Abstract
A mosaic is figured of two deformation interferograms for 1992-7 and 1992-8, which shows that all seven volcanoes on the islands of Fernandina and Isabella (except Ecuador volcano) deformed. Gerro Azul and Fernandina showed evidence of inflation, co-eruptive deflation and shallow dyke intrusion. Sierra Negra, which had not yet erupted, showed temporary and variable deformation and uplift modelled by a shallow inflating sill. Inflation in 1997-8 was accompanied by 'trapdoor' faulting on a steeply-dipping fracture system in the caldera, and repeated trapdoor faulting has formed an arcuate intra-caldera ridge in Sierra Negra.