Tilt and levelling stations detected uplift at Galeras, starting in 1989, with peak uplift rates between June and November 1991 (Ordoñez and Rey, 1997). The source was modelled as a magmatic body, which rose from a depth of 2-3 km in late 1990 to less than 500 m in Dec. 1991.
3 cm of subsidence were detected at Galeras during an ALOS survey of Colombian volcanoes (Parks et al., 2011). The deformation occurred between Dec. 2007 and Jan. 2008, coincident with an eruption on Jan. 17 2008, and was modelled as a deflating magma body with 6.5 x 10⁵ m³ volume loss at 2 km depth. The same source was modelled by tilt to have a volume loss of ~ 7 x 10⁵ m³ at 1.4 km depth between 17 and 19 Jan. 2008 (Parks et al., 2011).