East Pacific Ridge

Elevation model of the South Pacific. The East Pacific Ridge can be seen in the right half of the picture as an approximately north-south running band in lighter shades of blue. At its southern end it merges into the more east-west oriented Pacific-Antarctic Ridge.

Above: “ Black smoker ” on the north east Pacific ridge (approx. 21 ° N).
Below: material sample from the chimney of a "black smoker" from the same region.

The East Pacific Ridge is a mid-ocean ridge in the southeastern Pacific . It is around 10,000 kilometers long and forms the plate boundary between the Pacific Plate , which forms the majority of the Pacific Basin, and part of the North American Plate , the Cocos Plate , the Nazca Plate and part of the Antarctic Plate , which runs approximately in a north-south direction . At its northern end, on the Gulf of California at around 32 ° N, the East Pacific Ridge merges into the San Andreas Transform Fault, and in the south at around 55 ° S into the Pacific-Antarctic Ridge . The East Pacific Ridge has two triple points, from each of which a mid-ocean ridge branches off to the east. To the north, near the equator, the Galapagos Ridge , which forms the border between the Cocos and Nazca plates, and to the south, at about 35 ° S, the Chile Ridge , which forms the border between the Nazca and Antarctic plates.

Current spread rates

The East Pacific Ridge is a center of spreading from which the Pacific Plate drifts westward while the other plates move eastward relative to the ridge. The spread rates on the East Pacific Ridge are generally relatively high in a global comparison. Because the absolute movement of the North American Plate is also directed to the west or it rotates clockwise, the spread rate in the Gulf of California is still relatively low at a little less than 5 cm per year, but it is already approaching the maximum value of the Mid-Atlantic Ridge . The rate of spread increases further to the south. In the northwest of the coconut plate ( Rivera microplate ) it is around 6 cm per year, at the Galapagos triple point around 12 cm per year and at the border between the Pacific plate and the Nazca plate, it reaches the highest value in the world at up to 14.5 cm per year .

Due to the high spreading rates, the East Pacific Ridge, unlike the Mid-Atlantic Ridge, does not have a pronounced central rift.

Historical geology

More than 30 million years ago, the East Pacific Ridge reached even further north. Due to a relatively rapid westward drift of the North American Plate, however, fewer new oceanic lithosphere was formed there than was subducted on the western edge of North America . As a result, the North American Continental Bloc eventually reached the ridge and the plate boundary was transformed into a transform fault , the San Andreas Fault. The San Andreas Fault merges to the north into an active, albeit only small, ridge system (see →  Juan de Fuca ridge ), which is considered an isolated relic of the old East Pacific ridge.

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1. ^ Charles DeMets, Richard G. Gordon, Donald F. Argus: Geologically current plate motions. Geophysical Journal International. Vol. 181, No. 1, pp. 1–80, doi: 10.1111 / j.1365-246X.2009.04491.x ( Open Access ), pp. 52 ff.
2. ↑ Ken MacDonald: What Is The Mid-Ocean Ridge? Ocean Explorer. National Oceanic and Atmospheric Administration, United States Department of Commerce
3. ↑ Patricia A. McCrory, Douglas S. Wilson, Richard G. Stanley: Continuing evolution of the Pacific-Juan de Fuca-North America slab window system - A trench-ridge-transform example from the Pacific Rim. Tectonophysics. Vol. 464, No. 1-4, 2009, pp. 30-42, doi: 10.1016 / j.tecto.2008.01.018 .