what's the diameter of one of these cables? are they literally laid on the ocean floor?
And yes, they are laid on the floor, mostly. In shallows they may be armored against sharks or plowed in to protect against anchors.
The Neal Stephenson, WIRED article is an excellent read, but honestly unless you have a new Safari or some bookmarklet to extract the content from the surrounding flashing lights and popping ads you will probably go blind before you finish it.