Mid-ocean ridges such as the Mid-Atlantic Ridge are places in the Earth's system of tectonic plates where new crust forms and the plates move away from one another. Powered by magma rising and falling in the mantle, these undersea mountain ranges are formed by numerous eruptions of basalt lava along their length.
Because in almost all cases the eruptions take place deep below the ocean surface, mid-ocean ridges were only properly discovered in the 1950s. Scientists were surprised to find that hydrothermal vents along the ridges were home to life forms able to survive in complete darkness.
Image: A diver swims between the Eurasian and North American plates in Thingvellir lake, Thingvellir National Park, Iceland. Iceland is one place where a mid-ocean ridge can be seen on land and in shallow waters.(credit: Wild Wonders of Europe/Lundgre)
Iain Stewart explains how the Earth's crust is divided.
Dr Iain Stewart visits the Mid-Atlantic Ridge in Thingvellir, Iceland, a place where it's possible to see the divide between two of the Earth's plates on land.
Iceland's volcanism is linked to its position on the Mid-Atlantic Ridge.
Professor Iain Stewart discusses Iceland's volcanoes, including the massive eruption that created the island of Surtsey in 1963. Iceland's position on the Mid-Atlantic Ridge makes it a volcanically active place.
Volcanic chimneys found near mid-ocean ridges are a strange sight.
When scientists began to investigate mid-ocean ridges they discovered huge volcanic chimneys associated with underwater hot springs called hydrothermal vents. Some of these chimneys are known as black smokers because of the black mineral-rich, extremely hot water that jets from them.
A mid-ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges (chains), typically having a valley known as a rift running along its spine, formed by plate tectonics. This type of oceanic ridge is characteristic of what is known as an oceanic spreading center, which is responsible for seafloor spreading. The production of new seafloor results from mantle upwelling in response to plate spreading; this isentropic upwelling solid mantle material eventually exceeds the solidus and melts. The buoyant melt rises as magma at a linear weakness in the oceanic crust, and emerge as lava, creating new crust upon cooling. A mid-ocean ridge demarcates the boundary between two tectonic plates, and consequently is termed a divergent plate boundary.
The mid-ocean ridges of the world are connected and form a single global mid-oceanic ridge system that is part of every ocean, making the mid-oceanic ridge system the longest mountain range in the world. The continuous mountain range is 65,000 km (40,400 mi) long (several times longer than the Andes, the longest continental mountain range), and the total length of the oceanic ridge system is 80,000 km (49,700 mi) long.