New Caledonia (Nouvelle-Calédonie) is an overseas collectivity of France located in the subregion of Melanesia, with a geography that makes the continental island group unique in the southwest Pacific. Among other things, the island chain has played a role in preserving unique biological lineages from the Mesozoic. It served as a waystation in the expansion of the predecessors of the Polynesians, the Lapita culture. Under the Free French it was a vital naval base for Allied Forces during the War in the Pacific.

The archipelago is located east of Australia, north of New Zealand, south of the Equator, and just west of Fiji and Vanuatu. New Caledonia comprises a main island, Grande Terre, the Loyalty Islands, and several smaller islands. Approximately half the size of Taiwan, the group has a land area of . The islands have a coastline of . New Caledonia claims an exclusive fishing zone to a distance of and a territorial sea of from shore.Kowasch M. and Batterbury, S.P.J. (eds.). 2024. Geographies of New Caledonia-Kanaky: environments, politics and cultures. Springer Open Access. http://doi.org/10.1007/978-3-031-49140-5

New Caledonia is one of the northernmost parts of an almost entirely (93%) submerged continent called Zealandia which rifted away from Antarctica between 130 and 85 million years ago (mya), and from Australia 85–60 mya. (Most of the elongated triangular continental mass of Zealandia is a subsurface plateau. New Zealand is a mountainous above-water promontory in its center, and New Caledonia is a promontory ridge on the continent's northern edge.) New Caledonia itself drifted away from Australia 66 mya, and subsequently drifted in a north-easterly direction, reaching its present position about 50 mya.Boyer & Giribet 2007: 355 Given its long stability and isolation, New Caledonia serves as a unique island refugium—a sort of biological 'ark'—hosting a unique ecosystem and preserving Gondwanan plant and animal lineages no longer found elsewhere."New Caledonia has long been considered a Gondwanan refuge where archaic groups have survived for 80Ma." "New Caledonia: a very old Darwinian island?" Philippe Grandcolas,1* Jérôme Murienne, et al., Philos Trans R Soc Lond B Biol Sci. 2008 October 27; 363(1508): 3309–3317.a window into the unique evolutionary history of this part of the world. Initially this biota lived along the New Zealand-New Caledonia coast of Gondwana, but following Cretaceous breakup of this southern supercontinent the fossils record terrestrial and marine evolution on and around the New Zealand "ark" set adrift in the Southwest Pacific." See HAYWARD B.W. (2009).- Protecting fossil sites in New Zealand .- In: LIPPS J.H. & GRANIER B.R.C. (eds.), PaleoParks – The Protection and conservation of fossil sites worldwide.- Carnets de Géologie / Notebooks on Geology, Brest, 2009for scholarly usage of the exact term "biological ark" in context of the Gondwanan breakup: "This globally significant ‘biological ark’, is attributed to Australia's long geographic isolation from other parts of the world." "Potential of ecotourism to protect natural remnant areas within the urban environment " Fiona Prince The University of Western Australia, Department of Environmental Engineering, 2002At the end of Jurassic (135 My), Gondwana started to break apart. The oldest grounds of current New Caledonia were then located on the eastern margin of this continent as part of the Australian block. Towards the end of Cretaceous, about 85 million years ago, this old New Caledonia broke away and so did New Zealand. New-Caledonia was then isolated... As a result, New Caledonia is now a kind of "Jurassic Park" particularly with regards to its vegetation which is highly endemic and which has kept archaic characteristics." Gondwana super-continent. Jean-Jacques Espirat, author of Étude géologique de régions de la Nouvelle Calédonie and member of the Bureau de Recherches Geologiques et Minieres compares it to Noah's Ark: "La Grande Terre de la Nouvelle-Calédonie s'est séparée il y a 70 millions d'années (au Crétacé terminal) du continent de Gondwana (groupant à l'origine les terres qui se sont séparées pour former l'Australie, l'Antarctique, l'Amérique du Sud, l'Inde, Madagascar et l'Afrique). Telle l'Arche de Noé cette Nouvelle Calédonie de la fin du Crétacé embarquait la flore de cette époque." La faune et la flore de Nouvelle-Calédonie. (French)

Composition

New Caledonia is made up of a main island, the Grande Terre, and several smaller islands, the Belep archipelago to the north of the Grande Terre, the Loyalty Islands to the east of the Grande Terre, the Isle of Pines to the south of the Grande Terre, the Chesterfield Islands and Bellona Reefs further to the west. Each of these four island groups has a different geological origin:

The New Caledonia archipelago, which includes Grande Terre, Belep, and the Île des Pins was born as a series of folds of the Earth's mantle between the Permian period (251–299 mya) and the Paleogene and Neogene periods (1.5–66 mya). This mantle obduction created large areas of peridotite and a bedrock rich in nickel. The Loyalty Islands, a hundred kilometers to the east, are coral and limestone islands built on top of ancient collapsed volcanoes originating due to subduction at the Vanuatu trench. The Chesterfield Islands, to the northwest, are reef outcroppings of the oceanic plateau. The Matthew and Hunter Islands, at east, respectively, are volcanic islands that form the southern end of the arc of the New Hebrides.

The Grande Terre is by far the largest of the islands and the only mountainous island. It has an area of , and is elongated northwest–southeast, in length and wide. A mountain range runs the length of the island, with five peaks over . The highest point is Mont Panié at elevation. The total area of New Caledonia is , of those being land.

A territorial dispute exists with regard to the uninhabited Matthew and Hunter Islands, which are claimed by both France (as part of New Caledonia) and Vanuatu.

Zealandian origin

The New Caledonian archipelago is a microcontinental island chain which originated as a fragment of Zealandia, a nearly submerged continent or microcontinent which was part of the southern supercontinent of Gondwana during the time of the dinosaurs. The Grande Terre group of New Caledonia, with Mont Panié at as its highest point, is the most elevated part of the Norfolk Ridge, a long and mostly underwater arm of the continent. While they were still one landmass, Zealandia and Australia combined broke away from Antarctica between 85 and 130 million years ago. Australia and Zealandia split apart 60–85 million years ago. Although biologists consider it contrary to the evidence of surviving Gondwanan lineages, geologists consider the logical possibility that Zealandia may have been completely submerged about 23 million years ago. While a continent like Australia consists of a large body of land surrounded by a fringe of continental shelf, Zealandia consists almost entirely of continental shelf, with the vast majority, some 93%, submerged beneath the Pacific Ocean. This viewpoint is not universal. Bernard Pelletier argues that Grande Terre was completely submerged for millions of years, and hence the origin of the flora may not be local in nature, but due to long distance-dispersal.Pelletier B., 2007. "Geology of the New Caledonia region and its implications for the study of the New Caledonian biodiversity", in: Payri C. E., Richer de Forges B. (eds.) Compendium of marine species of New Caledonia, Doc. Sci. Tech. II7, second edition, IRD Nouméa, pp 19–32.

Zealandia is in area, larger than Greenland or India, and almost half the size of Australia. It is unusually slender, stretching from New Caledonia in the north to beyond New Zealand's subantarctic islands in the south (from latitude 19° south to 56° south, analogous to ranging from Haiti to Hudson Bay or from Sudan to Sweden in the Northern Hemisphere). New Zealand is the greatest part of Zealandia above sea level, followed by New Caledonia.

Given its continental origin as a fragment of Zealandia, unlike many of the islands of the Pacific such as the Hawaiian chain, New Caledonia is not of geographically recent volcanic provenance. Its separation from Australia at the end of the Cretaceous (65 mya) and from New Zealand in the mid-Miocene has led to a long period of evolution in near complete isolation. New Caledonia's natural heritage significantly comprises species whose ancestors were ancient and primitive flora and fauna present on New Caledonia when it broke away from Gondwana millions of years ago, not only species but entire genera and even families are unique to the island, and survive nowhere else.

Since the age of the dinosaurs, as the island moved north due to the effects of continental drift, some geologists assert that it may have been fully submerged at various intervals. Botanists, however, argue that there must have been some areas that remained above sea level, serving as refugia for the descendants of the original flora that inhabited the island when it broke away from Gondwana. The isolation of New Caledonia was not absolute, however. New species came to New Caledonia while species of Gondwanan origin were able to penetrate further eastward into the Pacific Island region.

Climate

The climate of New Caledonia is tropical, modified by southeasterly trade winds. It is hot and humid. Natural hazards are posed in New Caledonia by cyclones, which occur most frequently between November and March. While rainfall in the neighboring Vanuatu islands averages two meters annually, from the north of New Caledonia to the south the rain decreases to a little over . The mean annual temperature drops over the same interval from , and seasonality becomes more pronounced. The capital, Nouméa, located on a peninsula on the southwestern coast of the island normally has a dry season which increases in intensity from August until mid-December, ending suddenly with the coming of rain in January. The northeastern coast of the island receives the most rain, with having been recorded near sea level in Pouébo.

Terrain The terrain of Grande Terre consists of coastal plains, with mountains in the interior. The lowest point is the Pacific Ocean, with an elevation of 0 m, and the highest is Mont Panie, with an elevation of .

The Diahot River is the longest river of New Caledonia, flowing for some . It has a catchment area of 620 square kilometres and opens north-westward into the Baie d'Harcourt, flowing towards the northern point of the island along the western escarpment of the Mount Panie.

In 1993, 12% of New Caledonian land was used for permanent pasture, with 39% occupied by forests and woodland. In 1991, of the land was irrigated. A current environmental issue is erosion caused by mining exploitation and forest fires.

Biological isolation