The Physical Landscape of Oceania

The Physical Landscape of Oceania

Oceania is a realm like no other. Nowhere else can one find some of the unique wildlife in this realm, and no other region is as isolated. Oceania is the only world region not connected by land to another region. This is a region of the world at a crossroads where global changes in climate and pollution could have profound effects. The region of Oceania includes Australia, the realms of the Pacific Islands, and the polar regions of the Arctic and the Antarctic. While some regions share a distinct cultural or colonial history and others share a common physical landscape, the region of Oceania is connected more by its isolation than by a shared physiography or human experience.

Australia dominates the region in terms of size, economics, and population. It has the unique designation of being both a sovereign state and a continent. Often, Australia and New Zealand are considered a single region (see Figure 10.1), but while the two countries share cultural and historical similarities, their physical landscapes are quite different. Australia lies in the middle of its own tectonic plate, making it relatively geologically stable.

Australia has no active volcanoes and has had only a small number of large earthquakes. Its tectonic position also limits its relief, and much of the continent is relatively flat. An exception to this is the Great Dividing Range, which runs along the coast of Eastern Australia. This series of mountain ranges affects Australia's climate by providing orographic rainfall along the coast and dividing the core population center from the rest of the continent.

Figure 10.1 Physical Map of Australia and New Zealand (CIA World Factbook, Public Domain)

The other key geographic feature of Australia is its vast interior, known as the Outback (see Figure 10.2). This remote area of extensive grassland pastures supports one of the world's largest sheep and cattle industries. However, the Outback's ecosystem is quite fragile. With limited precipitation and vegetation, overgrazing puts the region at risk for desertification. In addition, although this region was the center of population for Australia's indigenous groups, ranching in the Outback has created land ownership issues.

Figure 10.2 View of Australian Outback and Mount Conner (© Gabriele Delhey, Wikimedia Commons, CC BY-SA 3.0)

One of the most well-known features of Australia's geography lies just off the coast: the Great Barrier Reef. This massive underwater reef is the world's largest coral structure and stretches over 2,300 kilometers (1,400 miles). However, warming ocean temperatures and pollution have been a significant environmental threat to the Great Barrier Reef in recent years.

Unlike its geologically stable neighbor, New Zealand is situated at the intersection of the Pacific Plate and the Australian Plate (see Figure 10.3). Its two large, mountainous islands and numerous small islands are prone to both earthquakes and volcanoes. New Zealand is younger than Australia geologically and has a far more varied topography.

On New Zealand's North Island alone, you could spend the morning surfing on a sandy beach, the afternoon picnicking in the rolling green hills where the fictional city of Hobbiton was filmed, and the evening skiing on an active volcano, Mount Ruapehu. New Zealand's South Island is home to a number of stunning fiords, more commonly found in Scandinavia, where they are spelled fjord.

Figure 10.3 Map of the Tectonic Plates of Oceania (United States Geological Survey, Public Domain)

The islands of the Pacific to the north and east of Australia and New Zealand are divided into three regions (see Figure 10.4). New Zealand is part of the islands of Polynesia, from the prefix "poly" meaning "many." Polynesia is a large, triangular region stretching from New Zealand to Easter Island to the Hawaiian and Midway Islands.

West of Polynesia and to the northeast of Australia are the islands of Melanesia, including New Guinea, the Solomon Islands, and Fiji. Europeans called the region "Melanesia" from the Greek prefix melan- meaning "black," referring to the darker skin they believed characterized the people of this realm. North of Melanesia are the tiny islands of Micronesia, from the prefix "micro" meaning "small." There are over 2,000 islands in Micronesia.

Figure 10.4 Map of Australia and the Pacific (Map by User:Kahuroa, Wikimedia Commons, Public Domain)

The islands of the Pacific can be divided into two groups based on their physical characteristics. The high islands like Hawaii are volcanic, meaning they were formed from volcanoes, and thus have a relatively high relief. This high relief and volcanic soils enables the high islands to have fertile soil and ample rainfall, which in turn supports a diverse agricultural system and relatively large populations.

In contrast, the low islands of the Pacific are comprised mostly of coral and, as their name implies, are generally low in elevation. Most of the islands in the Pacific, particularly in Micronesia, are low islands. These islands may only rise a few feet above the water, and their dry, sandy soil makes farming difficult. Fresh water is often in short supply in the low islands. As a result, these islands typically have much smaller populations.

 The relatively large coral island that comprises the country of Niue, for example, rises to a maximum of 60 meters (less than 200 feet). The low elevation of these islands makes them vulnerable to natural disasters, such as tropical cyclones, and to changes in sea elevation due to rising global temperatures. In the country of Tuvalu, an island chain located between Hawaii and Australia, the highest point is a mere 4.6 meters (15 feet) above sea level and the island has sustained severe damage from cyclones during its history.

A number of low islands of in the Pacific form atolls, ring-shaped chains of coral islands surrounding a central lagoon (see Figure 10.5). Typically, the lagoon is actually a volcanic crater which has eroded beneath the water. Most of the world's atolls are found in the Pacific Ocean and their land areas are generally quite small.

Figure 10.5 Satellite Photo of the Atafu Atoll in Tokelau (NASA Johnson Space Center, Public Domain)

In general, the islands of the Pacific have warm, tropical climates with little seasonal extremes in temperature. Some islands experience seasonal, primarily orographic rainfall. These relatively warm temperatures help support tourism throughout the region. Throughout New Zealand and the core area of Australia, east of the Great Dividing Range is primarily a maritime climate. This climate zone features cool summers and winters with few extremes in temperature or rainfall.

Also included in Oceania are the earth's polar regions. In the North Pole is the Arctic Ocean, the world's smallest and shallowest ocean. Although it may appear to look like a landmass covered in snow on many globes, there is no landmass below the North Pole. The ocean is covered by a sheet of sea ice throughout the year and the entire body of water is almost completely ice-covered in winter. In the South Pole is Earth's southernmost continent, Antarctica. This continent is around twice the size of Australia and is almost entirely covered with ice. It is not home to a permanent human settlement.

Source: Caitlin Finlayson, https://worldgeo.pressbooks.com/chapter/oceania/#chapter-359-section-1
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License.

Biogeography in Australia and the Pacific

The relative isolation of Oceania defines it as a region but has also contributed to perhaps its quirkiest characteristic: its distinctive wildlife. Biogeography is a branch of geography that explores the spatial distribution of the world's flora (plant life) and fauna (animal life).

While every world region has its own unique plants and animals, some of the creatures found in Australia and the Pacific are found nowhere else on Earth. A number of world regions have an impressive degree of biodiversity, meaning there is a wide variety of species present. These regions are generally located in the tropics. British biogeographer Alfred Russel Wallace was one of the first to try and determine the boundary of Australia and Southeast Asia's unique plants and animals in the 19th century.

Geography is more than the where, however, but is also a discipline that asks "Why?" Why does Australia have such unique, and frankly a bit frightening at times, flora and fauna? Why are monotremes, mammals that lay eggs rather than give birth to live young, only found in the isolated regions of Australia and New Guinea? It is the isolation of this region that's key. 200 million years ago, Australia was situated on the far reaches of Pangaea, the last supercontinent (see Figure 10.9).

Around 175 million years ago, Pangaea began to break apart. During the same time period, the earliest mammals were evolving, diverging first from egg-laying reptiles and then continuing to adapt and change. Early egg-laying monotremes were found throughout Pangaea but eventually went extinct in the other world regions, out-competed by more evolutionarily advanced mammals. Australia and New Guinea, however, broke away before more advanced mammals arrived, and thus monotremes remained. The only modern monotremes are the platypus and the echidna.

Figure 10.9 Map of Pangaea with Modern Continental Outlines (© User:Kieff, Wikimedia Commons, CC BY-SA 3.0)

In addition to monotremes, Australia is home to the world's largest and most diverse array of marsupials, mammals that carry their young in a pouch. A number of marsupials are also found in Central and South America, and just one species lives in North America: the Virginia opossum, more typically referred to as a "possum." In Oceania, well-known marsupials include the kangaroo, koala, wombat, and the Tasmanian devil. The Kangaroo, in particular, is a widely used symbol of Australia, and kangaroo meat, though controversial, can be found throughout Australia.

Australia is not just home to cuddly marsupials like koalas, wallabies, and quokkas, though. It is also home to some of the world's deadliest creatures. There are more deadly snakes in Australia than in any other country in the world, including the taipan, which is considered by some to be the world's most venomous. An episode of the children's television show "Peppa Pig" was actually banned in Australia because it featured a "friendly spider," and local officials believed it would send the wrong message to Australian children in a country where spiders can be deadly. Offshore, Australia's box jellyfish can kill simply by the pain inflicted by its sting, which can send the body into shock.

Another key area of biodiversity is New Zealand, particularly in terms of its flora. Its isolation allowed for species of trees that have remained relatively unchanged for the past 190 million years. Several species of birds in New Zealand, such as the moas, went extinct due to hunting shortly after humans first arrived in the region.

Few mammals existed in New Zealand before human settlement and the arrival of the first mammals here, such as rats and weasels, led to widespread extinctions of native species that had never had to evolve to compete with these predators. Rabbits specifically proved to be a particularly troublesome invasive species, which refers to a species of plant, animal, or fungus that is not native to an area but spreads rapidly. Early settlers to New Zealand brought rabbits for fur and meat, but the high reproductive capacity of rabbits quickly proved troublesome, and by the 1880s, rabbits had a considerable negative effect on agriculture.

 The solution in the late 19th century was to introduce stoats, ferrets, and weasels, natural predators of rabbits. Unfortunately, these species proved devastating to local bird species and had only minimal impact on the increasing rabbit population. Cats were similarly introduced, but they, too, caused the extinction of several bird species and a native bat. (The children's story about the old lady who swallowed the fly comes to mind). These species are still seen as some of the biggest threats to New Zealand's wildlife.