( CNN ) -- Imagine this : Floating in freezing water for 20 hours a day , over seven excruciating days , beneath a 90-meter iceberg which may or may not collapse on you , crushing you to death . Why would anybody to do this ? To surf a wave , of course . The man crazy -- or brave -- enough to dream up such a challenge , is Garrett McNamara . The same man who surfed the world 's biggest wave -- a 24-meter monster -- off the coast of Portugal in 2011 . It would be too easy to describe the 45-year-old American as an `` adrenalin junkie . '' Instead , McNamara 's addiction to `` the rush , '' as he so frequently describes it , is so all-consuming it 's practically the life-giving blood pumping through his veins . It 's also the reason the father-of-three risks his life in one of the most dangerous , and jaw-droppingly breathtaking , extreme sports on the planet -- glacier surfing . Glacial gladiator . In 2007 , McNamara became the first person to surf a glacier wave -- a wave created when a 75-meter chunk of ice broke off from a massive glacier in Alaska . As the block of ice plummeted into the Copper River , it created a two-meter-high wave which McNamara surfed -- the first and probably only person ever to ride such a swell . `` It was the closest I 've ever come to death , '' said the man who has surfed nine-story waves on the most rugged coastlines in the world . `` I was up to my neck in water , looking up at this 90-meter tall glacier , waiting for the ice to break off and hoping that it 'll fall straight into the water -- because if it falls flat you 'll be squashed under it . '' McNamara spent a week camped out at the glacier , spending up to 20 hours a day in the freezing water , waiting for the ice to break off and give him the most exhilarating ride of his life . `` I wanted to go home after the first day , '' McNamara admitted . `` But it 's fun to be the first to do something . It 's a totally new experience -- no one can tell you what it feels like , what to expect . '' Tiny terror . Even as a child growing up in Pittsfield , Massachusetts , McNamara was always testing the boundaries of danger . `` My brothers said I was always the craziest , always pushing buttons , '' he said . `` When I was five-years-old I was jumping off two-story buildings . '' When McNamara was 11 years old his family moved to Hawaii , where he replaced his hobby of skateboarding with surfing -- `` From the very first day , I fell in love with it , '' he said . By 17 , he was competing in the prestigious Hawaiian Triple Crown and for the next decades traveled the globe as part of the professional surfing circuit . `` I really just want to get beautiful barrels , '' he said . `` You 're in your own world . It 's a place where time stands still , where all you can hear is your heart beat . '' Big wave hunter . Then in the 1990s came one of the most revolutionary developments since the sport began -- tow-surfing . For the first time , surfers could be towed out to the biggest waves in the world with a jet ski -- and McNamara was quick to jump on board . `` Danger is real . But fear is something we create , '' he said . `` We create fear when we think about the future and what could happen -- I 'm in the moment . '' Watching McNamara in action , a tiny speck skidding down the towering face of a nine-story wave , is enough to make your stomach drop . But he remains almost nonchalant . `` If you look at the statistics , it 's a lot more dangerous to ride down a highway than a big wave , '' he said . `` If you do n't make the wave , the jet ski will come get you . In 2000 we started using life jackets , so as long as you can hold your breath under water for long enough , you 're OK. '' Record breaker . It 's perhaps that practical attitude which has seen McNamara smash surfing records . In 2011 he rode the biggest wave in the world -- a 24-meter monster in Nazare , Portugal . Earlier this year he returned to the same spot to ride another huge wave , that may have been up to 30 meters high . `` I 'm looking for the rush , '' McNamara said . `` But lately I 've had a really hard time finding it . `` When I surfed the glacial wave it was mind-bending , it was the heaviest rush . But since that day I 've found it difficult to get that rush in the ocean . It made me realize how comfortable I feel on big waves . '' McNamara 's describes his obsession with that elusive rush as `` like a monkey on my back . '' Though he chuckles as he adds : `` I think the monkey 's starting to lose his grip . ''
Glacier wave surfing : Is this the world 's wildest extreme sport ? Portugal surfer Daredevil the first person to ride a glacial swell . Garrett McNamara also rode biggest ocean wave , 24-meter monster off U.S. . Says he is chasing `` the rush . '' But admits thrill is gone after glacier stunt .