What?
Rogue waves are defined as waves greater than 15m high, or two to three times higher than surrounding waves. There are three types:
Walls of water: Travel up to 10km across the ocean
Three sisters: Groups of three short-lived giant waves
Single, giant storm waves: Up to four times the height of surrounding waves but collapse after a few seconds.
Advertisement
How?
It’s not known how or why they form, but there are two leading theories:
Constructive interference — several smaller waves overlap
Non-linear Schrödinger effect — a wave soaks up energy from its neighbours. Currents, wind, sea floor and coast shape may also play a part.
Where?
Rogues are most common where strong currents run against the primary direction of waves, such as in the North Atlantic, off the coast of Namibia and off western and southeastern South Africa. But they can occur anywhere.
When?
One study suggests that three of every 10,000 ocean waves achieve rogue status. In 2001, a 21-day satellite scan across 1.5 million square kilometres of the world’s oceans (about 0.5 per cent of the total) detected ten waves higher than 25m.
How often?
Because rogue waves are rare and short-lived, they do not often hit ships. But in the past two decades ten merchant ships longer than 200m have been lost at sea every year. Rogue waves are the chief suspects in most cases.
How much?
Advertisement
A rogue wave that hit the harbour wall at Alderney in 2004 had a pressure of 745 kilopascals, or 74.5 tonnes per square metre. Most ocean-going ships are built to withstand a pressure of 150 kPa and may break up at 300kPa.
So they’re not tsunamis, then?
No. A tsunami is not one wave but a series, generated by disturbances such as earthquakes, landslides, volcanic eruptions or explosions. Tsunamis lose energy and slow down as they approach land, but also grow taller — the reason why they can cause such devastation.
Monsters of the deep
34m Pacific Ocean, 1933: The highest rogue wave hit the US Navy tanker Ramapo.
Advertisement
30m South Atlantic, 2001: The Bremen and Caledonian Star cruiseliners had windows smashed by the same monster wave.
29m North Atlantic, 1995 Captain Ronald Warwick of the QE2 said the wall of water looked like the “white cliffs of Dover”.
28m North Atlantic, 1942: The Queen Mary was carrying more than 16,000 US troops when she was broadsided and nearly capsized.
26m Draupner oil rig, North Sea, 1995: The Norwegian oil platform was hit by a rogue wave, the first to be scientifically recorded and verified.
25m North Atlantic, 1966: The Italian cruise ship Michelangelo was holed, killing three people.
Advertisement
21m North Atlantic, 2005: The Norwegian Dawn was struck by a wave that reached the tenth deck and flooded scores of cabins.
20m Mid-Atlantic, 1978: Wreckage from the MS Munchen was found, including a lifeboat normally stored 20m above the waterline which had been bent.