What measures are taken to avoid this? I read somewhere that these cable are not actually buried into the ground, but rather lay on top of the ground. That sounds very risky to me?
They are buried only when close to shores or in other high risk areas. There is no point in burying a cable if the sea bed is 3 miles under the surface. There is still danger, from animals biting into the cable (sharks are known to do this). But the cables are wrapped in steel cables so not even a shark should be able to cut through.
> There is no point in burying a cable if the sea bed is 3 miles under the surface.
There is a point, it's just not something we're able to do. You can get the cable onto the sea bed by lowering it from the surface. We know how to get to the surface.
To bury it, you'd need to run a digging operation at the bottom of the ocean.
...which we're able to do, we do somewhat similar digs for offshore oil all the time, but it's not worth the gargantuan expense. The risk of leaving it exposed is worth it.