In the 1950s,mapping of the Earth's ocean floors byMarie Tharp,Bruce Heezen,Maurice Ewing, and others revealed that the Mid-Atlantic Ridge had a strangebathymetry of valleys and ridges,[7] with its central valley beingseismologically active and theepicenter of manyearthquakes.[8][9] Ewing, Heezen and Tharp discovered that the ridge is part of a 40,000-km (25,000 mile) long essentially continuous system ofmid-ocean ridges on the floors of all the Earth's oceans.[10] The discovery of this worldwide ridge system led to the theory ofseafloor spreading and general acceptance ofAlfred Wegener's theory ofcontinental drift and expansion in the modified form ofplate tectonics. The ridge is a feature whose contribution to the breakup of thesupercontinent ofPangaea, in the period from about 200 to 160 million years ago, is considered in the modelling of such breakup in modern tectonic theory, where subduction and mantel plumes mechanisms are hypothesised to be primary, although historically this was contentious.[11][12]
In Iceland the Mid-Atlantic Ridge passes across theÞingvellir National Park, a popular destination for tourists
The Mid-Atlantic Ridge includes a deeprift valley that runs along the axis of the ridge for nearly its entire length. This rift marks the actual boundary between adjacent tectonic plates, wheremagma from themantle reaches the seafloor, erupting aslava and producing newcrustal material for the plates.
Near theequator, the Mid-Atlantic Ridge is divided into the North Atlantic Ridge and the South Atlantic Ridge by theRomanche Trench, a narrow submarinetrench with a maximum depth of 7,758 m (25,453 ft), one of the deepest locations of the Atlantic Ocean. This trench, however, is not regarded as the boundary between the North and South American plates, nor the Eurasian and African plates.
Approximate surface projection on Atlantic Ocean of Mid-Atlantic Ridge (purple). Associated fracture zones (orange) are also shown. Click to expand map to obtain interactive details.[13]
The islands on or near the Mid-Atlantic Ridge, from north to south, with their respective highest peaks and location, are:
The submarine section of the Mid-Atlantic Ridge close to southwest Iceland is known as theReykjanes Ridge. The Mid-Atlantic Ridge runs through Iceland where the ridge is also known as theNeovolcanic Zone. In northern Iceland theTjörnes fracture zone connects Iceland to theKolbeinsey Ridge.
Basaltic rocks of the Mid-Atlantic Ridge observed by theHerculesROV during the 2005Lost City Expedition
The ridge sits atop a geologic feature known as theMid-Atlantic Rise, which is a progressive bulge that runs the length of the Atlantic Ocean, with the ridge resting on the highest point of this linear bulge. This bulge is thought to be caused by upward convective forces in theasthenosphere pushing theoceanic crust andlithosphere. This divergent boundary first formed in theTriassic period, when a series ofthree-armedgrabens coalesced on the supercontinentPangaea to form the ridge. Usually, only two arms of any given three-armed graben become part of a divergent plate boundary. The failed arms are calledaulacogens, and the aulacogens of the Mid-Atlantic Ridge eventually became many of the large river valleys seen along theAmericas andAfrica (including theMississippi River,Amazon River andNiger River). TheFundy Basin on the Atlantic coast of North America betweenNew Brunswick andNova Scotia inCanada is evidence of the ancestral Mid-Atlantic Ridge.[14][15]
