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52-474: The Auckland volcanic field is an area of monogenetic volcanoes covered by much of the metropolitan area of Auckland , New Zealand's largest city, located in the North Island . The approximately 53 volcanoes in the field have produced a diverse array of maars (explosion craters), tuff rings , scoria cones, and lava flows. With the exception of Rangitoto, no volcano has erupted more than once, but

104-536: A Mataaho ("The Mountains of Mataaho"), or Ngā Huinga-a-Mataaho ("the gathered volcanoes of Mataaho"). Many of the volcanic features of Māngere can be referred to as Nga Tapuwae a Mataoho ("The Sacred Footprints of Mataoho"), including Māngere Lagoon , Waitomokia , Crater Hill , Kohuora , Pukaki Lagoon and Robertson Hill . Many of the Māori language names of volcanic features in the field refer to Mataaho by name, including Te Pane o Mataaho ( Māngere Mountain ), Te Tapuwae

156-507: A Mataoho (Robertson Hill) and Te Kapua Kai o Mataoho (the crater of Maungawhau / Mount Eden ). Many of the maunga (mountains) were occupied by substantial Māori pā (fortifications) before Pākehā settlement , and many terraces and other archeological remnants are still visible. Many of the cones have been levelled or strongly altered, in small part due to the historical Māori use, but mostly through relatively recent quarrying of construction materials (especially scoria ). However many of

208-518: A framework for interaction of civil defence and emergency services during an eruption. Auckland also has a seismic monitoring network comprising six seismometers —including one 250 metres (820 ft) deep at Riverhead —and three repeaters within the region that will detect the small tremors likely to precede any volcanic activity. This is likely to give between a few hours and several days' warning of an impending eruption, and its approximate location. Auckland War Memorial Museum , itself built on

260-424: A full-scale eruption—would be substantial, ranging from pyroclastic surges to earthquakes , lava bombs , ash falls , and the venting volcanic gas , as well as lava flows . These effects might continue for several months, potentially causing substantial destruction and disruption, ranging from the burial of substantial tracts of residential or commercial property, to the mid-to-long-term closures of major parts of

312-594: A lava flow from Mt St John flows through Sandringham, Morningside, Western Springs, and out to the Waitematā Harbour , forming Te Tokaroa Reef , which reaches within 500 m of Kauri Point, Birkenhead. Some lava flows contain caves, for example at Wiri, Three Kings, and One Tree Hill. Rangitoto Island is the most recent volcano, erupting around 600 years ago. Apart from the summit, it is composed of Pahoehoe (smooth) and ’A’a (broken) lava flows, which are still largely bare of vegetation or soil. It also has lava caves, near

364-598: A lava lake that now forms the top of Table Mountain . Active geothermal systems , similar to those that now exist near Rotorua , were present around 6 Ma, and produced the gold and silver deposits that were later mined in the Coromandel gold rush . Later (5-2 Ma), volcanic activity moved further south to form the Kaimai Ranges . The Hauraki Plains and Hauraki Gulf represent a rift valley . The Coromandel Ranges used to be much closer to Auckland, and

416-748: A rapidly deepening basin developed further to the east, in the Auckland area. These Early Miocene volcanoes, along with the Northland Allochthon , eroded and deposited most of the material that makes up the Waitemata sandstones and mudstones in the Waitemata Basin . The Waitemata sandstones and mudstones form the cliffs around the Waitematā Harbour and East Coast Bays , and land further north up to Cape Rodney , with outcrops further south down to Mercer and Miranda. Lahars produced

468-559: A tribe of patupaiarehe , supernatural beings living in the Waitākere Ranges , who used deadly magic from the earth to defeat a war party of patupaiarehe from the Hunua Ranges . In some traditions, the fire goddess Mahuika creates the volcanic field as a way to warm Mataaho, after his wife leaves and takes his clothing. Because of their close association to Mataaho, the volcanic features can be collectively referred to as Nga Maunga

520-591: Is a stub . You can help Misplaced Pages by expanding it . Geology of the Auckland Region#Northland Allochthon The Auckland Region of New Zealand is built on a basement of greywacke rocks that form many of the islands in the Hauraki Gulf , the Hunua Ranges , and land south of Port Waikato . The Waitākere Ranges in the west are the remains of a large andesitic volcano, and Great Barrier Island

572-649: Is inferred from its distinctive magnetic anomaly (Junction Magnetic Anomaly or JMA) and xenoliths in the Auckland Volcanic Field. Some Murihiku rocks occur to the east of the JMA, forming the Taupiri and Hakarimata Ranges, but it is assumed that these rocks have been shifted to their present position. Hunua Terrane Greywacke lies beneath the Auckland Region on the eastern side, as far south as

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624-473: Is now sea to the west of the Auckland Region, near the Kaipara Harbour and Waitākere Ranges (22-16 Ma), and Waikato Heads (14-8 Ma). The Waitākere volcano has mainly been eroded, but conglomerate from the volcano formed the Waitākere Ranges . The Waitākere Ranges also contain many dikes, volcanic plugs, etc., that formed part of this volcano. While the volcanic activity occurred to the west,

676-694: Is rare for volcanoes to be actually on the fault line. The structure of these Auckland regional faults and the resulting fault blocks is complex but like the volcanic field their locations can be postulated to be related to gravitational variations and where the Stokes Magnetic Anomaly passes through this section of the North Island. The field is part of the Auckland Volcanic Province which comprises four volcanic fields with intra-plate basaltic volcanism starting in

728-466: Is still active. It covers the area from Wiri in the south, through the Auckland isthmus, to Lake Pupuke and Rangitoto Island in the north, and contains around 50 vents. The field contains many maar craters, generated by eruptions where the magma encountered water, and a series of explosive eruptions produced a large crater, surrounded by a tuff ring. Examples include Lake Pupuke, Onepoto , Tuff Crater, Ōrākei Basin , Pukaki Lagoon , etc. Many of

780-612: Is the Cave of a Thousand Press-ups to the east of Maungakiekie/One Tree Hill . Two impressive depressions caused by lava cave collapses are the Puka Street Grotto and the nearby Hochstetter Pond, also known as Grotto Street Pond, in Onehunga. For most of the 200,000 years that the field has been erupting, the planet has been in glacial periods (ice ages) where sea levels were much lower due to water being locked up as ice, and

832-626: The Auckland volcanic field . Other monogenetic volcanoes are tuff rings or maars . A monogenetic field typically contains between ten and a hundred volcanoes. The Michoacán-Guanajuato field in Mexico contains more than a thousand volcanoes and is exceptionally large. Monogenetic fields occur only where the magma supply to the volcano is low or where vents are not close enough or large enough to develop plumbing systems for continuous feeding of magma. Monogenetic volcanic fields can provide snapshots of

884-536: The Hunua Ranges , and outcrops in the Hunua Ranges, many islands in the Hauraki Gulf ( Waiheke , Motutapu , Motuihe , Tiritiri Matangi , Kawau , etc.), and Tawharanui Peninsula . It sometimes includes Chert and Argillite . The rocks are generally fine grained and highly deformed. It was formed in Late Triassic to Late Jurassic times (220-145 Ma). The Morrinsville Terrane Greywacke lies beneath

936-757: The Kaipara Harbour and Albany areas. The rocks came from the northeast, and were emplaced in reverse order, but the right way up. The original rocks are of Cretaceous to Oligocene age (90-25 Ma), and include mudstones, limestone and basalt lava. These rocks outcrop around Silverdale, Warkworth, and Wellsford, reaching as far south as Albany. A volcanic arc became active to the west of the current land in Northland in Miocene times (23 Ma), and gradually moved south down to Taranaki . It produced mainly andesitic strato-volcanoes. Volcanoes were produced in what

988-667: The Okete volcanic field generated the Bridal Veil Falls . Activity then moved to the Ngatutura volcanic field , south of Port Waikato in early Pleistocene times (1.8-1.5 Ma). Little remains of this field. Activity then moved to the South Auckland volcanic field, in the area from Pukekawa north to Waiuku and Papakura , in mid Pleistocene times (1.5-0.5 Ma), producing over 100 eruptions. This field includes

1040-403: The 14 Tūpuna Maunga (ancestral mountains) of Tāmaki Makaurau / Auckland, was vested to the collective. The legislation specified that the land be held in trust "for the common benefit of Ngā Mana Whenua o Tāmaki Makaurau and the other people of Auckland". The Tūpuna Maunga o Tāmaki Makaurau Authority or Tūpuna Maunga Authority (TMA) is the co-governance organisation established to administer

1092-518: The 14 Tūpuna Maunga. Auckland Council manages the Tūpuna Maunga under the direction of the TMA. Since the field is not extinct, new volcanic events may occur at any time, though the usual period between events is, on average, somewhere between hundreds to thousands of years. There has been at least one eruption in every 2,500 years over the last 50,000 years. However, the effects of such an event—especially

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1144-462: The 290-metre (950 ft)-long Wiri Lava Cave . There can be an association with lava caves and the formation of rootless cones due to their mechanism of formation and a rootless cone was suggested to exist at Wiri being Matukutūreia . This may not be quite the case even though at least one steam only driven eruption occurred close to Matukutūreia. The second-longest individual cave in the Auckland field, some 270 metres (890 ft) in total length,

1196-802: The Auckland Region on the eastern side, south of the Hunua Ranges, and further east to the Coromandel Peninsula . The rocks are generally coarser grained, with massive sandstones and conglomerate. It was formed in Late Jurassic to Early Cretaceous times (160-120 Ma). The Te Kuiti Group Rocks overlie the basement rocks, and are present in Northland , Auckland, the Waikato , and King Country , although they have often been eroded or covered. Rocks containing coal were formed from swampland in Late Eocene times (37-34 Ma). The land sank and

1248-614: The Auckland Region on the western side, and outcrops south of the Waikato River . The Murihiku Terrane is considered to be an accretionary wedge of mainly volcanogenic forearc sediments. It was formed in Late Triassic to Late Jurassic times (220-145 Ma). A line of Dun Mountain-Maitai Terrane rocks are assumed to pass north–south through the centre of the Auckland Region, separating the Murihiku Terrane and Waipapa Composite Terrane. The existence of this terrane at depth

1300-435: The Kaipara Harbour. The Āwhitu Peninsula (the west coast from Waikato Heads up to Manukau Heads), and the coastal barriers north and south of the entry to the Kaipara Harbour, are essentially consolidated sand dunes, built up over the last few million years. The black sand on the west coast beaches is known for its high iron content, and is “mined” north of Waikato Heads, being extracted by electromagnets. The iron comes from

1352-539: The Ngatutura, South Auckland and Auckland fields since then. The Alexandra Volcanic Group composed of basaltic stratovolcanoes and its associated Okete Volcanics which erupted over short periods, between 1.8 and 3 Ma ago, from at least 27 tuff rings , or scoria mounds, surrounded by lava flows. The largest volcano of the Alexandra volcanics, Pirongia erupted last about 900,000 years ago. At Maungatawhiri

1404-477: The North Shore near Takapuna , is a volcanic explosion crater. A few similar craters such as Ōrākei Basin are open to the sea. The field has produced voluminous lava flows that cover much of the Auckland isthmus . One of the longest runs from Mt Saint John northward, almost crossing the Waitematā Harbour to form Meola Reef . More than 50 lava tubes and other lava caves have been discovered, including

1456-556: The Waitemata and Manukau Harbours were dry land. All the volcanoes probably erupted on land except for Rangitoto, which erupted during the current interglacial (warmer) period. The Auckland region lies within the Australian Plate , about 400 kilometres (250 mi) west of its plate boundary with the Pacific Plate . The volcanoes are located south of a geological region called the Northland Allochthon , and with

1508-652: The coarser Parnell Grit , found in many headlands around the East Coast Bays. Greywacke pebble beaches can be seen forming a layer in Waitemata sandstone cliffs on Motutapu Island . Shortly after (18 Ma), a volcanic arc developed further east to create the Coromandel Ranges and undersea Colville Ridge . The initial activity was andesitic , but later became rhyolytic (12 Ma). In the Kauaeranga Valley , volcanic plugs remain, as does

1560-658: The country's infrastructure such as the Port of Auckland , the State Highway network , or the Auckland Airport . It is possible that several volcanoes could erupt simultaneously. There is strong evidence that eight erupted within a span of 3000 years or so, between 31,000 and 28,000 years ago. Most eruptive events in the field have been small volume, very constrained in time, typically involving less than 0.005 km (0.0012 cu mi) of magma making its way to

1612-585: The crater rim of Pukekawa , has an exhibition on the field, including the "Puia Street multi-sensory visitor experience", which simulates a grandstand view of an eruption in Auckland. The volcanoes within the field are: Monogenetic volcanic field Many monogenetic volcanoes are cinder cones , often with lava flows, such as Parícutin in the Michoacán-Guanajuato volcanic field , which erupted from 1943 to 1952. Some monogenetic volcanoes are small lava shields , such as Rangitoto Island in

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1664-568: The craters have been breached by the sea, and are now filled with mud. The eruption of Lake Pupuke caused the Wairau River, which used to come out around Shoal Bay , to change its course to north of Milford. Dry fire-fountaining eruptions have produced scoria cones. Examples include North Head , Mount Victoria , Mount Eden , Mount Hobson , Mount St John , One Tree Hill , Mount Roskill , Three Kings , Mount Albert , and Mount Māngere . Some produced substantial lava flows. For example,

1716-432: The initial eruption was of fine-grained volcanic tuffs, thought to be comminuted by water interacting with magma, followed by strombolian activity and lava flows. North of Papanui Point violent phreatomagmatic eruptions have formed tuff rings of airfall and pyroclastic surge deposits. The Okete Volcanics include basanites , alkali olivine basalts , hawaiites , and lavas with ultramafic xenoliths . Lava flows from

1768-522: The lava flows at Hunua Falls, scoria cones that form the Bombay Hills , Pukekohe and Pukekawa, and tuff rings at Pukekohe and Onewhero . The rich soils used for market gardening in this area are the product of the Hamilton Ash tephra formation, not the weathering of the South Auckland volcanic field. The Auckland volcanic field , is believed to have started around 250,000 years ago, and

1820-857: The mountains have been administered variously by the New Zealand Crown , the Auckland Council (or its former bodies including the Auckland City Council and Manukau City Council) or the Department of Conservation . In the 2014 Treaty of Waitangi settlement between the Crown and the Ngā Mana Whenua o Tāmaki Makaurau collective of 13 Auckland iwi and hapū (also known as the Tāmaki Collective), ownership of

1872-423: The north to Matukutururu (Wiri Mountain) in the south, and from Mount Albert in the west to Pigeon Mountain in the east. The first vent erupted at Pupuke 193,200 ± 2,800 years ago. The most recent eruption (about 600 years ago and within historical memory of the local Māori ) was of Rangitoto, an island shield volcano just east of the city, erupting 0.7 cubic kilometres of lava . The last volcano to erupt

1924-484: The northern volcanoes located over early Miocene sedimentary deposits of the Waitematā Group of rocks and the southern volcanoes over post Miocene sediments. A large proportion of the volcanoes in the field, particularly those with cone structures, lie within 500 metres (1,600 ft) of inferred or known faults, with the qualification that these are inactive historic faults and unlike in many other volcanic fields it

1976-495: The other eruptions lasted for various periods ranging from a few weeks to several years. Rangitoto erupted several times and recently twice; in an eruption that occurred about 600 years ago, followed by a second eruption approximately 50 years later. The field is fuelled entirely by basaltic magma , unlike the explosive subduction -driven volcanism in the central North Island, such as at Mount Ruapehu and Lake Taupō . The field ranges from Lake Pupuke and Rangitoto Island in

2028-425: The recent sand dune deposits of the Āwhitu and South Kaipara Peninsulas. Recent basaltic volcanic activity has produced many volcanic cones throughout the Auckland Region, including the iconic and youngest volcano Rangitoto Island . As with most of New Zealand, the basement rocks of the Auckland Region are composed of greywacke (indurated sandstone, siltstone and mudstone). Murihiku Terrane Greywacke lies beneath

2080-506: The remaining volcanoes are now preserved as landmarks and parks. The warmer northern sides of the mountains were also popular among early Pākehā settlers for housing. In the 1880s, Takarunga / Mount Victoria and Maungauika / North Head were developed as military installations due to fears of a Russian invasion . The cones are also protected by a 1915 law, the Reserves and Other Lands Disposal and Public Bodies Empowering Act 1915, which

2132-550: The rift valley is assumed to have developed about 2 Ma ago, due to the clockwise rotation of the eastern North Island, that stretched the land between Auckland and East Cape. The Waikato River used to flow from Karapiro , through the Hinuera Gap , and Hauraki Plains, to come out on the east coast in the Hauraki Gulf. The sediment from Oruanui eruption of Lake Taupō caused the river to change direction, and come out to

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2184-543: The same amount of upwelling magma that might be expected to destroy an area of 0.3 km (0.072 cu mi) if there is no ground water interaction. Modelling has suggested that the next eruption in the volcanic field is likely to be associated with water and in the area extending from the central city to its north and northeast suburbs surrounding and including the Waitemata Harbour . Within New Zealand

2236-462: The sea transgressed, and calcareous sandstone, mudstone, and limestone was deposited in Oligocene times (34-24 Ma). The coal deposits outcrop near Huntly and Maramarua , where they are mined. Flaggy limestone bluffs are located in the area south and west of the Waikato River . In Early Miocene times (24-21 Ma), a series of thrust sheets were emplaced over Northland, extending as far south as

2288-404: The south, at Okete , near Raglan in late Pliocene times (2.7-1.8 Ma). Activity has since moved north through the Ngatutura , South Auckland and Auckland fields since then. Tāmaki Māori myths describe the creation of the volcanic field as a creation of Mataaho (the guardian of the earth's secrets) and his brother Rūaumoko (the god of earthquakes and volcanoes), made as punishment against

2340-420: The surface. However the same amount of magma can have an order of magnitude different impact. An underwater eruption which is more likely to be explosive resulted in the formation of the 0.7 km (0.43 mi) wide Ōrākei crater that destroyed an area of 3 km (0.72 cu mi) by crater formation and base surge impact. This contrasts with the about 0.5 km (0.31 mi) diameter cone produced by

2392-528: The track up to the summit, that are very accessible to visitors. While the ages of individual volcanoes in the Auckland volcanic field are somewhat uncertain, the following ages have been obtained: Over the last few million years, rhyolitic pumice deposits from the centre of the North Island have been washed down into the Auckland area, and form substantial deposits around the Hauraki Plains and Manukau Harbour, Western Waitematā Harbour, and even up into

2444-428: The underlying region beneath the surface, and may be useful in studying the generation of magma and the composition of the mantle since the single eruption produced would match that of the chamber from which it erupted. The magma supplying such fields is thought to have rapidly ascended from its source region, with only short resident times (decades or less) in shallow magma chambers . This volcanology article

2496-618: The volcanic hazard of the field is graded below that of Taupo Volcanic Zone volcano's but is likely to be perceived by the population affected as a greater potential nuisance if it occurs Various operative structures, plans and systems have been set up to prepare responses to volcanic activity within the urban areas, mainly coordinated in the Auckland Volcanic Field Contingency Plan of the Auckland Regional Council , which provides

2548-605: The west. Rivers around Auckland, that now flow to the east, such as the rivers around Clevedon, used to flow to the west, and deposited rocks from the Coromandel Ranges in the Manukau Harbour . The Auckland Volcanic Province comprises the Auckland, South Auckland, Ngatutura and Okete volcanic fields. Intra-plate basaltic volcanism in the Auckland region started in the south, at Okete, near Raglan in late Pliocene times (2.7-1.8 Ma), and has moved north through

2600-559: Was formed by the northern end of the Coromandel Volcanic Zone. The Auckland isthmus and North Shore are composed of Waitemata sandstone and mudstone, and portions of the Northland Allochthon extend as far south as Albany . Little Barrier Island was formed by a relatively isolated andesitic volcano, active around 1 to 3 million years ago. The Manukau and South Kaipara Harbours are protected by

2652-481: Was much bigger than all others, with Rangitoto making up 41 per cent of the field's entire volume of erupted material with characteristics as to slope and symmetry around the eruptive vents seen in basaltic shield volcanoes as might be expected in a volcano, that may have buried other volcanoes, and now known to have a 1000-year odd eruptive history. The field's other volcanoes are relatively small, with most less than 150 metres (490 ft) in height. Lake Pupuke, on

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2704-720: Was passed due to early concern that the distinctive landscape was being eroded, especially by quarrying. While often ignored until the late 20th century, it has amongst other things minimised severe changes to Mount Roskill proposed by Transit New Zealand for the Southwestern Motorway . In March 2007, New Zealand submitted the volcanic field, with several specifically named features, as a World Heritage Site candidate based on its unique combination of natural and cultural features. At that time, only 2 per cent of more than 800 World Heritage Sites worldwide were in this "mixed" category. For most of Auckland's post-1840 history,

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