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Fiordland, the beauty of the mountains

The Fiordland is one of the most magical places in New Zealand. It is also known for its grandiose geology between fiords and mountains. In this article, we will explain  the mountains formation. Its geology is very different from the rest of the South Island. It is also known for its many lakes as Lake Marian. Indeed, as mentioned in a previous article, the formation of the Southern Alps is the result of the collision between the Australian-Indian plate and the Pacific plate.

Here it is a subduction which has led to Fiordland mountains formation.



Sunset at Fiordland


For all definitions: go to this page.
For the time scale is here!



Fiordland mountains formation


Before 20 million years

400 million years ago (Devonian), New Zealand was in the bottom of the sea. The sediments has accumulated for millions of years, deposited one on the other.

Subsequently, about 300-200 million years ago (Permian-Triassic), the collision between the Australian-Indian and the Pacific plate led to first mountains formation in the South Island.



collision plaques
Collision between the Australia plate (at left) and Pacific plate (at right). The collision has resulted South Alps formation.


Around 30 million years (Paleogene), the mountains are back in the ocean following a descent of the earth’s crust.

After 20 million years


Geology diverges for Fiordland from the rest of New Zealand 20 million years ago. The Australian-Indian plate will subdue under the pacific plate.


subduction fiordland
Subduction in the Fiordland. The Australo-Indian plate passes under the pacific plate. By Oxford Academic – Oxford University Press


That means we have a plate that goes under another plate when they join together. This is the same mechanism that can be found in the North Island, which I refer to for more information on subduction. However, if in the north it is the pacific plate that subducts (passes below) the Australian-Indian plate. In the Fiordland we have the opposite! The subdued Australian-Indian plate under the pacific plate in the area called Puysegu Trench.


Puysegu Trench
Puysegu Trench, trench where is the subduction. by

During this subduction, many rocks rise to the surface from the depth. These characteristic rocks of the earth’s crust will appear in the Fiordland mountains.


The rocks of Fiordland


Plutonic rocks


It is possible to see many volcanic rocks (basalt, diorite, granite, etc.). These volcanic rocks originate from an ancient continent called Zealandia.



Zealandia at bottom of the ocean. In red, green and yellow it’s New-Zealand


These rocks are plutonic rocks directly from the depths of the Earth. Plutonic rocks form by slow cooling of a deep magma. The slower the cooling (typically several tens of thousands of years), the larger large crystals formation(at least visible to the naked eye).


Diorite in Fiorland at Homer tunnel

Metamorphic rocks


It is also possible to see other rocks, metamorphic rocks. A metamorphic rock is a rock whose formation originates in transformation to a sedimentary, magmatic or other metamorphic rock. It is the changes in the pressure and temperature parameters that craft rocks. In the Fiordland mountains, most of the metamorphic rocks present are gneiss.

gneiss fiordland
Gneiss from Fiordland. By Departement of Conservation

Like plutonic magmatic rocks, these rocks are found in the Fiordlands mountains following their extraction from the depths of the Earth.



The greenstone, translated in French by “jade” and in Māori by “pounamu”, is a gem. It is a crystal formed by a pressure and temperature given to the Earth. In Māori culture there are many traditions and is much used as jewelry, ceremonial object, etc …


jade greenstone
Greenstone. By culture et tradition du monde


For all definitions: go to this page.
For the time scale is here!



Road in Fiordland



Joceyn Thrnton, « The field guide to New Zealand Geology, An introduction to rocks, minerals and fossils»;   Pinguin Books

Hamish Campbell & Gerard Hutching; « In search of ancient New-Zealand »; Pinguins books

Geoffrey E. Batt and Jean Braun, «The tectonic evolution of the Southern Alps, New Zealand: insights from fully thermally coupled dynamical modelling», Geophysical Journal International, 1998

J.Davey and Euan G. C. Smith, «The tectonic setting of the Fiordland region, south-west New Zealand», Geophysical Journal International, 1982

Peter Blattner (1978) Geology of the crystalline basement between Milford Sound and the Hollyford Valley, New Zealand, New Zealand Journal of Geology and Geophysics, 21:1, 33-47, DOI: 10.1080/00288306.1978.10420720

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