I've heard that these are anomalies introduced by the way the sonar/radar surveys were done. This ships scan the ocean floor by moving in patterns, then all the data is correlated and assembled into a map. Sometimes a pattern emerges afterwards that is clearly non-natural, but it's just an artifact of the process.

This topic came up very prominently last year when eager watchers of Google maps claimed to have discovered the streets of ancient Atlantis on the ocean floor. Turns out, not so much.