The Galapagos Islands, a remote archipelago in the Pacific Ocean, are known for their unique biodiversity, which famously inspired Charles Darwin’s work on evolution. The geology of this chain is constantly being shaped by powerful forces deep within the Earth. The question of how many of these islands are still forming speaks directly to the dynamic volcanic origins of the ecosystem, creating a sharp contrast between the younger western islands and the older eastern ones.
The Driving Force: The Galapagos Hotspot
The formation of the Galapagos Islands is a direct consequence of a geological phenomenon known as a mantle plume, or hotspot, located beneath the Earth’s crust. This stationary plume is a region of hot rock that rises from the deep mantle, generating magma. The magma then breaks through the ocean floor, building up massive shield volcanoes.
The island chain is created because the Nazca tectonic plate, upon which the islands sit, is constantly moving eastward. This continuous plate motion drags the newly formed volcanoes away from the fixed heat source. The result is a conveyor belt of islands, with the youngest landmasses situated directly above or nearest to the hotspot’s influence in the west. This mechanism explains the distinct age gradient across the archipelago, with islands in the east being millions of years older than those in the west. The Nazca plate’s movement, estimated to be around 37 to 79 millimeters per year, ensures that the process of island formation is continuing.
The Answer: Defining the Active Islands
Determining how many islands are “still forming” relies on defining this term as being volcanically active or having recently experienced eruptions that add new landmass. The majority of the ongoing formation is concentrated on two main islands in the far west: Isabela and Fernandina. These islands lie closest to the mantle plume. Of the approximately 21 emergent volcanoes in the Galapagos, 13 are classified as active.
The largest island, Isabela, is composed of six distinct shield volcanoes that have coalesced, five of which are considered active: Wolf, Darwin, Alcedo, Sierra Negra, and Cerro Azul. These volcanoes are among the most frequently erupting in the entire chain. Wolf Volcano, the archipelago’s highest peak, had a recent eruption in January 2022. Sierra Negra, which features one of the world’s largest volcanic calderas, last erupted in 2018.
Fernandina Island, situated immediately west of Isabela, is the third largest and youngest island, with its single, highly active volcano named La Cumbre. Fernandina is the most volcanically active island in the archipelago. La Cumbre is known for its frequent eruptions, consistently adding new lava flows and expanding the island’s land area, with one of the most recent occurring in May 2024.
The Geological Lifecycle: From Formation to Extinction
Once the islands move eastward, away from the direct influence of the Galapagos hotspot, they enter geological extinction. The magma supply is reduced, leading to the volcanoes becoming dormant and eventually inactive. The erosive forces of wind, rain, and ocean waves begin to dominate over the constructive forces of volcanism.
The islands also begin a slow process of subsidence, sinking back into the ocean due to several factors. The lithosphere cools and contracts as it moves away from the plume, causing the crust to drop. The weight of the massive volcanic edifice also causes the underlying tectonic plate to flex and depress. This slow, steady sinking is compounded by wave action, which gradually reduces the island’s size and elevation.
The older islands in the east, such as San Cristóbal and Española, showcase the final stages of this lifecycle. They are more rounded, lower in elevation, and covered in thicker soil, showing the effects of millions of years of erosion. Eventually, all islands in the chain will subside below sea level, leaving behind a series of flat-topped, submerged mountains known as seamounts.