North Island Volcanic Plateau

View of the Central Plateau from the Desert Road showing the three active peaks: Snow-capped Ruapehu (left), conical Ngauruhoe (centre) and broad-domed Tongariro (right)

The North Island Volcanic Plateau (often called the Central Plateau and occasionally the Waimarino Plateau) is a volcanic plateau covering much of central North Island of New Zealand with volcanoes, lava plateaus, and crater lakes.

Location and description

The plateau is approximately 100 km east-west and the north -south distance is about 130 km.

Extensive ignimbrite sheets spread east and west of the Taupo Volcanic Zone centred around the huge dormant supervolcanic caldera Lake Taupo, the largest lake in Australia or New Zealand, which last erupted 2000 years ago. The volcanic area includes the three active peaks of Mount Tongariro, Mount Ngauruhoe, and Mount Ruapehu in the south, and extends beyond Rotorua in the north reaching almost to the Bay of Plenty coast. The western boundary of the plateau forms an escarpment beside the Mamaku and Kaimai Ranges, but further south is less distinct. In the east, the plateau runs up to the foot of the Ahimanawa, Kaweka and the fertile Kaimanawa mountain ranges. Finally, west of the plateau stands the volcano Mount Taranaki (in Egmont National Park).

Two of the country's longest rivers, the Whanganui and the Waikato have their headwaters on the plateau.

Geology

The tallest mountain Ruapehu, is an Andesite cone that was once twice as high but has been eroded. All of the cones are composite stratovolcanoes made up of layers of lava and tephra. They are in the intermediate category meaning they have a moderate amount of silica in the magma. The percentage of silica is the deciding factor in the thickness or viscosity of the lava. This contrasts with ignimbrite which is a gas-rich material ejected from the ground at high speed forming a giant white hot fountain 55kilometres high. 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, trapping air inside. Especially around Lake Taupo the eroded ignimbrite includes pieces of 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. The lower, welded layers of the ignimbrite sheets are more dense, though still porous. These lower compressed layers often show the glint of heated silicon specks. This stone, called Hinuera stone(after the quarry of origin), is used for building cladding. The ring plain around the central volcanoes is formed from numerous lahars or mudflows that occur when either the crater lake water is ejected from Ruapehu or snow is melted, during an eruption. The water runs down the mountain picking up ash, lapilli, blocks and bombs as well as previously eroded rock forming a thick dense mud that is capable of picking up car sized rocks. An old lahar flow is visible from the approach road to Whakapapa ski field. In December 1953 a sudden lahar at night on Mt Ruapehu knocked out the rail bridge at Tangiwai causing three carriages of the Wellington-Auckland express to plunge into the Whangaehu River killing many passengers. The last major eruption in the area was the last eruption from the Lake Taupo volcanic complex 1800 years ago which ejected lava and especially wind blown tephra over a wide area to the north and north east of the North Island. About 30cubic kilometres of material were released making this the biggest volcanic event in the world in the last 5,000 years.

The entire area is above 300 metres, with a considerable proportion of it more than 800 metres above sea level. The plateau has a mild climate although the temperature regularly falls below freezing in winter and snow can fall between March and October.The period of maximum snow is July to September. Sudden blizzard conditions can be experienced on the volcanoes in winter. These blizzards have killed climbers as recently as the 1980s.The Desert Road on State Highway 1 is often closed by snow in winter for brief periods.

Flora

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 Taupo and other volcanoes. To the west of the three large volcanoes, the land is rough forested hill country, while the north close to Lake Taupo is more fertile and undulating and much has been cleared for farming. The forest used to extend to the west coast and there are still patches of natural vegetation in wetlands including the Horowhenua floodplains.

However to the east of Taupo the barren, ash-laden soils and harsh alpine climate leave the high land largely bare and unprofitable, capable of growing only scrubby plants. This area is known as the Rangipo Desert although it is not a true desert as the annual rainfall is over 1,000mm PA and the real reason for the low and sparse vegegation was the mass sterilization of seeds caused by the 20,000-year-old Taupo eruption, which swept white-hot ignimbrite through this valley. Prior to this cataclysmic event this area was forested and stumps of charcoalized trees can be seen where soil has eroded. Around Taupo itself there are geothermal areas with specialised plant life such as the prostrate kanuka (a subspecies of kunzea ericoides).

Further to the east of the plateau lies more rough hill country in the Kaimanawa Ranges, a popular hunting area for wild Red deer.The tops of the mountains are open and tussock covered.Helicopters and light aircraft can land on a rough air strip.Hunting range in the bush is often 50m or less but in the open tops the range can be much further. The area to the South,around Lake Moawhango is richer in plant life. Finally there are areas of beech forest and alpine vegetation at higher elevations throughout the region.

Fauna

The northern side of the plateau especially is home to wildlife including birds such as the North Island kokako wattlebird (Callaeas cinerea wilsoni), New Zealand Kaka, and large populations of brown kiwi (Apteryx australis) and blue duck (Hymenolaimus malacorhynchos). The area to the south of the plateau and down to Wellington is home to a variety of lizards including Whitaker's skink (Cyclodina whitakeri), forest gecko (Hoplodactylus granulatus) and Wellington green gecko (Naultinus elegens punctatus). Wetlands throughout the region support waterbirds and fish including the endemic brown mudfish.

Threats and preservation

The lowland areas are quite highly populated and therefore urban development, agriculture and forestry are a major threat to natural habitats there. One block of lowland forest remains in and around Whanganui National Park and large areas of the uplands are protected either by Maori tradition or in national parks of which Te Urewera is the largest. The four North Island national parks, which surround the plateau, are Te Urewera, Whanganui, Egmont and New Zealand's first national park, the World Heritage listed Tongariro National Park. Introduced species and livestock grazing are now major threats to some endemic species. 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 and Banana passionfruit and gorse can take over from indigenous species. Finally grazing by goats and possums can eradicate others such as kamahi, kaikawaka (Libocedrus bidwillii) and montane totara. Therefore smaller islands off the coast of Wellington have been used as a refuge for North Island birds and reptiles whose habitats may be threatened now or in the future.

Also the Volcanic Plateau region has the largest area of man made forest in the Southern Hemisphere. Nearly all the trees are Pinus radiata which were bought in for trials at Rotorua in 1899 from Kew Gardens,London. The tree, a native of Monterey, California, grew very fast in the poor soils. Mass planting was initially carried out by prisoners in the 1920s and then by the unemployed on a large scale during the Great Depression. 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. They also introduced selective breeding methods which was the standard way of improving the trees until tissue culture was introduced in the 1990s. Trees take 25–30 years to reach full height. 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.This is done bu either dipping or more usually, pressure treatment. New Zealand has pioneered the use of Radiata timber and plywood in small craft boatbuilding. Untreated clear timber or plywood is used that is then encapsulated in epoxy resin after construction. The key reason is the low cost of the wood rather than any inherent properies of the wood which is of moderate weight but fractures easily when bent, when dried to 12% moisture. One of the largest ply factories in New Zealand is located on the Volcanic Plateau at Tokoroa. Although planting by hand is still done on steeper land, most seedlings are now planted with the help of machines.

Urban areas in the region include the towns of Taihape in the south, Ohakune the carrot-growing capital of NZ in the west, and Taupo in the north, with Turangi a major trout fishing base at the south of Lake Taupo and by the Kaweka Ranges in the east, The majority of the population of the area lives close to the shores of Lake Taupo, with some smaller settlements to the east of the volcanoes. These make their living largely through tourism, including skiing in the winter season, trout fishing, especially on the Tongariro river or by forestry in the plateau's northeast, which includes the Kaingaroa Forest or by working on the extensive Hydro Electric power system.

History

The Māori population during the Archaic period was sparse. Only two moahunter period sites have been discovered to date. The best known is the Whakamoenga cave near Taupo. The cave was in use about 600 years ago and three moa bones, obsidian flakes, hollow pumice stone ash holders, pumice floats, a fishing net, bird spears, pieces of hue (gourd) and bracken remains have been found. The other moahunter site is at Tokoroa.<Anne Leahy Study, University of Auckland, 1962/63>. The tangata whenua are the Ngāti Tūwharetoa. Their paramount chief is Tumu te Heuheu, who was knighted in 2009. They moved into this area after splitting away from the Arawa tribe on the east coast. The boundary between Arawa and Tuwharetoa is a small island 400 metres north of Huka Falls on the Waikato River. Their main marae is on the southern shores of Lake Taupo at Waihi near the Tokaanu geothermal area. 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.

The Rangipo region is largely uninhabited. It is used by the New Zealand Army, based at Waiouru in the south, and by the Rangipo prison farm in the north and Rangipo underground HEP station to the east. During the 1960s The Tongariro power scheme redirected the flow of water from many of the streams and rivers that drain the central peaks. The water was channelled into canals, tunnels and storage lakes to provide water for 2 HEP stations at Rangipo and Tokaanu. The water then flowed into Lake Taupo increasing its input by 20%. 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 extra water boosted the amount of water available to the 10 other HEP stations on the Waikato River which flows from the north end of the lake and is its only exit.

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. The cure for this was discovered by an Australian scientist in 1936 but the application of cobalt at the rate of 30cc per Ha was only possible after World War II making use of war surplus planes and ex WW2 pilots for aerial topdressing. The cobalt was mixed with crushed phosphate rock which was obtained cheaply from Nauru Island in the West Pacific. The resulting mix was called Super Phosphate.

The site is close to Tangiwai, the scene of New Zealand's worst railway disaster on Christmas Eve, 1953 ,when 151 were killed when the rail bridge was destroyed by a lahar flow from Mt Ruapehu. The largest farm in the North Island was established off the Taupo-Napier road and is called Lochinver Station. The station was largely developed by construction millionaire Bill Stephenson and his family using heavy earthmoving equipment in the 1960s and 1970s. The high country sheep and cattle station has several airstrips, 21 houses and 200km of roading. It normally carries 100,000 breeding ewes and about 8,000 cattle. It has extensive shelter belts of contorta pine, improved rye-grass pasture and grows crops of swedes and barley. The farm is open to tourist and school group bus tours.

Popular culture

The Cold Kiwi Motorcycle rally, NZ's largest rally. , has been held on the Plateau since 1972. Initially at 6 Crossroads on army land near the highest point on the Desert Road, it has now moved to a new site 6 km west of Waiouru on the Ohakune Road. The event is run by Ruapehu Motorcycle club in early Sept each year. The average temperature is -8C at night. Bikers sleep in their own tents but the club provides competitions, souvenirs, hot food and drinks, a bonfire, live bands and WC's. Tourism is an economic mainstay of the region with a wide range of largely outdoor attractions from trout fishing, flyfishing on Tongaroro River or harling on Lake Taupo, tramping, Mountain biking, deer or pig hunting, horse riding to snowskiing/boarding on Mt Ruapehu.

The one day Tongariro Alpine Crossing from the Mangatepopo Valley across Mt Ngauruhoe and Mt Tongariro is considered one of the greatest one-day walks in the world. The 19.2 km track is well marked and popular but trampers should be quite fit and well equipped as the route is exposed, especially during the winter months(April to September). There are two well equipped huts on the route. Detailed guidance is available from the Mt Ruapehu Visitors Centre. The Sir Edmund Hillary Outdoor Pursuits Centre is located on the site of an old construction camp. Started by mountaineer Graham Dingle in the 1970s, this centre offers valuable outdoor training experience and skills to secondary school groups and others. Train and engineering enthusiasts will enjoy the Raurimu Spiral - a railway masterpiece where the main trunk rail line spirals upwards 132m via a tunnel and 180 degree hair pin bends so the passengers near the head of the train can see the rear carraiges heading in the opposite direction. This was the last stage to be built in the main trunk railway line completeted in 1900. A YMCA, which used to be the local primary school, is located nearby for accommodation.

References

• Geology - South Auckland Land District, from An Encyclopaedia of New Zealand, edited by A. H. McLintock, originally published in 1966. Te Ara - The Encyclopedia of New Zealand, updated 26 September 2006. Accessed 2007-07-06.
• Landscape - North Island, from An Encyclopaedia of New Zealand, edited by A. H. McLintock, originally published in 1966. Te Ara - The Encyclopedia of New Zealand, updated 26 September 2006. Accessed 2007-07-06.
• Chapters 1-3, The Volcanic Plateau, District Report 07, Rangahaua Whanui, Waitangi Tribunal. Accessed 2007-07-06.
• Ignimbrite cliffs, from Eileen McSaveney and Simon Nathan.
• 'Geology – overview', Te Ara - the Encyclopedia of New Zealand, updated 13 April 2007. Accessed 2007-07-06.
• Tony Nightingale. 'Government and agriculture - State-funded research', Te Ara - the Encyclopedia of New Zealand, updated 20 November 2008.