Fiords

New Zealand's fiords are found along the southwest coast of the South Island. They give their name to the region and also our largest national park, Fiordland National Park. Fiords are not simply a water feature or a land feature but are a special combination of both, where the sea partly fills steep-sided valleys once excavated by glaciers. Fiords are a majestic reminder of the powerful forces that sculpted our land around 20,000 years ago.

Fiord information

North Fiord, Lake Te Anau, Fiordland
National Park

Glaciers in Fiordland flowed out to meet the sea during the ice ages. Like all 'fast- flowing' mountain glaciers, as they ground their way downwards they excavated their valleys into steep-sided U-shapes. The ice was so thick that the bases of the larger glaciers were generally below the sea level in their lower reaches. After the climate had warmed again and the glaciers had retreated inland, the glacial valleys were flooded by a combination of meltwater and the rising sea. Today the fiords in Fiordland have a water depth of up to 440 m.

At the entrance to a fiord from the ocean, the water depth is typically about 100 m which is much shallower than further inside the fiord. This is caused during glaciation by two things; the base of the glacier rising towards the sea-level of the time, and the dumping of moraine (boulders and gravels carried within the ice) in front of the glacial snout.

The rocks of Fiordland are different from those of the Southern Alps further north, playing an important role in why we have fiords there today. Fiordland rocks are mainly diorite, granite, granulite and gneiss, all coarsely crystalline rocks formed at high temperatures deep in the Earth's crust. They are particularly hard and strong, so there has been little erosion or collapse of the valley walls since the ice melted. The low erosion rate means a relatively small amount of gravel and debris has flowed into the fiords, so they haven't filled in and still exist. In contrast, other great glacial valleys further north were formed in weaker rocks. Some of these valleys would originally have been fiords but they were rapidly filled in with erosion debris after the main glacier retreat occurred about 15,000 years ago.

Wet Jacket Arm, Dusky Sound,
Fiordland National Park

Sounds vs fiords

Most of the fiords in New Zealand are named as 'sounds', for example Milford Sound, Doubtful Sound and Dusky Sound. 'Sound' is a general, non-technical term which is used in various ways in different parts of the world for more-or-less narrow branches of the sea. In the case of the Marlborough Sounds at the other end of the South Island, it refers to seaflooded river valleys. 'Fiord' is a more specific term for very steep-sided glacial valleys now occupied by the sea, as in the Norwegian 'fjords'.

Characteristics of fiords

Hanging valleys are common in fiords. These are valleys perched high above a larger valley or the fiord itself, formed during glaciation by a larger glacier 'cutting off' the end of smaller glaciers where they met. Since the larger glacier had much deeper ice, the two valley floors were formed at dramatically different heights. Once the ice had retreated, the smaller valley is left higher and ends abruptly in steep cliffs where it once met the edge of the bigger, deeper glacier. Waterfalls are common at the end of hanging valleys as streams which now occupy them plunge over the steep cliffs where they meet the main valley.

Scratches and gouge marks made by boulders embedded in the last glacier ice about 15 000 years ago are still visible today on the steep rock walls of the fiords. When out on the water in a fiord you can appreciate the scale of the glaciation as some of these marks and glacier smoothing of the walls are many hundreds of metres above you while the base of the fiord is many hundreds of metres below you underwater.

First visitors to the fiords

In Māori legend, the fiords were excavated not by glaciers, but by Tu Te Raki Whanoa, a godly figure who possessed a magical adze and who uttered special karakia (incantations).

Early Māori visited these fiords in search of food and greenstone, but only a few stayed for more than several weeks at a time. European navigators, including Captain Cook, entered some of the fiords in the eighteenth century, and were followed by sealers, then whalers and gold miners.

New Zealand's fiords are home to a wide variety of plants and animals, including much-loved creatures such as bottlenose dolphins/aihe, New Zealand fur seals/kekeno, Fiordland crested penguins/tawaki and little blue penguins/kororā.

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Life underwater

Black coral and butterfly perch

The environment below the water in Fiordland is as unique as its acclaimed landscape above. Beneath the water, the mountains continue to plunge down as steep rock walls until they reach the flat floor of the fiords, which are covered in mud. Runoff from rainfall on the mountains creates a freshwater layer on the surface of the saltwater. This can range from small areas in front of river mouths when rivers are low, to a sheet several metres thick extending most of the way to the ocean after heavy rainfall, which is indeed much of the time.

This freshwater layer is stained a brown colour because of chemicals called tannins that are washed out of the vegetation on land. (Tannins are the same chemicals that create tea's brown colour.) This dark layer on the surface of the fiords limits the amount of light penetrating to depth, restricting most of the marine life to the top 40 m. This calm and relatively warm band is home to a wide diversity of sponges, corals and fish that are usually found in a variety of habitats from sub-tropical to cool and deep water environments.

One of the most distinctive species located in New Zealand's fiords is black coral, which is usually found in low-light conditions at very great depths elsewhere in the oceans but grows relatively close to the surface here. Fiordland has one of the world's largest populations of black coral trees (about 7 million colonies), with some of them up to 200 years old. Another special group of creatures found in the fiords are the brachiopods, clam-like animals that are sometimes called 'living fossils', as they have remained relatively unchanged for over 300 million years.

Mudflats, Milford Sound, Fiordland
National Park

Although the fiords extend to depths of over 400 m, life peters out quickly below the top 40-m band of water. For this reason and because of the general steepness of the fiord walls, the area of suitable habitat for most creatures is much smaller than might be expected relative to the total fiord areas. This small habitat area combined with the fact that many of the marine species found here only grow a few centimetres each year makes Fiordland's marine populations vulnerable to over-exploitation and damage.

Threats

New Zealand's fiords face a number of threats that may damage the unique biodiversity found there. These include:

• Invasion of unwanted marine organisms introduced from vessel hulls, ballast water or equipment.
• Pollution including oil spills and the disposal of sewage and rubbish into the Fiordland marine environment.
• Physical damage including the impacts of structures, such as wharves and moorings, and landslips. Landslips are a natural event, but the number and frequency of slips can be accelerated by the loss of vegetation due to possum and deer browse.
• Increased amounts and extent of freshwater due to the input of freshwater from the Manapouri power scheme into Doubtful Sound.

How can you help?

Please help protect New Zealand's fiord habitats by disposing of any rubbish or waste properly, by cleaning any watercraft carefully before entering the fiords, and by observing fishing limits and restrictions.

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