According to Countryaah, Australia is the biggest country while Nauru is the smallest one in Oceania. In Australia, the western half is occupied by a flat plateau, 300 m above sea level. in medium height. Over this, mountain areas rise up to 1,500 m above sea level. Deserts and salt lakes are common. To the east lies the Great Australian Basin, where the southeastern part is mainly the Murray and Darling River floodplains. The eastern highlands consist of mountain ridges, streams and plateaus. Outside, to the east, the Great Barrier Reef extends from Torres strait in the north to the tropic.
In New Zealand, the western part of the South Island is dominated by a mountain range with Mount Cook (3,764 m asl) being the highest peak. The chain is heavily glacial eroded and has large modern glaciers. The eastern part of the South Island is lowland. The North Island is also mountainous. Active volcanoes and hot springs are common.
New Guinea is characterized by mountains all over the island from northwest to southeast. Some parts reach over 4,000 meters above sea level. and are sometimes snow-clad. Deeply cut valleys are common. Larger lowland areas are found only in the south, especially around the rivers Fly and Digul. See also the sections on terrain shapes and bedrock in the articles of Australia, New Zealand and New Guinea on AbbreviationFinder.org.
The small islands of the Pacific are of three types. The volcanic islands are high, e.g. Tahiti (2,241 m asl) and Pohnpei in the Carolinas (790 m asl). The topography can be dramatic with steep slopes and deep cuts. On the larger islands, sandy beaches and mangrove swamps are common. Active volcanism occurs e.g. in Hawaii and the Savai’i among the Samoa Islands. The volcanic islands are often bordered by coral reefs. These can eventually form coral islands, mainly atolls, e.g. Bikini in the Marshall Islands and Johnston Island. The atolls rarely reach more than a few meters above sea level. They surround a shallow lagoon. In some cases, the atoll has been raised to form a limestone plateau some ten meters above sea level. One such island is Nauru, while Vava’u in the Tonga Islands has been raised several times and consists of several terrace-like plateaus. New Caledonia, Bougainville and Viti Levu in Fiji are examples of islands of complex origin, where older granitic bedrock forms flat plateaus and younger volcanic parts are tall and steep.
Oceania lies within two large lithospheric plates, the Pacific plate and the Indian-Australian plate. Australia is located quite far on the latter plate and has constituted a geologically stable area since the end of the Paleozoic (about 245 million years ago). Other parts of Oceania have been strongly influenced by the plate movements during tertiary and quaternary times (about 65 million years ago to the present). Thus, the collision between the plates has resulted in extensive rock chain formation and volcanism, e.g. in New Zealand and New Guinea. Along the collision zone there are also curved chains of volcanic islands, so-called arches. Parallel to these runs an adjacent deep-sea tomb, where oceanic crust is pressed down and destroyed, so-called subduction. The islands east and north of the collision zones are also geologically young formations and mostly of tertiary to quaternary age.
Western and central Australia form a stable craton, which is largely built up by an indigenous shield. The oldest part of the shield is in the west, where it consists of granite arches and greenstone belts (more than 2,500 million years old). In the central parts of Australia, the indigenous rock consists mostly of metamorphic and sedimentary rocks from Proterozoic (about 2,500–570 million years before today). In the interior of Australia, the indigenous mountain is often covered by younger, fanerozoic deposits. in the Macdonnell Mountains and the Musgrave Mountains. During the Paleozoic period (about 570–245 million years before today), the continent expanded to the east through the formation of continental crust. The mountain range along the east coast was folded and joined to Australia during Tasmanorogenesis, a mountain range formation that terminated in the younger Paleozoic.
Until the beginning of the tertiary period (about 55 million years ago), Australia was part of the giant continent Gondwana. By this time, Australia was splitting from Antarctica and the Indian-Australian plate began moving north. New Zealand’s separation from Australia and Antarctica started already in the younger Cretaceous (about 85 million years ago).
The quaternary period is characterized by significant climate change; tracks for icing, e.g. moraine and meltwater deposits are found in the mountainous areas of Tasmania, Northern Island (New Zealand), New Guinea, Hawaii and New South Wales (Australia). More extensive ice cover was found along the entire western part of the South Island (New Zealand). In the inner, dry parts of Australia, there were large so-called pluvial lakes during the cold times. The largest of these was Lake Dieris, of which there remains only one drainless salt lake, Lake Eyres.
About 45% of Australia is covered by desert soils. In the north-west and south, they gradually reach the coast. Chestnut-colored earth moons border the central desert land area. Lateritic earth moons also occur, mainly along the north coast. A belt with vertical insoles goes in an arc from north to south within the Great Dividing Range. Special types of pod-like earth moons occur along the east coast as well as in the southwest. These, like the brown soils, are often cultivated and transformed into cultural soils. Mountain earth moons occur, among other things. in the Great Dividing Range.
In New Guinea, as well as on most small islands in Polynesia, Micronesia and Melanesia, there are central mountain areas where mountain earth and lateritic soils alternate, while lateritic soils dominate the coastal areas. Even in New Zealand and Tasmania, mountain earth moons dominate, while coastal areas are dominated by various pod-like earth moons.
Most of Oceania has a tropical climate with a strong maritime feel. Exceptions include the interior of Australia, which has arid climates (desert climate and steppe climate), Australia’s southernmost parts with warm-temperate climate and dry season in summer (Mediterranean climate), and Australia’s east coast and New Zealand, both of which have warm-tempered climates with rainfall spread throughout the year.
The climate conditions in Oceania’s island world are otherwise determined – due to the large dominance of open water – mainly by the large-scale and very regular circulation. It is the subtropical high-pressure cells and their migrations, the intertropical convergence zone with its various locations during the year, and the prevailing winds, the passages, which mainly affect the climate and the weather in the island world of Oceania. The pass winds are more or less constant blowing from the northeast in the northern hemisphere and from the southeast in the southern hemisphere. They are most pronounced around 30 ° north latitude and so on, while in the equatorial zone where they meet (“the doldrums”), most prevail in the wind. This wind system is less pronounced in the summer, as a heat low pressure over Asia causes the wind gusts to be replaced by the southeast monsoon. Tropical storms (typhoons, hurricanes) occur in western Micronesia during July – November, when the surface water is around 27 °C. They are often followed by heavy rain and can cause major damage to low coral islands. The temperature in the island world of Oceania is very uniform and stable, 25-27 °C. Only during winter can the furthest from the equator be 20 °C. Precipitation amounts are also regular, about 2,000 mm per year in a belt just north of the equator. However, the topography of the individual islands has a strong impact and gives great variations in rainfall. However, some atolls at the equator suffer from drought, which can even be more than a year.
Flora and fauna
Many of the smaller islands are coral islands surrounded by coral reefs with rich marine fauna.
The flora of these islands is poor and consists mostly of bush vegetation with screw palm trees, occasional coconut trees and often also Casuariʹna equisetifoʹlia. In larger coral islands and volcanic islands, however, species richness is large, with many endemic species. In the west, palms and conifers of the genus Aʹgathis and Araucaʹria are typical features. Bamboo, rattan palms and banana plants are common as undergrowth, and often screw palms are a tangible feature. In many places, coconut palm and sago palm, as well as breadfruit trees, are native to the area.
The fauna is poor, and among mammals there are only bats and moths naturally. Among land birds, pigeons are richly represented with, among other things, many species of fruit pigeons and emperor pigeons. Many species of birds, whales and other sea birds nest on islands or stay here for part of the year. Typical features are nodal terns, tropical birds and frigate birds. Some islands are important egg-laying sites for sea turtles. In the west, lizards of the ham are richly represented, and in the waters around the islands there are sea snakes. Among the invertebrates are the palolomask sea chest mask, which occurs around the Samoa Islands, Fiji and Tonga Islands and is considered a delicacy by the locals.
The natural flora and fauna of Hawaii contains many unique forms.