The Galápagos Islands, located in the Pacific Ocean about 1,000 kilometers (600 miles) west of Ecuador, are renowned for their extraordinary biodiversity. This remote archipelago has captivated scientists and travelers alike with its unique wildlife, much of which is found nowhere else on Earth. Understanding the geological processes that formed these islands provides insight into their distinct character and the evolution of their isolated ecosystems.
Formation Through Volcanism
The Galápagos Islands are volcanic in origin, forming as a “hotspot” of magma rises from Earth’s mantle beneath the Nazca Plate. This stationary hotspot continuously generates molten rock, while the Nazca Plate slowly moves eastward over it at a rate of approximately 5 to 7.9 centimeters (2 to 3.1 inches) per year. This dynamic interaction results in a chain of islands, with new ones forming as older ones are carried away from the hotspot.
Defining Geological Features
The Galápagos Islands are primarily composed of basaltic rock, a type of volcanic rock common in oceanic eruptions. This basaltic lava is fluid, leading to the formation of broad, gently sloping structures known as shield volcanoes. These volcanoes often resemble an inverted soup bowl due to their gradual slopes. Many of these volcanic peaks feature calderas, which are large, circular depressions formed when a volcano’s magma chamber empties and its roof collapses. The islands also exhibit numerous lava tubes, which are natural tunnels created by flowing lava that has cooled and solidified on its exterior while the interior molten rock continued to flow.
Stages of Island Development
Due to the fixed hotspot and moving Nazca Plate, the Galápagos Islands display a clear age progression. Islands closer to the hotspot, such as Fernandina and Isabela in the west, are geologically younger and remain highly volcanically active, often featuring rugged, fresh lava landscapes with minimal soil development. In contrast, islands located further east, like San Cristóbal and Española, are significantly older, some dating back several million years. These older islands have experienced more erosion and weathering, leading to more developed soils and the growth of lush vegetation. This age difference creates diverse habitats across the archipelago, reflecting distinct stages of geological maturity.
Distinguishing from Other Island Types
The Galápagos Islands stand apart from other island classifications due to their specific volcanic origin. Unlike “continental islands,” which were once connected to a mainland, the Galápagos formed in the middle of the Pacific Ocean, far from any landmass. They also differ from “coral islands,” formed by the accumulation of reefs and marine organisms. While coral exists around the Galápagos, their fundamental structure is volcanic, built from layers of hardened lava. This unique formation history underscores their classification as a volcanic archipelago.