The May 2005 eruption of Fernandina volcano, Galápagos, occurred along circumferential fissures parallel to the caldera rim and fed lava flows down the steep southwestern slope of the volcano for several weeks. This was the first circumferential dike intrusion ever observed by both InSAR and GPS measurements and thus provides an opportunity to determine the subsurface geometry of these enigmatic structures that are common on Galápagos volcanoes but are rare elsewhere. Pre- and post- eruption ground deformation between 2002 and 2006 can be modeled by the inflation of two separate magma reservoirs beneath the caldera: a shallow sill at ~1 km depth and a deeper point-source at ~5 km depth, and we infer that this system also existed at the time of the 2005 eruption. The co-eruption deformation is dominated by uplift near the 2005 eruptive fissures, superimposed on a broad subsidence centered on the caldera. Modeling of the co-eruption deformation was performed by including various combinations of planar dislocations to simulate the 2005 circumferential dike intrusion. We found that a single planar dike could not match both the InSAR and GPS data. Our best-fit model includes three planar dikes connected along hinge lines to simulate a curved concave shell that is steeply dipping (~45-60°) toward the caldera at the surface and more gently dipping (~12-14°) at depth where it connects to the horizontal sub-caldera sill. The shallow sill is underlain by the deep point source. The geometry of this modeled magmatic system is consistent with the petrology of Fernandina lavas, which suggest that circumferential eruptions tap the shallowest parts of the system, whereas radial eruptions are fed from deeper levels. The recent history of eruptions at Fernandina is also consistent with the idea that circumferential and radial intrusions are sometimes in a stress-feedback relationship and alternate in time with one another. © 2010 Springer-Verlag.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The manuscript was greatly improved by helpful reviews from Sang-Ho Yun and Scott Rowland. This research was supported by grants from the National Science Foundation Earth Sciences Program (EAR-9814312, EAR-0004067, and EAR-0538205), and in part by the NOAA Vents Program (PMEL contribution #3559). Michael Ramsey (University of Pittsburg) and Scott Rowland (University of Hawaii) kindly assisted with acquiring and processing the ASTER satellite imagery. ENVISAT radar data were provided by the European Space Agency through Cat-1 project #3493. Clay Hamilton at upwarp.com created the illustration in Fig. 13. The Charles Darwin Research Station and the Galapagos National Park Service provided invaluable logistical assistance. Beth Bartel, Erika Rader, Glyn Williams-Jones, Nathalie Vigouroux, Terry Naumann, and Kim Whipple helped in the field during our 2002 and 2006 GPS surveys. This paper is dedicated to the memory of our late friend, colleague, and co-author Daniel J. Johnson.
ASJC Scopus subject areas
- Geochemistry and Petrology