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28-572: It extends eastward to the seismically active Mid-Atlantic Ridge at the Azores triple junction plate boundary where it meets the Eurasian plate and Nubian plate . and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust . The interior of the main continental landmass includes an extensive granitic core called a craton . Along most of

56-588: A lake some 60 mi (97 km) long and 30 mi (48 km) wide. In 1884 and 1891 the Colorado River had escapement flow into the Salton Sink. The 1891 flood created a lake that covered an area 30 mi (48 km) long and 10 mi (16 km) wide. A larger 1905 Colorado flood escaped into a diversion canal, forming the Alamo and New Rivers and creating the current Salton Sea in

84-566: Is actually a new plate beginning to converge with the North American plate, consistent with the standard model of rift zone spreading centers generally. A few hotspots are thought to exist below the North American plate. The most notable hotspots are the Yellowstone (Wyoming), Jemez Lineament (New Mexico), and Anahim (British Columbia) hotspots. These are thought to be caused by a narrow stream of hot mantle convecting up from

112-784: Is the topographic low area within the Salton Trough , an active tectonic pull-apart basin . The Salton Trough is a result of crustal stretching and sinking by the combined actions of the San Andreas Fault and the East Pacific Rise . The Brawley seismic zone forms the southeast end of the basin and connects the San Andreas Fault system with the Imperial Fault Zone to the south. The Salton Buttes are rhyolite lava domes within

140-655: The Bouvet triple junction in the South Atlantic. Although the Mid-Atlantic Ridge is mostly an underwater feature, portions of it have enough elevation to extend above sea level, for example in Iceland . The ridge has an average spreading rate of about 2.5 centimetres (1 in) per year. A ridge under the northern Atlantic Ocean was first inferred by Matthew Fontaine Maury in 1853, based on soundings by

168-800: The Caribbean Sea and the Motagua Fault through Guatemala . The parallel Septentrional and Enriquillo–Plantain Garden faults running through Hispaniola and bounding the Gonâve microplate , and the parallel Puerto Rico Trench running north of Puerto Rico and the Virgin Islands and bounding the Puerto Rico–Virgin Islands microplate , are also a part of the boundary. The rest of the southerly margin which extends east to

196-652: The Mississippi River , Amazon River and Niger River ). The Fundy Basin on the Atlantic coast of North America between New Brunswick and Nova Scotia in Canada is evidence of the ancestral Mid-Atlantic Ridge. Salton Sink The Salton Sink is the low point of an endorheic basin , a closed drainage system with no outflows to other bodies of water, in the Colorado Desert sub-region of

224-743: The Snake River Plain , while the Anahim hotspot is most notable for the Anahim Volcanic Belt in the Nazko Cone area. For the most part, the North American plate moves in roughly a southwest direction away from the Mid-Atlantic Ridge at a rate of about 2.3 centimeters (~1 inch) per year. At the same time, the Pacific plate is moving to the northwest at a speed of between 7 and 11 centimeters (~3-4 inches) per year. The motion of

252-684: The Sonoran Desert . The sink falls within the larger Salton Trough and separates the Coachella Valley from the Imperial Valley , which are also segments of the Salton Trough. The lowest point of the sink is 269 ft (82 m) below sea level, and since 1906 the 343-square-mile (890 km ) Salton Sea has filled the lowest portion of the sink to a water depth of up to 43 ft (13 m). The Salton Sink

280-709: The Tjörnes fracture zone connects Iceland to the Kolbeinsey Ridge . The ridge sits atop a geologic feature known as the Mid-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 the asthenosphere pushing the oceanic crust and lithosphere . This divergent boundary first formed in

308-520: The Triassic period, when a series of three-armed grabens coalesced on the supercontinent Pangaea 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 called aulacogens , and the aulacogens of the Mid-Atlantic Ridge eventually became many of the large river valleys seen along the Americas and Africa (including

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336-482: The USS Dolphin . The existence of the ridge and its extension into the South Atlantic was confirmed during the expedition of HMS Challenger in 1872. A team of scientists on board, led by Charles Wyville Thomson , discovered a large rise in the middle of the Atlantic while investigating the future location for a transatlantic telegraph cable . The existence of such a ridge was confirmed by sonar in 1925 and

364-745: The equator , the Mid-Atlantic Ridge is divided into the North Atlantic Ridge and the South Atlantic Ridge by the Romanche Trench , a narrow submarine trench 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. The islands on or near

392-596: The Earth's core–mantle boundary called a mantle plume , although some geologists think that upper mantle convection is a more likely cause. The Yellowstone and Anahim hotspots are thought to have first arrived during the Miocene period and are still geologically active, creating earthquakes and volcanoes. The Yellowstone hotspot is most notable for the Yellowstone Caldera and the many calderas that lie in

420-588: The Mid-Atlantic Ridge and marks the boundary between the North American plate and the South American plate is vague but located near the Fifteen-Twenty fracture zone around 16°N. On the northerly boundary is a continuation of the Mid-Atlantic Ridge called the Gakkel Ridge . The rest of the boundary in the far northwestern part of the plate extends into Siberia . This boundary continues from

448-558: The Mid-Atlantic Ridge, from north to south, with their respective highest peaks and location, are: Northern Hemisphere (North Atlantic Ridge) : Southern Hemisphere (South Atlantic Ridge) : The submarine section of the Mid-Atlantic Ridge close to southwest Iceland is known as the Reykjanes Ridge . The Mid-Atlantic Ridge runs through Iceland where the ridge is also known as the Neovolcanic Zone . In northern Iceland

476-643: The North American plate in contact with the Pacific plate as the San Andreas Fault. The Juan de Fuca , Explorer , Gorda , Rivera , Cocos and Nazca plates are remnants of the Farallon plate. The boundary along the Gulf of California is complex. The gulf is underlain by the Gulf of California Rift Zone , a series of rift basins and transform fault segments from the northern end of the East Pacific Rise in

504-414: The basin has filled many times, creating a lake some 105 mi (169 km) in length and nearly 300 ft (91 m) deep. Its most recent incarnation is evidenced by fish traps found some 30 ft (9.1 m) below the high-water mark that were estimated to be between 300 and 1,000 years old. In recent times, the 1862 Colorado River flood waters reached the Salton Sink, filling it and creating

532-480: The basin which were active 10,300 (± 1000) years BP. A large lake, Lake Cahuilla , existed in the area from about 20,500 to 3,000 years ago and left evidence as wave-cut benches on the higher portions of the Salton Buttes. A beach mark outlines the shoreline of ancient Lake Cahuilla where archeologists found rock fish traps and charred remains of razorback sucker and bonytail bones. High water lines suggest

560-670: The edges of this craton are fragments of crustal material called terranes , which are accreted to the craton by tectonic actions over a long span of time. Much of North America west of the Rocky Mountains is composed of such terranes. The southern boundary with the Cocos plate to the west and the Caribbean plate to the east is a transform fault , represented by the Swan Islands Transform Fault under

588-933: The end of the Gakkel Ridge as the Laptev Sea Rift , on to a transitional deformation zone in the Chersky Range , then the Ulakhan Fault between it and the Okhotsk microplate , and finally the Aleutian Trench to the end of the Queen Charlotte Fault system (see also: Aleutian Arc ). The westerly boundary is the Queen Charlotte Fault running offshore along the coast of Alaska and the Cascadia subduction zone to

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616-691: The floor of the Atlantic Ocean , and part of the longest mountain range in the world . In the North Atlantic, the ridge separates the North American from the Eurasian plate and the African plate , north and south of the Azores triple junction . In the South Atlantic, it separates the African and South American plates. The ridge extends from a junction with the Gakkel Ridge (Mid-Arctic Ridge) northeast of Greenland southward to

644-411: The hypothetical supercontinent of Pangaea that began some 180 million years ago. The Mid-Atlantic Ridge includes a deep rift valley that runs along the axis of the ridge for nearly its entire length. This rift marks the actual boundary between adjacent tectonic plates, where magma from the mantle reaches the seafloor, erupting as lava and producing new crustal material for the plates. Near

672-410: The mouth of the gulf to the San Andreas Fault system in the vicinity of the Salton Trough rift/ Brawley seismic zone . It is generally accepted that a piece of the North American plate was broken off and transported north as the East Pacific Rise propagated northward, creating the Gulf of California. However, it is as yet unclear whether the oceanic crust between the rise and the mainland coast of Mexico

700-592: The north, the San Andreas Fault through California , the East Pacific Rise in the Gulf of California , and the Middle America Trench to the south. On its western edge, the Farallon plate has been subducting under the North American plate since the Jurassic period. The Farallon plate has almost completely subducted beneath the western portion of the North American plate, leaving that part of

728-517: The plate cannot be driven by subduction as no part of the North American plate is being subducted, except for a small section comprising part of the Puerto Rico Trench ; thus other mechanisms continue to be investigated. One study in 2007 suggests that a mantle convective current is propelling the plate. Mid-Atlantic Ridge The Mid-Atlantic Ridge is a mid-ocean ridge (a divergent or constructive plate boundary ) located along

756-403: The ridge is part of a 40,000-km (25,000 mile) long essentially continuous system of mid-ocean ridges on the floors of all the Earth's oceans. The discovery of this worldwide ridge system led to the theory of seafloor spreading and general acceptance of Alfred Wegener 's theory of continental drift and expansion in the modified form of plate tectonics . The ridge is central to the breakup of

784-567: Was found to extend around Cape Agulhas into the Indian Ocean by the German Meteor expedition . In the 1950s, mapping of the Earth's ocean floors by Marie Tharp , Bruce Heezen , Maurice Ewing , and others revealed that the Mid-Atlantic Ridge had a strange bathymetry of valleys and ridges, with its central valley being seismologically active and the epicenter of many earthquakes . Ewing, Heezen and Tharp discovered that

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