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Finally, fast-spreading ridges open up at a rate of 4 to 8 inches (10 to 20 centimeters) per year.
Their rift valleys are much smoother in appearance.
The features of continental landscapes are mirrored by similar features on the ocean basins.
Plateaus, plains, valleys, rolling hills, and volcanic cones and mountains are found beneath the waters of the oceans, just as they are on dry land.
Ridges that are classified as medium spread at a rate of 2 to 4 inches (5 to 10 centimeters) per year.
The valleys of these ridges may be up to 3 miles (5 kilometers) across and range in depth from 165 to 655 feet (50 to 200 meters).
Iceland (in the North Atlantic), the Azores (west of the coast of Portugal), and Tristan de Cunha (in the south Atlantic midway between southern Africa and South America) are examples of such islands.
The large depression that is created between the spreading sections is known as a rift valley.
Mid-ocean ridges are divided into three groups depending on their spreading rates: slow, medium, and fast.
On average, these small valleys are only 330 feet (100 meters) wide and 33 to 66 feet (10 to 20 meters) deep.
In most locations, mid-ocean ridges are 6,500 feet (1,980 meters) or more below the surface of the oceans.