The Geological History of the Galapagos Islands

The volcanic archipelago we know as the Galapagos Islands is situated almost 1,000kms off the coast of Ecuador, in South America, distributed over both sides of the Equator. With a landscape of extreme diversity and great beauty, the geology and natural history of this fascinating region are of enduring interest.

For those who come to the islands on a Galapagos holiday, along with the endemic wildlife, the intriguing story of how they came to form is what lends it such a unique appeal.

Islands Formed by Fire

The area is located right on the Nazca tectonic plate, so is in a constant state of movement. Anywhere from 3-10 million years ago (relatively recent in the history of the universe) the archipelago was formed by constant volcanic eruptions as the tectonic plate (which is part of the Earth's crust) moved over particularly hot areas of the Earth's central core – the "mantle". (This is different to land-based mountain ranges that occur when two tectonic plates collide.) After repeated eruptions in the same spot over millions of years, the volcanic earth was forced through the surface of the ocean to form the islands of the archipelago.

Because this repeated volcanic action occurred over several millennia, some of the islands in the chain are considerably older than others. Espanola and San Cristobal on the eastern side, for example, appeared several millions of years before the western islands of Fernandina and Isabela, which are probably only a couple of hundred thousand years old.

There is still major volcanic activity in the area and the landscape is dynamic. There has been as many as 50 eruptions in the past two centuries, creating new land formations and, more worryingly, posing a threat to the survival of the delicate ecosystem of the archipelago.

A Landscape of Extremes

Geologically, all the islands in the chain are the same – formed as a single volcano – except for the largest, Isabela, which is made up of six merged volcanoes. They are characteristically cone-shaped, with countless steep slopes created by the layering action of constant and sustained volcanic eruptions. There is a huge diversity in the heights of the islands, with some as much as 5,000m above sea level and others as little as a few metres.

Due to the ongoing eruptions, the landscape is dotted with lava fields, where molten lava has fallen and cooled. There are also countless lava tubes running beneath the surface of the landscape. These underground tunnels once carried lava from deep in the Earth's core, but today can be explored without any danger.

In stark contrast, as well as the lunar-like lava fields and dramatic volcanic peaks, the islands are characterised by their idyllic sandy bays and beaches, which are brushed by the clear waters of the Pacific Ocean.

A Memorable Galapagos Holiday

Understanding the story behind its formation is a vital part of gaining a deeper insight and appreciation of this strangely beautiful archipelago. For anyone intending to travel here on a Galapagos holiday, delving into the fascinating realms of the region's geology can serve to make the experience even more fulfilling.

Marissa Ellis-Snow is a freelance nature writer with a special interest in the unique wildlife of the Galapagos Islands. Marissa chooses the expert-led Galapagos holiday itineraries organised by Naturetrek, which have brought her unforgettable sightings of a wide range of wildlife in one of the most spectacular regions on Earth.

Writer and Online Marketing Manager in London.