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New map of East Cape a mine of information - 01/11/2001

A new geological map of the East Coast, compiled by geologists Colin Mazengarb and Ian Speden, shows the region in more detail than ever before.

Geology of the Raukumara Area

Geology of the Raukumara Area

It updates the last geological maps of the area, published in the mid-sixties, and draws on a vast amount of published and unpublished material, plus new research, to produce a detailed and comprehensive summary of the geology of the area.

Geology of the Raukumara Area covers 11,700sqkm of the East Coast from Wairoa in the south to Opotiki.It is the latest of a new series of geological maps of New Zealand published by the GNS Science Limited (GNS). The series of 21 maps was started in 1996 and is scheduled for completion in 2008.

It takes the form of a 52-page well-illustrated book with a large folded map tucked into a sleeve in the back cover. The illustrations, which include stunning colour aerial photographs taken by one of New Zealand's leading landscape photographers Lloyd Homer, are accompanied by simple explanations that can be understood by a non-technical audience.

The map is a synthesis of a large database, held by GNS, containing many layers of digital information that can be combined with other databases or customised to produce a wide range of derivative products at various scales.

" The Gisborne District Council recently used the database to evaluate potential landfill sites, and in the preparation of a general hazard assessment of the entire district," map compiler Colin Mazengarb of GNS said.

" The map and digital database will be an invaluable tool for engineers and land use planners, for those involved in managing natural hazards including erosion, for oil and gas exploration companies, and for scientific research," Gisborne-born Mr Mazengarb said.

The geology of the East Coast is some of the most complex in New Zealand and Mr Mazengarb said he had enjoyed the challenge of presenting it coherently and accurately.

For Ian Speden, a retired director of the predecessor organisation of GNS - the New Zealand Geological Survey - the project enabled him to publish a vast amount of fieldwork he had collected over a number of summers mainly during the 1970's. This work significantly improves the knowledge of a very complex area north of Te Puia.

The map is a milestone in that it is the first time that such a wide range of up-to-date information on the East Coast has been brought together in one volume, Mr Mazengarb said.

During the six-year mapping and research project that has given rise to the publication he has identified some new geological structures that have potential to hold reservoirs of oil and gas. However, further investigations would be needed to determine if hydrocarbons were present in any quantity.

The East Coast features New Zealand's highest concentration of oil and gas seeps - where gas, and in some cases oil, appear naturally at the surface. The seeps, which inspired the first search for oil and gas in the region over a century ago, have been recorded systematically in the map.

Also recorded are landslides, the biggest of which covers 18sqkm and rates as one of the biggest in New Zealand.

While most large landslides are dormant, given the right conditions, they have the potential to fail suddenly causing environmental damage and economic loss.

A number of newly discovered active faults are also shown in the map. However, nearly all of these are in rural areas and pose little risk to populated areas.

As well as in-depth coverage of geological and tectonic history, the map text includes sections on engineering geology and geological hazards, plus information on hot springs, groundwater, quarried aggregate and limestone, metallic minerals, and offshore geology and bathymetry (the shape of the seafloor). Identified under the latter aresubmarine canyons and large slope failures.

The map does not detail soil types, but focuses on the main underlying rock types. It is available from GNS at $25.