Dennis Geist, University of Idaho geology professor since 1990, has been working in the Galapagos Islands for the entirety of his 30-year career.
Recently, Geist and a team of researchers published an article that explains the volcanic islands’ geology in a new way.
The article that will appear in February’s edition of the scientific journal Nature Geoscience and it titled “Mantle flow and multistage melting beneath the Galapagos hotspot revealed by seismic imaging.”
According to Geist, the article couples the research done on the surface of islands with seismic activity below the surface.
“Our goal was to find out why there were volcanoes in this part of the Earth,” Geist said. “Now, to get a volcano, the Earth has to melt … and so, by mapping out the interior of the Earth with seismic waves, we can at least see where the melting was taking place.”
The team utilized seismic activity to outline key points that get to the heart of how the islands were formed, as well as how they function.
According to the article, tomographic images of the mantle beneath the Galapagos indicates evidence of plume-lithosphere-ridge interactions, as well as an understanding of viscous coupling between oceanic plates and upper layer of the earth’s mantle.
“We were able to image a mantle plume — a big upwelling in the earth’s mantle that causes the volcanoes in the Galapagos,” Geist said.
According to Geist, the mantle plume was not where they thought it might be. Instead, it is displaced from the most active volcanoes. Mantle plumes, such as the Galapagos, Hawaii and Tahiti, are supposed to follow the direction of tectonic plate migration, Geist said.
The plate below the Galapagos, Nazca, moves in an eastward direction. However, the volcanic plume moves in a perpendicular motion upward and away from the tectonic plate’s migration.
“Their results show that something is keeping the plume from following the movement of the plate,” said Eric Mittelstaedt, UI assistant professor of geodynamics.
The team was able to see the mantle plume using earthquake waves. Seismometers were deployed a decade ago so that, like a CAT scan piercing skin to reveal the inner body, scientists could peer below the surface of the earth.
The team of researchers collected data for three to four years, and has since been processing the complex information. Due to the fact that every earthquake emits shock waves that pass beneath the Galapagos, there is an immense amount of data to be processed, Geist said.
Another aspect of the research highlights how the team was able to — on the basis of earthquake waves — map out where rocks were melting in the Galapagos. These melting rocks help form the volcanoes on the islands. Like the mantle plume, these melting rocks were not where the team expected them to be.
Based at the University of Oregon, the team was led by Douglas Toomey and his doctoral student Darwin Villagomez. Emilie Hooft of the UO Department of Geological Sciences and Sean Solomon of the Lamont-Doherty Earth Observatory at Columbia University also aided the research and writing process.
Geist’s role was one of collaboration. In part, he provided ideas on how to interpret the data gathered by his research group.
Throughout Geist’s time in the Galapagos, he has invited dozens of undergraduate, graduate and doctoral students to work with him in this unusual chain of islands.
Jake Smith can be reached at [email protected]