Scientists hope a better understanding of when, where and how mammoth oceanic waves form can someday help ships steer clear of danger. How frequently do they occur? Just how do they come about? Are there areas or conditions where they are more likely?  Before any answers could be attempted, scientists first had to characterize a rogue (or freak) wave. The widely accepted definition, is a wave roughly three times the average height of its neighbours.

This is a somewhat arbitrary cut-off. Really, they are just ‘unexpectedly large waves’ No one is certain yet just how frequently freak waves form; accurate numbers are extremely difficult to collect given the waves’ rare and transient nature. With more sophisticated monitoring and modeling—and as first-hand accounts are taken more seriously—the waves prevalence appears to be rising. Rogue waves are all short-lived, and because ships are not everywhere, the probability that a ship encounters one is relatively small. But with increasing amounts of oceanic traffic in the future, the likelihood of encountering them is getting larger. Some areas seem to breed the waves more than others.

Computer models have been used to determine that regions where wave energy is strongly focused could be up to 10 times more likely to generate a freak wave. Approximately three of every 10,000 waves on the oceans achieve rogue status, yet in certain spots—like coastal inlets and river mouths—these extreme waves can make up three out of every 1,000 waves. A paper describing these results was published last month in the Journal of Physical Oceanography.

Forming fearsome waves Various theories exist for how rogue waves form. The simplest suggests that small waves coalesce into much larger ones in an accumulative fashion—a faster one-meter wave catches up with a slower two-meter wave adding up to a three-meter wave, for example. Waves might actually communicate—sometimes in a bad way—and produce more constructive interferences. By communicating, we means exchanging energy. And because the conversations aren’t necessarily balanced, communication can get amplified enough that a high-intensity large wave develops. In other words, one burgeoning wave can actually soak up the energy of surrounding waves. Again, in those places where variations in water depths and currents focus wave energies, this line of communication can get especially busy.

Certain conditions such as winds and wave dissipation, however, could not be included, limiting the simulation’s predictive power. If a wave propagates from east to west, and the current moves west to east, then a wave starts to build up. The wave basically climbs the current’s wall, rising out of what appears to be nowhere. Rogue waves have in fact been more common in regions such as the east coast of South Africa where surface waves meet currents running in the opposite direction.

Focusing on forecasts -The only way to really know what is going on in the unpredictable oceans is to watch however, the investments in the instruments and time necessary for such fieldwork are immense. Focusing on an optical wave analogue may actually help scientists limit where they need to look. Light waves travel in optical fibers similarly to water waves traveling in the open ocean. Mapping light-wave conditions to the ocean could uncover parallel parameters that give rise to water waves.

With more direct observations of ocean behavior. we can make a theoretical prediction, but then we have to go out and see if nature agrees. If it does, the results could provide a prediction scenario—made visible on maps—of hot spots that could change today. This could work much like tornado forecasting. Forecasts could be crucial in helping future ocean liners evade the voracious sea monsters.