Satellite Data Yield New Understanding Of How Galapagos Volcanoes Are Formed
The chance transit of a satellite over the April 2009 eruption of Fernandina volcano
November 05, 2013
HAWAI`I ISLAND, Hawaii — The chance transit of a satellite over the April 2009 eruption of Fernandina volcano — the most active in South America’s famed Galápagos archipelago — has revealed for the first time the mechanism behind the characteristic pattern of eruptive fissures on the island chain’s volcanoes, according to a new study by University of Miami (UM) and U.S. Geological Survey (USGS) scientists. Their model not only sheds light on how Galapagos volcanoes grow, which has been a subject of debate since Darwin’s time, but may also help in forecasting the locations of future eruptions, adding to the vast scientific knowledge acquired by study of this iconic island chain.
In the study, Marco Bagnardi, a doctoral candidate at the UM Rosenstiel School of Marine & Atmospheric Science (RSMAS) and visiting scientist at USGS’ Hawaiian Volcano Observatory, analyzed surface deformations on Fernandina from European Space Agency (ESA) ENVISAT satellite images acquired just two hours before the 2009 eruption. He sought to explain why Hawaiian and Galápagos volcanoes, while similar in some respects, show different eruptive patterns. Eruptions from Hawai‘i’s volcanoes tend to occur along narrow radial rift zones, while the shields of western Galápagos volcanoes have eruptive fissures circumferential to the summit near the calderas but oriented radially on the flanks below.
Bagnardi found that magma began moving away from Fernandina’s reservoir as a sill, or horizontal feature, before rotating vertically and erupting as a radial fissure on the volcano’s southwest flank. A sill also fed the 2005 eruption at Fernandina, but that magma moved upward to form a circumferential fissure closer to the volcano’s summit. These data suggest that sills feed all eruptive activity in the Galápagos but that they rotate in different ways as they propagate toward the host volcano’s surface.
“Our findings have literally turned our perspective by 90 degrees, Bagnardi said. “For decades, we thought that eruptions in the Galápagos were starting with the intrusion of vertical blade-like bodies. We now know this is not the case.”
UM RSMAS is part of a long-term satellite-based monitoring program of the Galápagos volcanoes using Interferometric Synthetic Aperture Radar (InSAR), a technique that uses repeat satellite observations to measure millimeter-scale ground displacements Bagnardi credited the extremely fortunate; timing of data collected by the ENVISAT satellite, which passed over the island just when magma was already on its way toward the surface. Fernandina erupts every four-five years, on average, and satellites pass over the archipelago only once every several days, he said.
The team theorizes that Hawaiian and Galápagos volcanoes behave differently because neighboring volcanoes of the Galápagos grew concurrently and did not affect one another as they formed. Hawaiian volcanoes, however, grow sequentially, meaning that older volcanoes control the structural development, including eruptive patterns, of younger edifices.
Based on the relations between deformation and eruptions at Fernandina in 1995 and 2005, the authors argue that the next eruption of Fernandina will be from a circumferential fissure on the southwest side of the caldera in the area uplifted by the 2009 sill intrusion.
“Unfortunately, we are still not able to predict the timing of future eruptions, in the Galápagos or elsewhere,” Bagnardi said. “However, providing a forecast for the location and type of eruption is a step in the right direction.
Satellite imagery used in the study was also provided by the Japanese Space Exploration Agency (JAXA). This research was supported by the National Aeronautics and Space Administration (NASA) and the National Science Foundation (NSF).
April 2009 eruption at Fernandina Volcano, Photo by Paula Le Vay (from http://www.galapagos.org/about_galapagos/geologic-history/)
ENVISAT satellite interferogram showing the deformation produced by the April 2009 eruption at Fernandina. Each color fringe corresponds to ~3 cm of surface displacement. In yellow the area covered by lava flows erupted during this event.
The paper in Earth and Planetary Science Letters, “A New Model for the Growth of Basaltic Shields Based on Deformation of Fernandina Volcano, Galápagos Islands,” by Marco Bagnardi, Falk Amelung and Michael P. Poland, is available online.
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