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New map of Christchurch, Canterbury Plains and Chatham Islands - 06/07/2009

A new geological map covering the Christchurch City, Canterbury Plains and the Chatham Islands has been completed by a team of geologists following six years of fieldwork.

Christchurch map coverage

Area covered by new Christchurch map

The map, which shows the region’s geology in more detail than before, has been generated from a computer database using Geographic Information Systems (GIS) technology, which means it can be updated regularly as new information comes to hand.

The map complements existing geological maps of the area, and combines a vast amount of published and unpublished material, plus new research. The large full-colour 1:250,000-scale map is tucked into a sleeve in the back cover of a 67-page companion book, which contains many colour diagrams and landscape photographs.

Geology of the Christchurch Area covers almost 10,000 square kilometres of Canterbury and the Chatham Islands. It extends from Amberley in the north to the Rakaia River in the south and west to Porters Pass.

It is the latest in a series of geological maps covering the whole of New Zealand, published by GNS Science. Started in 1996, the series of 21 maps is scheduled for completion in 2010, with Christchurch being the 16th to be completed. The map series is called QMAP, which stands for “quarter-million scale map”.

The map text summarises the geology and tectonic development of the Christchurch region, including the “greywacke” ranges, the alluvial Canterbury Plains, and the ancient volcanoes of Banks Peninsula and the Chatham Islands.

The most significant advance on this map is the depiction of active faults and folds (where movement has occurred in the recent geological past) beneath the gravels of the Canterbury Plains.

Avon River

Active faults and folds offshore from North Canterbury are also shown. Cross-sections show subsurface interpretations to a depth of 5km, including information from oil exploration drillholes that have been completed over the years.

Arguably the main geological hazard for the Canterbury area is earthquake shaking, from the major Alpine Fault (west of the map area) and from local faults. Tsunami have also affected coastal areas of Canterbury and the Chatham Islands, and in particular the harbours of Banks Peninsula, in historic times. Slope instability is widespread in hill areas, including the loess deposits of Banks Peninsula and the soft rocks of North Canterbury.

The main geological resources are aggregate, limestone, clay and coal, with the potential for oil and gas discoveries in some areas. Groundwater resources beneath the Canterbury Plains are substantial, but are vulnerable to contamination.

The six year government-funded project involved several geologists and field assistants. The co-authors, Jane Forsyth, David Barrell and Richard Jongens, acknowledge support from many organisations, particularly Canterbury and Lincoln universities, and NIWA. They would also like to thank the many landowners and Department of Conservation, who allowed land access.

Digital data from which the map was produced is already being used extensively in a number of applied and scientific projects. End users expected to benefit include regional councils, engineers, developers, scientists, and mineral and petroleum exploration companies. People with an interest in geology and in the Christchurch region would also find the map useful.

The map and text is available from GNS Science for $35 at 08/05/2012.