Why does the ocean floor deepen away from the ridges?

Answer 1

The plates are converging or submerging at the ridges forming "mountains" in the ocean floor, therefore creating valleys where the floor deepens.

Answer 2

There is confusion in the answers given here. Undersea mountains and deep canyons are nothing to do with spreading ridges as such. They are what they are described as - ridges!

Spreading ridges are at the 'growing edges' of tectonic plates. Lava rises and gradually pushes the plates apart. This rising therefore pushes the edges of the plates up slightly.

Look at porridge or thick soup simmering in a pan. As convection causes hot liquid to rises to the surface it pushes the surface up. As it moves away it subsides to the general level of the fluid.

So the answer is really that it is not the ocean floor deepening that is observed but the fact that the lava pushes up the edges of the plate where it is pushing upward.

Answer 3

Ocean ridges are simply mountains underwater. Think of the mountains here on earth. Doesn't the land around the mountains get flatter as you go out farther away? It's kind of the same. There's also subduction zones under the ocean. Ocean ridges are where crust is pushed up and the subduction zones are where crust is taken back into the earth. Trenches, such as the Marianas Trench, are some of the very deepest parts of the oceans.

Answer 4

There may be some effects contributing to "flattening" the ocean floor with increasing distance from the ridges:
- the thicker oceanic crust is the deeper it sinks due to its weight into the upper mantle and gets melted again
- even under water there are erosive processes (e.g. chemical weathering)