#fernandina

To this day, interesting discoveries occur on these islands, although sometimes it requires a bit of luck. In 2009, an eruption began at Fernandina volcano. The exact timing of that eruption was recorded by the U.S. GOES weather satellite, which recorded the appearance of the heat plume in the volcano. Fortunately, a few hours beforehand, the European Envisat satellite passed over this island and took a radar image of the island.

The type of radar used, InSAR (Interferometric Synthetic Aperture Radar) is exceptionally well-tuned to observe changes in the Earth’s landscape. When several images are overlain, minute changes in topography, as can occur from erosion, earthquakes, or even volcanism, can be accurately measured.

Since this measurement was taken almost immediately before the start of the eruption, the volcanoes deformation during the eruption could be precisely determined. A group led by scientists at the University of Miami studied the InSAR measurements of this eruption and found that it showed a fascinating detail of these volcanoes.

In Hawaii, the best-studied volcanic system in the world, magmas come to the surface in vertical cracks known as dikes that intrude over and over in the same spots. These dikes can be imaged in measurements like InSAR and even found in the field. Yet, the structure of Galapagos volcanoes has been recognized as different; dikes don’t always occur in the same locations like they do in Hawaii. There are some dikes but they don’t stay in the same spot.

In this Galapagos eruption, the magma did not come up vertically; it came out of the magma chamber horizontally. Geologists have a term for this as well; a horizontal layer of magma is called a sill.

The magma in Galapagos eruptions comes out of the magma chambers horizontally and then eventually bends upwards into a vertical dike as it approaches the surface. For this reason, these volcanoes never form localized rift zones where vertical dikes intrude in the same place, giving the Galapagos volcanoes a different structure from Hawaiian ones.

In Hawaii, new eruptions often start at the top of the volcano and then migrate into the rift zones. This research suggests a different mechanism for the Galapagos; when a sill forms, it creates stresses at the edge of the sill. Once put under stress, those rocks become weaker and it is these locations, near the edge of a previous sill, where the next eruptions tend to begin. This research therefore will help predict which areas on the Galapagos are at the greatest risk for volcanic eruptions in the near future.

-JBB

Image credit: Andrew Miller (creative commons license) http://www.flickr.com/photos/govmilliken/1477995619

Original paper (subscription): http://www.sciencedirect.com/science/article/pii/S0012821X13003919