Volcano-tectonic history and volcanic hazard assessment of the 22.5-29°S segment of the Central Volcanic Zone of the Andes

Abstract

Evaluating volcanic hazards typically focusses on single eruptive centres or spatially restricted areas, such as volcanic fields. Expanding hazard assessment across wide regions (e.g., large sections of a continental margin) has been rarely attempted, due to the complexity of integrating temporal and spatial variability in tectonic and magmatic processes. In this study, I investigate new approaches to quantify the hazards of such long-term active and complex settings, using the example of the 22.5-29°S segment of the Central Volcanic Zone (CVZ) of the Andes. This zone records ~35 Myr of uninterrupted volcanic activity comprising a vast variety of activity types, edifice forms and erupted compositions. It hosts hundreds of volcanic features with youthful morphologies, including the site of one of the largest Holocene explosive eruptions known in the world, the Cerro Blanco eruption at ~4.2 ka BP. Despite these features, there has been no comprehensive investigation of the volcanic history of the region, nor its volcanic hazards. Through this study, a long-term probabilistic volcanic hazard assessment for the 22.5-29°S segment of the CVZ is developed. This began with the creation of a volcanic geospatial database covering the last 35 Myr. The next step was to examine the wider tectonic history of the region and spatio-temporal drivers of volcanism. Furthermore, in order to gain new insights into the volcano-tectonic history of the region, the volcanic database was used to analyse the volumetric eruption rate over the last 35 Myr, and to track temporal variations in the main orientation of the volcanic arc. Finally, I developed a computer code to process such large volumes of data and help objectively delineate hazard zones in regions with different types of volcanism (e.g., monogenetic vs. polygenetic). The main volcano-tectonic and spatio-temporal patterns correlate well with the southward passage of an oceanic hotspot track during the Miocene. A response time of ~10-12 Myr is estimated between ridge subduction and the onset of high-flux magmatism at 22.5-24°S (~9 Ma) and 25-26°S (~5.5 Ma). If this trend continues, the 26.5-27.5°S segment, which hosted the Cerro Blanco eruption, is likely to experience a magmatic flare-up in the next few Myr.