The Galapagos Islands are an archipelago of volcanic islands located around the equator in the Pacific Ocean. The islands are located on the Nazca Plate, which is an active tectonic plate shifting underneath the South American Plate. An active mantle plume has caused each island to form as the Nazca Plate has shifted. The most recent active eruption of the volcanic islands took place in May 2015 at Wolf Volcano on the western island of Isabela. The Galapagos Islands geology has played an integral role in the evolution of living things. Understanding the Galapagos Islands geology can help you to gain a great appreciation for the beauty and unique features that each of the islands has to offer during your vacation.
Each of the largest Galapagos Islands is its own volcano, except for the largest island. Isabela is actually made up of six volcanoes that came together and joined in a single land mass above sea level. Isabela is thought to have formed from these six volcanoes about 2 million years ago, which makes it a young land mass. The westernmost islands are the most volcanically active. Continued eruptions and lava flows mean that each of the western islands continues to grow and add both height and land area. The islands also continue to change in shape with the volcanic activity. Therefore, the scenic beauty of the Galapagos lies right at their volcanic makeup and geologic diversity.
According to the Galapagos Islands geology, the young islands have a distinctive round shape that is typically linked with volcanic activity. This is because of the continued volcanic eruptions. With each eruption, a new layer of solid material is deposited onto the island, making it taller and larger. Eruptions occur at fissures and not from a central conduit, just as it happens on continental volcanos. On average, each island rises in height by about 3 to 4 inches per year. The eruptions have created features such as steep slopes and cliffs that rise above the sea. The islands range in height from just a few meters to more than 5,000 feet above sea level. Over the past 200 years, more than 50 volcanic eruptions have taken place in the Galapagos Islands. These eruptions have created new land that has been colonized by the unique flora and fauna. The new areas have also provided opportunities for evolution to occur, such as in the pāhoehoe lava flow on Santiago Island, or any of the newer eruptions. Charles Darwin’s views on the geology of the Galapagos were absolutely diverse based on his opportunities of seeing older and younger islands.
The islands closest to the South American coast are the oldest in the chain. San Cristóbal and Española are the two easternmost islands (check our Eastern Islands itinerary where these islands are included). As the perpetually moving Nazca tectonic plate has moved toward the east, it passed over the hot spot where lava flows up and out of the Earth’s crust. This allowed each island to form through separate eruptions. San Cristóbal and Española are millions of years older than Isabela and Fernandina, which are at the western end of the chain. During your visit, this means that you may see different types of volcanic features and landscapes on the islands.
Volcanic eruptions release hundreds of thousands of tons of ash and rock. When the debris settles and lava flows harden, new surfaces are created. Erosion from wind and the action of the Pacific Ocean waves break down the rock and turn it into soil. The older islands have deeper soil as a result of their age and the time that it takes to break rocks down into fertile soil. The rich volcanic soil is an ideal host for many plants. The depth of the soil has allowed for trees to take root. With this rich soil, the older islands are home to extensive forests. The forests and heavily vegetated areas provide great living environments for animals. The plants and trees provide food and shelter, allowing the animals to thrive. When visiting the islands, you will be able to discover the greater variety of flora and fauna on the older islands.
Because of their volcanic history, the Galapagos Islands geology have some unusual land features. The volcanic calderas of the Galapagos are unusually large when compared with the overall size of the volcanoes. Over time and with continued eruptions, the calderas have occasionally broken on one or more sides. The calderas have a lower elevation, allowing for micro-climates where distinct plants and animals can live. These areas also collect water and tend to have a more consistent temperature than the areas with a higher elevation. On Genovesa Island, part of the caldera broke away and dropped below sea level, allowing for the formation of Darwin’s Bay. These shallow areas allow marine life to colonize the continental shelf, resulting in spectacular collections of tropical fish and protected areas where larger fish and marine mammals can come close to shore. The easternmost islands have the deepest calderas, which result from a combination of weathering and the thickness of the lava flows when the volcanoes were active. The western islands have shallower and more gently sloped calderas, which make for exciting times when exploring the islands.
Blog Reviewed & Edited by: Francisco Dousdebés
All Images: Francisco Dousdebés