Subsurface Magmatic Processes in the Western Galapagos Islands from High-Resolution Interferometric Radar Deformation Measurements

Stanford University, Stanford CA

Investigators

Abstract

Zebker 0001096 Interferometric synthetic aperture radar (InSAR) observations of the Western Galapagos during 1992-1999 show that at least six out of the seven volcanoes on the islands of Isabela and Fernandina have been deforming, some at unusually high rates. Four volcanoes are inflating, including Sierra Negra on southern Isabela Island at rates of up to 0.9 m/year. The total uplift of Sierra Negra during 1992-99 is more than 2.5 m. The uplift is caused by pressure increases in shallow magma chambers beneath the volcanoes at depths 1.5-3.0 km. Two other volcanoes, Cerro Azul on Isabela Island and Fernandina volcano, erupted during the observation period. These volcanoes show a complicated pattern of pre-eruptive inflation, co-eruptive deflation, and localized deformation due to shallow intrusions. Amazingly, decades-old lava flows are continuing to subside at the present time. The high-resolution spatially-dense InSAR data can be used to constrain subsurface magmatic processes. Preliminary results indicate that some of the observed signals are well-modeled by simple symmetric pressure sources, while others cannot be explained by such models. Data from Sierra Negra volcano appear to require episodic faulting, or other inelastic deformation, accompanying inflation. The investigators propose to investigate the current activity and its relation to subsurface processes using a combination of new observations and model development, as enabled by radar interferometry. They will use the observations to constrain the geometry and volume changes of magma chambers beneath the volcanoes, the dynamics of flow between storage chambers and intrusive/eruptive dikes, and the role of faulting and inelastic deformation associated with sustained magma chamber inflation. They also will examine temporal variability in these processes as evidenced in the InSAR measurements. Analysis of these high-resolution InSAR observations of Galapagos volcanism requires creation and validation of interferograms, development of inverse methods suited to InSAR data, and extension of these methods to derive detailed models of subsurface activity and inelastic response in the overlying rock. Specifically, the team will i) develop analytical methods that capitalize on the dense nature of the InSAR observations, ii) extend modeling capability by examining more physically realistic magma chamber geometries, iii) examine inelastic response observed in some Galapagos calderas, iv) test whether there is evidence that the magmatic systems at the various volcanoes are coupled or interacting, and v) study the extraordinary observation of subsidence of lava flows that are up to 20 years old.