What Is a Mid-Ocean Ridge? - Definition

Mid-ocean ridges are formations of underwater mountain ranges that extend across the entire ocean floor. They are the result of the activity or movement of oceanic tectonic plates. These plates continually move and create new rock at their margins as magma emerges. Ridges are important because they are a source of volcanic and seismic activity. They also play an important role in the formation of the ocean floor, as well as the chemical composition of the sea.

The reason a mid-ocean ridge forms is due to two oceanic plates pulling apart. As the two plates move away from each other, a fracture zone is created on the ocean floor. The fracture is a place where molten magma emerges which is then cooled by the ocean water and the formation of new oceanic crust begins.

Mid-ocean ridges have some characteristics similar to any mountain system on the Earth's surface. For example, they have a formed terrain with elevations between 2,000 and 3,000 meters throughout the Earth's development. They have very rugged profiles with deep valleys, slopes and ledges that can eventually break through to the surface. When they do so they can form new volcanic islands or even groups of volcanic islands.

The most striking characteristic of MORs is the large recessed rim that runs the entire length of the ridge. This division is called a crack or rift. A rift valley is a permanently active volcanic ‘seam’ of land. This is the site responsible for the passage of magma from the center of the planet to the upper crust where it gradually accumulates, stabilizes and cools.

Volcanic activity in the ridges manifests itself in different ways. Although the rifts are strips where there is continuous activity, it is not very strong. Thousands of submarine fumaroles (vent in the Earth's surface for volcanic gases) and volcanoes themselves are scattered throughout the 60,000 kilometers of mountain ranges that span the globe. The minerals involved in this exchange support life in its most basic form.

All of this suggests that the seafloor is constantly being renewed. Magmatic material accretes and moves over time to create the entire strip of ground above sea level that hosts known mineral resources.

Learn more about how new land is formed above sea level with our article on how mountains are created.

We have already explained that the formation of mid-ocean ridges is due to a fracture is generated in the ocean floor. A chain of submarine volcanoes forms along the fracture, which are fed by an updraft of magma from the Earth's mantle. As the magma cools and solidifies, new oceanic crust is created. This is what makes mid-ocean ridges unique, as they are a place where new oceanic crust is constantly being generated.

As crust formation occurs, older oceanic plates move away from the MOR and toward the ocean margins. This process is known as seafloor spreading. As the plates move away from the ridge, they become cooler and denser. Eventually, they sink below the continental plates or collide with other oceanic plates in what are known as subduction zones.

One of the most interesting aspects of mid-ocean ridges is that they are associated with intense volcanic activity. Along these submarine ridges, volcanoes and fissures form where magma emerges to the surface. This results in the eruption of lava and the creation of new volcanic structures, such as cones and hydrothermal vents.

Mid-ocean ridges also play a crucial role in the circulation of the oceans. Seawater seeps into the rocks on the ocean floor through cracks and fissures. It is then heated by nearby magma. This warm water rises back to the surface, creating ocean currents that carry nutrients and heat throughout the ocean. This influences global climate overall.

Mid-ocean ridges also impact the chemistry of ocean waters. Due to the composition of the materials under the oceanic crust, breaks in this crust and the emergence of magma result in vast amounts of minerals entering the sea. These include manganese, silicon, iron and sulfur. The reactions of various isotopes speeded by the heat can cause various structures to be formed. The mineral composition can affect organisms in various ways.

Mid-ocean ridges also cause the sea level to rise. This is also a result of sea level spreading. However, this process occurs over a very long period of time. Global climate change is causing the increase of sea levels to occur at a never-before-seen rate.

Learn about another threat to the world's seas with our article on the consequences of ocean plastics.

There are various mid-ocean ridges across the world's oceans. One important characteristic is that their name is a misnomer. Not all oceanic ridges are in the middle of the ocean. We can learn more with examples of the biggest mid-ocean ridges in the world:

• Mid-Atlantic Ridge: this is one of the best-known mid-ocean ridges and runs the length of the Atlantic, dividing it into two halves. The Mid-Atlantic Ridge is especially famous because it was in this region that the theory of continental drift and plate tectonics was first proposed by Alfred Wegener in the 20th century. This MOR is also home to the the Rift Valley, an impressive geological fault with valleys and underwater mountains.
  
  
• East Pacific Ridge: located in the Pacific Ocean, this ridge is the longest mid-ocean ridge in the world and stretches from Antarctica to the Gulf of California. It is known for being one of the areas with the most intense volcanic activity, with numerous submarine volcanoes and hydrothermal vents. It is also the location of the deepest point in the ocean, the Mariana Trench.
  
  
• Arctic Ridge: the Arctic Ridge is located in the Arctic Ocean and extends through the waters surrounding Iceland and the Faroe Islands. It is one of the youngest mid-ocean ridges and shows significant volcanic and seismic activity. In addition, hydrothermal vents have been discovered in this area that are home to a rich biodiversity and unique species adapted to extreme conditions.
  
  
• Southwest Indian Ocean Ridge: this mid-ocean ridge is located in the southwestern Indian Ocean, near the coast of Africa. It is known for its association with the hotspot of volcanic activity of La Réunion, home to the famous Piton de la Fournaise volcano. Volcanic activity on this ridge has led to the formation of volcanic islands, such as the Mascarene Islands. Learn more about the eruption of volcanoes in our related article.

Now that you have learned more about the definition of mid-ocean ridges and their characteristics, we recommend reading this related article on whether the Atlantic and Pacific ocean mix with each other.

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