New Geological Map of Fiordland Decade in Making

Much of Fiordland geology consists of hard igneous rocks, many of which have been deformed by tectonic forces. Here, GNS Science geologists Drs Ian Turnbull and Richard Jongens climb a cliff face on the outer Fiordland coastline south of Bligh Sound to examine deformed igneous rocks. The steeply dipping rock layers show the tilting effect of tectonic forces over millions of years.

MEDIA RELEASE from GNS Science
27 MAY 2010
New Geological Map of Fiordland a Decade in the Making

Seven summers of fieldwork in remote parts of Fiordland by a group of geologists culminated this week with the publishing of a new geological map covering this World Heritage area.

The geologists spent 370 days in the field clambering over difficult terrain - often for weeks at a time - mapping, sampling and recording information on rock types and other geological features.

Publication of the Fiordland geological map by GNS Science marks the end of one of the most demanding projects in the organisation’s national mapping programme – called QMAP (Quarter-million scale map).

The QMAP series of geological maps covers the whole of New Zealand and started in 1994. The series of 21 maps is scheduled for completion later this year, with QMAP Fiordland being the 18th to be published.

The new map, which shows Fiordland’s geology in more detail than ever before, has been generated from a computer database using Geographic Information Systems (GIS) technology. This 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. It combines published and unpublished material, including several PhD thesis studies from Otago University, with a great deal of new research, to produce a comprehensive compilation of the geology of this rugged and remote area.

The large full-colour 1:250,000-scale map is tucked into a sleeve in the back cover of a 97-page companion book. It includes stunning colour photographs of Fiordland landscapes by Lloyd Homer, illustrations of the great variety of Fiordland rocks, and numerous diagrams summarising aspects of the geology.

Geology of the Fiordland Area covers about 12,000 square kilometres of Fiordland. This includes the whole of the Fiordland massif, from Milford Sound to Puysegur Point and Foveaux Strait in the far southwest. It includes lakes Te Anau, Manapouri, and Monowai in the east, and Hump Ridge in Western Southland. The map also extends offshore to include the steep submarine slopes west of Fiordland beneath the Tasman Sea.

The region contains New Zealand’s oldest known plutonic (igneous) rocks, and large areas of metamorphosed sedimentary rocks closely related to the rocks of Northwest Nelson.

Much of the region is underlain by granite and diorite. The strength of these rocks has been a factor in the formation of the steep and high landscape. Multiple glaciations have worn away softer rock. Fiordland also has New Zealand’s southernmost dormant volcano, at Solander Island.

Geologists made several advances in geological knowledge during this mapping project. They discovered previously unknown rock formations and tested theories about economic minerals.

The sedimentary rocks of eastern and southern Fiordland show promising signs of hydrocarbons, with the greatest potential being in Foveaux Strait. In contrast, the new work has confirmed only traces of economic minerals in Fiordland

A summary map shows the landslide deposits of Fiordland, and highlights the extreme landslide hazard in the region. It also shows one of the world’s largest landslides at Green Lake.

This 13,000-year-old landslide occurred when 27 cubic kilometres of a mountain range collapsed into the valley below and covered an area of 45 square kilometres in rubble.

The map compilers have also recognised the effects of past earthquakes, preserved in uplifted terraces and beach deposits around the southern and western coastlines.

The surface effects of several major earthquakes which occurred during the compilation of the map have been included, making it very up-to-date.

Earthquakes are the most salient geological hazard in the area, which lies above a zone where the Australian tectonic plate is sinking beneath Fiordland.

Movement on the plate boundary – the southern end of the Alpine Fault – will cause major earthquakes in the future.

In spite of this, geologists have not found many “active” faults in Fiordland. The few that are present mostly lie along the eastern margin near Manapouri and Monowai. These active faults are considered to have potential to rupture again in the future.

The seven-year government-funded project involved several GNS Science geologists and numerous field assistants. The GNS Science team acknowledges input from numerous staff and students at Otago, Canterbury, Sydney and Macquarie universities.

The map compilers would particularly like to thank the Department of Conservation, which allowed access to the whole of Fiordland National Park, including restricted areas such as the Murchison Mountains. The team also wishes to thank the helicopter and boat crews, who transported them to many remote locations around Fiordland.

Digital data from which the map was produced are already being used extensively in a number of applied and scientific projects. End users expected to benefit include DoC, regional councils, engineers, earth scientists, and petroleum exploration companies. People with an interest in geology and in Fiordland in general will also find the map and text useful and informative

The map and text are available from GNS Science (sales@gns.cri.nz) for $30.

ENDS

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