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New map rich in history as well as latest techonology - 16/05/2002

A new geological map of the Auckland area shows the region in more detail than ever before.

New map of Auckland area

It updates existing geological maps of the area, published in the 1960s, and combines a vast amount of published and unpublished material, plus new research, to produce a valuable resource about Auckland's geology.

Geology of the Auckland Area covers 11,800sqkm of the greater Auckland region, including southern Northland, northern Waikato, and the Coromandel Peninsula. Also covered is the Hauraki Gulf, including Great Barrier Island.

At the southern end of the map are Huntly and Te Aroha and at the northern boundary is Wellsford.

It is the latest of a new series of geological maps covering the whole of New Zealand, published by the GNS Science Limited (GNS). Started in 1996, the series of 21 maps is scheduled for completion in 2008.

It takes the form of a 74-page well-illustrated book with a full colour folded map at 1: 250,000 scale tucked into a sleeve in the back cover. Illustrations in the book, which include many photos taken by one of New Zealand's leading landscape photographers Lloyd Homer, are accompanied by explanations that are mostly in plain language.

The map text summarises the geology and tectonic development of the Auckland region, and highlights aspects of economic geology and potential geological hazards.

Seven pages are devoted to a wide range of geological resources in the Auckland region including ironsand deposits on the west coast, and metallic mineral deposits mainly in the Coromandel Peninsula.

It details extensive non-metallic resources, such as coal and peat deposits, in the Waikato and Hauraki Plains respectively. Also covered are groundwater, cold water springs, and hot water.

The map lists commodities currently being extracted as sand, rock and gravel aggregate, limestone, coal, ironsand, gold, silver, and groundwater.

It also reminds us that manganese and copper were mined at Kawau Island between 1845 and 1869.

Kauri gum was also a major export earner for the Auckland region between 1850 and 1900 with more than 400,000 tons shipped overseas.

The map was compiled by GNS geologist Steve Edbrooke, who specialises in the geology of the Auckland and Waikato regions.

Onshore exploration for hydrocarbons has been unsuccessful to date, but the offshore sedimentary basin west of Auckland is rated as prospective. It is part of a continuous offshore basin that extends between Taranaki and Northland.

The map shows extinct seafloor volcanoes off Auckland's west coast, plus many geological faults beneath the continental shelf west of Auckland.

Volcanic risk within the Auckland urban area is high because of the concentration of population, buildings, transport and communications systems, and economic activity, together with the uncertainty of predicting the time and location of the next eruption in the still-active Auckland volcanic field.The highest hazard zone will be within 4km of anyfuture eruption centre. However, ashfall could affect areas up to 30km from the eruption centre.

Volcanoes started to appear in Auckland about 140,000 years ago - the Domain and Lake Pupuke being among the first. Rangitoto is the biggest and most recent; it formed about 600 years ago.

Geologists estimate the Auckland field has a life of about 1 million years, so geologically speaking, it is still young. There has been a trend to bigger and more frequent eruptions in the Auckland area during the past 20,000 years.

" The next eruption is unlikely to occur at an existing volcano. The Auckland field tends to produce single-episode eruptions with each event at a new location, " Mr Edbrooke said.

Earthquake hazard in Auckland is one of the lowest in New Zealand, but Aucklanders occasionally feel shaking from distant earthquakes. The Wairoa Fault in the Hunua Ranges and the Kerepehi Fault which runs through the centre of the Hauraki Plains are the only known active faults in the area covered by the map. Scores of inactive faults are also shown.

The Drury Fault, which runs between Ardmore and Pokeno, may have potential for future activity, Mr Edbrooke says.

" It has the appearance of an active fault, but more work is needed to confirm its status."

The improved understanding of the origin of a large volume of displaced rocks in southern Northland has allowed them to be mapped with greater certainty.

" We now know that these rocks were originally deposited northeast of Northland and were brought to their present location by tectonic forces."

The map also gives a more consistent and more complete picture of the geology of Coromandel Peninsula. Previously the area east of Thames had not been adequately mapped.

Mr Edbrooke said city, district and regional councils had already made use of the digital data from which the map was produced. Others expected to benefit from the map database include planners, engineers, developers, scientists, mining companies, and oil exploration companies. People with an interest in geology and Auckland's history would also find it useful.

The map is available from the GNS Science Limited for $25.

Contact: Steve Edbrooke,
Geologist,
GNS,
Ph: 04-570-1444