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Mid-Ocean Ridge

What goes on under the sea? Our oceans are so deep that the bottom of the ocean is a very mysterious place. We still don’t know a lot about what lies below the ocean’s surface. We do know, however, that the ocean floor is not flat. That’s because there are mid-ocean ridges that make the sea floor uneven! 

An image of ridges underwater.

There is much more to the ocean than meets the eye above the water!

What is a Mid Ocean Ridge?

A mid ocean ridge is basically a submerged mountain range. Imagine a connected series of mountains, but underwater! Mid ocean ridges form a ridge system across the Earth’s oceans. The entire mid ocean ridge system is a total of 49,700 miles long! This is the longest mountain range on the planet, even longer than mountain ranges on the ground! These ridges can also reach as high as 3,000 feet above the seafloor. 

An image of a mountain range on land.

Mid ocean ridges are even longer than the mountain ranges that we normally see.

Formation

Mid ocean ridges form at divergent plate boundaries. This is when two tectonic plates are spreading apart.
 
When the two plates pull apart, magma from the Earth’s core rises to fill the gap on each side. As the magma pushes above the mantle, the pressure decreases and cools down the hot, molten rocks. This creates areas of basaltic rock that raises above the sea floor! There is also typically a rift running in the middle of a mid-ocean ridge. 

An illustration of the different types of plate boundaries.

Mid-ocean ridges are formed at divergent plate boundaries.

Mid ocean ridges are geologically active. This means that they experience volcanic eruptions as well as earthquakes! Any area that was this active on land would be extremely dangerous! More volcanic bursts make the ridges spread. This is seafloor spreading. This might sound like a lot, but most ridges only spread approximately 4 inches each year! 

The Forces at Play

Two forces help form mid ocean ridges: ridge push and slab pull. The name ridge push is a little bit misleading. Think about it as more like gravitational pull. Gravity pulls the top layer of rock on the lithosphere down the slope of the asthenosphere. Imagine a heavy object slowly moving down a playground slide! 
 
Slab pull happens at subduction zones, where one tectonic plate sinks under another. Slab pull is the force that the sinking edge of a plate exerts on the rest of the plate. You can use your jacket as an example. Leave something heavy in your jacket pocket, then put it on the edge of the table. The weight of the object will pull the jacket down – similar to slab pull! 

An image of a subduction zone .

Slab pull happens mostly at subduction zones.

Here are some of the ridges that live in our oceans! 
  •  Mid-Atlantic Ridge in the Atlantic Ocean
  •  Southwest Indian Ridge in the Atlantic and Indian Oceans
  •  Explorer Ridge in the Pacific Ocean
  •  East Pacific Rise in the Pacific Ocean
  •  Pacific-Antarctic Ridge in the Pacific Ocean