The geography of Papua New Guinea describes the eastern half of the island of New Guinea, the islands of New Ireland, New Britain and Bougainville, and smaller nearby islands. Together these make up the nation of Papua New Guinea in tropical Oceania, located in the western edge of the Pacific Ocean.
Papua New Guinea is largely mountainous, and much of it is covered with tropical rainforest. The New Guinea Highlands (or Central Range) run the length of New Guinea, and the highest areas receive snowfall—a rarity in the tropics. Within Papua New Guinea Mount Wilhelm is the highest peak, at . There are several major rivers, notably the Sepik River, which is long, which winds through lowland swamp plains to the north coast, and the Fly River at in length, which flows through one of the largest swamplands in the world to the south coast. The Highlands consist of a number of smaller ranges running west to east, such as the Finisterre Range which dominates the Huon Peninsula to the north of the city of Lae. At it is the world's third largest island country.
Papua New Guinea has one land border—that which divides the island of New Guinea. Across the 820 km (509 mi) border is the Indonesian provinces of Papua, Highland Papua and South Papua. Papua New Guinea's border with Indonesia is not straight; the border loops slightly to the west along the Fly River in the south-central part of New Guinea, on the western edge of Papua New Guinea's Western Province. There are maritime borders with Australia to the south and Solomon Islands to the southeast.
Physical geography
Papua New Guinea extends over , including a large mainland a number of islands. The country lies just south of the equator, and shares a land border with Indonesia, and maritime borders with Australia, the Solomon Islands, and the Federated States of Micronesia. The island of New Guinea lies at the east of the Malay Archipelago. The country is separated from Australia's Cape York Peninsula by the shallow Torres Strait. To the west of this strait is the shallow Arafura Sea, while to its east is the much deeper Coral Sea. The Gulf of Papua covers much of the southern coast, while the Solomon Sea lies east of the mainland.
The total coastline is longer than , and the country has an exclusive economic zone of . the largest fisheries zone in the South Pacific. The territorial waters and exclusive economic zone were established by the National Seas Act 1977. The country covers two timezones, with the Autonomous Region of Bougainville an hour ahead of the rest of the country.
is land and is water. This makes it the 3rd largest island country in the world. Its mainland coastline is long.
Geologically, the island of New Guinea is a northern extension of the Indo-Australian tectonic plate, forming part of a single land mass which is Australia-New Guinea (also called Sahul or Meganesia). It is connected to the Australian segment by a shallow continental shelf across the Torres Strait, which in former ages lay exposed as a land bridge, particularly during ice ages when sea levels were lower than at present. As the Indo-Australian Plate (which includes landmasses of India, Australia, and the Indian Ocean floor in between) drifts north, it collides with the Eurasian Plate. The collision of the two plates pushed up the Himalayas, the Indonesian islands, and New Guinea's Central Range. The Central Range is much younger and higher than the mountains of Australia, so high that it is home to rare equatorial glaciers.
The geological history of New Guinea is complex. It lies where the north-moving Indo-Australian plate meets the west-moving Pacific plate. This has caused its highly variable geography both on the mainland and on its islands. Tectonic movement is also the origin of the country's active volcanos and frequent earthquakes. The country is situated on the Pacific Ring of Fire, with altogether 14 known active volcanos and 22 dormant ones. The area south of the mountainous spine is part of the Australian craton, with much of the land to the north being accreted terrain. Both the mainland and the main island groups of the Bismarck Archipelago and the Bougainville are dominated by large mountains. Altogether, one estimate mountains cover at least 72% of the country. Of the rest, 15% are plains and 11% swamps. The country includes about 600 islands of various sizes. Another suggests mountains and hills make up 52%, while defining 19% as plans and plateaus, and 18% as floodplains. The remaining land was classified as volcanic or littoral.
The New Guinea Highlands lie within a spine of mountain ranges which run along the centre of the island from Milne Bay in the very southeast of Papua New Guinea through to the western end of Indonesian New Guinea. One of these mountains is Mount Wilhelm, which at is the highest point in the country. Between these mountains are steep valleys, which have a variety of geological histories. The populous region referred to as the Highlands has shorter mountains than those to its northwest and southeast, and includes some relatively flat areas between the mountains.
North of the central mountain belt, a large depression is drained by Sepik River in the west, and the Ramu and Markham Rivers flow through a graben in the east. The depression continues into the waters east of the mainland, forming the New Britain Trench. The northwest coast hosts the Bewani Mountains, Torricelli Range, and Prince Alexander Mountains, which the Sepik River separates from the Adelbert Range further east. East of this, the Huon Peninsula contains the Finisterre Range and the Saruwaged Range. Much of this northern coastline is made up of former seabed that has been raised, and the area remains tectonically active, prone to earthquakes and landslides. West of the Sepik river the northern coastline is highly exposed to the ocean, with no outlying islands, a lack of fringing reefs, and Sissano Lagoon the only sheltered bay. The Sepik river however is navigable for about half of its length.
The Sepik-Ramu river system extends across the north of the mainland, while the Fly River flows out the south. Both are surrounded by lowland plain and swamp areas. These form two of the nine drainage basins of the mainland. The other two major basins surround the Purari and Markham Rivers. Within this land lies over 5,000 lakes. Of these, only 22 exceed , the largest being Lake Murray at .
The only geologically stable part of the country is its southwestern lowlands, which form the largest contiguous lowland area. The volcanic Mount Bosavi lies in the north of these plains, and the coastal areas can be slightly hilly, especially towards the mouth of the Fly River. Forming a barrier between this area and the highland interior are the tall Southern Fold Mountains. Lake Kutubu lies within this mountain range. The Fly River, which originates in the central mountains, is navigable for the majority of its length.
Other large rivers in the country include the Musa, Kikori, Turama, and Wawoi.
The Papuan Peninsula (considered the island's "tail", and thus also known as the "Bird's Tail Peninsula") in the east contains Mount Lamington volcano and the Hydrographers Range on its northern side. Further east, the area around Cape Nelson has more volcanoes, including Mount Victory and Mount Trafalgar. In its centre runs the Owen Stanley Range, It has a number of sheltered bays, including Milne Bay, Goodenough Bay, Collingwood Bay, and the Huon Gulf. The small islands off the southeast, including the D'Entrecasteaux Islands, the Trobriand Islands, Woodlark Island, and the Louisiade Archipelago total just over .
The major islands off the northeast of the mainland form along two arcs. One includes small islands near the mainland and the large island of New Britain. While New Britain is mostly not volcanic, volcanic activity along its north and especially in the Gazelle Peninsula around Rabaul has created fertile soil. The other island arc links Manus Island, New Hanover, New Ireland, and Bougainville. Bougainville hosts three large volcanoes. The area of these islands is around .
The capital of Port Moresby lies on the southern coast. The city of Lae lies towards the east on the northern coast. Only around 2% of the country is regularly cultivated.
The border between Papua New Guinea and Indonesia was confirmed by a treaty with Australia before independence in 1974. The land border comprises a segment of the 141° E meridian from the north coast southwards to where it meets the Fly River flowing east, then a short curve of the river's thalweg to where it meets the 141°01'10" E meridian flowing west, then southwards to the south coast. The 141° E meridian formed the entire eastern boundary of Dutch New Guinea according to its 1828 annexation proclamation. By the Treaty of The Hague (1895) the Dutch and British agreed to a territorial exchange, bringing the entire left bank of the Fly River into British New Guinea and moving the southern border east to the Torasi Estuary. The maritime boundary with Australia was confirmed by a treaty in 1978. In the Torres Strait it runs close to the mainland of New Guinea, keeping the adjacent North Western Torres Strait Islands (Dauan, Boigu and Saibai) under Australian sovereignty. Maritime boundaries with the Solomon Islands were confirmed by a 1989 treaty.
Including all its islands, it lies between latitudes 0° and 12°S, and longitudes 140° and 160°E.
The northernmost point is Mussau Island (1°23' S), southernmost point is Sudest Island (11°65' S), easternmost point is Olava, Bougainville (155°57' E) and the westernmost point is either Bovakaka along the Fly River border with Indonesia or Mabudawan (140°54' E).
Papua New Guinea has several volcanoes, as it is situated along the Pacific Ring of Fire. Volcanic eruptions are not rare, and the area is prone to earthquakes and tsunamis because of this. The volcanic disturbance can often cause severe earthquakes, which in turn can also cause tsunamis. Papua New Guinea is also prone to landslides, often caused by deforestation in major forests. The mountainous regions of Papua New Guinea are the areas most susceptible to landslides causing damage.
Offshore islands include the small, forested Admiralty Islands, the largest of which is Manus, to the north of the main island of New Guinea. These have a distinct plant and animal life from the main island but the natural forest has been cleared in places for logging and agriculture.
A 2019 global remote sensing analysis suggested that there were of tidal flats in Papua New Guinea, making it the 25th ranked country in terms of tidal flat area.
Rivers
Soil Soil quality and composition in Papua New Guinea is highly varied, however the tectonic activity in the country means the soils are relatively young. Over half of the country has Inceptisol soils, while a quarter are Entisols. Around 14% are Ultisols, including a large area in Western Province,. Of the rest, a quarter of New Ireland Province is covered in Alfisols, while a third of East New Britain Province is covered in Mollisols.
Natural disasters The country is at risk of earthquakes, tsunamis, volcanic eruptions, floods, landslides, and droughts. Papua New Guinea is famous for its frequent seismic activity, being on the Ring of Fire. On 17 July 1998, a magnitude 7.0 earthquake struck north of Aitape. It triggered a 50-foot-high tsunami, which killed over 2,180 people in one of the worst natural disasters in the country.
In September 2002, a magnitude 7.6 earthquake struck off the coast of Wewak, Sandaun Province, killing six people.
On 25 February 2018, an earthquake of magnitude 7.5 and depth of 35 kilometres struck the middle of Papua New Guinea. The worst of the damage was centred around the Southern Highlands region.