Marni Sheppeard does not drive. The avid mountaineer has never learned and never will. She says it's too dangerous.

This is partly why the physics student and her fellow student Sonja Rendell took the bus from Christchurch into Arthur's Pass National Park early on the morning of December 21.

The other reason was the break-up the day before of Rendell and her boyfriend. He was supposed to go with them and was going to drive.


Originally other university friends were also planning to make the three-day tramp, but came that Sunday morning only the two women remained keen.

They met in the centre of town - neither owns a car - as it was closer to where Rendell lives, and boarded the shuttle.

Two-and-a-half hours later they were dropped off at the Waimakiriri River bridge a few kilometres south of the Arthur's Pass village.

They planned to be out again in three days. Sheppeard was heading west for Christmas with friends at Fox Glacier and had loaded her pack with presents. Rendell had a day of present shopping planned for Christmas Eve, and Christmas Day celebrations with her family.

Instead, they spent seven extra nights huddled in a cavity no bigger than a coffin, high on a rocky mountainside. Their survival, and the good condition they were in when discovered on Tuesday, amazed those searching for them.

Experts credit Sheppeard's extensive experience and level-headed approach with saving their lives.

It was to be Rendell's first big tramp, but Sheppeard already had six years of mountain experience.

Her passion for alpine climbing began on a ski trip in Europe - one of many funded by "a rich boyfriend" - which included some climbing.

"I thought about it and realised the climbing was safer than the skiing we were doing. So when I got home I did a couple of courses and got into it from there."

Since then Sheppeard has conquered various New Zealand climbs, including Mt Cook.

By comparison, this planned three-day trek was "no big deal". The day had dawned clear and sunny and the pair headed for Carrington Hut along the riverbed, gradually getting higher. The going was good but they took their time.

This was Sheppeard's first tramp since falling into a crevasse when climbing in the Swiss Alps in August, resulting in a smashed ankle. That incident was her first rescue experience - she was airlifted to hospital and had pins inserted in her ankle to fix it.

It was not an adventure she planned to repeat.

As tramping huts go, Carrington Hut is large and serves adventurers planning to go in a variety of directions. Other people were in the hut, but after a dinner of pasta and mashed potato, prepared by Rendell, the women took to their sleeping bags for an early night.

"I hadn't been tramping for so long so I was tired, and Sonja always likes to go to bed early. So we didn't talk much to the other people," said Sheppeard.

Monday also dawned sunny. The women set off soon after 6.30am and were expecting a six-hour tramp to Julia Hut.

A couple of hours into the walk they came across an unexpected barrier. A large, wide block of ice had formed on the rocks and to climb over it would have required crampons. On the right-hand side of the ice was a steep incline mainly of scree - too loose to attempt to climb. The left side was bluffs and gullys that looked slightly daunting for Sheppeard - let alone for Rendell, who had no experience in such rugged country.

"So it was either go back to Carrington Hut, which neither of us wanted to do - but in hindsight I really should have - or figure out another way."

Above them they could see the flatter track on which they wanted to travel, and it did not look too far. Sheppeard consulted the map.

"I thought actually it did not look too bad to go up this gully and up and around to the Harman Pass."

But it was rough going and further than Sheppeard expected.

The rocky ground was steep and sharp. Parts of the climb were scree that slipped and offered no handholds. The flatter track with less rock and sprigs of tussock was tantalisingly close, but "like the cliche, oh so far away".

Way out of her depth, Rendell was not happy.

"And reasonably so. I should not have taken her anywhere like that," said Sheppeard.

The women stopped in a shallow crack in the gully. It was 3pm and the weather was fine.

"We thought that if we stopped there we would both be in a better frame of mind to finish off the last bit, and it really wasn't much further from there to the flat bit and then back down on to the normal trail."

Days after her rescue, Sheppeard admits it was a scary climb even for her.

"But especially for Sonja, and I really should not have put her in that position. She did really well, considering."

A change in the weather undid the plan to finish the last part of the climb to safer ground. Rain set in. The women unzipped their sleeping bags and tucked them around themselves - the synthetic one keeping some of the rain off and the down one keeping them as warm as possible and sheltered from the wind.

They knew they could not move until the weather cleared. They had reached a point of no return, and retracing their steps was no option. Sheppeard said the terrain was dangerous enough to climb up, so getting back down - shrouded by cloud with the terrain made slippery in the rain - would "probably be a suicide mission, or close to it".

Their home was a small rocky hole, and it was not comfortable. There were two positions the pair could alternate between. One woman would sit on a flat rock and be more comfortable but have her upper body out of the crack, exposed to the wind and rain.

The other would be lower under the ground level, completely sheltered but squatting on sharp rocks with almost no space to move. This hole was to be their refuge for eight days.

Right from the start of the rain Sheppeard knew they could be in for a long stay.

"I knew it could rain for weeks in the mountains. So I figured chances were we'd be there for three days, five days, six days."

This was not information she chose to share with Rendell.

" 'God no, tomorrow it will clear,' I told her. And I told her every day. So after about the fourth day it was starting to wear thin. She knew I knew differently, and eventually she started arguing that it rains in the mountain for weeks and weeks."

As the rain fell, varying from torrential downpours to steady drizzle, and the temperature dropped Sheppeard told Rendell neither was allowed to sleep in case hypothermia set in.

Experience had taught her about the risk of letting core body temperature drop, as it does during sleep, without being able to warm up again. "That's one thing that I don't think Sonja understood. We had to stay awake. It was really hard and as time dragged on, of course, we got more and more tired and started dozing."

When staying awake means staying alive "you try anything".

"I don't really know any songs but I was singing anything I could think of. Stupid nonsense, anything. 'Let's boogie all night', anything to try and help us move."

As well as noise, sharp shocks to keep each other from drifting were needed. In the first few days and nights that meant slapping each other in the face to wake them. That eventually progressed to full fist punches.

"We had to. We needed the fright to keep us going, keep the adrenalin pumping."

They also talked a lot, mainly about the things they would have once they got home. They turned some of those plans into chants, like "warm dry blankets, warm dry blankets, warm dry blankets".

A comfortable bed, dry clothes and pina coladas were high on the wishlist.

Food was another topic but, at least initially, it was not something the women were without.

In the first few days they ate whatever they wanted of their supplies, whenever they wanted. Sheppeard's strategy was that they needed to keep up their full strength as long as possible.

After two days they began to ration their food but their low activity levels meant they were able to string out the supplies. They ate mostly dried foods - noodles, pasta, packets of Raro - but they also had muesli bars, cheese, salami and a tin of oysters.

On Christmas Day - day three of their ordeal - they cracked open the bottle of "good Aussie red" Sheppeard had been carrying to share with the friends she had intended to spend the day with on the West Coast.

Water was more of a concern. Using their pot and pan they collected rainwater, which did not satisfy them, but kept them going.

On the night of December 28 the rain and sleet turned to snow.

Down at the Department of Conservation visitor centre in Arthur's Pass, where the then two-day-old search operation was based, search co-ordinator senior constable Phil Simmonds was slightly apprehensive about what the deteriorating weather would mean for the women.

More than 40 people were on the ground looking for them as well as helicopters, but a wide area had already been covered and there was no sign of life yet.

Like Rendell, he was relying on Sheppeard's experience to save them.

As his rescue operation was planned and executed, Sheppeard was sitting high above the office running through the basics of search and rescue procedure with Rendell.

Her experience in the mountains had not just been climbing for fun. In Wanaka, where she lived for several years, Sheppeard joined the search and rescue team and was trained for alpine operations.

Many of those out looking for her were good friends from her Wanaka days.

"It was one thing that was really interesting to talk about and a positive way to waste a lot of time. We were figuring out who they would be talking to and what they were finding out to piece together how we got here.

"I knew they would break into my house. They found a razor of mine and took it for DNA ... they were starting to think about, you know, bodies and stuff."

One temporary stumbling block for the investigators was the bus the women took to the national park - the company had lost its record of their trip. If other people had not known of their plans, this could have been crucial in helping to find them.

The snowfall induced what Sheppeard said was her second big no-no - the first being going off the track and into the gully.

"I know you're not supposed to eat the snow because it burns too much energy, but we did. It just felt so nice and so fresh. We ate and ate."

They also collected it and the water it produced lasted until half an hour before they were spotted.

The days dragged on but were not as bad as the nights, when it was harder to stay awake. The pitch-black darkness made shifting positions in their tiny camp difficult as they became disoriented.

Arguing over "who's bum was supposed to be on what rock" degenerated into a screaming match, but Sheppeard believes that was healthy in keeping them going.

"One night I was deliberately arguing just to keep us awake and active. In the end I suppose we were both fit and determined enough to cope. Of course we had our moments. You know a week up there is a very long time, but Sonja kept me positive and helped me to keep going as well as much as I was doing that for her."

As well as the threat of hypothermia, Sheppeard was concerned about frostbite. The pair had discarded their boots to try to reduce the swelling in their feet and instead kept them warm with their hands.

She was particularly concerned for Rendell's feet, which went numb several days into their ordeal.

"Frostbite was a major consideration and, yes, I did think we might lose toes or even our feet. But I figured it was better to be alive with no feet than to be dead on a mountain."

The thought of death crossed both their minds.

After a few nights of rain and no sleep a tearful Rendell said she would not be able to cope with another day. An upbeat Sheppeard regaled her with every mountain survival story she had ever heard.

They were also comforted by the sound and sight of helicopters searching - although it also left them frustrated. Cloud prevented the helicopters flying as high as the women's camp.

They knew that, but the frustration got to them. "We were saying, 'Why can't the bloody idiots see us'. We were standing up and screaming.

"It was disheartening. There were times that Sonja would stand up and wave, even though it was so heinously cold and exposed, she was just so excited about the choppers. And I'd be saying, 'Forget the choppers, they're not going to see us, just get back down here under the sleeping bag'."

Although the ordeal continued, the last night the pair spent in the mountains gave them hope. By midnight the stars were beginning to shine through the cloud and by dawn on December 30 the sky was completely clear.

"We knew the next day would be fine. And just the thought, never mind whether they would find us or not, just the thought of the sun coming out was just amazing. Being able to stop shivering after so many days of just shivering on and off."

The women knew they would not be able to "get up early and hike off" but they discussed drying out their feet in the sunshine and maybe in the afternoon putting their boots on and clambering over the rest of their rocky path.

But it was not a plan Sheppeard wanted to have to try.

"I was really worried about our feet. They were absolutely shocking and I was just really, really hoping the choppers would find us that day."

They tried to make themselves more visible - something that was pointless before as no helicopters were flying high enough - and spread their sleeping bags and clothes on the rocks.

Sheppeard tried waving a mirror for an hour, deflecting the sun off it towards Carrington Hut. Rendell waved her long white pyjama pants any time a chopper came near.

That morning they watched the Iroquois helicopter for an hour as it swept across the valley below them and gradually past the peaks around them.

"We were constantly following them around, going, 'Come higher, come higher'. And then it did."

It was Sheppeard's sister Gina who spotted the women first. She had arrived at the search base from Australia the night before, joining Rendell's sisters who were keeping vigil at the base from when the search began.

Sergeant Dan Harker had taken the group up in the air to show them the terrain the searchers on the ground were dealing with.

It was a job he was glad to have volunteered for. When they headed off, morale among the family was very low, as it was for the search co-ordination team - not that they were saying that publicly.

Seven nights in the cold, wet mountains is a long time to survive for anyone with limited supplies.

Later that day Harker and Phil Simmonds would have handed their operation over to Sherp Tucker from the Nelson search and rescue squad, and taken a much- needed break. "So finding them could not have come at a better time," Harker joked at the base on Tuesday, after the women were safely back on the ground. "I would have hated to have missed all this. So often my job ends in telling families we've found bodies. This is the best buzz."

When running a search of that level it is extremely difficult not to get emotionally involved. Many of the search advisers working at the base - hardy men with years of local mountaineering knowledge - were reduced to tears when word came in the women were safe.

For Dave Saunders, a 40-year veteran of search and rescues in Canterbury, the successful rescue was "another reason to be involved in the next search. People can survive incredible things, and we can find them in even the most extreme circumstances. Some people do the wrong thing in the hills and they die. Some people do the wrong thing and they live. We like those."

On the mountainside the women had no idea who was on board when the Iroquois spotted them. But they were positive they had been seen once one of the airforce crew hung out of the open door and gave them the thumbs-up.

"It was amazing relief. So amazing."

The women were winched out of their week-long home and checked briefly as they flew back to Arthur's Pass. Later in hospital they were subjected to a fuller medical check and kept in overnight for observation.

But both escaped with good health. Two days later their feet are still swollen and they have cuts and bruises on their hands.

New Year was quiet. Sheppeard still hasn't had the pina colada but "it's on the cards".

For Rendell, the experience may be enough to put her off tramping for "a good long time".

And Sheppeard has a lot of research to do for the rest of the summer, so her next jaunt will be some time off. But the experience, combined with her rescue out of the Swiss Alps, has inspired her to get involved again with SAR.

"It does mean I can give something back and I think that's really important."

She will tackle the mountains again, but will never put a climbing buddy at risk.

"I promised Sonja I would never do that to anyone again. So I would have to think very carefully about going off trail with other people. It's obviously something I'm not good at. But when I'm on my own, I don't see why I shouldn't be able to do what I want. What's the point in living if you don't take any risks?"