The interplay between catastrophic sector collapses and magmatic processes at active basaltic volcanic systems

Abstract

Lateral or sector collapses are catastrophic landslides that can destroy and reshape the morphology of volcanic edifices transforming geomorphology, hydrology, and ecosystems in the long term. They have killed thousands in the last few centuries, becoming among the most threatening and harmful volcanic phenomena for human populations. However, some aspects of their occurrence, dynamics, and implications still need to be better understood. On the other hand, volcanoes characterised by low-silica products (i.e., mafic volcanoes) are generally related to small-to-moderate explosive eruptions, and their hazard is underestimated. I explore the intersection between lateral collapses and mafic volcanoes. Are these volcanoes more unstable and prone to collapse than other systems dominated by silica-rich products? Will a recently collapsed volcano retain its original activity? Furthermore, do lateral collapses impact the magmatic feeding systems of those volcanoes, and how? To address these questions, this thesis contains four integrated contributions. Firstly, I investigated the occurrence of lateral collapses in mafic systems through a detailed literature review to determine the factors contributing to volcanic instability and the evidence of the magmatic system response to the collapse. Secondly, I studied the 7.1 ka lateral collapse of Antuco volcano (Southern Andes, Chile) using field stratigraphy, geochronology, sedimentology, and facies analysis to determine the causes and impacts of the collapse. Thirdly, the chronologically sampled products of the pre-and post-collapse Antuco edifice were studied to determine magma storage-ascent conditions during the post-collapse stage. Finally, I reconstructed the growth and collapse of a contemporaneous basaltic edifice during the 2021 Tajogaite Volcano eruption (La Palma, Canary Islands) using field, laboratory, and remote sensing tools. The findings suggest that the instability of basaltic volcanoes depends on factors intrinsically related to volcano emplacement, edifice dimensions, magma intrusions and eruptive styles. Recently collapsed volcanoes may not retain their original activity, especially if the collapse reactivates dormant parts of the plumbing system. Finally, in large-scale collapses (>1 km3), the magmatic system can be impacted for thousands of years. In contrast, modest collapses would not produce such modifications but change the vent architecture. These results are relevant for volcanic hazard assessment and monitoring techniques to reduce volcanic risk in communities near gravitationally unstable or recently collapsed volcanoes.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Mike Burton (Supervisor) & Margherita Polacci (Supervisor)