<P> If spreading continues past the incipient stage described above, two of the rift arms will open while the third arm stops opening and becomes a' failed rift' . As the two active rifts continue to open, eventually the continental crust is attenuated as far as it will stretch . At this point basaltic oceanic crust begins to form between the separating continental fragments . When one of the rifts opens into the existing ocean, the rift system is flooded with seawater and becomes a new sea . The Red Sea is an example of a new arm of the sea . The East African rift was thought to be a "failed" arm that was opening somewhat more slowly than the other two arms, but in 2005 the Ethiopian Afar Geophysical Lithospheric Experiment reported that in the Afar region, September 2005, a 60 km fissure opened as wide as eight meters . During this period of initial flooding the new sea is sensitive to changes in climate and eustasy . As a result, the new sea will evaporate (partially or completely) several times before the elevation of the rift valley has been lowered to the point that the sea becomes stable . During this period of evaporation large evaporite deposits will be made in the rift valley . Later these deposits have the potential to become hydrocarbon seals and are of particular interest to petroleum geologists . </P> <P> Sea floor spreading can stop during the process, but if it continues to the point that the continent is completely severed, then a new ocean basin is created . The Red Sea has not yet completely split Arabia from Africa, but a similar feature can be found on the other side of Africa that has broken completely free . South America once fit into the area of the Niger Delta . The Niger River has formed in the failed rift arm of the triple junction . </P> <P> As new seafloor forms and spreads apart from the mid-ocean ridge it slowly cools over time . Older seafloor is therefore colder than new seafloor, and older oceanic basins deeper than new oceanic basins due to isostasy . If the diameter of the earth remains relatively constant despite the production of new crust, a mechanism must exist by which crust is also destroyed . The destruction of oceanic crust occurs at subduction zones where oceanic crust is forced under either continental crust or oceanic crust . Today, the Atlantic basin is actively spreading at the Mid-Atlantic Ridge . Only a small portion of the oceanic crust produced in the Atlantic is subducted . However, the plates making up the Pacific Ocean are experiencing subduction along many of their boundaries which causes the volcanic activity in what has been termed the Ring of Fire of the Pacific Ocean . The Pacific is also home to one of the world's most active spreading centers (the East Pacific Rise) with spreading rates of up to 13 cm / yr . The Mid-Atlantic Ridge is a "textbook" slow - spreading center, while the East Pacific Rise is used as an example of fast spreading . Spreading centers at slow and intermediate rates exhibit a rift valley while at fast rates an axial high is found within the crustal accretion zone . The differences in spreading rates affect not only the geometries of the ridges but also the geochemistry of the basalts that are produced . </P> <P> Since the new oceanic basins are shallower than the old oceanic basins, the total capacity of the world's ocean basins decreases during times of active sea floor spreading . During the opening of the Atlantic Ocean, sea level was so high that a Western Interior Seaway formed across North America from the Gulf of Mexico to the Arctic Ocean . </P>

What is the rate of spreading at the east pacific rise is this considered fast or slow
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