Posted by on June 15, 2005 at 15:21:29:
The ten-storey Mexican wave
A new record has been set for the largest swell, American oceanographers report
WHEN seafarers described them in tones of awe, sceptical landlubbers dismissed them as fantasy. Now scientists believe that they have evidence of the largest wave yet recorded.
It happened on September 16 last year when Hurricane Ivan stormed across the Gulf of Mexico and tore into the coast of Alabama, accompanied by 130mph winds and storm surges 8ft high.
While still out at sea, oceanographers report, the hurricane also produced a series of giant waves, one of which stood 91ft (27m) from crest to trough, the height of a ten-storey building and a new world record for a wave recorded by instruments.
But science, like old salts’ tales, is fallible. The seabed instruments that measured the surge were turned off at the moment the winds reached their peak, and scientists from the Naval Research Laboratory at Stennis Space Centre, Mississippi, have had to employ a computer model to predict that, while they were not looking, at the height of the storm the wave reached 131ft.
By comparison, the tsunami wave that swept across the Indian Ocean last December stood about 30ft high as it hit shorelines, although in some parts of Indonesia it was reported to have reached 65ft.
The greatest wave of all is not yet upon us. Scientists predict that if a future volcanic eruption sends a large part of the island of La Palma in the Canaries into the sea, it could cause a wall of water 2,950ft high. Reassuringly, they do not expect the event this century.
The Alabama wave last year comfortably exceeded the previous record for a wave, of 86ft, measured by the ocean weather ship Weather Reporter in the Atlantic on December 30, 1972. Giant waves are difficult to record because measuring buoys floating on the surface of the sea are usually wrecked by the intense storms.
Luckily, the eye of Hurricane Ivan passed over an array of 14 water pressure sensors spread over 38 miles of seafloor 100 miles off the Alabama coast. They are intended to measure the rise and fall of tides but also capture the height of waves. Their results are used for tracking the spread of algal blooms, jellyfish or oil spills from wells in the Gulf of Mexico.
They missed the height of the Hurricane Ivan waves because their work requires them to operate only every few hours.
But they did record that the sea currents generated by the hurricane broke another world record: the maximum current on the seafloor was 2.25 metres per second, compared with the Gulf Stream, which reaches top speeds of about 1.5 metres per second.
“We didn’t expect to measure hurricane waves,” William Teague, of the oceanographic team, said. “We were amazed at the strength of the currents and the size of the waves. It has changed our whole thinking of what could happen out at sea and what structures, like oil rigs, could get wiped out.”
Seven oil rigs were sunk and another 24 badly damaged in the storm. But the worst damage was to submarine pipelines, ruptured by submarine landslides. The hurricane caused the deaths of 116 people across the Caribbean, and insurance claims totalled $28 billion, making Ivan one of the costliest natural disasters in history.
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