The 12-mile-long trail called the Tongariro Alpine Crossing begins in tussock grassland, then climbs past lava cliffs and glacial moraines (heaps of debris piled up by former glaciers) to the base of Ngauruhoe, where hikers willing to endure a couple of hours trudging up scree can make a side trip to the top of the volcano. The main route ascends the slopes of Tongariro to the top of Red Crater. Steaming like the gate to hell, Red Crater is named for the rock around its mouth, given a chestnut hue by oxidized iron. Surrounding swaths of black lava testify to the crater's long history of eruptions, continuing through the late 1800s.
On the downslope from Red Crater, three lakes fill explosion pits stained by minerals in shades of emerald that gave them the Maori name Ngarotopounamu. Soon after, the crossing passes another lake, Te Wai-whakaata-o-te Rangihiroa, or Blue Lake. Indeed, on a clear day its water seems torn from the sky above. The trail then descends grassy hillsides and passes steaming volcanic vents to finish in dense forest along a tumbling stream called Mangatipua.
On the southwestern slope of Ruapehu, ancient woodlands of a different sort survive by a quirk of geography. The great bulk of Ruapehu sheltered this forest from the massive Taupo volcano blast of A.D. 186, while trees for miles in all other directions were flattened. An easy trail winds under soaring rimu, matai, and kahikatea trees laden with ferns, while below, tree ferns spread their lacework fronds, and kamahi trees seem to be frozen in the throes of a hula-like dance.
This lushness, like Tongariro's innumerable rocky streams and waterfalls, is fed by clouds that drift from the Tasman Sea to release their moisture against the mountain slopes. In the North Island's highlands you'll have ample opportunity to perfect your own definitions of fog, mist, drizzle, sprinkle, light rain, and rain, and the subtle distinctions among them.
Coexisting with Tongariro's beauty are serious conservation and cultural issues. Like the rest of New Zealand, the park's ecosystem suffered terrible losses from the introduction of alien species, from rats brought by the earliest Maori to rabbits, stoats, Australian possums, and cats brought by Europeans. Native birds, which evolved without mammalian predators for millions of years, were devastated and survive today at only a fraction of their former numbers. Even as the kiwi, the bizarre, flightless bird, became the beloved symbol of New Zealand, it almost died out in the wild, its eggs and young devoured by stoats.