They are very vulnerable, about as thin as the thick bunched electrical cables running on power lines, not the single one, but the one that has them bunched up.
Sharks, anchors, salvage ships, american/russian spy work, earthquakes. Lots of things can cut the connection unfortunately.
RandomMemory wroteAlso I'm very curious, how does this cable keep getting cut. Isn't it super thick and deep? So it can't be boats that's for sure.