(CNN) -- In April 2003, Aron Ralston made the gut-wrenching decision to hack off his arm to free himself after a boulder had pinned him to the ground in a remote area of the Utah Canyons. Today, Ralston draws on that determination to continue climbing mountains and sharing his story of survival.
Ralston's journey that spring changed the young man both physically and mentally.
"I was transformed, as I was in that canyon," the avid outdoorsman and mountaineer told CNN's Anderson Cooper in an interview last September.
In 2003, Ralston, then 27, was climbing alone in Blue John Canyon in southeastern Utah. He told no one about his planned route, a decision he would come to regret.
He had just scrambled over an 800-pound boulder when it came loose and sent the young man flying down the canyon wall. The boulder came to rest on his right hand, trapping him for five days with little food or water.
"There was pain. There was panic. There was the realization that, at first, I couldn't get my arm out, even though I was just thrashing my body about," he told CNN. "And what followed from there was 45 minutes of just ... hurtling my body against the boulder, trying to heave and lift from beneath it to pull it maybe towards me and try to dislodge it."
After struggling to come to terms with his predicament, Ralston began considering his options. Over the next several days, he drank his own urine to stay hydrated and experimented with the idea of amputating his arm with a pocketknife, but he had no way of sawing through two bones in his arm.
Ralston also began using his digital camcorder to record last messages for his family. "I'm sorry," he told them. "You guys make me proud."
On the sixth day of his ordeal Ralston realized that amputating his arm was the only way he would survive. He had no tools capable of sawing through the bones in his arm, so he bent his arm down and, using his body as a lever, snapped the bones in half.
"I bent my arm farther and farther, and then finally, this cracking, splintering sound, kind of like a cap gun, then, POW! It echoed up and down the canyon. I knew that I had broken my bone. And yes, it hurt. It hurt a lot," he told CNN.
Next, Aron carefully cut away at his arm, trying to avoid major arteries until last when he could quickly tighten a tourniquet that he'd fashioned from the tubular insulation of his CamelBak, a backpack designed to hold water.
Ralston likens the pain he felt when he cut the nerves in his arm to sticking his entire arm in a vat of hot magma.
"At the same time, that pain was just one more thing I had to do, and it was, in some sense, a very beautiful feeling, too. ... It was liberation," he told CNN.
But the outdoorsman was not out of danger yet. Ralston still had nearly four hours of hiking ahead of him as he made his way out of the canyon.
With blood dripping down his legs and covering his shoes, Ralston walked until he came upon a family hiking. They helped him reach rescuers who were searching for him near the trailhead.
"He was absolutely coated in blood. His shoes were covered with blood," rescue helicopter pilot Terry Mercer recalled. "And as they loaded him in the helicopter, the deputy reached in and said, 'He's amputated his arm; we've got to go to the hospital quick.' "
Ralston chronicled his harrowing experience in the best-selling book, "Between a Rock and a Hard Place," published in 2004. And he shares the lessons he learned from his ordeal as a motivational speaker.
"I had to make a decision to go forward not knowing what was going to come," he told CNN. "And that was important, that I took action in that moment, overcoming that fear."
Today, Ralston continues to take action. With the aid of a custom-made prosthesis, Ralston recently completed a climb of nearly 23,000 feet to the summit of Mount Aconcagua in Argentina, the highest peak in South America.
He says the drive to climb the next mountain is what sustains him.
The Park Service later retrieved Ralston's hand, using a crew of men and a winch and jack to lift the boulder. At Ralston's family's request, his hand was cremated and his journey came full circle when he returned to the place where he'd been trapped for six days to scatter the ashes.
"I sprinkled some of the ashes up canyon ... and (I) cried tears of absolute joy that I was alive. Being able to complete that circle is a beautiful part of that whole experience, too," he told CNN.