Abstract
An unrest event occurred at the Cerro Azul volcano, Galápagos Islands, South America, in March 2017, leading to significant surface deformation on the southern Isabela Island, without eruption or surface rupture. We collected single-look complex synthetic aperture radar (SAR) images sensed by the Sentinel-1A satellite, obtaining eight differential interferograms, of which four showed extensive surface displacement during the co-unrest period. Geodetic data indicated that the unrest continued from 18 March to 25 March, reaching a negative peak displacement of −32.9 cm in the caldera and a positive peak displacement of 41.8 cm on the south-east plain in the line-of-sight direction. A joint magma source deformation model, consisting of a Mogi source below the caldera and a sill source south-east of the caldera, was inverted by the Markov chain Monte Carlo method combined with the Metropolis–Hasting algorithm, acquiring the best fit with the four interferograms. The magma transport mechanism of the event was explained by magma overflowing from the compressive Mogi to the tensile sill source, resulting in the observed “∞”-shaped deformation fields. Additionally, we investigated previous events with eruption rifts and lava lakes in 1979, 1998, and 2008, and proposed a potential hazard of tectonic volcanic activity for further volcanic susceptibility research in the Cerro Azul area.
Highlights
Volcanic tectonic activity can lead to a series of volcanic eruptions and deformation events, and so understanding internal magma sources is crucial for explaining the deformation and dealing with the disaster risks [1,2,3,4,5]
Observation from interferometric synthetic aperture radar (InSAR) is one of the most available data sources in modern geodetic technology and is one of the most suitable sources for geodetic inversions; as such, it is commonly used in volcanic geodetic research [14,16,17,18,19,20]
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Summary
Volcanic tectonic activity can lead to a series of volcanic eruptions and deformation events, and so understanding internal magma sources is crucial for explaining the deformation and dealing with the disaster risks [1,2,3,4,5]. Magma sources exist under volcano craters where surface deformation rates occurring with the activity largely depend on magma supply rates and storage depths [1,8,9,10,11,12]. Surface deformation in unrest events is essential for comprehensively understanding volcanic characteristics, where geodetic observations with high precision and wide coverage provide accurate references for volcanic activity and modelling [1]. In view of the limited number of Global Positioning System (GPS) stations on Isabela, observations from the InSAR technique provided valuable geodetic data, helping us to restore the surface deformation field during the unrest event. We collected InSAR observations from the Sentinel-1A satellite during the unrest period of the Cerro Azul volcano, recovering the surface deformation field during this event. We assessed volcanic hazard in this area by comparing magma source deformation models with records from previous eruptions
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