An anonymous reader writes: New field studies out of MIT found that "internal waves" — massive waves below the surface of the ocean — can reach enormous sizes. The most powerful internal waves known to science are in the South China Sea, and they can be over 500 meters high. These waves mix disparate layers of ocean water, and contribute to evening temperatures between various bodies of water (abstract). The waves grow larger as they propagate, and carry on all year. These waves have enough mass to affect the earth-moon system: "To cut a long story short, it's not unreasonable to say internal waves play a role in the moon moving away or receding from the Earth. They are big enough that they affect large-scale celestial motions."