Sierra Negra

Sierra Negra, exhibited spatially and temporally variable deformation, with a maximum uplift of 2.7 m between 1992 and 1999, which can be modelled by a shallow inflating sill. Sierra Negra experienced particularly dramatic and variable ground deformation. A peak radar line-of-sight (LOS) displacement (range decrease) of 2.2 m between 1992 and 1998 (corresponding to 2.4 m of uplift; see Fig. 1) and 0.3 m during the September 1998 to March 1999 period. The corresponding displacement rates vary from 0.32 m yr^-1 during 1992–97, to 0.90 m yr^-1 during 1997–98, and 0.65 m yr^-1 during 1998–99. Ref 1.
The results of geodetic monitoring since 2002 at Sierra Negra volcano in the Galápagos Islands show that the filling and pressurization of an ∼2-km-deep sill eventually led to an eruption that began on 22 October 2005. Continuous global positioning system (CGPS) monitoring measured >2 m of accelerating inflation leading up to the eruption and contributed to nearly 5 m of total uplift since 1992, the largest precursory inflation ever recorded at a basaltic caldera. Ref 2.
Both InSAR and GPS data document a remarkable story of ~ 5 m pre-eruption uplift during 1992–2005, which was accompanied by at least three trapdoor faulting events on an intra-caldera fault system, in January 1998, April 2005, and just before the eruption in October 2005. The pattern of uplift observed in the InSAR data from different time periods during 1992–2005 is consistent with filling and pressurization of a 2.2 km deep sill under the caldera. Ref 3