In nature, waves are not nearly as predictable and orderly as they are in laboratories, computers, and mathematical equations. While features such as velocity, period, and length are easy to measure in controlled circumstances, in the open ocean they can be hopelessly confused. One moment a breaking curler rushes down the slope of a large swell, then a trough fills with the crest of a wave coming from the side or falls away into yet a deeper trough. The random and disorderly nature of waves in the oceans almost guarantees that they will occasionally produce waves of a higher order. An enormous freak wave with those characteristics struck the Queen Mary amidships south of Newfoundland while ferrying U.S. soldiers home at the end of World War II, rolling her to within a degree or two of capsizing.
Rogue waves can occur on relatively calm seas with no storms for hundreds of miles.
Such giants can suddenly reach several times the height of most of the waves around them, forming mid-ocean breakers that are probably responsible for at least some mysterious disappearances of ships. When such anomalous waves occur near shore, roaring down without warning on piers and rocky ledges, they sometimes sweep people to their deaths. When waves meet opposition in an oncoming current the wavelength is shortened and the wave is forced to become steeper and as much as two to four times higher. Examples can be seen on a relatively small scale at the mouths of rivers or estuaries, where the outflowing current creates high choppy waves that can be dangerous for small craft. When a current exceeding about four miles per hour is spread over a large area and involves massive amounts of water the danger is magnified.