A dense network of tiltmeters, EDM and levelling lines were installed at Nevado del Ruiz just before and following the November 1985 eruption. No long term deformation was detected between 1985 and 1988, but annual cycles of inflation and deflation were recorded by some tiltmeters (Banks et al., 1990). The deformation was temporally correlated with seasonal rainfall changes, and attributed to be due to changes in groundwater levels.
No deformation was detected at Nevado del Ruiz between 2006 and 2009 during ALOS surveys of Latin American volcanoes (Fournier et al., 2010, Parks et al., 2011). An ALOS interferogram from Jan. 2008 to Mar 2011 also did not find any deformation (detection threshold < 1 cm/year) (Lundgren et al., 2015).
Radarsat 2 interferograms between Dec. 2011 and Dec 2014 show inflation at a maximum linear rate of 3-4 cm/year, centred ~15 km south of Nevado del Ruiz (Lundgren et al., 2015). The deformation was modelled by an inflating mogi and spheroidal source at 14 km depth. Continuous GPS installed in 2010 also detected ~6 cm of inflation at Nevado del Ruiz during 2012 (Ordoñez et al., 2015).