The mountain is called Kan-gchenjunga, and at 28,169 feet above sea level it is the planet's third-tallest peak, an immense white wall in the sky north of Darjeeling, India. Like all great peaks of the Himalayas, Kangchenjunga's summit has been sought out by humans for decades. Climbers have traveled across the globe, trekking and camping for weeks through India or Nepal, then ascending for days -- boots kicking, ice axes in hand -- into air so thin you might stumble like a drunk.

It was on Kangchenjunga in 2002 that Mike Farris, a resident of Northfield, Minn., and a biology professor at Hamline University in St. Paul, climbed to 26,000 feet and witnessed the worst possible outcome of a high-altitude mountaineering expedition.

As he plodded uphill on the morning of May 24, two climbers from another team were approaching Kangchenjunga's summit. They would soon turn around, victorious after weeks of effort, while Farris -- dehydrated, hypoxic, feeling ill -- scanned the white void above, resigned that he might not make it to the top.

What happened next, a tragedy on the slope above Farris' stance, became a powerful point in a chain of events that prompted him in 2005 to begin writing a book.

An hour after leaving Kangchenjunga's summit, Chris Grasswick, a young Canadian among the pair coming off the high point, fell, snagging his foot on a rock, then sliding off an edge, ropeless, tumbling more than a thousand feet on the mountain's upper flank. In a single moment, Grasswick -- an airline pilot and experienced mountaineer with a wife waiting at home -- was gone.

Farris said the serious nature of what had just happened didn't at first register: "I was so exhausted and numb from the altitude that extreme emotion was not possible."

But as he hiked down the mountain with a half-dozen other climbers, oxygen grew thicker in the air and his head started to clear.

Grasswick and his partner were well-acclimated on Kangchenjunga, having spent days at a high camp to prepare for the summit bid. But Farris said the young Canadian was in a rush to get up the mountain, as he was due back to his job earlier than other climbers that season on the peak. Farris wondered how the physiological effects of altitude, combined with the external psychological pressure of a shortened trip timeline, may have affected Grasswick's descent.

A 52-year-old biologist and researcher who is three decades into his career, Farris made no hard conclusions, scientific or otherwise, about the accident on Kangchenjunga. Like most mountain climbers, he accepts that his sport is full of risk. But Grasswick's misstep, a stupid glitch of fate, could have happened anywhere.

Or maybe altitude affected his performance. Thin air and searing sun have certainly altered Farris' abilities in the high peaks, he knew. In addition to Kangchenjunga, Farris has climbed in Alaska, Argentina and Pakistan, spending nearly 40 weeks of his life on expeditions to peaks above 20,000 feet. "There are times where it takes two hours to get your boots on," he said. "Your brain just feels numb, like it's wrapped in cotton."

The body plays tricks -- even on a biologist

After Kangchenjunga, the final episode that prompted Farris' book came in 2005 on Pakistan's Broad Peak. Three hours away from the mountain's 26,401-foot summit, after weeks of effort and thousands of dollars spent, he was losing his battle to reach the top. His mind was slow. He was out of water, stopping to eat snow every 20 feet, throat dry in the alpine air.

"I had to decide whether to turn around or continue," he said. "Was it dehydration? Or cold? Or altitude sickness? Should I take a caffeine pill or altitude-illness medication?"

He never reached the top of Broad Peak. But for Farris, a college-level biology teacher, the disappointment of not knowing what to do with his own body on the mountain overshadowed his failure to plant a foot on the summit.

"The Altitude Experience: Successful Climbing and Trekking Above 8,000 Feet" (due in May from Globe Pequot Press) is Farris' 80,000-word answer to his own question. It presents the science of high-altitude physiology and psychology from a performance standpoint: You're on the glacier, looking up, ice ax in hand. Thin air and steep snow is your medium.

"Most books on the topic look at how to prevent altitude sickness," Farris said. "I took the approach of giving people information to help boost athletic achievement at altitude."

Safety is a No. 1 topic in the text. But Farris goes up a notch to provide tips for climbing, sleeping and breathing near the stratosphere.

In its 295 pages, "The Altitude Experience" tackles practicalities such as how to stay hydrated on the mountain, how to wash and stay clean, what to eat and which drugs to use as aids for acclimatization. Homesickness, stresses on relationships and other psychological concerns encountered after weeks away in the mountains are also covered.

The elusive question: Why?

There is an inevitable section on the "why" of his sport, too. "Why should we participate in this risky activity?" he writes. "Is it fair to family and friends?" Farris cites a study from 2002 that calculated about one in every 25 climbers coming off the summit of a mountain above 26,000 feet will perish. With Grasswick and Kangchenjunga, Farris saw this reality, these harsh odds, in the flesh.

"The Altitude Experience," like shelvesful of books before it, never gets to the "why" of it all. Farris quotes climbers and cyclists and sailors who have tried to explain or justify their extreme actions: It's an addiction. It's a thrill. Risk lets you live briefly -- but truly and intensely -- in the raw, present moment. Risk lets you escape.

This summer Farris is heading to Pakistan for 10 weeks on his fourth trip to this country. This time, his mountain of choice is K2, second-tallest in the world and statistically deadlier than anything he has touched. Dozens have perished on K2's flanks, and after 70 years of expeditions fewer than 20 Americans have ever stood on top.

Is Farris nervous? "I shouldn't be going if I am not," he said.

But he believes he is prepared. After months of training, and two years of researching, interviewing and experimenting for his book, Farris feels primed to perform.

K2's white pyramid soars to 28,251 feet, cutting clouds, grazing the jet stream. By late summer, if all goes as planned, Farris will be standing on top. He will pause for a few minutes, snap a photo, gasp for air above an oblivion of peaks. Then he will turn around to kick a boot in the steep snow. He will swing his ax into the ice, an anchor to steady his weight, one step at a time on the descent -- the long, slow journey down the mountain and back home again.

Stephen Regenold is a Twin Cities writer and author of the syndicated column