Garrett McNamara surfs 'highest ever' wave off Portugal 30 January 2013 Last updated at 10:53 An American man has ridden what may be the highest wave ever caught by a surfer, reportedly 100ft (30m) high. Garrett McNamara surfed the wave on Monday off the coast of Portugal, in the same spot where he surfed the current world-record wave of 78ft (24m) in November 2011. Experts will now have to certify the new record. The giant wave formed above an underwater canyon famous for being the world's biggest wave generator. "You are just going so fast," McNamara told ABC television. It's really, really similar to snowboarding on giant mountains. And you're just chattering, flying down this bumpy, bumpy mountain. Your brain is getting rattled. Your whole body is getting rattled. He said he was relieved to have avoided a rocky section of the coast. McNamara began surfing at 11 and turned professional six years later. Swell waves Swell waves can travel thousands of miles across the Atlantic from as far west as the Caribbean. Canyon The Nazare Canyon, which is an underwater valley the size of the Grand Canyon, helps concentrate the waves" energy. Shore As the water becomes more shallow, the waves slow down while maintaining their energy, so they become bigger. The gradient of the shoreline at the head of the canyon is ideal for producing plunging breakers which surfers love.