Auckland volcanic field

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An 1859 German map of the field.
An 1859 German map of the field.

The Auckland volcanic field is a generally monogenetic volcanic field in the North Island of New Zealand. Basaltic in nature, it underlies much of the metropolitan area of Auckland. The field's many vents have produced a diverse array of explosion craters, scoria cones, and lava flows. Currently dormant, the field is likely to erupt again within the next "hundreds to thousands of years" (based on past events), a very short timeframe in geologic terms.[1]

Contents

[edit] Features

[edit] Volcanoes

The first vents erupted at the Domain, Albert Park and St Heliers between 60,000 and 140,000 years ago. Since then approximately 50 vents have erupted. Each eruptive vent has generally only had a geologically short period of activity. One exception is Panmure Basin, where drilling has discovered a younger scoria cone buried under sediment within the larger and much older crater.[2]

The most recent eruption (about 600 years ago[3] and within historical memory of the local Māori iwis) was of Rangitoto, an island shield volcano just east of the city, erupting 2.3 cubic kilometres of lava. The eruptions have tended to become bigger over time, with Rangitoto making up almost 60% of the field's entire volume of erupted material. All of the volcanoes are relatively small, most being less than 150 meters in height.

[edit] Lava flows

The field has produced voluminous lava flows, which cover much of the Auckland isthmus. One of the longest runs from Three Kings northward, almost crossing the Waitemata Harbour to form Meola Reef. More than 50 lava tubes and other lava caves have been discovered, including the 290 metre long Wiri Lava Cave.[4]

[edit] Human context

[edit] Usage

Several of the volcanic cones were occupied by substantial Māori pa 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.[3] 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.[5]

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.[3] At that time, only 2% of more than 800 World Heritage Sites worldwide were in this "mixed" category.

[edit] Dangers

Since the field is not extinct, new volcanic events may occur at any time, though the usual period between events averages between hundreds and thousands of years. However, the effects of such an event, especially a full-scale eruption, would be substantial - ranging from earthquakes,[6] lava bombs, ash falls, venting volcanic gas to lava flows. These effects might continue for several months and cause substantial destruction and disruption. These might range from burial of substantial tracts of residential or commercial property to 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 International Airport.[1]

Various operative structures, plans and systems have been set up to prepare responses to renewed 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 defense and emergency services during an eruption. Auckland also has a Seismic Monitoring Network comprising six seismometers (including one 250 m deep at Riverhead) and three repeaters within the Auckland Region) that will pick up the small tremors likely preceding any such volcanic activity.[7] These tremors are likely to give some hours to some days of warning about an impending eruption and its approximate location.[6]

[edit] List of volcanoes

Mount Eden's crater.
Mount Eden's crater.

The volcanoes within the field include:

One Tree Hill with its obelisk.
One Tree Hill with its obelisk.
Rangitoto Island on the horizon.
Rangitoto Island on the horizon.

[edit] See also

[edit] References

  1. ^ a b Beca Carter Hollings & Ferner (2002). Contingency Plan for the Auckland Volcanic Field, Auckland Regional Council Technical Publication 165. Accessed 2008-05-12.
  2. ^ New Auckland volcano discovered - NZPA via The New Zealand Herald, 22 February 2008. Accessed 22 February 2008.
  3. ^ a b c Auckland Volcanic Fields submission (from the UNESCO World Heritage Centre, 2007-03-30. Accessed 2007-05-04)
  4. ^ Cave New World - David Lomas, Heritage New Zealand, Winter 2006. Accessed 2007-05-04.
  5. ^ "The volcanic hills are being destroyed..." - City of Fire, insert magazine in the The New Zealand Herald, Friday 15 February 2008
  6. ^ a b When the earth starts to shake - City of Fire, insert magazine in the The New Zealand Herald, Friday 15 February 2008
  7. ^ NZPA, New recorder boosts earthquake, volcano warnings, The New Zealand Herald, 2008-05-11. Accessed 2008-05-12.
  8. ^ History, Mt Hobson Remuwera management plan, Auckland City Council, 13 December 2000. ISBN 0908834500.

[edit] External links