Fogo erupted in April 1995 after 43 years of dormancy. About 46 10^6 m^3 of lava erupted during 7.5 weeks from vents on the SW flank of Pico do Fogo into Cha das Caldeiras. ERS SAR data between 1993–1998 show ground deformation due to a feeder dike but lack evidence for any volcano-wide deformation related to volume changes of a shallow magma reservoir. This suggests that Fogo is fed from a relatively deep, mantle-lithospheric source (>16.5 km depth), consistent with petrological data (Amelung & Day, 2002).
Since the eruption, a network of monitoring instruments were installed (Project VIGIL). This included seismic stations, a CO2 sensor and tiltmeters. The tiltmeter data has not identified any significant deformation. Instead current research is focused on the characterisation of environmental effects on tilt observations, using temperature, atmospheric pressure, rainfall and several other meteorological variables that are also recorded (Fonesca et al., 2003).
Between September 1998 and January 2001 a total of five GPS campaigns were conducted in the Fogo geodetic network. Both deflation episodes (April–November 1999) and inflation episodes (November 1999–June 2000) were interpreted. In general, it can be stated that the patterns of displacement reflect the major structural feature of the island (Fonesca et al., 2003).