Ground deformation at the Cerro Blanco caldera: A case of subsidence at the Central Andes BackArc

Abstract

Cerro Blanco Volcanic Complex (CBVC) is one of the youngest caldera complexes in the Southern Central Andes. Subsidence registered at CBVC has shown a slowdown in deformation velocity since 1992 (2.6 cm/yr) to 2010 (0.87 cm/yr). We update the deformation state of this caldera system by processing DInSAR data between 2003 and 2020 and GPS as a complementary tool. Results showed a circular deformation pattern of about 12 km diameter related to subsidence centered at CBVC throughout the entire period under analysis. Deformation rate decreased from 1 cm/yr for 2003–2009 period (Envisat data) to 0.7 cm for the 2012–2020 period (COSMO-SkyMed and Sentinel-1 data). Rate values were confirmed with GPS measurements during 2004 and 2013–2015. Analytical inverse modelling was used to infer the main characteristic of the source responsible for the measured displacement. Best-fitting solution corresponded to a spherical source located between 9 and 14 km from the surface with a volume decrease of about −0.013 km3/yr for the entire period. We propose that a combination of magmatic and geothermal dynamic as the origin of the continuous and slow subsidence observed in the CBVC as a consequence of the last eruption that occurred ca. 4 ka ago.