Researchers are aiming to help with the design of new North Sea oil platforms and offshore structures by understanding how unusually large ocean waves are formed.

A study has found when two exceptionally powerful and dangerous "rogue waves" intersect at an angle greater than 60 degrees it causes the ocean's surface to rise.

This phenomenon, which researchers say has been demonstrated in an experiment for the first time, is believed to have played a part in producing a 25-metre wave, known as the Draupner wave, which struck a North Sea oil platform in 1995.

Experiments were carried out in the FloWave Ocean Energy Research Facility at Edinburgh University.

Dr Ton van den Bremer, who led the study said: "This improves understanding of rogue waves, decades after this aspect of their behaviour was suggested.

"The more we know about this dangerous phenomenon, the better equipped we will be to design offshore structures and to navigate the oceans."

Researchers used a 25-metre circular tank to study the complex interactions that occur when waves cross in open water.

The testing tank is able to simulate ocean currents and waves of any type, which are monitored using overhead sensors.

Dr Mark McAllister, who took part in the research said: "These experiments provide new insight into how a heightened, or set-up, wave actually forms.

"They revealed that this behaves like a partial standing wave, which forms underneath waves as they cross.

"This insight allowed us to create a simple theory to predict when such waves might occur."

The study, published in the Journal of Fluid Mechanics, was carried out in collaboration with Oxford University and supported by the UK's Engineering and Physical Sciences Research Council.