For large stretches the deep ocean basin is flat. But seamounts, guyots, island arcs and trenches, all of which result at least in part from tectonic activity, break up the sameness.
Seamounts, guyots and island arcs form on the ocean floor as a result of a hot spot or mantle plume. While seamounts do not extend above the ocean surface, a guyot is tall enough to be eroded by wave activity and therefore has a flat top. An island ...