Plate tectonics form mid-ocean ridges. It looks like mountains under the water at the bottom of the ocean. Similar to a volcano, a mid-ocean ridge will produce magma and then the two plates seem to move away from each other. The ocean floor or crust is actually fairly new compared to the age of the rest of the Earth.
The Mid-Atlantic Ridge is also located under the ocean that is about 12 miles wide and about 1,000 meters tall. Other ridges are shorter like the East Pacific Rise, however, it spreads for many miles on the ocean floor. In order to form a mid-ocean ridge, there are two things that occur. They are the ridge-push and the slab pull. The push moves the plate away as the slab pull brings the plate down.
