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New geological map of Taranaki-Central North Island - 06/07/2009

A new geological map covering the Taranaki and Central North Island area has been completed by a team of geologists following six years of fieldwork.

Area covered by new Taranaki map

Area covered by new Taranaki 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map replaces existing geological maps of the area, published in the 1960s, and combines a vast amount of published and unpublished material, plus new research, to produce a valuable resource about Taranaki geology.

The large full-colour 1:250,000-scale map is tucked into a sleeve in the back cover of a 77-page companion book. It includes some stunning colour diagrams and landscape photographs.

Geology of the Taranaki Area covers 15,000sqkm of western and central North Island, from Mt Taranaki/Egmont and New Plymouth on the west coast to National Park on the slopes of Mt Ruapehu, and south to Feilding.

The map also extends offshore to include part of the Taranaki petroleum industry area.

It is the latest of 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 QMAP Taranaki being the 15th to be completed. QMAP stands for quarter-million scale map.

The map text summarises the geology and tectonic development of the Taranaki region, including the dormant and recently active andesite volcanoes on the Taranaki Peninsula and in the Central North Island.

The volcanic centres are separated by a largely unpopulated area between Stratford and Ohakune that is underlain by Miocene (5 to 20 million years) and younger mudstone sedimentary rocks. The mudstone papa rocks record a history of changing coastlines and basins in the area over the last 15 million years.

The most significant advances arising from this recent mapping is the recognition of several new active faults on the Taranaki Peninsula and also distinguishing the many young debris deposits (lahars) surrounding Mts Taranaki and Ruapehu. Many of these volcanic gravel deposits are quarried as a source of aggregate – one of the region’s most important economic resources.

The map compilers have also recognised the effects of past glaciation of the Central North Island volcanoes. Gravel deposits mapped on Mt Ruapehu result from glacial advances and retreats. Mt Taranaki, however, is considered too young to have supported any significant glaciers.

Perhaps the most salient geological hazard for the area is volcanic eruption. The likelihood of lava flows reaching major population centres is low, but ash fall that would accompany any future eruptions of either Taranaki or Ruapehu volcanoes is a significant hazard.

Debris flows (lahars) may also accompany eruptions and these could inundate low-lying areas. Extremely large landslides, such as when a portion of the volcanic edifice collapses, are also a possibility and may occur with only limited warning.

Relative to other parts of New Zealand, the Taranaki region has had a moderate level of earthquake activity since records began. However, shaking from both local and distant earthquakes has been recorded.

Many faults are shown as “active”, meaning that movement has occurred along them in the recent geological past. These faults are considered to have potential to rupture again in the future. Other geological hazards are landslides (particularly in the mudstone hill country), tsunami, erosion, flooding and sedimentation.

The six year government-funded project involved many geologists and field assistants, and support from many organisations. The map and text are a collaborative effort between the University of Waikato and GNS Science. We would particularly like to pay tribute to 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 Taranaki region would also find the map useful.

The map and text is available from GNS Science for $30