Southern Alps

The Southern Alps, officially known as Southern Alps / Kā Tiritiri o te Moana, are a massive mountain range.

They stretch along much of the length of New Zealand's South Island. The range is approximately 500 km long, running from the northeast to the southwest. A central feature is the Main Divide. This divide separates the water catchments of the island. The western side is more heavily populated. The eastern side has different water drainage patterns. Politically, the Main Divide marks the borders between several regions. It separates Marlborough, Canterbury, and Otago from Tasman and the West Coast.

The mountains are shaped by powerful geological forces. They sit on a plate boundary within the Pacific Ring of Fire. Here, the Pacific Plate pushes westward. It collides with the northward-moving Indo-Australian Plate. This collision has pushed up a 20 km thickness of rocks over 45 million years. Much of that rock has eroded away since then. Uplift has been most rapid during the last 5 million years. The mountains are still being raised today by tectonic pressure. This movement causes earthquakes along the Alpine Fault. Most motion along this fault is transverse, which means it moves sideways. However, other areas like the Hikurangi Trough show significant dip-slip motion.

Many names describe these peaks. The Māori name, Kā Tiritiri o te Moana, means "the Mirage of the Ocean." Legend tells of the explorer Māui sailing his waka along the west coast. A passenger saw a white blot on the horizon. They thought it was snow on a mountain range. Māui dismissed it as a glimmering mirage on the sea. He was proven wrong as they moved closer to land. The English explorer James Cook named them the Southern Alps on 23 March 1770. He admired their "prodigious height." Earlier, Abel Tasman had noted them in 1642. He described the coast as "a land uplifted high."

The geography of the range is defined by extreme heights and ice. Aoraki / Mount Cook is the tallest peak. It is the highest point in all of New Zealand at 3,724 meters. Sixteen other points in the range exceed 3,000 meters in height. Glacial valleys bisect the mountain ranges. Many of these valleys hold glacial lakes on the eastern side. Examples include Lake Coleridge in the north and Lake Wakatipu in the south.

The mountains contain over 3,000 glaciers larger than one hectare. The longest is the Tasman Glacier. It has retreated from its maximum size seen in the 1960s.

The climate is a humid maritime, temperate type. The range sits perpendicular to the prevailing westerly flow of air. This position causes massive differences in rainfall. The West Coast receives about 6,500 mm of rain annually. The area east of the Main Divide receives much less. This high precipitation helps glaciers grow above the snow line. The mountains also create a weather pattern called the Nor'west arch. Moist air is pushed up over the mountains. This forms an arch of cloud in a blue sky. The descending air on the lee side creates a foehn wind. This is a hot, dry wind known as a "Nor'wester." This wind is similar to the Chinook in Canada. It is excellent for glider pilots in places like Omarama.

Life in the Southern Alps is highly specialized. About 25% of New Zealand's plant species live in alpine habitats. These areas include grasslands and mountain beech forests at lower elevations. Higher up, the windswept slopes are covered in fellfield. Plants like the snow tōtara and Hebe shrubs have adapted to these conditions. Many animals are endemic, meaning they are found nowhere else. The rock wren lives in these high places. The mountain stone wētā can even freeze solid to survive winter. The kea is the world's only alpine parrot. It lives in forested foothills and high, cold areas.

Preserving this environment is a major priority. Much of the range is protected by national parks. These include Westland Tai Poutini, Mount Aspiring, and Aoraki / Mount Cook National Parks. These areas help protect native plants and animals. However, introduced animals pose a threat to indigenous life. Red deer, chamois, and Himalayan tahr can affect plant life. Introduced predators also threaten native birds and reptiles. Protecting these wild spaces ensures the survival of unique species like the great spotted kiwi and the orange-fronted kākāriki.