The Vegetation of New Zealand
2. Physical Features of New Zealand proper
2. Physical Features of New Zealand proper.
a. North Island.
Mountains. As a rule the land-surface is much broken, hilly, and in parts mountainous. The main range extends from the east of Wellington Harbour to the East Cape. The highest peaks are in the Ruahine and Tararua Mountains, but none reach 1800 m. and few more than 1520 m. The rocks are chiefly mudstones, sandstones and greywacke.
The centre of the island is a volcanic plateau much of which is, at an altitude of more than 600 m., but, northwards, gradually becoming lower, it extends to the Bay of Plenty. This area, within recent geological times, has been exposed to powerful volcanic action. The eruptions have been largely explosive and the present surface-pumice is the result. Even yet there is much thermal activity1 in the shape of boiling springs, geysers, mud volcanoes, &c, especially on a line connecting White Island, a volcano in the solfatara stage, and Ruapehu. From the highest portion of the Plateau rise the semiactive volcanoes, Ruapehu (2803 m.), Ngauruhoe (2291 m.) and Tongariro (1968 m.). The crater of Ruapehu is filled with ice in which lies a lake of, sometimes, extremely hot water, while small glaciers extend over the crater-rim and descend to comparatively low levels in the gullies.
1 1) In 1886, the supposed extinct volcano Tarawera, situated on the Volcanic Plateau burst forth forming a rent 19 km. long with a mean width of 108 m. and ejecting light scoria and volcanic dust over an area of 15,000 sq km.
The extreme north of the island consists of a small, narrow, much dissected tableland some 300 m. high, formed of hard igneous and sedimentary rocks. At one time this was disconnected from the mainland, but now is united by a narrow spit of recent and consolidated dunes.
Plains. An extensive plain of marine origin, the Wanganui, lies between the Ruahine Mountains and Mount Egmont extending to Ruapehu where it is over 600 m. altitude and bounded on the south by the coastline. The rock consists of marl enclosing beds of shells. This plain is deeply cut by numerous streams so that, in many places, there is a network of deep gorges, often extremely narrow. River-formed gravel plains, the upper soil of which is frequently extremely rich, occur east and west of the main range (Manawatu, Wairarapa and Hawkes Bay Plains). The Waikato Plain, formed of river-borne pumice, occupies much of southern Auckland; it extends from the Firth of Thames to the R. Waipa. Its surface, rarely more than 30 m. above sea-level, is extremely wet and swampy. Northwards from the Auckland Isthmus there is much low-lying ground.
Rivers. The land throughout is well watered, every gully containing tsi running stream. In many places, the rivers have cut deeply into the surface, so that gorges are a familiar feature. The rivers rising in the high mountains are of a torrential character, but this feature is much less marked than in South Island, while gently flowing streams are more common. Where the rivers have not cut deep beds the adjacent land is liable to be flooded and extensive swamps are so formed (Manawatu, Waikato, Bay of Plenty, Thames, Northern Wairoa, Awanui). The Rivers Waikato and Wanganui are the most important in point of size and drainage area.
Lakes. The largest lakes are on the Volcanic Plateau, the most important being L. Taupo. L. Waikaremoana in the East Cape district lies 600 m. above sea-level. So far as plant-life is concerned it is the natural ponds and shallow lakes met with in many places that are of most importance.
Sea-coast. The coast is about 2152 km. in length. The various outlying islands also fournish coastal conditions. A most important feature of the coast-line is the extensive dune-area of much of the west coast which extends inland in places for 12.8 km. Also, there are considerable dunes in the far north, and north-east on the coast of the Bay of Plenty, and at various places between Poverty Bay and Cape Turnagain.
1 1) Mount Te Moehau in the north of the Coromandel Peninsula, carries a few subalpine plants, but this in relation to frequent wind.
2 2) The Maungaraki Mts. (900 m.), extending northwards from C. Palliser; the Puketoi Hills (610 m.) in the east of Wellington; the volcanic Mt. Karioi and Mt. Pirongia near the coast of south-west Auckland; the Cape Colville Range; the high land culminating in Mt. Tutamoe (800 m.), south of Hokianga Harbour, and the high land north of the latter with Mt. Raetea (800 m.).
The coast is frequently rocky. The south and south-east coast-line in its southern part consists of cliffs of slaty shale. Further north, low cliffs of soft marl and mudstone occur fronted by a narrow beach with the stony surface worn quite flat. The north-east coast consists at first of steep slaty cliffs, but from Opotiki onwards the land as a rule is low. The shore-line of the Coromandel Peninsula consists mostly of slate cliffs, but volcanic rock is not uncommon. From Auckland to North Cape the coast is much broken and presents a great diversity of stations for plant-life. Low cliffs fringed by a sandy or stony beach are common. There are bold rocky headlands. Many of the rivers have wide mouths, but these are shallow and mud-flats are exposed at low water. The short north coast is frequently precipitious through truncation of the tableland.
Where dunes are absent on the south-west and west coasts there are cliffs, some volcanic (Maunganui Bluff, &c.), others limestone (Kawhia, west of Taranaki &c), and others of slaty shale (Reef Point, South Waikato Head &c).
Many miles of coast are without inlets, estuaries &c. With the exception of Wellington and Porirua Harbours in the south, nearly all of any moment are to be found on the east and west coasts of Auckland.
b. South Island.
Mountains. The surface is extremely mountainous. Commencing in the south there are two chains, the one composed of gneisses and granulite on the west, and the other of schist extending from the shore at Dunedin and joining the former between Lakes Wakatipu and Wanaka. The latter is continued in an unbroken line as the Southern Alps to Cook Strait; and its eastern slopes are formed of slaty shales and greywackes. Below the shales &c. on the west the rock is schist, but at low levels occasionally gneiss. Granite occurs in a few places. The loftiest peaks are situated at about the centre of the chain. They vary from some 3000 m. to 3766 m. (Mt. Cook). Proceeding north and south, the range gradually decreases in height, but for a long distance few peaks are lower than 1800 m. Many lofty ranges and spurs extend eastwards for 48 km. or thereabouts from the main Divide. These eastern mountains are especially characterized by the vast masses of unstable debris covering their slopes, locally known as "Shingle-slips".
The snow-line in the Southern Alps is perhaps, on an average, at about 2200 m. altitude, but it is not uniform and varies according to latitude, while also it is lower on the west than on the east. The central part of the range is heavily glaciated, the size of the glaciers being correlated with the altitude of the peaks. The Great Tasman Glacier is about 29 km. long and its terminal face 918 m. above sea-level. On the west, the Fox and Franz Josef Glaciers descend to less than 210 m. altitude. page 46Glaciers are wanting to the south of lat. 45° and;n the north they cease at a little to the north of lat. 43°. The eastern valley glaciers are generally covered with an enormous amount of moraine. The central Southern Alps form an unbroken wall, but to the north and south there are numerous passes, the lowest being the Haast (570 m.).
Besides the Southern Alps there are other lofty ranges. The Kaikoura Mountains are the two parallel ranges in the north east with several peaks exceeding 2400 m. altitude but they carry neither glaciers nor perpetual snow, except in small patches; their debris fields are of enormous extent. To the west of the Southern Alps, in the north-west, lie several rugged ranges which extend from near Greymouth to the north coast with many peaks of 1500 m. altitude. Banks Peninsula, on the east of Canterbury, is formed of much-denuded volcanic rocks, and reaches a maximum height of some 900 m In addition to the great ranges, there is on the east much hilly land some undulating, and within the high mountain area several extensive mtermontane basins.
Plains. Gravel plains formed by glacial or snow rivers are a striking feature of South Island topography. The most importan are: — The Canterbury Plain (161 km. long by 48 km. wide at its widest); the long narrow Westland coastal plain (200 km. long by 10 km. wide) and the Southland Plain extending from near Lumsden to Foveaux Strait. Flat as the Canterbury Plain appears to the eye, the surface near the foothills of the Southern Alps is more than 457 m. above sea-level. Borings for artesian water shew by the peat-deposits at different depths that there have been several changes in the land-surface during the formation of the plain.
Rivers. The numerous rivers issuing f om the glaciers or fed by melting snows, or frequent downpours, are torrential at first, their beds full of huge rocks over which the waters leap and foam. By degrees, the valleys shaped by former glaciers widen and are filled from side to side, it may be, by a flat stony bed over which, in anastamosing streams, the river wanders. Lower down, as the valley widens still more, or when the plain is gained, the river may flow between high permanent terraces that it has built, and frequently there is a series of such at different levels with portions of the ancient flood-plains at their bases. River beds 1 km. or more wide with terraces on either side are a common feature of the valleys and gravel-plains (Fig. 1).
Where a tributary stream in a mountain-valley joins a river the shingle of its bed spreads out as a fan. Such are present at the mouth of almost every gully, sometimes naked and active, at other times plant-clad and passive.
Glaciation. At the height of the New Zealand glacial period great glaciers extended throughout most of the high lands of South Island even as far east as the uppermost part of the Canterbury Plain and, on the page 47west in no few places to the sea Remains of ice-action are to be seen throughout the Southern Alps, and m the western range ot Nelson, except where in the drier parts excessive denudation has taken place. Cirques, hanging-valleys, moraines large and small, transported morainic materi 1, roches moutonnees ice-shorn hillsides, truncated spurs and U-shaped valle s are abundant, and both testify to the exrent of the glaciation and prov de special growing-places for plants. Gla?ial lakes are frequen and range from small tarns on moraines to the lakes, many kilometres in length and frequently of great depth, of Canterbury and Otago. In North Island, glaciation, if it occurred at all was evidently trifling.
Sea-coast. The coast-line about 2740 km, in length in general is little broken Notable exceptions are the Marlborough Sounds and Otago Fiords, the former drowned river-valleys the latter of glacial origin. Banks Peninsula contains a number ot mle s, some much-eroded, submerged, volcanic craters. There are also a few shallow estuaries, more or less closed by sand or gravel spots, whose floors are in part bare at low-water.
In many places, the coast is low and the shore sandy, so that long stretches of dunes occur. Shingly shores are frequent in many parts and correlated with the great river-beds
Rocky shores and cliffs are frequent at many points n the coast. In this regard, the most noteworthy are the rocky walls of the Otago fiords formed by lofty mountains rising from the water's edge as precipices for 1000 m. or more. These fiords extend inland for many kilometres and some of them almost reach Lakes Te Anau and Manapouri — themselves to all intents and purposes fiords also. Facing Cook Strait, in the north of the island, are also long arms of the sea penetrating the land, but such are not of glacial origin but are submerged river valleys
Coastal islands are few. The most important are those to the north of Marlborough and in Foveaux Strait. The Open Bay Islands on the west are composed of limestone, and although mere islets possess a remarkable plant-covering.
c. Stewart Island.
Stewart Island lies about 25 km. from South Island from which it is separated by Foveaux Strait, this nowhere more than 48 m. deep.
In shape the island is irregularly triangular. The surface is hilly, much broken and in parts mountainous, the peaks varying in height from 676 m. to 975 m. There is but little truly flat ground. East of the central range the land is low, but broken. At the head of Paterson Inlet a narrow valley, the Freshwater, extends northwards to the Ruggedy Mts., while, westwards, an opening widening out into an ancient dune-area, connects the valley and the west coast. West of Port Pegasus there is some low boggy moorland. The coast is in general rocky. At Mason Bay on the west is an extensive dune-area.page 48
Perhaps the most striking features of the island are Paterson Inlet and Port Pegasus. The former, a broad expanse of lake-like water, irregular in shape, enclosed by hills and dotted with forest-clad rocky islets, extends westward for 17 km. putting forth three diverging arms. Port Pegasus, situated in the south, runs parallel with the south-east coast for about 12 km., its entrance blocked by three islands.
There are a number of outlying rocky islets especially to the east and south-west, while to the north-west is the fairly large Codfish Island. Thirty-two kilometres to the eastward is the flat island of Ruapuke 7.6 km. long by 3.4 km. wide.