March 6, 2014
Magma Chamber Of Galapagos’ Sierra Negra Volcano Imaged In 3D
April Flowers for redOrbit.com - Your Universe Online
Some of the most active volcanoes in the world can be found in the Galapagos Islands. These volcanoes are responsible for more than 50 eruptions in the last 200 years. Even with such activity, scientists knew far more about the history of finches, tortoises and iguanas on the islands than the volcanoes upon which these unusual fauna had evolved.
A new study from the University of Rochester, published in the Journal of Geophysical Research: Solid Earth, is providing researchers with a more complete picture of the "plumbing system" that feeds the Galapagos volcanoes. The findings are also illustrating a difference between the Galapagos and another Pacific Island chain—the Hawaiian Islands.
"With a better understanding of what's beneath the volcanoes, we'll now be able to more accurately measure underground activity," said Cynthia Ebinger, a professor of earth and environmental sciences. "That should help us better anticipate earthquakes and eruptions, and mitigate the hazards associated with them."
Ebinger collaborated with Mario Ruiz from the Instituto Geofisico Escuela Politecnica Nacional in Quito, Ecuador, and others to bury 15 seismometers around Sierra Negra, the largest and most active volcano in the Galapagos Islands. Using these seismometers, the team measured the velocity and direction of sound waves generated by earthquakes as they traveled beneath the volcano. Understanding that the temperature and types of material that sound waves pass through change the behavior of those waves allowed the team to construct a 3D image of the plumbing system beneath the volcano. The team used a technique similar to a CAT-scan.
Just over three miles below the surface is the beginning of a large magma chamber that lies partially within old oceanic crust that had been buried by more than five miles of eruptive rock layers. The oceanic crust appears to have a thick underplating of rock that would have formed as magma became trapped beneath the crust and cooled. This is very similar to the processes that occur under the Hawaiian Islands.
The Galapagos has something else in common with the Hawaiian chain, as well. The data collected by the team suggests the presence of a large chamber filled with crystal-mush magma. Crystal-mush magma is cooled magma that includes crystallized minerals.
In a process very similar to how the Hawaiian Islands formed, the Galapagos Islands were created from a hotspot of magma located in an oceanic plate called Nazca, about 600 miles off the coast of Ecuador. The islands were formed as magma rose from the hotspot and eventually hardened. The Nazca plate inched westward, forming new islands in the same manner, creating the present-day Galapagos Archipelago.
Ebinger discovered a major difference between the two island chains during her study.
In the Hawaiian Islands, the major volcanoes are dormant because they have moved away from the hotspot that provided their source of magma. The Galapagos volcanoes are connected to the same plumbing system, Ebinger's team found. Using satellite imagery of the volcanoes, the team noticed that as the magma would sink in one volcano it would rise in another. This suggests that some of the youngest volcanoes had magma connections, even if those connections were temporary.
"Not only do we have a better understanding of the physical properties of Sierra Negra," said Ebinger, "we have increased our knowledge of island volcano systems, in general."
Image Below: This illustration shows the plumbing system beneath the Sierra Negra volcano. Credit: Cynthia Ebinger, University of Rochester