The Galápagos Islands are a volcanic archipelago on the equator in the eastern Pacific, about 1,000 km west of mainland Ecuador, the country they belong to. Their land area of roughly 8,000 km² is spread across 127 islands, islets and rocks scattered over some 45,000 km² of ocean; 19 islands are larger than 1 km², and Isabela alone, at 4,588 km², makes up close to three-fifths of the total. The highest point is Volcán Wolf on Isabela at 1,700 m. Every island was built by volcanoes rising from a hotspot in the mantle, none was ever joined to a continent, and the plants and animals that reached them by sea and air evolved into the endemic species that helped Charles Darwin think his way towards natural selection after his visit in 1835.
A hotspot under the moving Nazca plate
The islands sit on the Nazca plate, a slab of oceanic crust drifting east and south-east and diving under the South American plate at about 6.4 cm a year. Beneath this moving plate lies the Galápagos hotspot, where a plume of hot material rising through the mantle melts the base of the crust and feeds volcanoes on the seafloor. Because the plate keeps moving while the plume stays roughly in place, each volcano is slowly carried away from its source of magma, goes quiet, erodes and eventually sinks. A new volcano then grows over the hotspot behind it.
Volcanism in the region has been continuous for at least 20 million years, and the first islands formed at least 8 million years ago, possibly much earlier. Their older predecessors have already been carried east and drowned. The repeated eruptions have also built a submarine platform about 3 km thick under the whole chain, which is why the islands rise from relatively shallow water compared with the deep ocean around them. To the north, about 200 km away, lies the Galápagos Spreading Centre, the boundary where the Nazca and Cocos plates pull apart; the area is often described as the Galápagos triple junction.
The volcanoes do not look like those of Hawaii, the other textbook hotspot chain. Galápagos shield volcanoes are tall and rounded rather than broad and gently sloping, set closer together and with larger summit calderas, a shape linked to the pattern of fissures that feed them: radial on the flanks, circular around the caldera rims. The circular fissures pour out stacks of short lava flows that steepen the summits.
Fernandina to San Cristóbal: island ages from west to east
The clearest sign of the conveyor belt is the age of the rocks. Read from west to east, the islands get steadily older, because the eastern ones were formed over the hotspot first and have since been carried away from it. Geological dating gives roughly 50,000 years for Fernandina, 650,000 years for Isabela, 1.1 million for Santiago, 1.7 million for Santa Cruz, 2.9 million for Santa Fe and 3.2 million for San Cristóbal.
The landscapes follow the same pattern. In the west, Fernandina and Isabela carry young, tall shield volcanoes with fresh black lava and deep calderas, built mostly of tholeiitic basalt. In the east, the volcanoes are lower, older, more eroded and lack calderas, and their soils support more vegetation. Fernandina has been the most active volcano in the archipelago since 1790, with recorded eruptions in 1991, 1995, 2005 and 2009 and more since, including 2018, 2020 and 2024, and in 1968 its caldera floor collapsed in what is described as the largest basaltic volcano collapse on record. Across the archipelago, nine active volcanoes erupted 24 times between 1961 and 2011.
Isabela, Santa Cruz and the inhabited islands
Isabela is the giant of the group. It is really six large volcanoes fused together by their lava flows: Ecuador, Wolf, Darwin, Alcedo, Sierra Negra and Cerro Azul. Volcán Wolf and Volcán Ecuador sit directly on the equator, so the island lies in both hemispheres. Sierra Negra is one of the busiest; its floor rose by 240 cm between 1992 and 1998 before an eruption in 2005, and it erupted again in June 2018, sending lava to the coast and forcing about fifty residents to evacuate.
After Isabela come Santa Cruz at 986 km² and Fernandina at 642 km². Santa Cruz, roughly in the middle of the chain, is home to the town of Puerto Ayora and the Charles Darwin Research Station. San Cristóbal, the easternmost of the large islands, holds the provincial capital, Puerto Baquerizo Moreno. Isabela, Santa Cruz and San Cristóbal are the three most populated islands and give their names to the province's three cantons; the 2022 census counted 28,583 residents, up from about 810 in 1941. Baltra, just north of Santa Cruz, carries the main airport, first built by the United States during the Second World War and later handed to Ecuador. The archipelago stretches about 220 km from Española in the south to Darwin Island in the north.
Altitude matters as much as position. On the larger islands, the coasts are dry, with cacti, thorny scrub and bare lava, while the highlands catch moisture from clouds and turn green and wooded. That split shapes the giant tortoise. The tortoise, called galápago in Spanish and the source of the archipelago's name, is native to seven islands. Where the highlands are humid and low plants are plentiful, the tortoises are large with domed shells; on dry islands they are smaller, with raised "saddleback" shells that let them stretch for higher food.
Humboldt, Panama and Cromwell currents on the equator
For islands on the equator, the Galápagos are surprisingly cool, and the reason is the sea. Three currents meet here. The Humboldt Current brings cold water up from the south along the coast of South America; the Panama Current brings warm water from the north; and the Cromwell Current, also called the Equatorial Undercurrent, flows east beneath the surface along the equator and wells up against the western islands. The Cromwell Current was only discovered in 1952 by Townsend Cromwell, an American fisheries scientist; it is about 400 km wide and runs some 5,600 km across the Pacific. Where it rises around Fernandina and western Isabela, it brings cold, nutrient-rich water that supports the archipelago's richest marine life.
The currents set the calendar too. From June to November comes the garúa season, with temperatures near the sea around 22 °C, steady south-easterly winds, drizzle and fog. From December to May the air and sea warm to around 25 °C, the wind drops and the sun shines between short, heavy downpours. El Niño years, every three to seven years, push warmer water in and cut off the nutrients; at the Charles Darwin Station, March rainfall was 249 mm in 1969 and just 1.2 mm in 1970.
The cold water explains some of the strangest residents. The Galápagos penguin is the only penguin living in the tropics, the flightless cormorant is the only cormorant known to have lost the ability to fly, and the marine iguana is the only lizard that feeds in the sea, grazing on algae along the lava shores.
Darwin's five weeks in 1835
HMS Beagle, on a British survey of the South American coast, reached the Galápagos on 15 September 1835. Darwin first went ashore on Chatham Island, now San Cristóbal, near the site of today's Puerto Baquerizo Moreno. The ship then moved on to Charles Island (Floreana), where the acting governor, Nicholas Lawson, told him that he could tell from the shape of a tortoise's shell which island it came from. Darwin noted the remark but paid it little attention at the time. On Albemarle (Isabela) he landed near Tagus Cove on 1 October and saw his first land iguanas, and he spent nine days collecting on James Island (Santiago) before the Beagle left for Tahiti on 20 October.
It was the mockingbirds, not the finches, that first caught his eye. Writing up his notes at sea, Darwin found that the specimens from Charles, Albemarle, James and Chatham each differed from island to island. The finches he had barely labelled by island. Only later, back in England, did the pattern of closely related but distinct species on neighbouring islands feed into the argument he published in On the Origin of Species in 1859. Today about 18 species are grouped as Darwin's finches, a standard example of one ancestor diversifying into many beak shapes for different foods. Ecuador had formally annexed the islands on 12 February 1832, three years before the Beagle arrived.
Ecuador's 1959 national park and the 1978 World Heritage listing
The islands paid heavily for their isolation once ships began to call. Whalers and pirates took giant tortoises by the thousand for meat, and introduced goats, rats and pigs ate out the vegetation of several islands. Tortoise numbers fell from more than 250,000 in the 16th century to a low of around 15,000 in the 1970s.
Protection began in earnest in 1959, the centenary of On the Origin of Species, when Ecuador declared 97.5 percent of the land area a national park, leaving out only the areas already settled. The Charles Darwin Foundation was set up the same year, and its research station on Santa Cruz opened in 1964. UNESCO listed the Galápagos as one of the first World Heritage Sites in 1978, and named them a biosphere reserve in 1985. The surrounding sea followed: a marine reserve was declared in 1986, and today the Galápagos Marine Reserve covers about 133,000 km² of ocean. In July 2010 the World Heritage Committee took the islands off its list of sites endangered by environmental threats or overuse.
The pressures have not gone away. The resident population grew far faster than mainland Ecuador's for decades, and the islands recorded 268,000 visitors in 2022. Many land at Seymour Airport on Baltra, rebuilt in 2012–13 as an "ecological airport" designed around solar power, wind and seawater desalination. For the wildlife that draws them, from the marine iguanas to the blue-footed boobies, see our guide to Galápagos wildlife; to place the islands within the country's Andes, Amazon and coast, read our overview of Ecuador's geography; and if you are planning around the garúa and the warm season, our note on the best time to visit the Galápagos sets out the months.