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Ocean waves as tall as an eight-storey building, once dismissed as maritime folklore, can be studied using waves of light, offering hope of predicting where these monsters may appear, United States researchers say.

"These giant waves have been featured in many famous literary works from the Odyssey to Robinson Crusoe, but they were just thought to be the subject of myth for a long time," said Daniel Solli of the University of California at Los Angeles, whose study appears in the journal Nature.

These rogue or freak waves can appear out of nowhere on an otherwise calm sea. Their extreme height - reaching some 30 metres tall - can batter a ship, smashing even modern vessels to bits.

"Scientists thought these were just sailors' yarns," he said, until they spotted one in the mid-1990s off an oil platform in the North Sea.

Now they are studying how they form. Dr Solli thinks the answer may be found by studying light waves, which behave similarly to water waves.

Dr Solli's team was studying the properties of light waves travelling in glass when they discovered optical rogue waves, freak brief pulses of intense light similar to the freak water waves.

He began looking at possible explanations and found a stark resemblance between the mathematical equations that describe rogue water waves and his rogue light waves.

When they examined these light waves further, they found a predictable change occurred that perturbed an otherwise normal-looking wave into becoming a rogue light wave.

Dr Solli thinks the same thing may be happening in the sea.

"Essentially there is a sweet spot or tickle spot. If you tickle the wave on this particular spot, it develops into one of these rogue waves," he said.

"It is highly likely a similar effect is at work in the water waves," he said.

If he is right, the finding could allow scientists to study these rare waves in a table-top experiment.

- Reuters