How often do freak waves occur?
No one knows for certain how often freak waves occur. Traditional theories of the ocean say the probability is once in every 10,000 years, but the latest data suggest that they take place more frequently. The satellite data from the German Aerospace Centre found over 10 waves in three weeks, but this is preliminary data not a statistically significant sample.
When do freak waves occur and why?
Freak waves occur in bad weather conditions when the average wave height is high and several big waves come together to create a monster. Technically this could happen when the wave size is small, but as the result is small no one notices. Waves can come together for four main reasons:
1. when wind pushes against a strong current (eg in South Africa)
2. when a shallow sea bottom focuses waves to one spot (eg in Norway)
3. by chance (hence the 1 in 10,000 year statistic)
4. when waves become unstable and start to self-focus
Scientists think the freak waves observed in the deep ocean are due to unstable waves self-focussing in bad weather conditions. It appears that there is a separate population of unstable waves in the ocean that can grow into freaks.
Are freak waves more likely in certain areas or situations?
Freak waves can occur in any ocean around the world, but there are certain areas where freak waves are more likely:
• South Africa - freak waves occur off the east coast of South Africa when there is a strong wind blowing in the opposite direction to the strong Agulhas Current. (The South African Weather Service now gives freak wave warnings.)
• Norway - the coast of Norway is another hotspot because the sea bottom can focus waves together to form monsters - in bad weather the shipping route is altered to avoid these areas.
• Pacific - certain areas of the Pacific are also notorious for freak waves, when typhoons whip waves up to huge heights.
Can scientists predict freak waves?
At the moment the only place where freak waves can be predicted is South Africa. There is no way of knowing when or where a freak wave will hit anywhere else. Scientists at the UK Meteorological Office are working on the problem and think they might have a solution. If Al Osborne's non-linear Schrodinger theory is right, then freak waves should occur whenever there is a peak in the energy spectrum (ie when a lot of energy is crammed into waves of a specific wavelength). So the Met Office has been looking back at recorded cases of freak waves, like the 1995 Draupner wave, to see if the spectrum is peaked. So far the theory holds up and they hope to come up with a practical way to warn ships about freak waves in the next couple of years.
Are freak waves the same as tsunamis or tidal waves?
No. Tsunamis and tidal waves are extremely rare events caused when either an earthquake or landslide displaces a large volume of water creating a single large wave. Freak waves are occurring far more regularly and seem to be a fundamental property of the sea.
How many ships have been sunk by freak waves?
No one knows how many ships have been hit or sunk by freak waves. A ship is lost at sea every week, but there is often surprisingly little detail as to why or what happened. Usually poor maintenance or human error is blamed, but it is likely that at least some of these losses may be related to freak waves.
Do ships need to be redesigned?
The risk from freak waves in uncertain. Ships are built assuming that in their 20 year lifespan there is no risk from freak waves. The new evidence suggests that the risk is higher than originally thought, but the data are far from conclusive. Until the risk is fully assessed, international maritime organisations and classification societies can't know what (if any) changes need to be made to ship specifications.
Should I be worried about going to sea?
If you weren't worried before, you shouldn't be worried now - according to Department of Transport statistics it's over ten times safer to travel by sea than it is to cross the road.
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