A map of the ocean basins (Fig. 5.1) shows that their most conspicuous topographic feature is the system of mid-oceanic ridges, the crests of which rise on average 1000–3000 m above the adjacent ocean floor. Such ridges extend through all the major ocean basins, with a total length in excess of 60 000 km. With the exception of the East Pacific Rise, they occur in the middle part of the oceans and essentially form a submarine mountain range, which rises to its highest elevation at the ridge crest and slopes away symmetrically on either flank. Topographically, they vary throughout their length, the East Pacific Rise being much broader and less rugged than the other ridges (Section 5.4). A rare terrestrial expression of the mid-oceanic ridge system occurs in Iceland, whose central graben is the extension of the Mid-Atlantic Ridge.
KeywordsPartial Melting Oceanic Crust Magma Chamber Ocean Floor Ridge Axis
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