Sailing too close to the wind

October 31, 2003

Giant belches from the deep could have claimed the lives of many unfortunate mariners. Scientists have found that a single bubble of methane erupting from the sea-bed could swallow a ship and send it plummeting into the depths.

Their work has bolstered arguments that many vessels could have succumbed to such a fate, helping explain mysterious loss of shipping in the Bermuda Triangle and the North Sea.

The ocean floor contains large quantities of gas hydrates - ice-like crystals of methane caged in by water molecules - that can erupt in large rising bubbles if disturbed by earth tremors, underwater landslides or violent weather.

Researcher David May and Joseph Monaghan, professor of computational mathematics at Monash University in Melbourne, Australia, released bubbles of gas in water trapped between two sheets of glass and observed the effects on a piece of acrylic shaped like a boat's hull.

They found that if the bubble was of a size comparable to the boat, catastrophe could follow.

In experiments and mathematical modelling, the scientists saw the bubble push a mound of water above it as it approached the surface, lifting the boat for a few moments. But this water then flowed off the sides of the bubble, creating deep troughs either side.

If the ship got caught as the waves crashed into the holes, it would get dragged underwater in a matter of seconds.

Surveys of the North Sea have revealed large quantities of gas hydrates and eruption sites. In 2000, scientists found an undamaged sunken trawler dating from the 1930s in an eruption site some 150km from Aberdeen.

Professor Monaghan said his findings, published in the American Journal of Physics , supported suggestions that the ship had fallen victim to methane.

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