The Southern Alps run 500 km north to south and are called Kā Tiritiri o te Moana in Māori. The tallest peak is Aoraki/Mount Cook (3,724m). The mountains are cut through with glacial valleys and lakes. The Southern Alps contained over 3,000 glaciers larger than a hectare, the longest of which – the Tasman Glacier (27km).
Geology of Southern Alps
New Zealand was originally part of the large supercontinent known as Gondwanaland, where New Zealand was side by side with Australia, Antarctica, Africa and India. This was New Zealand – but not as we know it. It was the oldest part of New Zealand – the West Coast of the South Island from Fiordland to Nelson.
The rest of New Zealand started its formation about 200 million years ago when the sediments destined to become the Southern Alps were slowly being eroded and deposited in large layers of sand and silt under the sea. As Gondwanaland started to move, intense heat and pressure changed and lifted the sedimentary sandstones into metamorphic rocks called schist. 120 million years ago ‘ancestral’ New Zealand had formed. It was approximately half the size of Australia, and was established with plant and animal life.
However, around 80 million years ago, the earth’s convection currents caused Gondwanaland to break up. Although originally still attached to Australia, it eventually separated and created the Tasman Sea, which stopped spreading about 60 million years ago. New Zealand, at this stage, was a series of hilly islands (like present day New Caledonia). Limestone, sandstone and mudstone accumulated in the shallow island seas. While New Zealand is considered an island nation, the islands of New Zealand are recognised as part of the continent Zealandia. This continent stretches from New Caledonia to the subantarctic islands, with 93% of its land mass underwater.
Eventually, about 25 million years ago, the largely undersea New Zealand was split in two, length wise, by the Alpine Fault (shown right), laying New Zealand across two major plates – the Pacific Plate and the Indo-Australian Plate.
As these two plates rotated and moved, colliding with each other and forcing up new land above the sea, the land was folded and faulted upward at various speeds. It became very rapid 2 million years ago during the Kaikoura Orogeny. Present uplift at Aoraki/Mount Cook National Park is approximately 5–10 mm per year.
The plates continue to move – the Pacific Plate is moving down under the Indo-Australian Plate in the North Island (subduction zone) at a rate of 50 mm per year and this is also happening to the south west of the South Island, but at a slower rate of 30 mm per year. In between (i.e. where Aoraki/Mount Cook National Park is), the Pacific Plate and Indo-Australian Plate are moving past each other along the Alpine Fault at a rate of 45 mm per year. Sudden movement of the plates, as a result of built-up pressure, causes earthquakes.
Evidence of this uplift is apparent in Aoraki/Mount Cook National Park, where sand, mud and silt have been metamorphosed and folded, faulted and fractured into schist, forming the large mountains in the park, e.g. vertical beds of silt and sandstone are evident on Nun’s Veil (head of Gorilla Stream) on the Liebig Range and beds of sandstone and siltstone layers on the north west side of Aiguilles Gorge.
It is estimated that approximately 25 kilometres of uplift has occurred in the Aoraki/Mount Cook National Park (compared to 18 kilometres in Arthur’s Pass) but erosion has kept pace with it – as fast as they are pushed up, they are worn down by agents of erosion. If it was not for water, wind and ice, in three million years Aoraki/Mt Cook would have been raised to five times its present height – or twice the height of Mt Everest.
Why are the ice cliffs blue?
Water looks blue because it absorb light at the red end of the spectrum, leaving only the blue light to reflect back to our eyes. Although snow is made of water, it looks white because it is full of air. Air bubbles reflect the full spectrum of light, which we see as the colour white - like in the foam of ocean waves or the head on a glass of beer. Glacial ice has compressed under its own weeight, squeezing out the air, so it looks blue like water.
About cache: The cache site is located on a viewpoint on the way to Mueller Hut. Start on the Kea Point Track at White Horse Hill car park. Follow the Kea Point Track to the Sealy Tarns turnoff. From Sealy Tarns follow the orange markers (every 200 metres) through the tussock. This is not a maintained track but an alpine route. After you ascent up to the hill you turn right, and take short side track to viewpoint. From this point you have an stunning panorama view to Mt. Sefton and of course to Mt. Cook. You can sit here and watch the mountains, glaciers and occasional avalanches. After that, you can follow the route to Mueller Hut. I recommend that, its about 20 minutes from here.
Logging requirements
To log this EarthCache, you must do the following and email me the results. You can go ahead and log your find, (you don't need to wait for permission) please dont post the answers online.
- When the Southern Alps were formed?
- On Stage 1: Describe the colour of the Tarns and why do you think the Tarns is this colour?
- At GZ: What geological features can you see from this place? (tell me at least three)
- Upload a photo of you or your GPS near the given cache co-ordinates (optional)
PLEASE NOTE: Please don't go close to the edge, it may be a dangerous.
