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Auckland volcanic field facts for kids

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Auckland Volcanic Field
Map of the Auckland Volcanic Field from 1859
Map of the field drawn by Hochstetter in 1859 and published in English in 1864
Highest point
Elevation 260 m (850 ft)
Geology
Age of rock Pleistocene and Holocene
Mountain type Volcanic Field
Type of rock Basalt
Last eruption c. 1400 CE

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. No volcano has erupted twice, but eruptions lasted for various periods ranging from a few weeks to several years. 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 Taupo. The field is currently dormant, but could become active again.

Features

The field ranges from Lake Pupuke and Rangitoto Island in 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 was much bigger than all others, with Rangitoto making up 41 per cent of the field's entire volume of erupted material. The field's volcanoes are relatively small, with most less than 150 metres (490 ft) in height.

Lake Pupuke, on the North Shore near Takapuna, is a volcanic explosion crater. A few similar craters such as Orakei 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 the 290-metre (950 ft)-long Wiri Lava Cave. The second-longest individual cave in the Auckland field, some 270 metres (890 ft) in total length, 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 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.

Human context

TerracingonOneTreeHill
Terraces carved by Māori into the slopes of One Tree Hill

Usage

Many of the volcanic cones were occupied by substantial Māori (fortifications) before European 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 several of the remaining volcanoes are now preserved as landmarks and parks. The cones are also protected by a 1915 law, the Reserves and Other Lands Disposal and Public Bodies Empowering Act 1915, which 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.

Dangers

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. However, the effects of such an event—especially 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 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.

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 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 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.

In 2013, scientists said new studies showed Rangitoto had been much more active in the past than previously thought, suggesting it had been active on and off for around 1000 years before the final eruptions around 550 years ago. Civil Defence officials said the discovery did not make living in Auckland any more dangerous, but did change their view of how an evacuation might proceed.

List of volcanoes

The volcanoes within the field are:

Volcanoes Age (thousand years) Height Location (Coordinates) Refs Images
Albert Park Volcano 145 Unclear 36°51′03″S 174°46′03″E / 36.8507°S 174.7675°E / -36.8507; 174.7675
Ash Hill 30.5 30 metres (98 ft) 37°00′10″S 174°52′03″E / 37.002754°S 174.867545°E / -37.002754; 174.867545
Boggust Park Crater 130 5 metres (16 ft) 36°57′19″S 174°48′49″E / 36.955413°S 174.813552°E / -36.955413; 174.813552
Cemetery Crater Unknown 33 metres (108 ft) 36°59′23″S 174°50′28″E / 36.989828°S 174.841082°E / -36.989828; 174.841082
Crater Hill 30.5 36°59′12″S 174°49′38″E / 36.986546°S 174.827135°E / -36.986546; 174.827135
Grafton Volcano 100 36°51′30″S 174°45′49″E / 36.858440°S 174.763624°E / -36.858440; 174.763624
Hampton Park Unknown 35 metres (115 ft) 36°57′03″S 174°53′44″E / 36.950925°S 174.89544°E / -36.950925; 174.89544
Kohuora 30.5 36°58′43″S 174°50′34″E / 36.97873°S 174.842691°E / -36.97873; 174.842691
Mangere Lagoon 50 36°57′25″S 174°46′39″E / 36.95702°S 174.77763°E / -36.95702; 174.77763
Matanginui/Green Mount 20 78 metres (256 ft) 36°56′24″S 174°53′54″E / 36.939911°S 174.898267°E / -36.939911; 174.898267
Matukutureia/McLaughlins Mountain 50 73 metres (240 ft) 37°00′49″S 174°50′46″E / 37.013511°S 174.845974°E / -37.013511; 174.845974
Maungakiekie/One Tree Hill 60 182 metres (597 ft) 36°54′0″S 174°46′59″E / 36.90000°S 174.78306°E / -36.90000; 174.78306
One Tree Hill, Auckland
One Tree Hill and its obelisk
Maungarahiri/Little Rangitoto 24.5 75 metres (246 ft) 36°52′31″S 174°48′35″E / 36.875407°S 174.809636°E / -36.875407; 174.809636
Maungarei/Mount Wellington 10 135 metres (443 ft) 36°53′35″S 174°50′47.6″E / 36.89306°S 174.846556°E / -36.89306; 174.846556
Maungataketake/Elletts Mountain 90 76 metres (249 ft) 36°59′41″S 174°44′51″E / 36.994635°S 174.747548°E / -36.994635; 174.747548
Maungauika/North Head 90 50 metres (160 ft) 36°49′40″S 174°48′43″E / 36.827751°S 174.81205°E / -36.827751; 174.81205
Maungawhau/Mount Eden 28 196 metres (643 ft) 36°52′37″S 174°45′50″E / 36.877°S 174.764°E / -36.877; 174.764
Mount Eden Crater Hollow Auckland
Crater of Maungawhau / Mount Eden
Motukorea/Browns Island 24 68 metres (223 ft) 36°49′50″S 174°53′41″E / 36.8306°S 174.8948°E / -36.8306; 174.8948
Mount Robertson/Sturges Park 24 78 metres (256 ft) 36°56′55″S 174°50′30″E / 36.948477°S 174.841726°E / -36.948477; 174.841726
Ōhinerau / Mount Hobson 34 143 metres (469 ft) 36°52′40″S 174°47′10″E / 36.877814°S 174.786156°E / -36.877814; 174.786156
Ohuiarangi/Pigeon Mountain 24.5 55 metres (180 ft) 36°53′20″S 174°54′11″E / 36.888846°S 174.903116°E / -36.888846; 174.903116
Orakei Basin 120 Sea level 36°52′02″S 174°48′47″E / 36.867124°S 174.81308°E / -36.867124; 174.81308
Otahuhu/Mount Richmond 30 50 metres (160 ft) 36°55′57″S 174°50′22″E / 36.932562°S 174.839451°E / -36.932562; 174.839451
Ōtuataua 15 64 metres (210 ft) 36°59′10″S 174°45′15″E / 36.98611°S 174.75417°E / -36.98611; 174.75417
Ōwairaka / Mount Albert 120 135 metres (443 ft) 36°53′26″S 174°43′12″E / 36.890475°S 174.720097°E / -36.890475; 174.720097
Puhinui Craters 50 22 metres (72 ft) 37°00′53″S 174°49′59″E / 37.01465°S 174.83296°E / -37.01465; 174.83296
Pukaki Lagoon 65 Sea Level 36°58′59″S 174°48′37″E / 36.982998°S 174.810226°E / -36.982998; 174.810226
Pukeiti 15 30 metres (98 ft) 36°59′02″S 174°45′26″E / 36.983756°S 174.757183°E / -36.983756; 174.757183
Pukekawa/Auckland Domain 100 36°51′33″S 174°46′33″E / 36.859158°S 174.775808°E / -36.859158; 174.775808
Puketāpapa / Mount Roskill 105 110 metres (360 ft) 36°55′S 174°44′E / 36.917°S 174.733°E / -36.917; 174.733
Pukewairiki 130+ 30 metres (98 ft) 36°56′39″S 174°51′57″E / 36.944078°S 174.865887°E / -36.944078; 174.865887
Pupuke 190 −57 metres (−187 ft) 36°46′48″S 174°45′58″E / 36.780115°S 174.766184°E / -36.780115; 174.766184
Rangitoto Island 0.6 260 metres (850 ft) 36°47′12″S 174°51′36″E / 36.786742°S 174.860115°E / -36.786742; 174.860115
Rangitoto from Achilles Point
Rangitoto Island on the horizon
Rarotonga / Mount Smart 20 87 metres (285 ft) (quarried) 36°55′6″S 174°48′45″E / 36.91833°S 174.81250°E / -36.91833; 174.81250
Styaks Swamp 20 36°56′10″S 174°54′01″E / 36.936138°S 174.900155°E / -36.936138; 174.900155
Takaroro / Mount Cambria 40 30 metres (98 ft) (quarried) 36°49′28″S 174°48′07″E / 36.824444°S 174.801933°E / -36.824444; 174.801933
Takarunga / Mount Victoria 35 87 metres (285 ft) 36°49′36″S 174°47′56″E / 36.8266°S 174.7990°E / -36.8266; 174.7990
Taurere / Taylors Hill 30 56 metres (184 ft) 36°51′51″S 174°52′12″E / 36.864223°S 174.869943°E / -36.864223; 174.869943
Te Apunga-o-Tainui / McLennan Hills 41 45 metres (148 ft) (quarried) 36°55′45″S 174°50′47″E / 36.929208°S 174.846468°E / -36.929208; 174.846468
Te Hopua-a-Rangi / Gloucester Park 20+ Sea level (reclaimed) 36°55′46″S 174°47′05″E / 36.9295°S 174.784734°E / -36.9295; 174.784734
Te Kopua Kai-a-Hiku / Panmure Basin 25 Sea level 36°54′18″S 174°50′58″E / 36.90495°S 174.849343°E / -36.90495; 174.849343
Te Kopua-o-Matakamokamo / Tank Farm 180 36°48′07″S 174°45′12″E / 36.8020°S 174.7533°E / -36.8020; 174.7533
Onepoto 185 36°48′29″S 174°45′03″E / 36.80818°S 174.75085°E / -36.80818; 174.75085
Te Kōpuke / Mount Saint John 75 126 metres (413 ft) 36°53′00″S 174°46′49″E / 36.883431°S 174.780196°E / -36.883431; 174.780196
Te Motu-a-Hiaroa/Puketutu 30 65 metres (213 ft) 36°57′55″S 174°44′50″E / 36.965186°S 174.747248°E / -36.965186; 174.747248
Te Pane-o-Mataaho/Māngere Mountain 50 106 metres (348 ft) 36°56′59″S 174°46′59″E / 36.9496°S 174.7831°E / -36.9496; 174.7831
Te Pou Hawaiki 28 Quarried 36°52′57″S 174°46′00″E / 36.88247°S 174.766726°E / -36.88247; 174.766726
Te Puke ō Tara / Otara Hill Unknown 89 metres (292 ft) (quarried) 36°56′50″S 174°53′54″E / 36.947105°S 174.898363°E / -36.947105; 174.898363
Te Tātua-a-Riukiuta / Three Kings 28.5 133 metres (436 ft) 36°54′11″S 174°45′17″E / 36.902926°S 174.754651°E / -36.902926; 174.754651
Te Tauoma / Purchas Hill 10 50 metres (160 ft) (quarried) 36°53′14″S 174°50′51″E / 36.887138°S 174.847476°E / -36.887138; 174.847476
Waitomokia / Mt Gabriel 20.3 20 metres (66 ft) (quarried) 36°58′37″S 174°46′13″E / 36.976981°S 174.770336°E / -36.976981; 174.770336
Whakamuhu/Saint Heliers/Glover Park – see Achilles Point 160 Sea level 36°50′36″S 174°51′50″E / 36.843390°S 174.863800°E / -36.843390; 174.863800
Wiri Mountain / Matukutūruru 30 80 metres (260 ft) (quarried) 37°00′26″S 174°51′30″E / 37.007334°S 174.858441°E / -37.007334; 174.858441
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