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Witnesses described a "". Snow and dust leapt skyward, thrown up by the large chunks of ice and rock that snapped off Mount Pumori, which rises from a valley opposite Mount Everest.

The 7.8 magnitude earthquake that struck Nepal on 25 April 2015, killing more than 8,000 people, triggered numerous avalanches in the Himalayas. At the time, Everest Base Camp was a temporary home to the hundreds of climbers, guides, Sherpa and other support crew for the 359 climbers who'd been granted permits to climb the world's tallest peak that year.

With no chance of outrunning the avalanche as it thundered toward them, climbers sought refuge wherever they could find it: in their tents, behind rocks, and even curled up in a ball on the ground. When the avalanche ended the survivors emerged from what little shelter they could find to a scene of devastation.

Tents were buried under ice, and equipment and bodies were strewn across the landscape.

A survivor interviewed by University of ÌìÃÀ´«Ã½ sports psychology researcher Dr Christian Swann described the feeling of helplessness: "You're looking at this white wall and … your mind thinks, 'do something', and you've got two seconds … so we ran inside, got under the table … and we're sitting in the tent, waiting for it to hit us..."

In total, 22 climbers died and more than 60 were injured, making it the deadliest disaster in the history of climbing Mount Everest. Yet, moments after the immediate danger passed, and conscious that climbers were still stranded at camps higher up the mountain, there were those who set about organising a recovery effort.

Mentally tough, or too tough for their own good?

The varied responses have given researchers deeper in extreme circumstances.

The idea of a mental edge - toughness, grit, determination ­- or that special something that separates elite athletes from the rest has captivated audiences and intrigued sports psychologists. Dr Swann, from UOW's says mental toughness has become a central topic in sport psychology.

"Athletes who report higher levels of mental toughness typically report a range of more positive outcomes, such as the ability to persevere when they are being tested, the ability to take on bigger challenges and typically having more confidence in what they do.

"So it's being studied by everyone from business to adventure sports to understand its affect on how people behave."

It's all in your head

Researchers generally agree that mental toughness involves the ability to maintain focus and make effective decisions under pressure and in the face of adversity.

Dr Swann, with his research partners Dr Lee Crust and Professor Jacqui Allen-Collinson from the University of Lincoln in the United Kingdom, looked to professional mountain climbers to explore the concept.

In the sport of mountaineering, mental toughness is not the bar for success, it's the minimum price required to play the game. Exhaustion, dehydration, extreme low temperatures and lack of oxygen can cause hypothermia, frostbite and acute mountain sicknesses with symptoms such as severe brain swelling (cerebral oedema) and water in the lungs (pulmonary oedema).

^{Dr Christian Swann interviewed survivors of the 2015 Mt Everest avalanche. Photo: Paul Jones}

If that isn't enough, environmental conditions such as the steepness of ground, crevasses, rock or icefall, and risk of avalanche make high-altitude mountaineering an extremely dangerous activity.

The mountaineers they interviewed all had many years experience climbing in the Himalayas and successfully summited several of the 14 peaks around the world that top 8000 metres, an altitude commonly known as the "death zone" where humans can survive for only a short period of time.

"The assumption prior to our research was that the ability to persevere, to deal with problems and keep pushing is great. Mental toughness gets you further."

Risk takers, not risk seekers

Through their interviews, a more sophisticated idea of mental toughness emerged. One that relied on experience, analytical thought and the idea that being "tough" could mean giving up on a dream that may be within sight and is not without significant physical, emotional and financial investment.

It's an idea of mental toughness that's a far cry from the "win-at-all-costs", macho stereotype.

"The climbers were telling us that mental toughness is the decision to say 'no' in some situations," Dr Swann says. "It's the decision to turn back. It's the decision to not take the easy option and just keep going, and hope you get there and hope you get back."

The ability to say 'no' when the risks outweigh the rewards and being able to maintain a balanced perspective came to the fore among the mountain climbers who identified as mentally tough.

The truly mentally tough mountaineers didn't take unnecessary risk, just being on the mountain was risky enough. The research painted a picture of people who took calculated risks, were serious about risk-management strategies, and who could clearly express and articulate their emotions throughout the climb.

It also shed light on the impacts of physical and mental stress on decision making. Mentally tough climbers indicated they used proactive and purposeful techniques to get them through life-threatening situations.

"One climber told his story about being stuck at 8,000-odd metres, virtually sitting on the side of the mountain waiting for the sun to go up. He said for the whole night he counted from one to five. Just over and over and over again.

"He's literally freezing. No tent, no shelter, no food and no water. Just sitting in his clothes, suffering, counting from one to five to keep his mind working and staying awake all night. That was his way of proactively managing stress."

The devil on your shoulder

Dr Swann says the key to mental toughness and good decision making was experience. A person could be mentally tough, but if they were inexperienced, they could potentially be too tough for their own good.

"Having a high level of mental toughness but low experience is actually a recipe for disaster," he says. These people can summit in perfect conditions, but lack the situational awareness to understand changing weather conditions or to pick up on the subtle cues the body provides when all is not well.

Experience, and the ability to understand and evaluate the conditions, also kept the climbers highly competitive nature in check. One participant in the research described it as the "devil on her shoulder". Yet it was experience of the technical side of climbing as well as, for almost all participants, witnessing death on peaks that provided a sense of perspective and helped redefine the idea of failure.

As one participant described of a colleague: "Before he went he said, 'summit or die, either way I win', and he got both. Now to me no summit is worth even the tip of my little finger".

Measuring success

While not summiting was disappointing, it was not considered a failure for mentally tough participants as long as they'd made every effort possible in the conditions.

"How you define success and failure is all relative to what your goal is. The easy thing is to have summiting as your goal. Having summiting as your goal, with the high chance of not making it, is a psychologically naive trait of climbers with lower mental toughness.

"Failure is losing someone or getting down and being sued by someone because of a massive falling out or somebody getting injured. Safety for these guys is first and foremost."

Dr Swann says that among the mentally tough climbers, maintaining perspective included ethical considerations.

"We found examples of climbers who haven't yet summited but have gone back three or four times to try again. They're on the ascent and the conditions are great. They see a climber struggling and know that person is not going to live without help.

"Do you sacrifice your last attempt to try and achieve a summit you've been thinking about exclusively for years to try and save a life? And again, the mentally tough climbers said that saving a life was more important and they'd stop to help their fellow climber get off the mountain."

Those critical ethical decisions and how they relate to mental toughness were delved into when Dr Swann and his colleagues interviewed survivors of the 2015 avalanche that crashed through Mt Everest Base Camp.

Tough, ethically speaking

"We had very little idea before this about what role mental toughness might play in a natural disaster," Dr Swann says. "Now it seems mental toughness actually is an important factor and allows you to respond proactively and constructively, as opposed to reactively.

Accounts from survivors report there were those who quickly grasped the magnitude of the disaster and immediately threw themselves into coordinating the rescue and recovery efforts.

"There was one guy who was carrying bodies across base camp all day. He wanted to be actively involved and doing as much as he could. Contrast that with the polar opposite response where people were going into their shell and sitting in their tents or curling up in a ball, literally in some cases, and not able to do deal with it."

The research also revealed unexpected responses, including reports of ethically questionable behaviour.

"When helicopters came to take bodies out, there were reports of people faking injury trying to get on the helicopter to get out quicker. Other climbers attributed it to lower levels of mental toughness.

"There were also reports of macho-style climbers, guys who were saying, 'ok, this is the biggest disaster ever, but we still want to summit. We still want to go up there'. And it literally took the Nepalese authorities to stop them."

When Mount Pumori unleashed its torrent of ice and rock it brought out the best and worst in the human spirit. It also refined the idea of what it means to be mentally tough: that sometimes packing your bags and going home to live another day is the tough course of action.

As one survivor reflected: "It makes you think how important things are. It makes you realise how short life can be…"