New Zealand Geology

By | December 1, 2021

New Zealand perhaps represents the eastern edge of a larger continental form, broken up and destroyed by a series of partial collapses, due to numerous fractures, which occurred at different times. The very complex series of marine deposits subsequent to the Mesozoic that can be observed in the archipelago would in fact demonstrate the various oscillation movements of the coastal areas. Especially noteworthy are, besides the Siluric, Carbonic and Triassic strata, also the more recent ones, of the Middle Cretaceous, and the marine formations of the Tertiary. The frequent volcanic phenomena attest to recent sinking, which are also due to the straits of Cook and Foveaux which divide the three main islands of the archipelago, very different from each other both as regards the relief and the geological constitution. So, for. e.g., while the Northern Island is especially characterized by the frequency and grandeur of volcanic and seismic phenomena, the South Island, mainly mountainous and alpine, has been particularly shaped by the glacial action, and, although not lacking here either, along the eastern coast, the recent volcanic rocks, essentially owes its origin to a large mountainous ridge formed by paleozoic rocks, which due to their poverty of fossils make the task of determining their precise age very difficult for the geologist. This grandiose wrinkling occurred during the Jurassic and Cretaceous periods, but the chains formed in those periods were later more or less completely destroyed under the action of the various exogenous forces, so that the marine transgression occurred in the Middle Cretaceous period covered the whole region already reduced to Penepian. Many facts would attest that even during the Jurassic the archipelago was joined to a continental mass extended towards the West. In fact, along the west coast, in front of the Paleozoic rocks of the New Zealand Alpine chain, a band of granite and gneiss still emerges, developed in a particular way in the SO., In the region of the fjords. Only in the Pliocene did the island undergo new corrugations that gave it its present appearance, and the large transverse fractures of the Cook and Foveaux straits, already mentioned, also date back to this period. For New Zealand 2007, please check extrareference.com.

The mountainous corrugation that runs from the SW. NE. through the whole of the South Island, it continues, but with much lower heights, also in the North Island, in the Ruahine Mountains, the only chain of the North Island, made up not of Paleozoic rocks, but dating back to the Triassic and Jurassic periods. Nowhere on the island do gneiss and granite emerge; to the west of the Ruahine Mountains, in fact, lies the large volcanic region of Lake Taupo in the northern part, all covered with recent volcanic materials, while the rest of the island is covered by sedimentary layers of the ancient and recent Tertiary and also of the Quaternary, from which emerge here and there, especially in the NO., rocks which, like those of the Ruahine range, date back to the Triassic and Jurassic periods.

The North Island, called Ika on Maui by the Maori, is much lower than the South Island. It is quadrangular in shape, with long appendages at the southern, north-eastern and north-western corners. An immense volcanic forge, it owes much of its current relief to the action of relatively recent endogenous forces.

The only corrugation chain of the island is the eastern one, of medium height and almost hilly, made up of Mesozoic rocks, which runs, directed from the SW. NE., from the Cook Strait to the East Cape, and which is called with the collective term of the Ruahine Mountains. The southern section is really known with the name of Monti Iararua, the northern one with the name of Monti Raukumara (Hikurangi 1709 m.); the central one is the real Ruahine range, whose peaks approach 2000 m. The short range of Kaimanawa is also of the same origin, which runs to the west, with a direction parallel to that of the Ruahine mountains, and which reaches 1737 m. The whole central and western part of the island is instead made up of reliefs of volcanic origin, distributed without apparent order over the plains of

The Taupo Basin, the largest lake in New Zealand, forms the center of this volcanic zone that reaches almost to the sea to the north, including the entire vast district of volcanic lakes. From the extended plain to S. del Taupo rise the Tongariro, a volcano with a very regular and still active conical shape (1968 m.), And the Ruapehu (2797 m.) The highest peak of the Northern Island, in whose crater surrounded by snow and ice formed a lake of thermal water. Hot springs, geisers, mud volcanoes, soffioni and sulfataras are especially common in the volcanic lake district, where the barren, stony and wild Tikitere valley is therefore called “hell”. Famous among geisers for its violent jet of dark and very hot water is the Waimangu. Also Mount Egmont or Taranaki, which in the south-western corner of the island rises up to 2522 m., Is nothing more than a grandiose extinct volcano, perpetually covered with snow. The volcanic reliefs, albeit small, are also numerous in the exile Peninsula of Auckland; thus the Isthmus of Auckland is nothing but a continuous succession of lava fields and craters forming a landscape similar to that of the Phlegraean Fields.

The volcanic region extends towards the NE. up to the Bay of Abundance with the Whakari volcano in the White Island and towards the New Zealand up to the Coromandel peninsula and the Island of the Great Barrier which rises with the volcanic Mount Hobson. Only between the Volcanic Lake District and Mount Egmont does a broad tertiary plain stretched out, bordered towards the S. by a recent low-lying coastal zone and crossed by the Wanganui and Manawatu Rivers.

The island is very rich in rivers and lakes. The main rivers originate in the central volcanic region and flow on the western or southern side; however, there are also rivers on the eastern side, such as the Ruamahunga, which flows into Palliser Bay, the Tukituki, the Ngaruroro, the Mohaka and the Wairoa, emissary of the picturesque lake Waikare. Considerable watercourses also flow into the Baia dell’Abbondanza; and among them are the Motu, the Whakatane and the Rangitaiki and then the Tarawera and the Maketu and, in the Gulf of Hauraki, the Waihu and the Piako. On the western coasts, the Wairoa which bathes the Auckland Peninsula flows out; the Waikato (350 km.), the largest river of the archipelago, which originates in the plain of Onetapu, on the eastern side of Ruapehu and crosses Lake Taupo; the Marakopa and the Mokau; then, already on the side of the Cook Strait, the Patea, the Wanganai (224 km.), the Wangaehu, the Rangitikei (184 km.) and the Manaweui (160 km.). Of the numerous lakes, the main ones are Taupo (626 sq. Km.), Located at the foot of the Kaingaroa plateau, and, further to the North., Rotorua (80 sq. Km.) Surrounded by woods in an enchanting landscape, the Rotoiti or Small Lake, the Rotoehu or Lago Fangoso, the Rotoma or Lago Bianco, while further to the South. there is the Tarawera, at the foot of the homonymous volcano, with other minor ones, all of volcanic origin.

New Zealand Geology