page_title: Geography of New Zealand
section_title: Geology
hierarchical_section_title: Geography of New Zealand / Physical geography / Geology
caption_attribution_description: English: Lake Taupo in New Zealand's North Island
context_page_description: New Zealand is an island country located in the south-western Pacific Ocean, near the centre of the water hemisphere. It consists of a large number of islands, estimated around 600, mainly remnants of a larger land mass now beneath the sea. The two main islands by size are the North Island and the South Island, separated by the Cook Strait. The third-largest is Stewart Island, located 30 kilometres off the tip of the South Island across Foveaux Strait. Other islands are significantly smaller in area. The three largest islands stretch 1,500 kilometres across latitudes 34° to 47° south. New Zealand is the sixth-largest island country in the world, with a land size of 267,710 km².
  New Zealand's terrain ranges from the fiord-like sounds of the southwest to the sandy beaches of the far north. The South Island is dominated by the Southern Alps while a volcanic plateau covers much of the central North Island. Temperatures rarely fall below 0 °C or rise above 30 °C and conditions vary from wet and cold on the South Island's west coast to dry and continental a short distance away across the mountains and near subtropical in the northern reaches of the North Island.
context_section_description: New Zealand is part of Zealandia, a microcontinent nearly half the size of Australia that gradually submerged after breaking away from the Gondwanan supercontinent. Zealandia extends a significant distance east into the Pacific Ocean and south towards Antarctica. It also extends towards Australia in the north-west. This submerged continent is dotted with topographic highs that sometimes form islands. Some of these, such as the main islands (North and South), Stewart Island, New Caledonia, and the Chatham Islands, are settled. Other smaller islands are eco-sanctuaries with carefully controlled access.
  The New Zealand land mass has been uplifted due to transpressional tectonics between the Indo-Australian Plate and Pacific plates (these two plates are grinding together with one riding up and over the other). This is the cause of New Zealand's numerous earthquakes and volcanoes.
  To the east of the North Island the Pacific Plate is forced under the Indo-Australian Plate. The North Island of New Zealand has widespread back-arc volcanism as a result of this subduction. There are many large volcanoes with relatively frequent eruptions. There are also several very large calderas, with the most obvious forming Lake Taupo. Taupo has a history of incredibly powerful eruptions, with the Oruanui eruption approx. 26,500 years ago ejecting 1,170 cubic kilometres (280 cubic miles) of material and causing the downward collapse of several hundred square kilometres to form the lake. The last eruption occurred c. 180 CE and ejected at least 100 cubic kilometres of material, and has been correlated with red skies seen at the time in Rome and China. The associated geothermal energy from this volcanic area is used in numerous hydrothermal power plants. Some volcanic places are also famous tourist destinations, such as the Rotorua geysers.
  The subduction direction is reversed through the South Island, with the Indo-Australian Plate forced under the Pacific Plate. The transition between these two different styles of continental collision occurs through the top of the South Island. This area has significant uplift and many active faults; large earthquakes are frequent occurrences here. The most powerful in recent history, the M8.3 Wairarapa earthquake, occurred in 1855. This earthquake generated more than 6 metres (20 ft) of vertical uplift in places, and caused a localised tsunami. Fortunately casualties were low due to the sparse settlement of the region. In 2013, the area was rattled by the M6.5 Seddon earthquake, but this caused little damage and no injuries. New Zealand's capital city, Wellington, is situated in the centre of this region.
  The subduction of the Indo-Australian Plate drives rapid uplift in the centre of the South Island (approx. 10 millimetres (0.39 in) per year). This uplift forms the Southern Alps. These roughly divide the island, with a narrow wet strip to the west and wide and dry plains to the east. The resulting orographic rainfall enables the hydroelectric generation of most of the country's electricity. A significant amount of the movement between the two plates is accommodated by lateral sliding of the Indo-Australian Plate north relative to the Pacific Plate. The plate boundary forms the nearly 800 kilometres (500 mi) long Alpine Fault. This fault has an estimated rupture reoccurrence interval of ~330 years, and last ruptured in 1717 along 400 kilometres (250 mi) of its length. It passes directly under many settlements on the West Coast of the South Island and shaking from a rupture would likely affect many cities and towns throughout the country.
  The rapid uplift and high erosion rates within the Southern Alps combine to expose high grade greenschist to amphibolite facies rocks, including the gemstone pounamu (jade). Geologists visiting the West Coast can easily access high-grade metamorphic rocks and mylonites associated with the Alpine Fault, and in certain places can stand astride the fault trace of an active plate boundary.
  To the south of New Zealand the Indo-Australian Plate is subducting under the Pacific Pla
caption: The scalloped bays indenting Lake Taupo's northern and western coasts are typical of large volcanic caldera margins. The caldera they surround was formed during the huge Oruanui eruption.
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