The Galapagos Islands are a remote archipelago of volcanic peaks straddling the equator in the Pacific Ocean. Lying approximately 600 miles off the coast of South America, these islands owe their existence to a powerful, deep-seated heat source within the Earth. The unique formation process has resulted in a chain of islands that are constantly being created and destroyed. The archipelago is entirely volcanic in origin, a direct result of molten rock pushing up through the ocean floor for millions of years. This geological history shaped the islands’ diverse landscapes, from barren lava fields to lush highlands.
The Tectonic Setting
The entire archipelago is situated on the Nazca Tectonic Plate, a large segment of the Earth’s crust moving beneath the ocean. This plate is currently moving eastward or east-southeastward at a slow but steady pace, roughly 5 to 7.9 centimeters per year. The Nazca Plate is on a path that will eventually lead it to collide and subduct beneath the much larger South American Plate. This constant, unidirectional motion of the crustal plate is the primary driver behind the distinctive arrangement and geological life cycle of the islands.
The Stationary Hotspot
The engine responsible for the islands’ creation is the Galapagos Hotspot, which is fundamentally a mantle plume. This plume is an intensely hot, relatively narrow column of superheated rock rising from deep within the Earth’s mantle. The plume is significantly hotter than the surrounding rock, making it less dense and causing it to rise buoyantly. The key characteristic of this hotspot is its long-term immobility; it remains fixed in one location while the tectonic plate slides over it. As the plume head nears the Earth’s surface, the lower pressure causes the rock to melt, generating a continuous supply of magma.
Building the Islands
The magma generated by the hotspot is basaltic, meaning it is low in silica content and highly fluid. When this molten material breaches the ocean floor, it erupts in a relatively gentle, effusive manner, avoiding explosive volcanic events. Over hundreds of thousands of years, the accumulation of countless fluid lava flows builds up immense, broad volcanic structures from the seabed. These structures are classic shield volcanoes, characterized by their gently sloping sides. The most active and largest island, Isabela, is a composite of six such shield volcanoes that have merged above sea level.
The Conveyor Belt Effect
The interplay between the stationary hotspot and the moving Nazca Plate creates a geological pattern known as the “conveyor belt effect,” which dictates the life cycle of the archipelago. As the plate continues its eastward motion, the newly formed volcanic island is slowly carried away from the fixed heat source, resulting in a distinct age gradient. The westernmost islands, such as Fernandina and Isabela, are the youngest and most volcanically active, sitting nearest to the hotspot. Conversely, the islands to the east, like Española and San Cristóbal, are significantly older, with ages reaching over 3.2 million years. As these older islands drift away from the magma supply, their volcanoes become dormant and then extinct, beginning a process of slow erosion and subsidence back into the ocean.