The Galapagos shield volcanoes on the islands of Fernandina and Isabela are among the most active volcanoes on Earth with an average of 2-3 eruptions every 10 years. The investigator's previous radar interferometric study demonstrated how actively the Galapagos volcanoes deform, and how well this can be measured with radar interferometry. All but one of the 7 volcanoes show evidence for magma intrusion resulting in uplift of the volcanic edifice at rates between a few mm/yr to 0.9 m/yr (Amelung et al., 2000). In this project the investigators will obtain a dense time series of interferograms to map, document and interpret the deformation of Galapagos volcanoes with high temporal resolution (~35-70 days). A dense time series of interferograms will address the following issues: Do subsurface magmatic intrusions occur in pulses or are they continuous in time? If in pulses, how long do they last? Does the intrusion rate increase prior to an eruption? Is the center of magmatic inflation stationary or does it migrate vertically or horizontally prior to an eruption? Do intrusions at different volcanoes occur simultaneously or are they separated in time? Are the volcanoes fed by a common or by different deep magma sources? These questions should be addressed by the dense spatial and time coverage the proposed InSAR observations.