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Galapagos History | < 1 MIN READ

The Volcanic History of the Galapagos Islands – How did the Galapagos Volcanoes Form?

User Avatar Written by: Santa Cruz II
View of the overwhelming eruption of Sierra Negra Volcano.

Though wildlife is the typical draw, there are other equally fascinating aspects to the natural world of the Galapagos. These include the islands themselves, their volcanic nature, and the unique way in which they were geologically formed. What is also intriguing is that the different geologic ages of the archipelago play an intrinsic role in the evolutionary history of the islands. Learn about Galapagos volcanoes and it’s an interesting story.

How Do Volcanoes Form?

Volcanoes are areas where the crust of the earth is thinner or more active than other places and liquid magma is allowed to escape. As it breaks the earth’s surface it becomes lava, which then cools into new rock. Repeated eruptions can form lava cones that make up the distinct shape of active volcanoes. Volcanoes appear in two ways: They can be created where two tectonic plates push against one another, as is the case with the volcanoes that make up the Pacific ring of fire, or they can be formed in a thin section of a tectonic plate where a fixed jet of magma called a magma plume exists. This phenomenon is called a hot spot and is the way in which volcanic island chains like Hawaii and the Galapagos were formed.

How Does a Hot Spot Work?

A hot spot requires two conditions in order to form volcanoes: It needs a thin section of a tectonic plate (this typically means sea floor, as continents are much thicker) as well as a fixed jet of magma called a magma plume. This is a place where magma consistently shoots against the rock in the same place due to the inner currents of the earth. The magma plume works much like a hot faucet on a block of ice; instead of melting the entire area, it will create a hole in the surface. As the magma breaks the surface and spills onto the ocean floor, it cools and forms a layer of rock. The next large wave of magma will create a second layer of rock over the first, and this will continue until the magma has built a seamount with a hole in the center for the magma plume. This becomes a shield volcano, and ultimately an island.

Tectonic plates are the reason that hot spots form an entire island chain instead of a single volcano. As the plates gradually move, the center of the volcano gets further away from the active flow of the magma plume and will eventually become dormant. However, the magma plume will begin to wear down a new section of seafloor that has now moved over the top of the magma plume once it becomes easier for it to flow straight upward than it is to move sideways and out of the previous volcanic hole. A second island is then formed. This is why we have a series of cones and not a single volcanic trench.

 

The Volcanic Story of the Galapagos Islands

The Galapagos Islands sit in the upper western corner of the Nazca Plate, which is moving southeastward at about the rate that your fingernails grow. Their tectonic location is also near the spreading center which divides the Nazca Plate from the Pacific Plate. Espanola and Santa Fe are the two oldest islands, and they are believed to be around 3.5-4 million years old. Fernandina Island is the westernmost island and the youngest at about 0.7 million years old. All of the islands have a single cone, with the exception of the island of Isabela, which was formed by a chain of six active Galapagos volcanoes. Currently, the plume is believed to be out west and under the water between Fernandina and Isabela. When putting all these forces together, it is easy to understand why volcanic archipelagos are so incredibly interesting.

 

Because the islands were formed as a chain, volcanic ages vary depending on where you are; western islands bear younger rocks, while eastern islands bear older rocks. Landscapes, therefore, are quite varied depending on where you are. For those explorers who consider themselves “geotourists”, the volcanic landscapes here will satisfy the most discerning interests.

Which Galapagos Volcanoes Are Still Active?

Galapagos volcanos: sierra negra

The last eruption of Sierra Negra volcano was in 2018

There are 12 Galapagos volcanoes, which range from being dormant to regularly active. They include:

  • Pinta: This dormant volcano sits on an island of the same name. It last erupted in 1928.
  • Marchena: This volcano is considered recently dormant, but it last erupted in 1991. It has one of the largest calderas (volcanic lakes) of any in the islands.
  • Genovesa: The top of this volcano sits right at sea level, and it was very young fresh-looking lava. However, no recorded eruptions have taken place.
  • Wolf: This is the where we find the highest point of all Galapagos volcanoes and is located on Isabela Island. It erupted amazingly in 2015 and has done so four times since the 1970s. It has steeper sides and a higher proportion of lava flow during eruptions than the other Galapagos volcanoes in the archipelago.
  • Ecuador: This volcano sits on the equator for which it has been named. It is a part of Isabela island’s volcano chain. It is considered dormant and is believed to have last erupted around 1150. When sailing right along its coastline you will witness its collapsed caldera with many features such as volcanic benches and a vast caldera floor.
  • Darwin: This young volcano on Isabela Island was named for the scientist who made the Galapagos world renowned. It last erupted in 1813.
  • Santiago: This volcanic island last erupted in 1906. Darwin, when exploring the lava flows from this volcano, was able to find shards of marmalade pots embedded in the lava left by retreating buccaneers in the 1600s.
  • Fernandina: Considered the most active of the Galapagos volcanoes, it last erupted in 2009 and sits on an island of the same name.
  • Alcedo: The lowest and smallest of the Isabela volcanoes, Alcedo last erupted in 1993. It is a unique volcano because it is the only one that has produced pumice as a result of very violent eruptions.
  • Santa Cruz: This dormant volcano is one of the oldest in the island chain, and the last eruption date is unknown. Academy Bay, famous for its town Puerto Ayora and the Charles Darwin Research Station is a great place for observing many faults that have resulted in downfaulting of this area.
  • Santa Fe: This ancient volcano is believed to have last erupted during the Pleistocene era.
  • Cerro Azul: This volcano’s name means blue mountain. It sits on Isabela and is one of the most active in the archipelago. A dozen eruptions have been recorded since 1850, the most recent from 2008.

Blog Reviewed & Edited by: Francisco Dousdebés
All Images: Francisco Dousdebés