Galapagos Island Volcanoes Are Hiding Explosive Magma Deep Beneath Surface

Researchers have discovered that some seemingly "monotonous" volcanoes with reliable patterns of low-level activity may be hiding a secret deep below the surface—magma which has the potential to erupt explosively.

Volcanoes around the world vary significantly when it comes to the kind of eruptions they produce. Some may lie dormant for decades, centuries or even millennia before explosively and violently erupting—think Mount St. Helens in 1980, for example.

On the other hand, many volcanoes reliably spew out lava consistently for thousands, or even hundreds of thousands of years, like those in Hawaii, Iceland and the Galápagos Islands.

These reliable lava flows are made up of molten basalt—a common form of volcanic rock—that tend to be very uniform in their chemical make up.

The lava flows sometimes cause damage to buildings close to the volcano, but because they are normally slow-moving, they pose much less risk to life than larger, sudden, explosive eruptions.

For a study published in the journal Nature Communications, an international team of volcanologists conducted research on remote islands in the Galápagos Archipelago—which belong to Ecuador—to better understand why some volcanoes on Earth erupt chemically uniform lava consistently over long periods of time.

"These 'monotonous' volcanoes aren't uncommon but it's hard to imagine how magmas stored throughout the Earth's crust—between around 10-15 kilometers [around 6-9 miles] in depth—can have identical chemical compositions," Michael Stock, lead author of the study from Trinity College Dublin, Ireland, told Newsweek. "A lot of things happen on a magma's journey to the surface!"

Stock and colleagues from the U.S., U.K. and Ecuador studied two Galápagos volcanoes, Wolf and Fernandina, that have only erupted uniform basaltic lava over the course of their entire lifetimes. The team used state-of-the-art analytical techniques to measure microscopic crystals in erupted lava flows above the surface of these volcanoes.

"You can read crystal compositions like tree rings—from the inside out, they preserve a history of their journey to the surface, including the compositions of the different magmas that they grew from," Stock said.

This analysis showed that even volcanoes that produce chemically consistent lavas at the surface over thousands of years can have a whole range of different magmas in their sub-volcanic plumbing systems. In fact, the team found magmas that were similar in composition to those that erupted at Mount St. Helens in 1980, which have the potential to produce explosive activity.

"Magmas are more likely to erupt explosively when they have higher silica and water concentrations," Stock said. "The water forms gas bubbles—the same as carbon dioxide in cola—but the high silica content makes the magmas very sticky. The gas bubbles can't escape so pressure builds up, generating an explosive eruption."

Galápagos, volcano, eruption
The 2015 eruption at Wolf volcano in the Galápagos Archipelago. Gabriel Salazar, La Pinta Yacht Expedition

The researchers say the reason that the volcanoes they studied in the Galápagos have produced chemically consistent lava flows for millennia is because they are located in an area where there is a very high volume of new basalt magma moving through the Earth's crust.

As the basalt moves through the crust, it mixes with smaller volumes of chemically diverse magmas at higher levels and "overprints" their chemical signatures.

"To continue the fizzy drink analogy, you can think of it like having a drop of cola in the bottom of a glass and then filling it with water. Even through the cola is there, you still essentially have a glass of water. Same here—small volumes of chemically diverse magma, mixing with a large volume of ascending basalt," Stock said.

However, the latest results indicate that under certain circumstances, the chemically diverse magmas beneath volcanoes like those the team studied in the Galápagos could rise to the surface. This could cause a shift towards periods of unexpected explosive activity in these volcanoes, the researchers said.

"This was really unexpected. We started the study wanting to know why these volcanoes were so boring and what process caused the erupted lava compositions to remain constant over long timescales. Instead we found that they aren't boring at all—they just hide these secret magmas under the ground," Stock said in a statement.

While the researchers say there is no evidence to suggest that the Galápagos will change their eruption style any time soon, the study does help us to understand why some volcanoes have changed from producing consistent lava flows to explosive eruptions in the past. This could have significant implications for volcano monitoring and hazard assessment.

"The study will also help us to better understand the risks posed by volcanoes in other parts of the world—just because they've always erupted a particular way in the past doesn't mean you can rely on them to continue doing the same thing indefinitely into the future," Stock said.

Karen Harpp, a professor of geology at Colgate University, who was not involved in the study, told Newsweek the latest paper is "a critically important step forward in our understanding not just of Galapagos volcanoes, but of volcanoes in general."

"The research reveals key insights into how magma behaves in volcanic plumbing systems, the parts of the volcanoes we never get to see because we are limited to studying lava erupted on the surface of the planet."

"The results reported by Stock and his co-workers illustrate how much what we see at the surface of a volcano is controlled by its magma supply, which in turn informs us about the fundamental planetary phenomena responsible for those volcanoes, mantle plumes," Harpp said.

Update 8/3/20: This article was updated to include additional comments from Karen Harpp.