In 1978 the MS Munchen sent a garbled Mayday message from the mid-Atlantic. The ship was never found but an exhaustive search found just a few bits of wreckage, including an unlaunched lifeboat which had been stowed 20 metres above the water line. One of its attachment pins had twisted as if hit by an extreme force. The culprit was believed to be a rogue wave.
In 1995 the Draupner Platform in the North Sea was hit and damaged by a freak wave. Fortunately its onboard measuring equipment was still working and recorded a wave of 25.6 metres in height. This was the first rogue wave to be confirmed by actual scientific evidence.
What are Rogue Waves?
Once dismissed as a nautical myth, rogue waves (also known as freak waves, extreme waves, killer waves, monster waves and abnormal waves), are large, spontaneous ocean waves that occur far out to sea. They can be described as waves with a height of more than twice the significant wave height (SWH). This is defined as the mean of the largest third of waves in a wave record. In more simple language, they are not necessarily the biggest waves, but they are surprisingly large waves for a given sea state. They are not Tsunamis, which are set in motion by mass displacement, such as a sudden movement of the ocean floor during an earthquake. These develop at high speed over a wide area and are not usually noticeable in deep water. They become dangerous as they approach the land and the ocean floor becomes shallower. Because of this, Tsunamis do not usually present a threat to shipping out at sea. In the 2004 Asian Tsunami the only ships lost were in port. A rogue wave, on the other hand, is highly localised and frequently occurs far out at sea, or where a number of physical factors such as strong winds and fast currents converge, causing a number of waves to join together.
History
Stories about freak waves of around 30 metres in height have been told for centuries. These apparently could appear without warning, in mid-ocean, surprisingly travelling against the prevailing wind and current direction and often in clear weather. They have been described as looking like an almost vertical wall of water preceded by a deep trough. A ship encountering such a wave would be very unlikely to survive the tremendous pressures exerted by the weight of breaking water and would almost definitely be severely damaged or even sunk in a matter of moments.
Lighthouses, such as the Eagle Island lighthouse in 1861, and the Fastnet lighthouse in 1985, were both struck by waves of over 40 metres in height. In 1966 the SS Michelangelo had a hole torn in her superstructure and heavy glass smashed 24 metres above the water line. There were 3 deaths recorded during this incident. In 1980 the first mate on board the Esso Languedoc photographed a 25-30 metre wave as it washed across the stern of the French supertanker. In 1995 the Master of the cruise liner Queen Elizabeth 2 described a wave looking like the White Cliffs of Dover, which came out of the darkness. The vessel attempted to “surf” the near vertical wave to avoid being sunk.
During the twenty-first century several vessels have been damaged by waves between 21 and 30 metres in height. In February 2000, a British oceanographic research vessel sailing in the Rockall Trough in the west of Scotland, encountered one of the largest waves ever recorded by scientific instruments in the open ocean with a SWH of 18.5 metres and individual waves up to 29.1 metres. The US Naval Research Laboratory detected a freak wave caused by Hurricane Ivan in the Gulf of Mexico in 2004. It was about 27.7 metres high from peak to trough and around 200 metres long. Vessels are not alone in their risk from rogue waves. It has been suggested that the loss of several low-flying aircraft, such as helicopters on Search and Rescue missions, may be attributed to these types of waves.
Evidence – Myth or Reality?
On average about one ship is lost every week in the world’s oceans. This is thought to be mainly due to bad seamanship, poor maintenance or severe weather, but it now seems likely that a small percentage is due to encounters with freak waves. However, although rogue waves have been blamed as a likely cause for the sudden, unexplained disappearance of many ocean-going vessels, there is little clear evidence to support the claims. Radar data from the North Sea’s Goma oilfield recorded 466 rogue wave encounters in 12 years. Evidence such as this has helped to convert previously sceptical scientists.
Oceanographers and meteorologists have, for a long time, used a mathematical system called the Linear Model to predict wave height. This assumes that waves vary in a regular way around an average wave height. It suggests that there will rarely be a wave higher than 15 metres. Although one of 30 metres could happen, it would be unlikely to occur more than once in 10,000 years. That is the theory! The reality is that they do happen with surprising frequency.
More recently, satellites have been used to establish the existence of rogue waves. The European Space Agency (ESA) is using its European Remote Sensing Satellite (ERS) to study their origins and to try to predict their occurrence. In December 2000 the European Union initiated a scientific project called MaxWave to confirm widespread occurrences of rogue waves, study their behaviour and consider their implications for ship and offshore structure design. Data from ESA’s ERS satellites were used to carry out a global rogue wave census and in 2004, after analysing radar images of world wide oceans taken over a period of three weeks, MaxWave found 10 waves of 25 metres or higher, an astonishing number for such a relatively short time span. ESA have undertaken another project, named Wave Atlas, to survey the oceans over a longer period of time and develop the most accurate estimate possible for the frequency of rogue waves.
Some theories
- Rogue waves are often associated with sites where ordinary waves encounter ocean currents and eddies. The strength of the current concentrates the wave energy, forming large waves. Examples have occurred in the notoriously dangerous Agulhas current off the east coast of South Africa and also in the North Atlantic where the Gulf Stream interacts with waves coming down from the Labrador Sea.
- Data shows that rogue waves also occur in areas well away from currents, possibly being associated with weather fronts and lows. Sustained winds from long-lived storms, exceeding 12 hours, may enlarge waves moving at an optimum speed in sync with the wind.
- In the field of Quantum Physics, a concept called the “Schrodinger Equation” is based on the belief that in certain unstable conditions waves can steal energy from their neighbours. Adjacent waves shrink, while the one at the centre can grow to an enormous size.
The implications
Current ships and offshore platforms are built to withstand a maximum wave height of only 15 metres and about 15 tonnes of pressure per square metre. If they are hit by a rogue wave they will have to endure a wall of water up to twice that height and a pressure in the region of 100 tonnes.
Facts like these make us realise how little we know about our oceans and remind us to treat them with respect. How many more secrets do they hold?
Author- Dee White