A mid-ocean ridge is an underwater mountain range, typically having a valley known as a rift running along its spine, formed by plate tectonics.

Mid-ocean ridges have different shapes depending on how fast they are spreading, how active they are magmatically and volcanically, and how much tectonic stretching and faulting is taking place. Scientists believe that the most likely reason for the different shapes is due to the strength of the ocean crust at these different sites, and how cold and brittle the upper part of the tectonic plate is.

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, with a total length of about 60,000 km

A composite map showing the ocean floor clearly reveals the mid-ocean ridge system, which appears here as dark "seams" extending through the oceans.

There are two types of mid-ocean ridges: fast-spreading and slow-spreading. Fast-spreading ridges like the northern and southern East.

Slow-spreading ridges like the Mid-Atlantic Ridge have large, wide, rift valleys, sometimes as wide as 6 to 12 miles and very rugged terrain at the crest. The Mid-Atlantic Ridge moves at an average of 1 inch per year.

Fast-spreading ridges are "hotter," meaning that more magma is present beneath the ridge axis, and that more volcanic eruptions occur.

FUN FACT:We didnt send divers down to explore the Mid-Ocean Ridge until 1973 four years after Neil Armstrong walked on the moon --when a French-American crew of seven entered the 9,000-foot-deep Great Rift in the French submersible Archimede.