A Geophysical Survey of Active Volcanism in the Central and Southern Andes

Book excerpt: The subduction of the Nazca plate beneath the South American plate results in great earthquakes and active volcanism along the Andean margin. The Central Volcanic Zone (CVZ) between 15°S and 28°S and the Southern Volcanic Zone (SVZ) between 33°S and 46°S are separated by a zone of flat slab subduction and differ significantly in the manifestation of current volcanic activity. The CVZ has been considered less hazardous due to the few number of historical volcanic eruptions compared to the SVZ, yet it contains the largest mid-crustal magma body on Earth and erupted at least 10,000 km3 of ignimbrite in the Late Miocene (10-1 Ma). In this dissertation, I use InSAR (interferometric synthetic aperture radar), thermal remote sensing, and seismology to investigate active volcanism in the Central and Southern Andes. InSAR and thermal remote sensing provide synoptic coverage along the volcanic arc, and seismic experiments allow further examination of selected volcanoes. I establish the first catalog of seismicity at Uturuncu volcano in Bolivia, where InSAR has observed continuous uplift since 1992, and find an unusually high seismicity rate for a Pleistocene volcano as well as swarm activity and triggered earthquakes. I then conduct a survey using satellite thermal infrared data to detect thermal hotspots related to volcanic activity throughout the CVZ and SVZ. I find hotspots at many volcanoes that had not previously been documented, with the CVZ containing more volcanoes with hotspots than the SVZ. One of the most thermally active volcanoes in the SVZ, Cordón Caulle volcano, experienced a large rhyodacitic eruption from 2011-2012. I use InSAR and petrology to model the pre-eruptive conditions at depth and coeruptive processes and find that a large, long-lived crustal magma reservoir must be present beneath Cordón Caulle. Finally, I carry out an InSAR survey of volcanoes in southern Peru, completing a regional study of volcano deformation in the CVZ and allowing for a comprehensive comparative analysis between the CVZ and SVZ.