Andesite magma in effusive eruptions cools to form dark grey lava if gas-poor or scoria if gas-rich.

[2] The other two most prominent volcanic mountains are Tongariro and Ngauruhoe part of a single composite stratovolcano, like Ruapehu made up of layers of lava and tephra.

On Christmas Eve 1953 a sudden lahar at night on Mt Ruapehu knocked out the rail bridge at Tangiwai, causing six carriages of the Wellington-Auckland express to plunge into the Whangaehu River, killing 151 people in New Zealand's worst railway disaster.

When the ignimbrite falls it flows outwards at high speed (600–900 km/h) and can travel many kilometres, even going up and over hills and mountains before it cools, often trapping air inside.

Especially around Lake Taupō the eroded ignimbrite includes pieces of quickly cooled pumice, a lightweight rock that floats on water.

The top, unwelded layer of the ignimbrite sheet is relatively soft and easily eroded by streams and rivers, which transport the pumice to the lake.

[4] An historic eruption at the north west edge of the plateau at Mangakino about 1 million years ago produced ignimbrite that 170 km (110 mi) away in Auckland is up to 9 m (30 ft) thick.

As is typical after such degassing events which are separated in considerable time, dome building by effusive eruption of low gas viscous rhyolite magma then occurred resulting in this case the formation of the Horomatangi Reefs about 200 years later.

The natural vegetation of the area includes the podocarp conifers including rimu (Dacrydium cupressinum), miro (Prumnopitys ferruginea), matai (Prumnopitys taxifolia), totara (Podocarpus totara) and kahikatea (Dacrycarpus dacrydioides) and hardwoods that once covered this whole area before the eruption of Taupō and other volcanoes.

To the west of the three large volcanoes, the land is rough forested hill country, while the north close to Lake Taupō is more fertile and undulating and much has been cleared for farming.

[9] However to the south of Taupō the barren, ash-laden soils and harsh alpine climate leave the high land largely bare and unprofitable, capable of growing only scrubby plants.

[10] Further to the east of the plateau lies more rough hill country in the Kaimanawa Ranges, a popular hunting area for wild red and sika deer.

[11] The northern side of the plateau especially is home to wildlife including birds such as the North Island kōkako wattlebird (Callaeas wilsoni), New Zealand kaka, and large populations of brown kiwi (Apteryx australis) and blue duck (Hymenolaimus malacorhynchos).

The lowland areas are quite highly populated and therefore urban development, agriculture and forestry are a major threat to natural habitats there.

Rats, cats and stoats prey on native reptiles and birds (including the kokako, blue duck and brown kiwi), while imported plants such as old man's beard, banana passionfruit and gorse can take over from indigenous species.

After World War II scientists from Norway settled in the region and helped develop ways of treating the soft pine to prevent rotting using pressure treatment with chemicals.

Most plantations use growth factor (GF) trees to guarantee very high quality (straight and knot-free) timber, however treatment by chemical salts is still required to stop rotting.

They still retain ownership of the peaks of the mountains which are considered sacred, as well as the Ketetahi hot springs on the north slope of Mt Tongariro.

The Māori people considered the volcanoes sacred and in traditional times wore woven flax eye shields to avoid looking at the peaks.

Most of the Tongariro river flow is not included in the power scheme due to its importance as a breeding area for brown and rainbow trout.

The productivity of pasture on the plateau was greatly improved in the 1950s once it was realised that the "bush sickness" suffered by local livestock was due to cobalt deficient volcanic soils.

It has extensive shelter belts of contorta pine, improved rye-grass pasture and grows crops of swedes and barley.

Tourism is an economic mainstay of the region with a wide range of largely outdoor attractions from trout fishing, flyfishing on Tongariro River or harling on Lake Taupō, tramping, Mountain biking centred on National Park, deer or pig hunting, horse riding to snowskiing/boarding on Mt Ruapehu.

The Sir Edmund Hillary Outdoor Pursuits Centre of New Zealand is located on the site of an old Italian tunneling construction camp.

Started by mountaineer Graeme Dingle in the 1970s, this centre offers valuable outdoor training experience and skills to secondary school groups and others.

Bikers sleep in their own tents despite the average temperature being −8 °C at night, but the club provides hot food and drinks, a bonfire, as well as competitions, souvenirs, live bands and toilet facilities.