The first deformation measurements of Colima were made with annual levelling surveys, and were complemented with GPS stations installed in the mid 1990’s (Murray & Wooler, 2002). They recorded a persistent subsidence at a rate of 5 mm/year, 1.1 km from the summit (levelling), and 93 mm/yr at the edge of the dome (GPS). The GPS also recorded horizontal displacements at a maximum rate of 23 mm/year near the dome. Simple deformation models were unable to fit the observations, and the deformation was thought to most likely be due to a combination of downslope creep, settling and compaction of the edifice, and gravitational spreading (Murray & Wooler, 2002).
EDM surveys conducted between May 1997 and Jan 1999 detected up to 4 m shortening at an accelerating rate peaking at 90 cm shortening from Oct-Nov 1998 before lava extrusion began on 20th Nov 1998 (Ramı́rez-Ruiz et al., 2002). The pre-eruption inflation was assumed to be caused by magma accumulating in the edifice.
Monitoring of tilt signals at Colima showed inflation between lava extrusion in Oct. 2004 and Vulcanian explosions in Feb. 2005, followed by subsidence in May – June 2005 (Zobin et al., 2011). Two magmatic sources were modelled for the deformation – one at 300-1800 m depth for the earlier inflation and one at 1800-2800 m depth for the later subsidence. The tiltmeters also recorded rapid inflation-deflation signals, caused by impulses from Vulcanian explosions in 2005, and with amplitudes correlated to the size of explosions recorded by seismometers.
Early InSAR studies of Colima did not observe any deformation between 2002-2010 most likely due to steep slopes, atmospheric noise and temporal aliasing (Pinel et al., 2011 and Chaussard el al., 2013, see Popocatepetl entry for full references). Spotlight TerraSAR-X imagery acquired 19 and 7 hours before an explosion on Jan 6th 2013 show up to 5 cm of pre eruptive deformation near the dome (Salzer et al., 2014). Modelling of this deformation is best fit by two shallow elliptical sources pressurising by 22-25 MPa. One source is at 150-300 m below the summit and the other only 10’s of meters below the summit within the lava dome.
Direct measurements of the dome have recently been feasible using pixel offset tracking of thermal infrared imagery. Cross-correlation of pixels from imagery in Feb 2011 records permanent dome growth of up to 0.3 m within 120 s, coincident with volcanic emissions (Walter et al., 2013).