Cycles of inflation and deflation were detected by a tiltmeter installed 2.5 km from the lava dome of Guagua Pichincha between September and December 1999 (Garcia-Aristizabal et al., 2007). The tilt signals were temporally correlated with VT and LP earthquake swarms, and the largest tilt change of 26 μrad corresponded with the growth of a small lava dome (0.5 million m³) between 18 to 21 November 1999. The inflation was followed by deflation on the 26 November 1999 when the lava dome collapse, suggesting the inflation was due to pressure build-up by the dome blocking the conduit (Garcia-Aristizabal et al., 2007).
A regional ALOS survey of Northern Andes volcanoes found the west flank of Guagua Pichincha to be inflating at a rate of 2.6 ± 0.5 cm/yr between 2007 and 2009 (Morales Rivera et al., 2016). The deformation was modelled by a Mogi source at a depth of 3 km inflating by 0.12 × 10⁶ m³, and is thought to be either hydrothermal or magmatic in origin.