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The Mid-Atlantic Ridge
The 16,000-kilometer undersea mountain range where the Atlantic Ocean is still being born
The longest mountain range in the Atlantic is almost entirely invisible. The Mid-Atlantic Ridge runs down the middle of the ocean from the Arctic to the far South Atlantic, a chain of volcanic peaks and a central rift valley where new seafloor is created. On each side the plates move apart by a few centimeters a year, which is why the Atlantic is wider today than when Columbus crossed it. In only a few places does the ridge break the surface: Iceland, the Azores, and a handful of remote islands. The ridge was the key evidence that convinced geologists, in the 1960s, that continents drift on moving plates.
The ridge stretches about 16,000 kilometers, from north of Iceland to near Bouvet Island in the South Atlantic, and is part of a global mid-ocean ridge system some 65,000 kilometers long. Its crest typically lies about 2,500 meters below the surface and rises 2,000 to 3,000 meters above the surrounding abyssal plains. In the North Atlantic it divides the North American and Eurasian plates, and in the South Atlantic the South American and African plates. Spreading is slow, about 2 to 5 centimeters a year. Transform faults offset the ridge in many places, and earthquakes along it seldom exceed magnitude 7. Above sea level it surfaces in Iceland, the Azores, St. Peter and St. Paul Archipelago, Ascension Island, and, close by, Tristan da Cunha.
Soundings for the first transatlantic telegraph cables in the 1850s hinted at a rise in mid-ocean, and HMS Challenger confirmed it in 1872. The German Meteor expedition mapped it with echo sounders in the 1920s, and in 1953 cartographer Marie Tharp identified the rift valley along its crest, the clue that led to seafloor spreading theory. Iceland is the ridge on land, where the plate boundary crosses Þingvellir and fuels frequent eruptions. On the Reykjanes Peninsula, nine eruptions along the Sundhnúkur crater row between December 2023 and August 2025 threatened the town of Grindavík. As of late summer 2026, the Icelandic Meteorological Office reported magma still accumulating beneath Svartsengi and considered another eruption likely.