It is in the axial zone that the Southern Alps
reach their highest altitude.
Rock is mostly greywacke
north of and including the Mt Cook area, and schist
further south.
The current rate of uplift is high, close to 10 mm/year in the
central part (Mt Cook), somewhat less away from it.
Total precipitation is very high: it can reach 15,000 mm (590
in.) per year on the main divide, and it is still about 4,000
mm (157 in.) at Mt Cook Village east of the divide.
The imprint of the last ice ages is well preserved,
and many glaciers are still present south of Arthur's Pass.
Some, like Tasman Glacier, Murchison Glacier, Hooker and Mueller
Glacier, are the longest in New Zealand. With its 28 km (17
miles), Tasman Glacier is the longest in the world for temperate
mountains of comparable altitude.
As a result the various landforms typical of high alpine areas
are widely displayed : very steep ground, many glaciers, cirques,
U-shaped valleys, scree slopes, moraines.
However the character of the mountains is not
uniform throughout the axial zone:
North of Arthur's Pass altitudes are moderate
(mostly below 2000 m/6560'), with no glaciers.
Altitudes rise south of Arthur's Pass
and small glaciers are present on the highest summits of south-western
Arthur's Pass National park (Mt Rolleston). However significant
glaciers appear only south of the Rakaia River, from the Mt
Whitcombe/Ramsay Glacier south-westwards. Large glaciated areas
(Garden of Eden and Garden of Allah ice plateaus) are present
in the upper reaches of the Rangitata River, as well as higher
mountains (Arrowsmith Range, 2795 m/9170').
The mountains of Mt Cook National Park
follow immediately to the south-west, in the upper reaches of
the Godley, Murchison, Tasman and Hooker rivers. These mountains
are the highest in the Southern Alps and New Zealand, and include
all summits over 3000 m (9842') except for Mt Aspiring. This
is a land of very steep ground, great altitude differences,
high rock and snow faces. It is still intensely glaciated (cf.
above). As a result the Mt Cook area has long been the centre
for mountaineering in New Zealand.
Further south-west altitudes drop but
significant glaciation is still present. A large glaciated area
(Volta and Bonar glaciers especially) surrounds Mt Aspiring
(3037 m/9964'), and between Dart and Rees valleys Mt Earnslaw
(2819 m/9249') is the last high mountain of the Axial zone.
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