MELISSA BLOCK, host:
It's easy to see what happens when a hurricane hits land. Just turn on the television. What happens over the deep sea is more of a mystery. A new study suggests that out in the ocean hurricanes may whip up hundred-foot waves, waves bigger than anyone thought. NPR's Nell Boyce reports.
NELL BOYCE reporting:
Last September, Hurricane Ivan was heading towards New Orleans. William Teague, who lives nearby, got ready to evacuate. Then the storm turned. It went right for some scientific instruments that Teague had installed a few months earlier.
Mr. WILLIAM TEAGUE (Stennis Space Center): First, you think, `Oh, great. It's going to miss our homes. But it's going over instruments. Oh, no. Will the instruments survive it?'
BOYCE: Teague studies deep-water currents. He works at the Naval Research Laboratory at Stennis Space Center in Mississippi. The previous May he and his colleagues had dropped monitoring devices about 75 miles offshore. They sat on the ocean bottom beneath deep water. Teague figured that the hurricane would ruin them. But when they retrieved the instruments, they had survived, and they'd measured some staggering waves during Ivan.
Mr. TEAGUE: What we found is there are extremely large waves that occur very frequently during extreme seas generated by hurricanes.
BOYCE: The waves averaged over 58 feet from the crest to the trough, the size of a six-story building. The biggest waves were over 90 feet. The underwater sensors could tell because as a wave passes over, the pressure increases and then decreases. The amount of pressure is directly related to the wave height. These sensors happened to be shut off during the worst part of the storm. Teague says if they'd been on during Ivan's peak winds...
Mr. TEAGUE: We calculate that we should have observed a wave that would have exceeded 130 feet.
BOYCE: Teague says these are the biggest waves ever scientifically measured in US waters. They're described in the journal Science. Waves like these won't reach the beach because they dissipate when the water gets too shallow to support them. But they're of interest to scientists who model hurricanes. Teague thinks that everyone has been underestimating how bad the seas can get.
Mr. TEAGUE: I think we have to be cautious of the way we use our past knowledge of extreme seas during intense storms. I think the extreme seas are bigger than we had ever anticipated.
BOYCE: Teague says measurements of big waves are rare. They're typically made by ocean-monitoring buoys floating on the surface. These usually get wrecked by big waves, and instruments that survive are typically just on the fringes of hurricanes. Of course, other than using underwater sensors and floating buoys, scientists can learn about big waves by personally taking their instruments into the teeth of the storm--if they dare.
Ms. PENNY HOLLIDAY (Researcher): Nothing had prepared me for the horrendous nature of these waves.
BOYCE: That's Penny Holliday, a researcher with the national oceanography center on the British coast. She and her colleagues were on a scientific expedition near Scotland when violent storms engulfed them. Since their ship had wave-measuring devices, they could tell that the waves averaged 60 feet; the biggest ones reached nearly 90 feet.
Ms. HOLLIDAY: It's quite terrifying actually because you--if you're looking out on the bridge, what you see is the ship kind of moving very slowly up the front of the wave, and then for a moment you're teetering on the top of a wave, looking down into this enormous hole in front of you. And the ship starts to sort of fall down the other side of the wave, and for a moment you think, you know, it's just going to keep on going down.
BOYCE: The experience, she says, has given her a new appreciation for sailors' anecdotal accounts of giant waves at sea, even if those waves weren't scientifically recorded. Nell Boyce, NPR News.
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