Rouge Waves!

A ‘rogue wave’ is large, unexpected, and dangerous freak wave!
Rogue, freak, or killer waves have been part of marine folklore for centuries, but have only been accepted as a real phenomenon by scientists over the past few decades.

Rogues, called ‘extreme storm waves’ by scientists, are those waves which are greater than twice the size of surrounding waves, are very unpredictable, and often come unexpectedly from directions other than prevailing wind and waves.

Most reports of extreme storm waves say they look like “walls of water.” They are often steep-sided with unusually deep troughs.

Since these waves are uncommon, measurements and analysis of this phenomenon is extremely rare. Exactly how and when rogue waves form is still under investigation, but there are several known causes:
Constructive interference. Extreme waves often form because swells, while traveling across the ocean, do so at different speeds and directions. As these swells pass through one another, their crests, troughs, and lengths sometimes coincide and reinforce each other. This process can form unusually large, towering waves that quickly disappear. If the swells are travelling in the same direction, these mountainous waves may last for several minutes before subsiding.

Focusing of wave energy. When waves formed by a storm develop in a water current against the normal wave direction, an interaction can take place which results in a shortening of the wave frequency. This can cause the waves to dynamically join together, forming very big ‘rogue’ waves. The currents where these are sometimes seen are the Gulf Stream and Agulhas current. Extreme waves developed in this fashion tend to be longer lived.

A giant wave in the Bay of Biscayne, in an image published in Fall 1993 issue of Mariner’s Weather Log. Credit: NOAA

How high is the highest wave?

Cinemagoers will be familiar with the thrill of giant waves. But what most people don’t know is that the film The Poseidon Adventure is based on an incident involving the Queen Mary in WWII. The famous liner was hit by a giant ‘wall of water’ while she was carrying 15,000 American troops to Britain in 1942. The ship listed to an astonishing 52 degrees and almos capsized. More recently, The Perfect Storm will be familiar to most, providing an account of the sinking of the Andrea Gail south of Newfoundland in 1991.
Such giant waves are rare, and seldom recorded by reliable oceanographic instruments. However, on 1 January 1995 a sensor on a platform in the central North Sea recorded a giant 60ft high wave crest, so ‘freak’ waves are not just tall tails. Giant waves can have disastrous consequences even for the largest ships and offshore structures.
Such waves are thought to be very rare but just how rare? What physics drives such waves? Is a ‘wall of water’ plausible? How should engineers design structures to survive rare but potentially catastrophic events?

Within the last years a high number of large ships has been lost. The causes of accidents are in many cases believed to be ‘rogue waves’. These are individual waves of exceptional wave height or abnormal shape

It is well known that extreme waves often occur in areas were waves propagate into a strong opposing current. A well known example where many large ships have encountered difficulties is the Agulhas current outside South Africa. The strong current going south meets strong swell from storms in the Antarctic Ocean.

found on deathwaves.com