Natural history

Geology

The South Island of New Zealand is split from Milford Sound in the south to the Nelson Lakes area in the north, by the Alpine Fault, approximately 500 km in length. The fault represents the onshore meeting of two tectonic plates, the Australian Plate to the west and the Pacific Plate to the east. Rocks on the south-east side of this fault closely match those on the north-west side of the fault.

Deep earthquakes, seldom felt, occur along this fault as the Australian Plate sinks below the Pacific Plate to the south of Milford Sound. Compressional and lateral movement of Milford Sound continues to build the Southern Alps. To the east of the North Island the Australian Plate overrides the Pacific Plate.

Fiordland National Park has some of the oldest rocks in New Zealand. Most are extremely hard crystalline rocks with slow erosion rates. Beginning about 500 million years ago, intense heat and pressure deep in the earths crust formed gneiss and schist. They have been thrust upwards by folding of the crust and fragmented by faulting. Igneous rocks have intruded into these rocks and in eastern parts of Fiordland a chain of volcanoes added a mixture of molten rock. Parts of Fiordland have also submerged under the sea at times, before again being uplifted. Layers of sandstone, mudstone and limestone seen in the mountains of Fiordland are a result of these periods of submersion. Over the last two million years periods of glaciations have occurred, forming the steep sided U-shaped valleys and lake beds, which dominate the Fiordland landscape.

Flora

Silver, red and mountain beech forest dominate the lower Clinton Valley. Around the slips and avalanche paths of the central Clinton Valley, colonising species such as fuchsia, wineberry, broadleaf and mountain ribbonwood are common. Beyond Mintaro Hut the track climbs through sub-alpine scrub and into the tussocks and alpine herb communities of the Mackinnon Pass.

In early summer the white flowers of the mountain buttercup, mountain daisies and snow marguerites can be seen. From the pass the track drops through a shrub land zone, including mountain three finger, the tree daisy (with yellow flowers), and a native broom (which has sweetly scented mauve flowers).

The lower Arthur Valley contains a more diverse forest due to higher rainfall and milder temperatures. Species present include silver beech, kamahi, miro, totara, fuchsia, mahoe and pate. Ferns, mosses and lichens are abundant through this section of track.

back to top