Mid Oceanic Ridges
Plate tectonics formed an underwater mountain range known as a Mid-Oceanic Ridge. It is made up of two mountain chains separated by a large depression. Mountain Ranges can have peaks as high as 2,500 metres, and some even rise above the ocean’s surface.
Various underwater expeditions and explorations have been conducted to study the ocean floor. These underwater explorations have revealed very different and spectacular features within the seas and oceans. When a tsunami occurs, everyone claims that it is the result of an earthquake beneath the sea floors. It is also true that the Earth’s tectonic processes occur along plate boundaries. These are distinct lithological portions that exist beneath the seas and oceans.
Modern ocean floor maps have greatly expanded our understanding of these underwater features. They also assisted us in understanding the theories underlying the earth’s ongoing tectonic processes. The morphological features of the ocean vary depending on their location, origin, morphology, lithology, and dynamics of the water masses.
This article discusses the Mid Ocean Ridges which is one of the Minor Ocean Relief Features that will be useful for the UPSC/IAS exam.
Read More: Major Ocean Relief Features
Mid Ocean Ridges Formation
The Mid Ocean Ridges are one of the most distinctive structures among them. The Mid Ocean Ridges, as the name suggests, are mostly found in the middle of ocean basins, where divergent plate boundaries exist. Many major tectonic processes have been identified by Plate Tectonics Theory, including the release of convection currents along Divergent Plate Boundaries, the origin of Mid Ocean ridges, and the spreading of the sea floor. All of these processes are ongoing phenomena on the planet.
Read about: Indian Ocean Dipole
Mid-Indian Ridge, a submarine ridge in the Indian Ocean that continues directly from the Mid-Atlantic Ridge; both are parts of the global midoceanic ridge system. The Mid-Indian Ridge enters the Indian Ocean from the South Atlantic and extends north to a point near Rodrigues Island, where it divides into two sections: one segment continues northward toward the Gulf of Aden, where it connects with the East African Rift System, and the second branch extends southeast toward the Macquarie Islands.
Carlsberg Ridge is a Mid-Indian Ridge located between the Gulf of Aden and Rodrigues Island. Because the ridge is linked to a belt of earthquake epicentres, it is seismically active.
Read More: Ocean Currents
Mid-Oceanic Ridges Types
Mid-ocean ridges vary in shape, also known as “morphology,” depending on how quickly they spread, how active they are magmatically and volcanically, and how much tectonic stretching and faulting occurs.
1. Fast-Spreading Mid-Ocean Ridge
Spreading more quickly Ridges such as the northern and southern East Pacific Rise is “hotter,” which means there is more magma beneath the ridge axis and more volcanic eruptions occur. Scientists believe that because the plate beneath the ridge crest is hotter, it responds to the divergent spreading process more fluidly. To put it simply, the ridge spreads more like hot taffy being pulled apart.
2. Slow-Spreading Mid-Ocean Ridge
The seafloor behaves like nougat or cold chocolate bars when pulled enough at slower-spreading ridges, such as the northern Mid-Atlantic Ridge. As the seafloor is pulled apart, the ocean crust at slow-spreading ridges breaks into ridges and valleys.
Read More: Ocean Waves
Mid Ocean Ridges Principal Characteristics
At the crests of the oceanic ridges, a new oceanic crust (and part of the Earth’s upper mantle, which together with the crust makes up the lithosphere) is formed. As a result, certain distinct geologic features can be found there. At the ridge crests, fresh basaltic lavas are exposed on the seafloor. As the seafloor spreads away from the site, these lavas are gradually buried by sediments. The flow of heat out of the crust at the crests is many times greater than anywhere else on the planet. Earthquakes are common along the offset ridge segments’ crests and transform faults. The analysis of earthquakes at ridge crests shows that the oceanic crust is under tension there.
The depths over oceanic ridges are rather precisely correlated with the age of the ocean crust; specifically, the ocean depth is proportional to the square root of crustal age. According to one theory, the increase in depth with age is caused by the thermal contraction of the oceanic crust and upper mantle as they are carried away from the seafloor spreading centre in an oceanic plate. Because such a tectonic plate is eventually about 100 km (62 miles) thick, a few per cent of contractions predict the entire relief of an oceanic ridge.
As a result, the width of a ridge can be defined as twice the distance between the crest and the point at which the plate has cooled to a steady thermal state. The majority of the cooling occurs within 70 million or 80 million years, by which time the ocean depth is approximately 5 to 5.5 km (3.1 to 3.5 miles). Slow-spreading ridges, such as the Mid-Atlantic Ridge, are narrower than faster-spreading ridges, such as the East Pacific Rise, because cooling occurs with age. Furthermore, a link has been discovered between global spreading rates and ocean water transgression and regression onto continents.
Read More: Ocean Tides
Mid-Oceanic Ridges Major Distribution
Oceanic spreading centres can be found in every ocean basin. A slow-rate spreading centre in the Eurasian basin is located near the eastern side of the Arctic Ocean. It can be followed south to Iceland, offset by transform faults. Iceland was formed by a hot spot directly beneath an oceanic spreading centre. The Reykjanes Ridge, which leads south from Iceland, lacks a rift valley despite spreading at 20 mm (0.8 inches) per year or less. This is thought to be due to the hot spot’s influence.
The Mid-Atlantic Ridge stretches from Iceland south to the extreme South Atlantic Ocean near 60° S latitude. Because it cuts through the Atlantic Ocean basin, it was previously referred to as a mid-ocean ridge. During the nineteenth century, the Mid-Atlantic Ridge was only vaguely known. The United States Navy’s Matthew Fontaine Maury prepared a chart of the Atlantic in 1855, identifying it as a shallow “middle ground.” American oceanographers Bruce Heezen and Maurice Ewing proposed in the 1950s that it was a continuous mountain range.
At fast rates, the crest has an axial high. The flanks of the slow-spreading rifted ridges have rough faulted topography, whereas the flanks of the faster-spreading ridges are much smoother.
The Southwest Indian Ridge, a very slow oceanic ridge, cuts the ocean between Africa and Antarctica. East of Madagascar, it connects the Mid-Indian and Southeast Indian ridges. The Carlsberg Ridge is located on the Mid-Indian Ridge’s northern end. It moves north, joining spreading centres in the Gulf of Aden and the Red Sea. Spreading is very slow at this point, but on the Carlsberg and Mid-Indian ridges, it approaches intermediate rates.
Southeast Indian Ridge spreads at a medium rate. This ridge extends southeastward from the western Indian Ocean, cutting the ocean between Australia and Antarctica. The Southwest Indian Ridge is distinguished by rifted crests and rugged mountainous flanks.
The Mid-Indian Ridge has fewer of these features, while the Southeast Indian Ridge has smoother topography overall. The latter also shows clear asymmetric seafloor spreading south of Australia. Magnetic anomalies show that rates on opposite sides of the spreading centre have been unequal many times over the last 50 or 60 million years.
Read about: Indian Ocean
The Pacific-Antarctic Ridge can be traced northeast from a point halfway between New Zealand and Antarctica to where it meets the East Pacific Rise off the coast of South America. At intermediate to fast rates, the former spreads. The East Pacific Rise extends northward to the Gulf of California, where it connects with the transform zone of the Pacific-North American plate boundary. The East Pacific Rise is currently spreading offshore from Chile and Peru at rates of 159 mm (6.3 inches) per year or more. At the mouth of the Gulf of California, rates drop to about 60 mm (2.4 inches) per year. The ridge’s crest is characterised by a low topographic rise rather than a rift valley.
The East Pacific Rise was discovered during the 1870s Challenger Expedition. Oceanographers such as Heezen, Ewing, and Henry W. Menard described it in its gross form during the 1950s and 1960s. Kenneth C. Macdonald, Paul J. Fox, and Peter F. Lonsdale discovered in the 1980s that the main spreading centre appears to be interrupted and offset a few kilometres to one side at various locations along the East Pacific Rise. However, the offset spreading centres’ ends overlap by several kilometres.
These were identified as overlapping spreading centres, a new type of geologic feature of oceanic spreading centres. Such centres are thought to be caused by interruptions in the magma supply to the crest along its length, and they define a fundamental segmentation of the ridge on a scale ranging from tens to hundreds of kilometres.
Many smaller spreading centres branch off from the larger ones or are hidden behind island arcs. Spreading centres can be found in the western Pacific on the Fiji Plateau between the New Hebrides and the Fiji Islands, as well as in the Woodlark Basin between New Guinea and the Solomon Islands. Between the East Pacific Rise and South America, near 40° to 50° S latitude, a series of spreading centres and transform faults exist.
A spreading centre can be found in the Scotia Sea, which lies between South America and the Antarctic Peninsula. The Galapagos spreading centre is located between the East Pacific Rise and South America near the Equator and runs east-west. A few hundred kilometres off the coast of the Pacific Northwest, three short spreading centres can be found.
The Gorda Ridges are located off the coast of northern California, the Juan de Fuca Ridge is located off the coasts of Oregon and Washington, and the Explorer Ridge is located off the coast of Vancouver Island.
Read about: Pacific Ocean
Spreading Centre Zones and Associated Phenomena
Since the 1970s, highly detailed studies of spreading centres using deeply towed instruments, photography, and manned submersibles have yielded new insights into seafloor spreading processes. Deep-sea hydrothermal vents and previously unknown biological communities have been the most significant discoveries.
Mid Oceanic Ridges UPSC
Plate tectonics formed an underwater mountain range known as a mid-oceanic ridge. It is made up of two mountain chains separated by a large depression. Mountain ranges can have peaks as high as 2,500 metres, and some even rise above the ocean’s surface.
Mid-ocean ridges are geologically significant because they occur along the type of plate boundary that results in the formation of a new ocean floor as the plates spread apart. As a result, the mid-ocean ridge is known as a “spreading centre” or a “divergent plate boundary.” The plates separated at varying rates of 1 cm to 20 cm per year.