The Galápagos Islands are characterized by their volcanic origin and remain one of the most volcanically active regions on Earth. This remote Pacific archipelago, located roughly 600 miles west of Ecuador, emerged from the ocean floor through millions of years of repeated eruptions. This geology provided the foundation for the extraordinary biodiversity that made the islands famous. The landscape is a dynamic mix of recent black lava fields and older, eroded volcanic structures.
The Geological Hotspot that Formed the Islands
The existence of the Galápagos is explained by the “hotspot” theory, describing an area of exceptionally hot magma deep within the Earth’s mantle. This mantle plume remains relatively stationary while the tectonic plate above it, the Nazca Plate, slowly moves eastward. As the plate drifts over the fixed hotspot, the intense heat melts the crust, creating volcanoes that eventually break the ocean surface to form islands. This process functions like a geological conveyor belt, continuously creating new islands in the west while older islands are carried away to the east.
The volcanoes that form the islands are predominantly shield volcanoes, similar in structure to those found in Hawaii. They are characterized by their broad, gently sloping sides, a result of highly fluid, low-viscosity basaltic lava. This lava flows easily and spreads out over large areas before cooling. The largest island, Isabela, is a unique formation where six massive shield volcanoes have coalesced to form a single landmass.
Geography of Active and Dormant Volcanoes
The archipelago displays a distinct age gradient: the oldest, most eroded islands are situated in the east, and the youngest, most active islands are in the west. Española Island, for example, is one of the oldest, dating back over three million years, and now shows no evidence of its original volcano. Conversely, westernmost islands, such as Fernandina and Isabela, are geologically the youngest.
Volcanic activity is concentrated on these western islands, which are positioned directly over the hotspot. Of the 21 emergent volcanoes in the Galápagos, 13 are considered active, with eruptions occurring every few years. Fernandina Island is home to La Cumbre volcano, one of the most active in the archipelago, with eruptions recorded in 2018 and 2024.
Isabela Island hosts the highest peak, Wolf Volcano, which rises to 5,600 feet and erupted most recently in January 2022. Another prominent active volcano on Isabela is Sierra Negra, which features one of the world’s largest calderas, measuring approximately six miles across. Sierra Negra erupted in 2018.
How Volcanic Activity Shaped Unique Life
The volcanic structures and their subsequent weathering created the isolated and varied environments necessary for the evolution of the islands’ unique life forms. Isolation from the South American mainland meant that only a limited range of ancestral species were able to colonize the barren lava flows. The harsh, new volcanic terrain forced these colonists to adapt, driving the process of natural selection.
The elevation of the massive shield volcanoes creates different climate zones on a single island, which encourages species diversification. The lower slopes are typically arid, while the higher slopes intercept moisture from the trade winds, leading to lush, humid zones in the highlands. This variation in habitat supports different populations of endemic species, such as the giant tortoises, which evolved distinct shell shapes and sizes on separate volcanoes and islands.
Specific volcanic features, like hardened lava flows, have been directly responsible for creating micro-habitats and physical barriers. These barriers isolated tortoise populations on Isabela Island, preventing interbreeding and leading to the evolution of five different subspecies on the same landmass. The collapse of volcanic calderas has also sometimes dropped the crater floor below sea level, forming protected bays and shallow marine conditions ideal for species like the marine iguana.