The Science Behind Garrett McNamara's Massive Waves

Experts say the canyon that exists off the coast of Nazare makes monster waves commonplace.

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Hawaiian surfer Garrett McNamara wowed the surfing community Monday as he apparently broke his own Guinness World Record for largest wave ever surfed when he caught what most news sources have said is a 100-foot wave off the coast of Nazare, Portugal.

Nazare is widely considered one of the best big-wave spots in the world because of its rare coastal geography. But, according to one oceanographer, the wave was likely smaller than 100 feet. Pat Caldwell, a friend of McNamara's and an oceanographer with NOAA, says he's seen a second angle of the wave that shows "the breaker is clearly well under 100 feet."

"The wave behind him is bigger," he writes in an E-mail to U.S. News. Caldwell estimates the wave was about 60 feet tall, smaller than the 78-foot wave McNamara surfed in Nazare last year.

Either way, experts agree the feat is impressive. Even without a storm, waves of 40 feet or more are relatively common, explains Joao Vitorino, an oceanographer with Portugal's Insituto Hidrografico who studies the area.

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"It's a complex region with a submarine canyon—when waves propagate over the canyon at different speeds, they start to converge near the shore," he says. "This increases the height of waves in the area."

The canyon is particularly special because it occurs just a few hundred feet off shore. Though the canyon can reach depths of a mile further offshore, it is closer to 500 feet deep near the coast. As additional waves start closer to shore, Vitorino says there is a "second amplification" of the wave, which can double its size.

"They're capable of promoting some conditions which lead to very big waves there," he says.

According to Vitorino, who McNamara consulted with this week, as well last year when he surfed a 78-foot wave, local wind conditions were very calm and there was no storm in the area.

U.S. surfer Garrett McNamara rests after a surf session at Praia do Norte beach in Nazare, Portugal. (Francisco Seco/AP)

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"He was here at the end of the summer to discuss what conditions would be needed to optimize all these [wave building] mechanisms. The idea that we could have a 30-meter [98 feet] high wave doesn't surprise me at all," he says.

Caldwell says that McNamara likely surfed a so-called "clean up" wave that occurs every hour or so during a swell.

"If that wave was a 'clean-up' … a rare roughly 90-foot breaker could have formed given the offshore swell characteristics that day. It would have taken lots of luck to be at the right spot at the right moment," Caldwell writes in an E-mail to U.S. News.

According to Falk Feddersen, an avid surfer who is also a scientist with the Scripps Institution of Oceanography, McNamara likely had to the "tow-in" method to catch the wave, meaning he was pulled by a Jetski towards the shore at speeds of up to 50 MPH.

"This is the kind of wave other surfers would call 'mushy'—it crumbles rather than [crashes] dramatically," he says. "There's not as much power in these kinds of waves, but when you get to this intensity and size, the wave clearly has plenty of power."

To see a photo of McNamara's record-breaking attempt, click here.

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