Pacific Rise is a long north-south welt of sea floor spreading that roughly parallels the Pacific coast of South America. The Rise is a constructive tectonic plate margin or divergent boundary lying along the eastern margin of the Pacific Ocean basin. The spreading zone separates the Pacific Plate to the west from (south to north) the Antarctic Plate, the Nazca Plate, Cocos Plate, Juan de Fuca Plate, and the North American Plate.

The volcanic Galapagos Islands are located above a hot spot on the Galapagos Rise, a spreading zone that extends east from a triple junction with the Pacific Rise. This triple junction separates the Pacific, Nazca, and Cocos plates. The Galapagos Microplate is a very small piece of crustal material located at this triple point.

The rise lies in part under the Gulf of California and is offset along the San Andreas Fault zone under southern California. The San Andreas is a transform fault boundary which ofsets the East Pacific Rise.

The oceanic crust is moving away from the East Pacific Rise to either side. On the eastern side the eastward moving plates meet the westward moving South American Plate and is being subducted under it. The belt of volcanoes along the Andes and the arc of volcanoes through Central America and Mexico are the direct results of this collision. To the north the volcanoes of the Cascades (including Mt. St. Helens) are the result of the subduction of the Juan de Fuca plate beneath the Noth American plate.

South of Easter Island the East Pacific Rise splits at another triple junction with the Chile Rise trending off to the east where is meets the subduction zone along the coast of southern Chile. The southern extension of the East Pacific Rise (called the Pacific-Antarctic Ridge, merges with the Mid-Indian Ridge at a triple juction south of New Zealand.

Along the East Pacific Rise the hydrothermal vents called black smokers were first discovered and have been extensively studied. The southern stretch of the East Pacific Rise is one of the fastest-spreading sections of the Earth's Ocean Ridge system.

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Last updated: 05-22-2005 15:38:40