Source of Galapagos eruptions is not where models place it

Birds flock not far from a volcano on Isabella Island, where two still active volcanoes are located. The location of the mantle plume, to the southeast of where computer modeling had put it, may explain the continued activity of volcanoes on the various Galapagos Islands. -  Douglas Toomey
Birds flock not far from a volcano on Isabella Island, where two still active volcanoes are located. The location of the mantle plume, to the southeast of where computer modeling had put it, may explain the continued activity of volcanoes on the various Galapagos Islands. – Douglas Toomey

Images gathered by University of Oregon scientists using seismic waves penetrating to a depth of 300 kilometers (almost 200 miles) report the discovery of an anomaly that likely is the volcanic mantle plume of the Galapagos Islands. It’s not where geologists and computer modeling had assumed.

The team’s experiments put the suspected plume at a depth of 250 kilometers (155 miles), at a location about 150 kilometers (about 100 miles) southeast of Fernandina Island, the westernmost island of the chain, and where generations of geologists and computer-generated mantle convection models have placed the plume.

The plume anomaly is consistent with partial melting, melt extraction, and remixing of hot rocks and is spreading north toward the mid-ocean ridge instead of, as projected, eastward with the migrating Nazca plate on which the island chain sits, says co-author Douglas R. Toomey, a professor in the UO’s Department of Geological Sciences.

The findings — published online Jan. 19 ahead of print in the February issue of the journal Nature Geoscience — “help explain why so many of the volcanoes in the Galapagos are active,” Toomey said.

The Galapagos chain covers roughly 3,040 square miles of ocean and is centered about 575 miles west of Ecuador, which governs the islands. Galapagos volcanic activity has been difficult to understand, Toomey said, because conventional wisdom and modeling say newer eruptions should be moving ahead of the plate, not unlike the long-migrating Yellowstone hotspot. </p

The separating angles of the two plates in the Galapagos region cloud easy understanding. The leading edge of the Nazca plate is at Fernandina. The Cocos plate, on which the islands’ some 1,000-kilometer-long (620-miles) hotspot chain once sat, is moving to the northeast.

The suspected plume’s location is closer to Isabella and Floreana islands. While a dozen volcanoes remain active in the archipelago, the three most volatile are Fernandina’s and the Cerro Azul and Sierra Negra volcanoes on the southwest and southeast tips, respectively, of Isabella Island, the archipelago’s largest landmass.

The plume’s more southern location, Toomey said, adds fuel to his group’s findings, at three different sites along the globe encircling mid-ocean ridge (where 85 percent of Earth’s volcanic activity occurs), that Earth’s internal convection doesn’t always adhere to modeling efforts and raises new questions about how ocean plates at the Earth’s surface — the lithosphere — interact with the hotter, more fluid asthenosphere that sits atop the mantle.

“Ocean islands have always been enigmatic,” said co-author Dennis J. Geist of the Department of Geological Sciences at the University of Idaho. “Why out in the middle of the ocean basins do you get these big volcanoes? The Galapagos, Hawaii, Tahiti, Iceland — all the world’s great ocean islands – they’re mysterious.”

The Galapagos plume, according to the new paper, extends up into shallower depths and tracks northward and perpendicular to plate motion. Mantle plumes, such as the Galapagos, Yellowstone and Hawaii, generally are believed to bend in the direction of plate migration. In the Galapagos, however, the volcanic plume has decoupled from the plates involved.

“Here’s an archipelago of volcanic islands that are broadly active over a large region, and the plume is almost decoupled from the plate motion itself,” Toomey said. “It is going opposite than expected, and we don’t know why.”

The answer may be in the still unknown rheology of the gooey asthenosphere on which the Earth’s plates ride, Toomey said. In their conclusion, the paper’s five co-authors theorize that the plume material is carried to the mid-ocean ridge by a deep return flow centered in the asthenosphere rather than flowing along the base of the lithosphere as in modeling projections.

“Researchers at the University of Oregon are using tools and technologies to yield critical insights into complex scientific questions,” said Kimberly Andrews Espy, vice president for research and innovation and dean of the UO Graduate School. “This research by Dr. Toomey and his team sheds new light on the volcanic activity of the Galapagos Islands and raises new questions about plate tectonics and the interaction between the zones of the Earth’s mantle.”

Co-authors with Toomey and Geist were: doctoral student Darwin R. Villagomez, now with ID Analytics in San Diego, Calif.; Emilie E.E. Hooft of the UO Department of Geological Sciences; and Sean C. Solomon of the Lamont-Doherty Earth Observatory at Columbia University.

The National Science Foundation (grants OCE-9908695, OCE-0221549 and EAR-0651123 to the UO; OCE-0221634 to the Carnegie Institution of Washington and EAR-11452711 to the University of Idaho) supported the research.

Hiking, horses and helicopter: Scientists deploy seismic network for study of Sierra Negra, Galapagos

An interdisciplinary team of scientists from the University of Miami, University of Rochester, University of Idaho-Moscow and the Instituto Geofísico, Escuela Politécnica Nacional (Quito, Ecuador) joined forces to study one the world's most active volcanoes, Sierra Negra in the Galápagos.  Each site includes a seismometer, battery and solar panel, and electronics to continuously record ground vibrations from local and distant earthquakes. The broadband seismometers were provided by the PASSCAL instrument center and will record data for the next three years. -  Falk Amelung, University of Miami
An interdisciplinary team of scientists from the University of Miami, University of Rochester, University of Idaho-Moscow and the Instituto Geofísico, Escuela Politécnica Nacional (Quito, Ecuador) joined forces to study one the world’s most active volcanoes, Sierra Negra in the Galápagos. Each site includes a seismometer, battery and solar panel, and electronics to continuously record ground vibrations from local and distant earthquakes. The broadband seismometers were provided by the PASSCAL instrument center and will record data for the next three years. – Falk Amelung, University of Miami

An interdisciplinary team of scientists from the University of Miami (UM), University of Rochester, University of Idaho-Moscow and the Instituto Geofísico, Escuela Politécnica Nacional (Quito, Ecuador) have joined forces to study one the world’s most active volcanoes, Sierra Negra in the Galápagos. The volcano’s last eruption occurred in 2005, deepening its 8 km (~5 mile) wide caldera by 4 – 5 meters (~13 – 16 feet). The previous eruption in 1979 produced more than 1 km3 (~0.7 miles3) of lava and was one of the largest eruptions of the 20th century.

The team consists of Dr. Falk Amelung, associate professor of Marine Geology and Geophysics at UM’s Rosenstiel School of Marine and Atmospheric Science; seismologists Dr. Cindy Ebinger of the University of Rochester and Dr. Mario Ruiz of the Instituto Geofísico, Escuela Politécnica Nacional de Quito; volcanologist Dr. Dennis Geist of the University of Idaho (Moscow); science teacher Lisa Hjelm from The Girls’ Middle School in Mountain View, California; Escuela Politécnica Nacional undergraduate geology student Daniel Pacheco; and Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL) engineer Eliana Arias-Dotson. They returned from an adventure that lasted nearly three weeks, which included hiking, riding horses and navigating dangerous waters to deploy an experimental seismic network of 16 stations around Isla Isabela, Galápagos. The broadband seismometers provided by the PASSCAL instrument center will record data for the next three years.

“With the satellite data we regularly collect here at the University of Miami, using a technique called satellite radar interferometry, we are able to see the underground location of the magma chamber. The new seismic data will allow us to corroborate our information and obtain proof that the magma chamber is actually 2 km. (~1.2 miles) down and to what depth it extends,” said Amelung. “Petrologists suggest that the chamber may extend to a depth of 10 km. (~6.2 miles), whereas geophysicists believe it might go only to a depth of 3 km. (1.8 miles) or so.” These new seismic data will be analyzed to provide the first 3-D pictures of the volcanic plumbing system, completing the picture derived from satellite and rock studies.

The team conducted eight dry and wet landings from a boat, placing sites along the coastline. The Galápagos-based Charles Darwin Foundation and Parque Nacional de Galápagos, both celebrating their 50th anniversary in 2009, assisted in providing horses and other support to transport equipment to more remote regions of Isla Isabela. However, the most challenging deployment took place in the center of the caldera, where scientists had to hike over miles of sharp, jagged igneous rock from the last lava flow. Geist arranged for a helicopter to fly the heavy equipment to a central drop site so they could navigate the unforgiving terrain, which tore into their hiking boots and required heavy duty work gloves to traverse.

Once set up, each site included a seismometer that had to be precisely leveled, a battery and solar panel, and electronics to continuously record ground vibrations from local and distant earthquakes. A number of the sensitive instruments were buried, but in areas where hard volcanic rock was present, the stations were left above ground and protected by rocks and other natural features.

The integrated seismic-geodetic study of the active magmatic processes at Sierra Negra volcano was funded by the National Science Foundation (NSF). An additional NSF grant was awarded to Hjelm for education and outreach. Her intent is to use data from this study to create a visualization of the interior of the volcano as an educational product for teens.