Solomon Islands' geography: two volcanic chains and a scatter of atolls in a large sea

How the islands line up in two chains

The main islands lie in two lines running northwest to southeast, Britannica records. The southern chain holds Vella Lavella, the New Georgia Islands, Savo and Guadalcanal; the northern holds Choiseul, Santa Isabel and Malaita. The two converge on Makira, also called San Cristobal. The national statistics office counts six large islands, Choiseul, New Georgia, Santa Isabel, Guadalcanal, Malaita and Makira, among 997 islands in all; Wikipedia counts six major islands and 992 smaller ones. The main islands are 140 to 200 kilometres long and 30 to 50 kilometres wide, and Guadalcanal, at 5,336 square kilometres, is the largest.

The chains are the southern part of a longer archipelago. Bougainville and Buka sit at its northwestern end and belong to Papua New Guinea, so the country's western border runs between islands that geology made one group. Outside the chains lie islands of a different kind. The Santa Cruz Islands, whose largest island is Nendö, lie about 555 kilometres east of Guadalcanal and more than 200 kilometres from any other island in the country. Rennell and Bellona lie to the south, and the Polynesian outliers Tikopia, Anuta, Sikaiana and Ontong Java are scattered to the east and north.

The islands are not all of one kind. The census report describes a range from high volcanic islands to raised coral atolls, low-lying islands, sand cays and rock outcrops, and the smallest are under a hectare. Wikipedia's geography article notes that many of the smaller islands are tiny atolls of sand and palm trees. The difference matters for the people on them: a high island has rivers, ridges and room to move inland, and an atoll has none of those.

The country spans about 1,448 kilometres from its westernmost to its easternmost island by Wikipedia's figure, and the census describes the main group as stretching about 1,700 kilometres from Bougainville to the northern islands of Vanuatu. Its extreme points are Ontong Java Atoll to the north, Fatutaka to the east, Indispensable Reef in Rennell and Bellona Province to the south and Mono Island in the Treasury group to the west. The Commonwealth Secretariat names Vanuatu to the southeast and Papua New Guinea to the west as the nearest neighbours.

Why the land area depends on who measured it

The sources give at least four figures for the land. The 2019 census report and Britannica both use 30,407 square kilometres. Wikipedia's main article gives a total area of 28,896 square kilometres, and its geography article, drawing on the CIA World Factbook, gives 27,986 square kilometres of land and 1,014 of inland water. The Australian foreign ministry gives 28,400 square kilometres, the figure this record carries. None of the sources on file explains the difference, and the census uses 30,407 for every density it calculates.

The sea is a matter of a different order. The exclusive economic zone, measured from archipelagic baselines, covers 1,589,477 square kilometres in both the census and the Factbook figures, and Wikipedia gives a coastline of 5,313 kilometres.

The census splits the land between nine provinces and the capital territory:

What raised the mountains and still shakes them

The islands belong to a volcanic arc that runs from New Ireland in Papua New Guinea to Vanuatu. The main phases of volcanism that built them fell between the Eocene and the Middle Miocene, and activity resumed no earlier than about 8 million years ago and continues now. The result is rugged country. Britannica describes the main islands as large and mountainous, and the range on Guadalcanal carries the country's highest point, Mount Popomanaseu, given as 2,332 metres in the Factbook figures Wikipedia uses and as 2,330 metres, or 7,644 feet, by Britannica. Wikipedia's figure carries a note that the summit is Popomanaseu and not Mount Makarakomburu.

Several volcanoes are active. Tinakula in the Santa Cruz group and Kavachi, a submarine volcano near New Georgia, have erupted every few years, according to Britannica, and Tourism Solomons calls Tinakula the country's most active volcano. Savo, 35 kilometres northwest of Honiara, last erupted in the 1840s; it has hot springs, and megapode birds breed on its thermal springs. Simbo Island has a solfatara, a vent that gives off only hot vapour and sulphurous gas.

Earthquakes are routine. The Australian government's travel advice, updated in September 2026, says shocks of magnitude 5.0 and above are felt routinely throughout the country, and the larger ones have reshaped coasts:

The death toll for 2007 is given as 52 by the regional assistance mission and Wikipedia and as several dozen by Britannica.

How rain and wind divide the year

The climate is tropical and oceanic, hot and humid with rain in every month, and Britannica notes that temperatures seldom exceed 32°C. The figures for rainfall vary with the source and the place. Britannica gives a usual 3,000 to 3,500 millimetres a year, Wikipedia an annual figure of about 3,050 millimetres and a mean temperature of 26.5°C, and the census report a range of 3,000 to 6,000 millimetres, citing the national meteorological service. The census report gives mean daily temperatures of 24°C to 32°C, against 23°C to 30°C over the previous ten years.

The year has two seasons. From November to April northwesterly winds bring the wet season, warmer and wetter, with squalls and occasional cyclones; from about May to October the southeast trades bring the dry season, with gusts at times of 30 knots or more. Tourism Solomons records that Honiara receives almost 70% of its yearly rain in the wet season, about 100 millimetres a month in the dry months against upwards of 300 in the wet ones, while Santa Cruz in the east receives 280 to 420 millimetres in every month. The Australian government's travel advice treats November to May as the cyclone season.

Cyclones that form in the Coral Sea usually veer towards Vanuatu, New Caledonia or Australia, but the outer islands have been hit hard. Cyclone Tia destroyed most of the housing and food crops on Tikopia in 1992, and Cyclone Zoe struck Tikopia and Anuta in December 2002, cutting off their 3,000 people. In April 2014 the tropical low that became Cyclone Ita dropped more than 1,000 millimetres of rain on the Gold Ridge mine on Guadalcanal in four days. The Mataniko River broke its banks in Honiara on 3 April and swept away homes and both of the city's main bridges. Wikipedia gives at least 23 dead and about 49,000 people affected; the regional assistance mission put those affected at about 52,000.

Where the plains are and where the forest goes

Heavily wooded mountains cover most of the islands. Britannica notes that there are extensive plains but that only those on the northern side of Guadalcanal have been developed for large-scale agriculture. The Factbook figures Wikipedia uses put arable land at 0.62% and permanent crops at 2.04% of the land in 2005, and the main article gives forest cover of 78.1% in 2022. Soils range from rich volcanic ground to relatively infertile limestone.

The forest has been cut fast. Global Forest Watch, as summarised on Wikipedia, records 239,794 hectares of tree cover lost from 2001 to 2024, about 8.7% of the tree cover of 2000. Most of the islands belong to the Solomon Islands rain forests ecoregion, which also covers Bougainville and Buka, while the Santa Cruz Islands belong to the Vanuatu rain forests ecoregion. Large kauri trees grow on Vanikoro and Santa Cruz, Tourism Solomons notes, and more than 230 varieties of orchids and other tropical flowers have been recorded in the country.

Guadalcanal shows how much the side of an island matters. Its northern coast holds the plains, the airfield, Honiara and the roads that run out of it to Lambi in the west and Aola in the east. The southern coast, known as the Weather Coast, lies on the far side of the main range from Honiara; Tourism Solomons describes remote villages along a rugged coastline there, reached by motorised canoe from Marau Sound at the island's eastern tip, and it was on that coast that the last armed group of the Tensions held out until 2003.

Wildlife on land is limited, as on most island groups, and Britannica lists pigeons, rats, bats, snails, lizards, frogs, turtles and the estuarine crocodile. The national statistics office records that land ownership and use are organised largely along tribal lines, while the state owns most land in the towns.

What lives on the reefs and on Rennell

A baseline survey of marine biodiversity in 2004 found 474 species of coral, nine of them possibly new to science. Marovo Lagoon in the Western Province, which Tourism Solomons describes as massive, has been proposed as a World Heritage site.

Rennell, the southernmost of the Solomon Islands, is a raised coral atoll about 86 by 15 kilometres, covering 37,000 hectares and clad in dense forest. At its southern end lies Lake Tegano, the atoll's former lagoon, its brackish surface at sea level and ringed by cliffs. East Rennell, the lake and the land and sea around it to three nautical miles, became a UNESCO World Heritage site in 1998, and in 2013 it was placed on the List of World Heritage in Danger because of logging in the west of the island. Of 50 bird species recorded there, 21 are endemic, and Crocker's sea snake lives in Lake Tegano and nowhere else. About 800 people live in four villages around the lake, and a management plan of 2007 recognises their customary rights.

Where people live on the islands

Most people live in small villages, where they garden, raise pigs and fish for much of their food, Britannica records. The census of 24 November 2019 found 72.4% of the population in rural areas and 27.6% in urban ones, and the report notes that most people live along the coast, though inland communities on Guadalcanal and Malaita are growing. Malaita is the most populous province and Honiara, on 22 square kilometres, the densest, with 5,916 people per square kilometre against a national 23.7.

Services follow the same split between town and village. The 2019 census found 78.3% of households with an improved source of drinking water, 90.6% in urban areas and 74.2% in rural ones, and 35.4% with improved sanitation, 83.8% urban and 19.0% rural. Only 15.3% of households were connected to the electricity grid, and 84.0% cooked mainly with wood or coconut, a share that reached 95.9% in rural households.

The coast brings its own exposure. In the 2019 census 16.8% of households reported exposure to sea-level rise, and in Central Province the share was 40.9%. Choiseul's provincial township lies less than two metres above sea level, and after consulting engineers, scientists and planners its people decided to build a new town on the adjacent mainland and move in stages, Tourism Solomons records. On Ranongga the 2007 earthquake worked the other way: uplift extended the shoreline by up to 70 metres and exposed many coral reefs.