Geography of the Bahamas: islands on two banks of limestone

How two limestone banks make the islands

Every island in the Bahamas stands on one of two submarine platforms, the Little Bahama Bank in the north and the Great Bahama Bank to the south, and the islands are the parts of those banks that happen to break the surface. Britannica describes the whole as an irregular submarine tableland rising from the depths of the Atlantic, separated from Florida and Cuba by deep-water channels. The Bahamas and the Turks and Caicos Islands together make up the Lucayan Archipelago, which continues south-east into the Mouchoir, Silver and Navidad banks.

The banks are made of limestone laid down in shallow water, and there is a great deal of it. Beneath the Great Bahama Bank the limestone is more than 4.5 kilometres thick. Since it could only have formed near the surface, the platform must have sunk under its own weight as it grew, at roughly 3.6 centimetres every 1,000 years, with new sediment keeping pace. The wider Bahamas Platform formed about 150 million years ago, soon after the North Atlantic opened, and about 80 million years ago the Gulf Stream flooded across it, drowning the Blake Plateau, cutting the Bahamas off from Florida and Cuba and splitting the south-east into separate banks.

The banks still grow. Coral reefs form their outer walls, and inside them oolites form where ocean water spreads over the shallows, warming by about 3 °C and growing about 0.5% saltier; cemented together, the grains become what geologists call grapestone. Sediment accumulates at about 20 millimetres every 1,000 years, and giant stromatolites are found off the Exuma Cays.

The chain runs more than 800 kilometres south-east from Grand Bahama, about 100 kilometres off Florida, to Great Inagua, about 80 kilometres from the eastern tip of Cuba, and it straddles the Tropic of Cancer between latitudes 20° and 28° north. Its extremes are Walker's Cay in the Abacos to the north, Matthew Town on Great Inagua to the south, the Elbow Cays of Bimini to the west and Mayaguana to the east. At Cay Lobos Bahamian territory comes within 22.5 kilometres of Cuba.

How many islands the banks carry depends on who counts and what counts as an island. Britannica gives nearly 700 islands and cays and more than 2,000 low rock formations, with about 30 inhabited; the Wikipedia geography article gives about 700 islands with between 30 and 40 inhabited. The land adds up to 10,010 square kilometres of a total area of 13,880, and the water between the islands is most of the country. The Exclusive Economic Zone is given as 654,715 square kilometres, and the Royal Bahamas Defence Force describes the territory it patrols as 470,000 square kilometres of ocean space.

How wind built the Bahamian ridges

There are no mountains. The highest point, Mount Alvernia on Cat Island, is given as 63 metres by Britannica and the record, and as 64 metres by the Wikipedia country article. New Providence, where most people live, reaches 37 metres, and the Bimini group rises no higher than 6. The dominant landform on the large islands is flat ground a few metres above the sea, and at least 80% of the land lies below 10 metres.

What relief there is was built by the wind. When sea level fell during the ice ages, oolitic sand on the exposed banks blew into dunes, and rainwater cemented the dunes quickly into rock, a limestone called eolianite that still shows the cross-bedding of the original sand. Overlapping dunes became ridges, most of them 30 to 45 metres high, with one on Cat Island reaching 60. Britannica notes that on islands fronting the Atlantic the ridges run along the north-eastern side, parallel to the long axis of the island, where the trade winds pushed the sand. Britannica notes that Eleuthera and Long Island carry many hills over 30 metres.

The low ground between the ridges holds lakes and swamps, and much of the rest of the surface is rock or mangrove.

Settlement follows the shelter and the harbours. Britannica notes that some villages sit on the calm leeward shore, as on Cat Island, while others face the north-east trade winds, as in the Abaco Cays, and that most grew where a natural harbour gave access for boats. The long drift of people from farming and fishing villages to the tourist and commercial centres has concentrated about two-thirds of the population on New Providence, by Britannica's reckoning, with Grand Bahama and Abaco the other islands to gain. The Wikipedia country article puts New Providence's share at 70%. The coast runs to 3,542 kilometres, and a remote-sensing survey put the area of tidal flats at 1,354 square kilometres.

Where the fresh water sits without rivers

The sources disagree on whether the Bahamas has a river at all. Britannica states that there are none; the Wikipedia geography article records one, on Andros, and names the Goose River among the country's bodies of water. Either way, running water plays almost no part in the landscape. The limestone weathers by solution instead, producing what geologists call Bahamian karst: potholes, sinkholes, beachrock, sea caves and inland caves that exist because there are no rivers to cut valleys, and blue holes such as Dean's Blue Hole. Several blue holes are aligned along the South Andros Fault.

Fresh water is found in the rock itself. Britannica singles out Andros for its abundance, and the Grand Bahama Museum describes a generous supply just below the surface of Grand Bahama, one of the reasons Freeport could be built there in the 1950s. Several islands, New Providence, San Salvador and Great Inagua among them, also hold large lakes.

The quantity is small. Total renewable water resources were estimated at 0.02 cubic kilometres in 2011, and only 10 square kilometres of land was irrigated in 2003. Arable land was put at 0.8% of the total in 2012, on soils that are fertile in places and thin almost everywhere.

What grows on the pine islands and dry south

Four northern islands, Grand Bahama, Abaco, Andros and New Providence, carry forests of Caribbean pine, the pineyards. Further south the woody cover is low tropical hardwood and scrub, and cactus and succulents are common. Three terrestrial ecoregions are recognised: Bahamian pine mosaic, Bahamian dry forests and Bahamian mangroves. Forest covered about 51% of the land in 2020, 509,860 hectares, the same area as in 1990.

Rainfall falls away to the south. Annual rainfall is given as about 1,120 millimetres by Britannica and 1,320 by the Wikipedia climate section, falling mostly from May to October, while Great Inagua in the far south receives less than 800. The early settlers raked salt on the drier islands, and Great Inagua is where the flamingos breed.

Land animals are small. Britannica lists frogs, lizards and snakes, none of them venomous, bats in coastal caves, the agouti, the raccoon, the iguana and the flamingo, the national bird, and notes that all have been reduced in number and range. The sea is richer, with conch and spiny lobster the two animals most people eat.

How the Bahamas came to protect its banks

Modern conservation in the Bahamas began with two surveys in the 1950s. The National Audubon Society found in the early 1950s that hunting was destroying the West Indian flamingo and enlisted two Bahamian flamingo hunters, Sammy and Jimmy Nixon, to guard the Inagua colony. In 1958 the naturalist Ilya Tolstoy led an expedition to the Exuma Cays, which developers wanted to buy, and its report recommended a trust on the model of the British National Trust.

The Exuma Cays Land and Sea Park was the result, covering 176 square miles, or 112,640 acres, of land and sea. The Bahamas National Trust dates the park to 1958 and Britannica to 1959, the year the Bahamas National Trust Act was signed, on 13 July. The Trust describes it as the first land-and-sea park anywhere; fishing, shelling and taking conch are banned inside it, and Defence Force officers are stationed at its headquarters on Warderick Wells. The government designated Inagua National Park in 1965 for the flamingo colony, which the Trust's own account, read in 2026, puts at more than 60,000 birds.

The size of the system has grown with it. Britannica refers to some two dozen national parks, and the Trust's park list, read in September 2026, counts 33.

What the weather does across the year

The climate is tropical savanna, warm all year, with two seasons. The wet season runs from May to October, when southeasterly air from the deep tropics brings short, heavy thunderstorms and daytime highs around 31 °C. The dry season runs from November to April, when northeast trade winds and the occasional cold front from North America bring highs nearer 25 °C and sometimes drought on the farms. Britannica gives a range from about 21 °C in winter to about 27 °C in summer, with extremes seldom below 16 °C or above 32 °C.

The Gulf Stream and the low latitude keep frost away entirely. None has ever been recorded, and the one report of snow in the islands' history came from Freeport on 19 January 1977, when snow mixed with rain was seen in the air for a short time. Average temperature has risen by about 0.5 °C since 1960.

The hurricane season runs officially from June to November, with most Bahamian hurricanes arriving from July to October. Hurricane Andrew in 1992, which caused damage estimated at $250 million, mostly to farms, was the strongest to strike the islands until 2019.

What Hurricane Dorian did to Abaco and Grand Bahama

Hurricane Dorian made landfall at Elbow Cay off Great Abaco at 16:40 UTC on 1 September 2019, at Category 5, with sustained winds of 298 kilometres per hour, gusts over 355 and a central pressure of 910 millibars. It moved very slowly, and between 1 and 3 September it struck Grand Bahama as well as Abaco. In Marsh Harbour more than 75% of homes were damaged and the airport runway was under water.

The assessment the government commissioned from the Inter-American Development Bank and ECLAC put the total cost at $3.4 billion, 72% of it physical damage, and found that Abaco bore 87% of the losses and 76% of the damage. It recorded 67 confirmed deaths and 282 people missing as of 18 October 2019, and 29,472 people whose homes or assets were damaged. Other estimates of the damage reached at least $7 billion. On 12 September 2019 more than 1,300 people were still listed as missing.

Storm surge did much of the harm on islands with little high ground. With at least 80% of the land below 10 metres, the Bahamas is expected to be highly affected by sea-level rise, and a global rise of 2 °C above pre-industrial levels is estimated to make extreme hurricane rainfall four to five times more likely there. Emissions were small, 2.94 million tonnes of greenhouse gases in 2023, and the government's stated aim is solar power at 30% of generation by 2033.