Long the subject of folklore among sailors, scientists have confirmed that rogue waves do exist. Rogue waves, or extreme storm waves, are more than twice the size of surrounding waves, are highly unpredictable, and often come from directions other than that of the prevailing wind and waves. There are a few known causes, including constructive interference (a process by which regular waves coincide and reinforce one another’s power until a very large wave is formed) and the focusing of wave energy (which occurs when waves formed by a storm develop unusually and dynamically join together, forming one very large 'rogue' wave.) Additional causes of rogue waves are a topic of ongoing research.