the ocean

From a scientific standpoint, it's because of tremors in the earth that occur because of small volcanic eruptions in the earth under the ocean and the patterns of the moon (the moon affects the tides, which has to do with the restlessness of the ocean). From an environmentalist (right word?) standpoint, perhaps it's because mother earth is angry with her children for hurting her so much. I'm not an environmentalist, to say the least, but I've heard it explained like that before. Hope that helps.