TheSouthern Alps (Māori:Kā Tiritiri o te Moana; officiallySouthern Alps / Kā Tiritiri o te Moana)[1] are amountain range extending along much of the length ofNew Zealand'sSouth Island, reaching its greatest elevations near the range's western side. The name "Southern Alps" generally refers to the entire range, although separate names are given to many of the smaller ranges that form part of it.
The range includes the South Island'sMain Divide, which separates thewater catchments of the more heavily populated eastern side of the island from those on the west coast.[2] Politically, the Main Divide forms the boundary between theMarlborough,Canterbury andOtagoregions to the southeast and theTasman andWest Coast regions to the northwest.
TheMāori name of the range isKā Tiritiri o te Moana, meaning "theMirage of the Ocean".[3][1]
TheEnglish explorerJames Cook bestowed the nameSouthern Alps on 23 March 1770, admiring their "prodigious height".[4] They had previously been noted byAbel Tasman in 1642, whose description of the South Island's west coast is often translated as "a land uplifted high".[5]
The Southern Alps run approximately 500 km[7] northeast to southwest. Its tallest peak isAoraki / Mount Cook, the highest point in New Zealand at 3,724 metres (12,218 ft). The Southern Alps include sixteen other points that exceed 3,000 metres (9,800 ft) in height (seeNZ mountains by height). The mountain ranges are bisected by glacial valleys, many of which are infilled with glacial lakes on the eastern side includingLake Coleridge in the north andLake Wakatipu inOtago in the south. According to an inventory conducted in the late 1970s, the Southern Alps contained over 3,000glaciers larger than one hectare,[8] the longest of which – theTasman Glacier – is 23.5 kilometres (14.6 mi) in length which has retreated from a recent maximum of 29 kilometres (18 mi) in the 1960s.[9][10]
New Zealand has a humid maritime, temperate climate with the Southern Alps lying perpendicular to the prevailing westerly flow of air. Annual precipitation varies greatly across the range, from 3,000 millimetres (120 in) at theWest Coast, 15,000 millimetres (590 in) close to the Main Divide, to 1,000 millimetres (39 in) 30 kilometres (19 mi) east of the Main Divide.[11] This high precipitation aids the growth ofglaciers above thesnow line. Large glaciers and snowfields can be found west of or on the Main Divide, with smaller glaciers farther east (SeeGlaciers of New Zealand).
Because of its orientation perpendicular to the prevailing westerly winds, the range creates excellent wave soaring conditions forglider pilots. The town ofOmarama, in the lee of the mountains, has gained an international reputation for its gliding conditions. The prevailing westerlies also create a weather pattern known as theNor'west arch, in which moist air is pushed up over the mountains, forming an arch of cloud in an otherwise blue sky. This weather pattern is frequently visible in summer acrossCanterbury andNorth Otago. The 'Nor'wester' is afoehn wind similar to theChinook of Canada, where mountain ranges in the path of prevailing moisture laden winds force air upwards, thus cooling the air and condensing the moisture to rain, producing hot dry winds in the descending air lee of the mountains.
The Southern Alps lie along a geologicalplate boundary, part of thePacific Ring of Fire, with thePacific Plate to the southeast pushing westward and colliding with the northward-movingIndo-Australian Plate to the northwest.[12] Over the last 45 million years, the collision has pushed up a 20 km thickness of rocks on the Pacific Plate to form the Alps, although much of this has been eroded away. Uplift has been most rapid during the last 5 million years, and the mountains continue to be raised today bytectonic pressure, causing earthquakes on theAlpine Fault and other nearby faults. Despite the substantial uplift, most of the relative motion along the Alpine Fault istransverse, notvertical.[13] However, significant dip-slip occurs on the plate boundary to the north and east of the North Island, in theHikurangi Trough andKermadec Trench. The transfer of motion from strike-slip on the Alpine Fault to dip-slip motion at these subduction zones to the north creates theMarlborough Fault System, which has resulted in significant uplift in the region.
In 2017 a large international team of scientists reported they had discovered beneathWhataroa, a small township on the Alpine Fault, "extreme" hydrothermal activity which "could be commercially very significant".[14][15]
The mountains are rich in flora with about 25% of the country's plant species being found above the treeline inalpine plant habitats and grassland withmountain beech forest at lower elevations (of the eastern side but not inWestland). The cold windswept slopes above the treeline are covered with areas offellfield. To the east, the Alps descend to theCanterbury-Otago tussock grasslands. Plants adapted to the alpine conditions include woody shrubs likeHebe,Dracophyllum, andCoprosma, the conifersnow totara(Podocarpus nivalis) andCarex sedge grasses.[16]
Wildlife of the mountains includes the endemicrock wren(Xenicus gilviventris). There are also a number of endemic insects adapted to these high altitudes, like flies, moths, beetles, bees, and themountain stone wētā, which can freeze solid over winter to survive thealpine conditions. The beech forests of the lower elevations are important habitat for several birds, such as thegreat spotted kiwi(Apteryx haastii), the South Islandkākā(Nestor meridionalis meridionalis), and theorange-fronted kākāriki(Cyanoramphus malherbi). Thekea can be found in the forested foothills as well as higher, colder elevations. It is the world's only alpineparrot, and was once hunted as a pest.
^Beck, Alan Copland (2009) [1966]."Topography". In McLintock, A.H. (ed.).Te Ara – the Encyclopedia of New Zealand.Archived from the original on 22 October 2012.
^Elder, Vaughan (18 May 2017)."Geothermal discovery on West Coast".Otago Daily Times.Archived from the original on 14 March 2018. Retrieved6 February 2021. 'Nobody on our team, or any of the scientists who reviewed our plans, predicted that it would be so hot down there. This geothermal activity may sound alarming but it is a wonderful scientific finding that could be commercially very significant for New Zealand.'
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