Mid Oceanic Ridges, Types, Characteristics & Significance

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.

Underwater expeditions have been conducted to study the ocean floor, revealing unique and spectacular features. Tsunamis are often caused by underwater earthquakes, which occur along plate boundaries where the Earth’s tectonic processes take place. Modern maps of the ocean floor have improved our understanding of these underwater features and the earth’s tectonic activities. The ocean’s characteristics vary based on location, origin, shape, type of rock, and water movement.

This article focuses on Mid Ocean Ridges, one of the minor ocean relief features, which 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

The Mid-Indian Ridge is a submarine ridge in the Indian Ocean connected to the Mid-Atlantic Ridge as part of the global mid-ocean ridge system. It starts in the South Atlantic and extends north to near Rodrigues Island, where it splits into two branches:

• one goes north toward the Gulf of Aden, linking with the East African Rift System, and
• the other heads southeast toward the Macquarie Islands.

The Carlsberg Ridge is a section of the Mid-Indian Ridge located between the Gulf of Aden and Rodrigues Island. This ridge is seismically active because it is linked to a zone of earthquake epicenters.

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

Ridges like the northern and southern East Pacific Rise spread quickly and are “hotter,” meaning there is more magma below them, which leads to more volcanic eruptions. 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

At slower-spreading ridges like the northern Mid-Atlantic Ridge, the seafloor behaves like nougat or cold chocolate bars when pulled apart. As it stretches, the ocean crust breaks into ridges and valleys.

Read More: Ocean Waves

Mid Ocean Ridges Principal Characteristics

At the crests of oceanic ridges, new oceanic crust and part of the Earth’s upper mantle are formed, creating distinct geological features. Fresh basaltic lavas are exposed on the seafloor, which are eventually covered by sediments as the seafloor spreads. The heat flow from the crust at these ridges is much higher than elsewhere on Earth, and earthquakes are common along the ridges and transform faults, indicating tension in the oceanic crust.

The depth over oceanic ridges is closely linked to the age of the crust; as the crust gets older, it sinks deeper. This sinking is due to thermal contraction as the crust moves away from the spreading center. The width of a ridge is defined by how far the crust has cooled down, which typically takes about 70 to 80 million years, by which time ocean depths reach about 5 to 5.5 km (3.1 to 3.5 miles).

Slow-spreading ridges like the Mid-Atlantic Ridge are narrower than faster-spreading ones like the East Pacific Rise because of this cooling process. There is also a connection between global spreading rates and changes in ocean water levels on 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.

Atlantic Ocean

• The Mid-Atlantic Ridge stretches from Iceland to the extreme South Atlantic Ocean near 60° S latitude.
• It was previously known as a mid-ocean ridge since it runs through the Atlantic Ocean basin.
• In the 19th century, knowledge of the Mid-Atlantic Ridge was limited.
• In 1855, the U.S. Navy’s Matthew Fontaine Maury created a chart identifying it as a shallow “middle ground.”
• In the 1950s, American oceanographers Bruce Heezen and Maurice Ewing suggested it was a continuous mountain range.
• The crest of the ridge has an axial high at fast spreading rates.
• The flanks of slow-spreading ridges have rough, faulted topography, while the flanks of faster-spreading ridges are smoother.

Indian Ocean

• The Southwest Indian Ridge is a very slow oceanic ridge located between Africa and Antarctica.
• It connects the Mid-Indian Ridge and the Southeast Indian Ridge east of Madagascar.
• The Carlsberg Ridge is at the northern end of the Mid-Indian Ridge, moving north to join spreading centers in the Gulf of Aden and the Red Sea.
• Spreading is very slow in this area, but on the Carlsberg and Mid-Indian ridges, it approaches intermediate rates.
• The Southeast Indian Ridge spreads at a medium rate, extending southeast from the western Indian Ocean between Australia and Antarctica.
• The Southwest Indian Ridge has rifted crests and rugged, mountainous flanks.
• The Mid-Indian Ridge has fewer of these features, while the Southeast Indian Ridge has smoother topography.
• The Southeast Indian Ridge also shows asymmetric seafloor spreading south of Australia.
• Magnetic anomalies indicate that spreading rates on opposite sides of the center have been unequal over the last 50 to 60 million years.

Read about: Indian Ocean

Pacific Ocean

• The Pacific-Antarctic Ridge stretches northeast from halfway between New Zealand and Antarctica to meet the East Pacific Rise off the coast of South America.
• It spreads at intermediate to fast rates.
• The East Pacific Rise extends north to the Gulf of California and connects with the Pacific-North American plate boundary.
• Currently, the East Pacific Rise spreads offshore from Chile and Peru at rates of over 159 mm (6.3 inches) per year, dropping to about 60 mm (2.4 inches) per year at the Gulf of California.
• The ridge’s crest has a low topographic rise instead of a rift valley.
• Discovered during the 1870s Challenger Expedition, the East Pacific Rise was described more fully by oceanographers in the 1950s and 1960s.
• In the 1980s, scientists found that the main spreading center is often interrupted and offset, creating overlapping spreading centers due to interruptions in the magma supply.
• Smaller spreading centers branch off from larger ones and can be found in various locations, including the Fiji Plateau, Woodlark Basin, Scotia Sea, and near the Galapagos Islands.

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.

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