Aron Ralston, 27, was climbing alone in a 3ft-wide crack in the Bluejohn Canyon, last Saturday, when he dislodged a massive boulder that rolled on top of his right arm.

The rock pinned his hand and forearm to the wall of the canyon, and unable to free himself, he settled down for what he expected to be a long wait for rescuers.

On Tuesday, three days later, having taken supplies for only a single day, Mr Ralston finished the last of his water. When he awoke from a fitful sleep on Thursday morning, Mr Ralston concluded that his location was so isolated that it was unlikely he would be found alive. The remoteness of the canyon, in an area 150 miles southeast of Salt Lake City, is attested to by its fame as a hideout of the outlaws Butch Cassidy and the Sundance Kid.

Equipped with only an 8cm (3in) penknife and a first-aid kit, Mr Ralston set about amputating his arm. Despite the pain, and faintness caused by rapid loss of blood, he severed the limb below the elbow.

He then applied a makeshift tourniquet, antiseptic cream and bandages from the first aid kit before trying to dislodge the boulder and recover his amputated limb. It proved too heavy to shift.

Still losing profuse amounts of blood, Mr Ralston then had to lower himself by rope to the floor of the canyon 25m (75ft) below. Unable to ride the mountain bike that he had used to reach the canyon, he set off on foot in the direction of his car.

On the way he stumbled across two hikers, who used their mobile phone to summon a rescue helicopter. It had been looking for Mr Ralston after he was reported missing by his employers, Ute Mountaineering in Aspen.

"It was amazing that he was walking on his own, losing as much blood as fast as he was," Sergeant Mitch Vetere, one of the rescuers, said.

"He was in some kind of bandage holding his arm up against his chest, and then he had it all wrapped up.

"He was in pretty rough shape, but he communicated with us all the way to the hospital. He's obviously one tough guy. I think he ought to be the next Superman."

He walked unaided from the helicopter to the emergency room of the Allen Memorial Hospital, Moab, after a 12-minute helicopter ride.

Later he was transferred to St Mary's Hospital in Grand Junction. He was still in a serious condition last night.

Sergeant Vetere returned by helicopter to Bluejohn Canyon to locate and try to reclaim Mr Ralston's arm in the hope that it could be surgically reattached, but he too could not move the boulder.

Rescuers and Mr Ralston's colleagues paid tribute to his bravery and survival skills. "I've never seen anybody who has the will to live and is as much of a warrior as Aron is and I've been doing this for 25 years," Steve Swanke, a park ranger at Canyonlands National Park, said. "He was superbly strong. He is a warrior."

This was not the first time that Mr Ralston had narrowly escaped death. When skiing on Resolution Peak, Colorado, in February, he was buried in an avalanche with only his head and one arm protruding. A friend dug himself out, then rescued Mr Ralston, and the two dug out a third friend. Mr Ralston's employer said: "Sometimes we get pretty scared with some of the things he's doing."

Mr Ralston has climbed 49 of the 55 Colorado peaks above 14,000ft (4,300m). His climb last Saturday was in preparation for an expedition to the Denali peak, formerly known as Mount McKinley, in Alaska, from which he planned a solo speed descent. His website - ww.geocities.com/aronralston - lays out his philosophy: "Life is empty and meaningless. It is in the emptiness that we create possibilities for extraordinary results."

Mr Ralston's self-amputation is not unique. Bill Jeracki, who was fishing in the Rocky Mountain streams near St Mary's Glacier in Conifer, Colorado, in 1993, became trapped by the left leg when a boulder fell on him. He cut off his leg at the knee with his bait knife, using fishing line as a tourniquet.

He then crawled to his car and drove to hospital. He now has an artificial leg and has resumed fishing.

When Donald Wyman, 37, was pinned to his bulldozer by a fallen tree while clearing forest in Punxsutawney, western Pennsylvania, in 1993, he called for help for an hour before concluding that there was no alternative but to amputate his broken leg below his left knee with a penknife.

He tied a shoestring round his leg for a tourniquet and tightened it with a wrench, cut off his leg, then crawled 30 metres to another bulldozer, drove it to his lorry, then drove to a farm.

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