"Oi! Peter! Rock," I yelled, as another boulder dislodged by climbers above bounded down the tephra slope, past the lambent flank of snow gleaming in morning sunshine and past my friend below. A bit too close for comfort, that one. But, my God, the view was amazing.
This was the first mountain climb for my two companions, although they had tackled marathons and triathlons and prodigious cycle rides. Somehow, I doubted that was the case for the mum and her three whippet-thin children who boarded the bus with us at National Park Backpackers earlier that morning. The youngest child was just 7, but they were clearly undaunted by the 19.4km walk ahead of them.
However, the death of a tourist in 2006 has focused attention on the inherent dangers of venturing into these mountains, more especially the sudden changes in the weather which can undo unprepared trekkers. This was the third attempt on the Crossing by one of my companions, after being defeated by the weather twice before.
Yet, still some people continue to ignore the warnings. The Mountain Safety Council raised the issue again last year after trampers were observed on the Crossing wearing Jandals and T-shirts, carrying only a shopping bag and an umbrella.
Our packed bus arrived at the Mangatepopo car park just before 8am. The first 1 hours of the walk were a fairly gentle uphill stroll through tussock and the black, petrified, pyroclastic flow left from an eruption on Ngauruhoe in 1975. As it was a Saturday, the trail head at Mangatepopo Saddle was crowded with a United Nations of walkers. Most continued on the Crossing but some, including us, started up the unmarked track towards the black summit of Ngauruhoe (2287m). The cone famously starred as the body double for Mt Doom in the Lord of the Rings films and some of the grimness of Mordor seems to cling to its dark, cloud-shrouded heights.
There is little sign of life, not even a single bird.
"So - who's carrying the ring?" calls out one American voice, eliciting a response of slightly nervous and jaded chuckles from the assorted climbers.
The mountain was considered tapu by local Maori and climbing it was strictly forbidden.
Nevertheless, a British man, John Bidwill, became the first Pakeha to reach the summit in 1839.
It is not without its dangers. Signs warn of volcanic activity and there have been plenty of rescues in recent years when people have been injured falling down the mountain or hit by flying rocks.
It's a steep haul up the slope, made more tiring by the constantly shifting sand and tephra underfoot.
The weather is schizophrenic - bright sun one minute, cold, wind-driven mist the next.
After about 1 1/2 hours we claw our way to the summit.
A 15-year-old girl and her 13-year-old brother are already there, smiling and shivering in the sudden chill, as is a Latin-American tourist who poses for photos beside the blackened, ice-limned crater. Another woman arrives at the crater edge, bleeding from grazes inflicted by a falling rock during the ascent.
On a clear day you can see Mt Taranaki from here but this is not one of those days.
The descent is rather quicker, especially for those who opt to glissade down the snow patch below the crater and "ski" down the scree slope. But, again, the danger of falling rocks is ever-present. Someone above me yells a warning and I look up to see a football-size boulder bounding my way. It's surprising how quickly you can run across the face of a mountain when your life is at stake.
Time is pressing after our diversion, with 13km of the Crossing still to cover. South Crater is surreal: a dead-flat desert between the cones of Ngauruhoe and Tongariro. There is another punishing climb to the smoking, sulphurous chasm of the Red Crater. Its burned and blasted vent is evidence of the power of these active volcanoes.
The option of continuing to the summit of Tongariro (1967m) beckons, but we've bagged our peak for the day and there's a bus waiting somewhere beyond these mountains. A slippery scree path threads down to the psychedelically lovely Emerald Lakes.
From the lakes the trail crosses a snow field, still surviving in the shade of the mountain, despite it being officially summer.
A short climb and the larger Blue Lake opens out below in another geographically incongruous setting.
The mist rolls in again as the track finally dips on a long, knee-wearing descent to Ketetahi Hut, past the smoking Ketetahi hot springs. The views out towards Lake Rotoaira and Lake Taupo are breathtaking, but it seems to take forever to complete the final few kilometres through scrub and native forest to Ketetahi car park, which is populated with sprawling hikers waiting for buses.
The mum and her three intrepid little hikers are there safe and sound, sunburned and footsore, but still smiling after conquering the Crossing and the summit of Tongariro.
After eight hours of tough walking it's a treat to sit in the bus and watch the wild beauty of National Park scroll past the window, luxuriating in that profound calm engendered by bodily exhaustion.
The massive, snow-clad bulk of Mt Ruapehu gleams in the afternoon sun ahead of us.
I look up at it and imagine what it must be like on those frozen slopes.
"You're next," I smile to myself.
CHECKLIST
Getting there: Most places to stay in Tongariro National Park can arrange transport to and from the start and finish of the Crossing at Mangatepopo and Ketetahi.
Where to stay: There are two huts on the Crossing at Mangatepopo and Ketetahi which can be booked through DOC.
What to take:
* Food and plenty of fluid
* Rainproof coat (and overtrousers if needed)
* Strong boots - the volcanic terrain is loose and uneven
* Woollen or polypropylene clothing (not cotton)
* Woollen hat and gloves
* Sun protection
* Map and compass
* In winter you may also need an ice axe and crampons and snow gaiters
The weather is probably the greatest challenge and danger in Tongariro National Park. It can change quickly and trampers need to be prepared for all conditions and to turn back if necessary, especially in poor visibility and strong winds.
