Image:
A view of the western front of the Southern Alps, as seen from Lake Matheson, Westland. The Alpine Fault runs right at the foot of the mountain, about 5 km (3.1 miles) away from the location of the photo. From there the mountain rises very steeply, to an altitude of approximately 1600 m (1 mile) in this photo. Fox Glacier and its contributing neve are immediately behind these first ranges. Photo NC.

The western Southern Alps form a long and narrow strip of mountain land rising very steeply east of the Alpine Fault towards the main divide. The summits of the main divide are typically between 15-25 km (9-15 miles) east of the Alpine Fault. Rocks are schist, with a gradual transition with the greywacke that is found further east. The rate of uplift is very high, exceeding 10 mm/year (0.4 in.).
Precipitation is considerable, increasing from about 3000 mm (118 in.) per year on the coast to 5000 mm (197 in.) in the foothills, 10,000 mm (394 in.) on the ranges and 15,000 mm (591 in.) in the high parts of the main divide.
All these factors combine to produce a very steep and dissected landscape, with deep valleys, steep rivers, gorges, and sharp ridges.

A consequence of the high precipitation is the presence of large snowfields and neves, as with the Olivine Ice Plateau in Mt Aspiring National Park, and the Garden of Eden and Garden of Allah Ice Plateaus on the main divide north-east of Mt Cook. The Franz-Joseph and Fox glaciers, which flow to the lowlands of the West Coast down to an altitude of 300 m (984'), also originate in large neves high on the west side of Mt Cook.

In addition to these purely geomorphological characters, the high rainfall also favours the growth of dense and continuous forest, which further contributes to the wildness and impenetrability of these mountains.The lowland podocarp forests are replaced by southern beech (Nothofagus) above 500-750 m (1640-2640'), covering all slopes from valley floor to timberline, while a very dense understory further adds to their impenetrability.