The Tongariro Crossing is regularly called the best day walk in New Zealand, but with big claims come big crowds. At the height of summer, up to 1000 people file across the 19-kilometre-long trail every day, passing between two volcanoes and witnessing a spectacle of steaming craters and neon-bright lakes.

To walk the Tongariro Crossing, however, is to experience only a small portion of the extraordinary volcanic landscape of Tongariro National Park.

Given to the country in 1887 by the Ngati Tuwharetoa Maori people, this was New Zealand's first national park and only the fourth in the world. If the Crossing is the condensed book, the 43-kilometre Tongariro Northern Circuit is the novel. One of New Zealand's nine listed Great Walks, the Circuit loops around Mount Ngauruhoe, the most striking of the North Island's volcanoes.

For most walkers, it's a three to four-day hike, taking in dramatic and vibrant volcanic scenes, including those along the Tongariro Crossing. Walk the Tongariro Northern Circuit and you are likely to be among dozens of walkers, rather than hundreds. There are also ways to do it and see almost nobody. I have come to the park with Adrift, a local guiding company with a concession to hike the Circuit and explore beyond the trail. In the next couple of days, we will effectively complete the Northern Circuit while walking for a large part off the Circuit.

One of the most exciting aspects of hiking in Tongariro National Park is that you are walking through a dynamic landscape. New craters open, land shifts and rocks rain from above. As recently as August 2012, Te Maari, a crater near the trail, erupted twice, spewing ash and rock kilometres into the sky. Tom Green, my guide, was just a couple of kilometres from the crater, guiding a group of walkers, at the time of the second eruption.

"The whole ground that day just went wallop," he says. "With all the eruptions, there's just so much more to see there now. It's changed big time. "

We begin walking from the tourist village of Whakapapa, at the foot of the volcanoes, hiking through thick beech forest that seems almost out of place in the otherwise harsh, barren landscape. Taranaki Falls bursts through a break in a line of lava cliffs, tumbling into the forest. The trail follows ancient lava flows as it funnels between Mount Ngauruhoe and Mount Ruapehu. The latter glows in full sun, while the former is clogged with cloud.

The ground is a carpet of pink heather, introduced by early English settlers to create a grouse moor. "There's a bit of a rule in the park," Tom says. "If it's got colour, it's not native."

Two hours from Whakapapa, we turn off the main trail and begin the climb to the Tama Lakes. As blazingly vivid as any of the lakes along the Tongariro Crossing, the Tama Lakes are pooled inside a line of impact craters, where boulders from the volcanoes crashed to earth like meteorites.

For most walkers on the Northern Circuit, the lakes are a side trip, but for us they're part of a byway, leading us towards solitude. Past Upper Tama Lake, we head off track, rising into a high hanging valley. I have hiked in Tongariro National Park several times and never have I seen anything as spectacular as the scene in this valley.

Black ridges frame the valley and grass tussocks dot the grey-black soil. Mosses grow in coral-like clusters on the clay pan of a dried lake. It's like the South American altiplano. On a fine day, the summit of Mount Ngauruhoe rises immediately above, towering one kilometre overhead.

"It's like a monster from here," Tom says, although today it's covered with cloud.

The hanging valley makes a natural arc around a ridge and we turn with it, descending off the slopes of Mount Ngauruhoe along the top of a 140-year-old lava flow, so young in geological terms that its sharp edges and red boulders still look as raw as an open wound.

For a time, everything looks desolate, but there is life here. At the toe of the lava flow, a spring pours from the ground. Along its edges plants grow green and lush, looking almost like an affront to the rest of the land.

Normal transmission isn't far away. Below the lava flow, near where we rejoin the Northern Circuit, is New Zealand's only desert. The Rangipo Desert was once covered in forest, but in the AD186 eruption that created Lake Taupo, said to have been the world's largest volcanic explosion of the last 5000 years, the forest was incinerated. No tree has grown back in almost 2000 years.

"This is Mordor," Tom says as we rise over a ridge 15 minutes' walk from the hut that will be our home this night. He means it literally. This section of the Rangipo Desert was used as the setting for Mordor in The Lord of the Rings movie trilogy. Standing here in the late afternoon, with lava boulders strewn across the barren pumice and sand, it seems a logical choice. It's a scene as fantastical and otherworldly as any in New Zealand.

Oturere Hut is prime hiking real estate, staring across the desert plain to the perfect volcanic cone of Mount Ngauruhoe and the steaming slopes of Red Crater.

At dawn, a crowd of hikers gathers outside as the rising sun electrifies the sky and catches the summit of the mountain, lighting it like magma.

Soon the crowd will disperse, heading off for another day of hiking along the Northern Circuit, although we are again diverging.

From the hut, the Northern Circuit crosses the desert plain to Red Crater, merging with the Tongariro Crossing high on the crater's slopes. Our course is a rocky ridge overlooking the plain. For the entire morning, we will be a few hundred metres above the trail. It's a truly cinematic view of Mordor, and we are alone.

When the wind blows from the north, it brings with it the sulphurous whiff of Te Maari. The distant boom of artillery tests at the nearby military base of Waiouru adds to the doomsday atmosphere. We rejoin the trail on the shores of Blue Lake, joining the crowds on the Tongariro Crossing. From here the trail descends towards Ketetahi Hut, on the northern flanks of the volcanoes.

At the first turn in a series of switchbacks just before the hut, Tom stops.

"This is where I was standing when Te Maari erupted," he says. To the west, just two kilometres away, Te Maari's craters are now visible, steaming as fiercely as a bushfire. "Te Maari is something we didn't even used to point out. It was just there, dormant, but it's front of stage now."

The ground by the trail is pitted with small craters from the rocks that showered the area when Te Maari erupted nearly two years ago. In their centres, like yolks, the rocks are still dusted in fresh yellow sulphur.

Nowhere is the impact of the rocks seen more vividly than at Ketetahi Hut, where a boulder smashed through the roof, crushing a bunk bed. Since that day, the hut has been used only as a day shelter.

"We always tell people there was a guy sleeping here and he heard the boom, sat up and the rock came through where his head was," Tom says.

"Then we tell them the truth, that no one was in the hut, which is quite amazing because there's almost always someone in it."

Ten years ago, I slept in Ketetahi Hut. There's a grim fascination in standing here again, so close to potential disaster as the earth continues to churn, boil and steam. If I return 10 years from now, who knows what I'll find? Tongariro National Park runs to its own geological beat.

The writer travelled as a guest of Tourism NZ.

TRIP NOTES

GETTING THERE

Air New Zealand operates daily flights from Sydney and Melbourne to Auckland, with connections to Taupo. See airnewzealand.com.au. Nakedbus.com operates a bus service between Taupo and Whakapapa and nearby National Park Village. See nakedbus.com.

HIKING THERE

Adrift offers guided three-day hikes on the Tongariro Northern Circuit ($NZ950), departing from National Park Village. See adrift.co.nz.

If hiking the Northern Circuit independently, permits need to be obtained from the Department of Conservation. Bookings are now open for the summer season. See doc.govt.nz/tongarironortherncircuit.

MORE INFORMATION

newzealand.com.

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MILFORD TRACK

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ROUTEBURN TRACK

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ABEL TASMAN COAST TRACK

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RAKIURA TRACK

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LAKE WAIKAREMOANA

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