Research Highlights

"Space-geodetic evidence for multiple magma reservoirs and subvolcanic lateral intrusions at Fernandina Volcano, Galápagos Islands"

by Ph.D. Student: Marco Bagnardi


Using Interferometric Synthetic Aperture Radar (InSAR) measurements of the surface deformation at Fernandina Volcano, Galápagos (Ecuador), acquired between January 2003 and September 2010, we study the structure and the dynamics of the shallow magmatic system of the volcano. Through the analysis of spatial and temporal variations of the measured line-of-sight displacement we identify multiple sources of deformation beneath the summit and the southern flank. At least two sources are considered to represent permanent zones of magma storage given their persistent or recurrent activity. Elastic deformation models indicate the presence of a flat-topped magma reservoir at 1.1 km below sea level and an oblate-spheroid cavity at 4.9 km b.s.l. The two reservoirs are hydraulically connected. This inferred structure of the shallow storage system is in agreement with previous geodetic studies and previous petrological analysis of both subaerial and submarine lavas. The almost eight-year-long observation interval provides for the first time geodetic evidence for two subvolcanic lateral intrusions from the central storage system (in December 2006 and August 2007). Subvolcanic lateral intrusions could provide the explanation for enigmatic volcanic events at Fernandina such as the rapid uplift at Punta Espinoza in 1927 and the 1968 caldera collapse without significant eruption.

Galapagos

Figure 1. Map showing the location of the Galápagos Islands relatively to South America and the Galápagos Spreading Center (GSC). Black arrows indicate the motion of the Nazca Plate (91) relative to the global hot spot reference frame. (b) Map of the western islands of the Galápagos Archipelago (Landsat 7 shaded-relief color composite image; bathymetry: GEBCO_08 Grid, version 20100927, http://www,gebco.net; topography: hole-filled seamless SRTM data V4). Six volcanoes on Isabela and Fernandina islands have been actively deforming during the last decade, and three of them erupted. For each volcano, dates of the latest eruptions are reported. The white square marks the area covered by subsequent figures in this paper.


Galapagos 3

Figure 2. Modeling results: deeper source, (a and b) ascending IS2 and (d and e) descending IS7, and August 2007 lateral sill intrusion, (g and h) ascending IS2 and (j and k) descending IS7, comparison between observed data and model predictions. (c, f, i, and l) Comparison between topography (in gray), observed (in blue) and modeled (in green) surface displacement along the A-A′ and the B′B′ traces. Surface deformation is modeled using an oblate spheroid for the deeper source (black star), and rectangular sills for the shallower source and the August 2007 intrusion (gray and blue rectangle respectively). For source parameters see Table 4. The solid and the dashed gray lines represent the coastline of Fernandina Island, the summit caldera rim and the caldera floor outline respectively.



Reference:

Bagnardi, M., and F. Amelung (2012), Space-geodetic evidence for multiple magma reservoirs and subvolcanic lateral intrusions at Fernandina Volcano, Galápagos Islands, J. Geophys. Res., 117, B10406, doi:10.1029/2012JB009465.