Five GPS campaigns were conducted between 1993 and 2002 at São Miguel island, which hosts three stratovolcanoes: Sete Cidades, Água de Pau (also called Fogo), and Furnas. The campaigns between 1993 to 2000 had few stations situated on Água de Pau, whilst the 2000 and 2002 campaigns focused on Sete Cidades and Água de Pau.
GPS campaign data between 1993 and 2002 show that deformation is driven by WNW–ESE tectonic extension at a rate slower than 5 mm yr⁻¹ (Trota et al., 2006). GPS time series between 2008 and 2013 also show evidence for tectonic extension (Okada et al., 2014).
During a period of volcanic unrest at  Água de Pau between 2011 and 2012, two further sources of deformation were identified: 1) Permanent edifice-scale inflation centered at NE summit of Fogo, and 2) minor-scale inflation-deflation reversals between Congro, a trachyte maar east of Água de Pau and Furnas volcanoes (Okada et al., 2014).