New Zealand Glacial Landscapes

What is a glacier?

A glacier is simply a large body of ice which is moving slowly downhill.   Glaciers form at high elevation where the volume of winter snow is greater than that lost by melting in summer.  When delicate snow flakes settle across the névé (accumulation basin) at the head of a glacier, they partially melt to form whitish granular snow called firn.  Over several years, as water seeps in and air is expelled under the weight of accumulating snow, the granules merge to form bluish glacial ice.  Under the pull of gravity the ice mass flows down-valley as though it were a stiff liquid, eventually melting in the warmer temperatures at lower elevation.  

Why are there glaciers on a South Pacific Island?

Above the Franz Joseph and Fox Glaciers stands a chain of spectacular peaks over 3,000m high including New Zealand’s highest peak, Aoraki/Mt. Cook (3754m).  This region, the highest part of the Southern Alps/Kā Tiritiri o te Moana, lies in the path of westerly airstreams which sweep in persistently from the Tasman Sea.  As moisture-laden winds and frequent storms climb the mountains, the air cools rapidly causing heavy rain and snowfalls.  Annual precipitation at the coast is a dramatic 3.2 metres but this rises to to an amazing 15 metres high on the slopes above.  The huge volumes of snow dumped on the upper slopes feed the 140 glaciers in Westland/Tai Poutini National Park.  The Franz Joseph and Fox glaciers are by far the largest, containing two thirds of of the glacial ice in the Park.

Why is there ice in a temperate rainforest?

Of the many glaciers along the Main Divide, only the Franz Joseph and Fox penetrate the lower forest zones.  This phenomenon is caused by their unique topographic setting, where an exceptionally broad, high block of land feeds huge amounts of ice and snow into two long, narrow valleys.  The vast mass of snow fed into these glaciers must be balanced by a large zone of melting down-valley.  To achieve this, the narrow tongue  of each glacier descends to an unusually low altitude bringing glacial ice down into the rainforest zone.

Panoramic tour of New Zealand Glacial Landscapes: Fox Glacier

 

 

Climate change and the history of advance and retreat

The Earth’s climate is constantly changing, temperatures varying from warmer than present to 4-6°C cooler during the Ice Ages.  The latest period of global warming began at the end of the last century and, in response, glaciers have been retreating.  The Franz Joseph and Fox Glaciers are unusually sensitive to climate changes because their large catchments feed into narrow valleys, and a change in snow accumulation produces dramatic changes at the terminus.  This is why the overall retreat of these glaciers this century has been punctuated by minor advances at about 20-year intervals.  The latest advance of the 80’s and 90’s is the most spectacular and comes after increased snowfalls on the Southern Alps.  In contrast the less responsive Tasman glacier in Mount Cook National Park has only thickened slightly in the trunk.

Maori Heritage

Māori understanding of the alpine world was based on the great creation myths of the waka of Aoraki and Tū Rakiwhānoa.  The deep significance of the great peaks, snowfields and glaciers of Te Waipounamu (the South Island) are preserved in the language.  The Māori names of the glaciers, Kā Roimata o Hine Hukatere (Franz Joseph Glacier) and Te Moeka o Tuawe (Fox  Glacier), are derived from a tūpana (ancestor) Tū Awe who fell to his death while exploring the area.  The bed of Te Moeka o Tuawe became his moeka (final resting place).  It is said that when his lover Hine Hukatere wept, the bed of the glaciers filled with her everlasting tears of ice.  The story enabled generations of Māori to commit to memory the unique landforms of the area.

Milford Sound

From [Tutoko Valley] towards Milford  the scenery opens up dramatically and the sharp Mitre Peak comes into view.  The sea fills a glacial valley more than 300m deep that ends towards the open ocean with an underwater terminal moraine reaching within 100m of the surface.  Other, smaller glacial valleys join from the sides; one of them contributes the mighty Bowen Falls, which at first are not visible, but can be reached easily on foot from the Milford Village.  The Milford Track ends at Sandfly point, across the head of the fjord, and trampers reach the village by foot.

Milford is a small commercial fishing centre, with the fishing port now located out of sight from the Milford foreshore.  The crayfish colonies of the reefs on the open coastline are a main target and require early morning work to make use of the calm water.  Around 10 o’clock a sea breeze tends to rise which can become very strong toward evening.  The fjord itself is rich with underwater life; blue and red cod, tarahiki and sea perch abound.  Because of the heavy rainfall -over six metres (240 inches) a year- a layer of fresh water covers the fjord surface to a depth  about 3m.  This prevents the growth of seaweeds and algae.  The fresh water also carries minute particles of vegetation from the forest which reduce the amount of sunlight reaching below.  Only a few years ago it was discovered that, because of the reduced light, normally deep-water fauna can exist here at much shallower depths.  Thus, 5 to 20m below the surface black coral trees, tube anemones, sea pens and brachiopods can be found living on the steeps fjord sides.  At sea level, crested penguins and fur seals are frequently seen.  On the Milford foreshore small tidal mudflats may seem unattractive at times, but are fully part of the natural environment.

Milford has been famous for its native birdlife and its early morning “bellbird chorus.”  However, since the arrival of man the bush has been invaded by rats and stoats, which have diminished native bird numbers and eradicated some of the flightless birds such as the kakapo parrot which until recently survived among the steep cliffs of Mitre Peak.  Man himself hunted the Moa to extinction.  Deer have damaged the forest extensively, but have been much reduced in number by helicopter hunting over the last 20 years.  Within the National Park, Wilderness Areas have been set aside for special protection.

Panoramic tour of New Zealand Glacial Landscapes: Hollyford River and Milford Sound

Text from The Franz Joseph and Fox Glaciers (Kā Roimata o Hine Hukatere and Te Moeka o Tuawe) from the Institute of Geological and Nuclear Sciences and  A Guide to Milford Sound New Zealand from the New Zealand 1989 Geological Survey