Displacement of Cerro Azul and Sierra Negra volcanoes, Galápagos Archipelago, during 2007–2009 and 2018–2021 measured from SBAS InSAR

Cerro Azul and Sierra Negra are two of the most active volcanoes in the Galápagos Archipelago, the eastern Pacific Ocean, with recent eruptions occurring in May-June 2008 and June-August 2018, respectively. In this study, surface displacements on the summit caldera of Cerro Azul and Sierra Negra volcanoes were investigated by applying the Small BAseline Subset (SBAS) technique to 13 ALOS-1 PALSAR images acquired from March 2007 to October 2009 and 94 Sentinel-1 SAR images acquired from April 2018 to April 2021. A subsidence of ~28 cm was observed outside the northern caldera rim of Cerro Azul from March to September 2008. Except for this period, the surface displacement of Cerro Azul was rarely observed from the ALOS-1 observations. Uplift on the summit caldera of Sierra Negra was observed during 2007–2009 and its velocity was varied by the eruptive phases of Cerro Azul. During the year preceding the eruption of Cerro Azul (March 2007 to March 2008), the summit caldera of Sierra Negra was uplifted at a velocity of 0.37 m/yr. However, the uplift velocity slowed to 0.14 m/yr between March 2008 and September 2008, when Cerro Azul erupted. For one year after the Cerro Azul eruption (September 2008 to October 2009), the uplift velocity of the Sierra Negra summit increased to 0.29 m/yr. The summit caldera of Sierra Negra was uplifted ~260 cm from April 2018 to April 2021, except for its eruptive phase when the surface displacement could not be observed from the SBAS result due to low interferometric coherence. The northern caldera rim of Cerro Azul subsided ~3 cm during the 2018 eruptions of Sierra Negra, then was uplifted by ~13 cm over the next 3 years.