New Guinea
Geography

New Guinea is an island to the north of the Australian mainland, south of the equator. It is isolated by the Arafura Sea to the west, and the Torres Strait and Coral Sea to the east. Sometimes considered to be the easternmost island of the Indonesian archipelago, it lies north of Australia's Top End, the Gulf of Carpentaria and Cape York Peninsula, and west of the Bismarck Archipelago and the Solomon Islands archipelago.

Politically, the western half of the island comprises six provinces of Indonesia: Papua, Central Papua, Highland Papua, South Papua, West Papua and Southwest Papua. The eastern half forms the mainland of the country of Papua New Guinea.

The shape of New Guinea is often compared to that of a bird-of-paradise (indigenous to the island), and this results in the usual names for the two extremes of the island: the Bird's Head Peninsula in the northwest (Vogelkop in Dutch, Kepala Burung in Indonesian; also known as the Doberai Peninsula), and the Bird's Tail Peninsula in the southeast (also known as the Papuan Peninsula).

A spine of east–west mountains, the New Guinea Highlands, dominates the geography of New Guinea, stretching over 1,600 km (1,000 mi) across the island, with many mountains over 4,000 m (13,100 ft). The western half of the island contains the highest mountains in Oceania, with its highest point, Puncak Jaya, reaching an elevation of 4,884 m (16,023 ft). The tree line is around 4,000 m (13,100 ft) elevation, and the tallest peaks contain equatorial glaciers —which have been retreating since at least 1936. Various other smaller mountain ranges occur both north and west of the central ranges. Except in high elevations, most areas possess a warm humid climate throughout the year, with some seasonal variation associated with the northeast monsoon season.

Another major habitat feature is the vast southern and northern lowlands. Stretching for hundreds of kilometres, these include lowland rainforests, extensive wetlands, savanna grasslands, and some of the largest expanses of mangrove forest in the world. The southern lowlands are the site of Lorentz National Park, a UNESCO World Heritage Site. The northern lowlands are drained principally by the Mamberamo River and its tributaries on the western side, and by the Sepik on the eastern side. The more extensive southern lowlands are drained by a larger number of rivers, principally the Digul in the west and the Fly in the east. The largest island offshore, Dolak, lies near the Digul estuary, separated by a strait so narrow it has been named a "creek".

New Guinea contains many of the world's ecosystem types: glacial, alpine tundra, savanna, montane and lowland rainforest, mangroves, wetlands, lake and river ecosystems, seagrasses, and some of the richest coral reefs on the planet.

The entire length of the New Guinea Highlands system passes through New Guinea as a vast watershed. The northern rivers flow into the Pacific Ocean, the southern rivers into the Arafura Sea and the Gulf of Papua. On the north side, the largest rivers are the Mamberamo, Sepik and Ramu. Mamberamo was born from the confluence of two large inland rivers. Tariku comes from the west to the east and Taritatu from the east. These rivers meander through swamps with huge internal descents and then merge. The Mamberamo thus formed reaches the ocean by breaking through the Coastal Mountains. Mamberamo River is navigable to Marine Falls. The Sepik is a much more important river. Similarly, it collects water from a spacious pool. It is 1,100 kilometers from the Victor Emanuel Range to the estuary, making it the longest river in New Guinea. The winding, muddy, sluggish river can be navigated for 500 km. Ramu is a 650 km long river. Its lower section is navigable, but its upper flow is high-falling, fast-flowing. The energy of the river is used by a power plant near the city of Kainantu.

On the south side, the most significant rivers are Pulau, Digul, Fly, Kikori and Purari. The largest river in the western part of the island is Digul. It originates from the Star Mountains, which rise to an altitude of 4,700 m. The coastal plain is bordered by a swamp world hundreds of kilometers wide. Digul is the main transport route to the fertile hills and mountains within the island. The river Fly is born near the eastern branches of the Digul. It is named after one of the ships of the English Royal Fleet, which first sailed into the mouth of the river in 1845. The total length of the river is 1,050 km. Smaller boats can sail 900 km on the river. The estuary section, which decomposes into islands, is 70 km wide. The tide of the sea can have an effect of up to 300 kilometers. Strickland, a tributary of the Fly, reaches the Papuan Plain through wild gorges. Fly and Strickland together form the largest river in New Guinea. The many rivers flowing into the Gulf of Papua form a single delta complex. The rivers of the island are extremely rich in water due to the annual rainfall of 2,000–10,000 mm. According to a modest calculation, the New Guinea River carries about 1,500 km /a (48,000 m /s) of water into the sea. Fly alone carries more water 238 km /a (7,500 m /s) than all the rivers in Australia combined.
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