Volcanic hazard assessment in monogenetic volcanic fields

Abstract

One of the most important tasks of modern volcanology, which represents a significant socio-economic implication, is to conduct hazard assessment in active volcanic systems. These volcanological studies are aimed at hazard that allows to constructing hazard maps and simulating different eruptive scenarios, and are mainly addressed to contribute to territorial planning, definition of emergency plans or managing volcanic crisis. The impact of a natural event, as a volcanic eruption, can significantly affect human life, property, infrastructures, and the environment. Long periods of quiescence are quite common in many volcanic areas and this often leads to a fall in the alert. The consequence is lack of preparation to deal with a volcanic crisis.

The present Ph.D. Thesis is focused on the development and application of different tools for the spatial and temporal analyses to assess volcanic hazard in monogenetic volcanic fields. Monogenetic volcanic fields are commonly not regarded as potentially dangerous and only a few studies concerning hazard assessment have been conducted in such environments. In the long-term hazard assessment, we assume that the future eruptive behaviour in the volcanic field could be similar to the last eruptive activity. First, we have developed a new tool, QVAST (QGIS for VolcAnic SuscepTibility), designed to carry out the spatial analysis. This tool allows to calculate the volcanic susceptibility of the area, i.e. the probability of new vent opening, using direct and indirect structural data. Second, we have developed a new tool, HASSET (Hazard Assessment Event Tree), to conduct temporal analysis. Combining both tools and the previous one, VORIS 2.0.1, that uses simulation models to predict the most probable eruptive scenarios and which areas could be affected by a future eruptive event, we can evaluate in a probabilistic way long-term hazard represented by a qualitative hazard map that allows us to identify different levels of hazard in the study area. In this thesis we present different case studies. The first example was carried out at El Hierro Island (Canary Islands), an island essentially characterized by basaltic volcanism with both Strombolian and Hawaiian activity. The last eruption on El Hierro occurred in 2011–2012 demonstrates the importance of reliable data and tools that can enable scientific advisors and decision-makers to consider possible future eruptive scenarios. The second case study was Deception Island (Southern Shetland Archipelago, Antarctica), which is the most active volcano in the South Shetland Islands and has been the scene of more than twenty eruptions over the past two centuries. We identified a number of significant scenarios using our GIS-based tools and evaluated the potential extent of the main volcanic hazards to be expected on the island. The last case study presented is La Garrotxa Volcanic Field (NE of Spain), which is a quaternary volcanic field, located in the Northeast of the Iberian Peninsula, and includes more than 50 well preserved volcanoes.

Finally, considering the importance of both quantity and quality of the available volcanic data and an optimum storage mechanism and as complement to the e-tools we have developed, we describe the design of a new spatial database structure, VERDI (Volcanic managEment Risk Database desIgn), which allows different types of data to be manipulated, organized, managed. The design of purpose-built databases should facilitate spatial and temporal analysis that will produce probabilistic hazard models for future vent opening, simulate volcanic hazards and assess their socio-economic impact, avoiding any duplication of information.

The methodologies described in this thesis establish the general guidelines of a procedure that facilitates undertaking volcanic hazard assessment in a systematic way, which can be easily applied to any volcanic area or system, and in particular to any monogenetic volcanic field.

Una de las tareas más importantes de la vulcanología moderna, que representa una implicación socio-económica significativa, es llevar a cabo la evaluación de la peligrosidad en los sistemas volcánicos activos. Estos estudios vulcanológicos están enfocados a la elaboración de mapas de peligro y la simulación de diferentes escenarios eruptivos, y están dirigidas para contribuir a la planificación territorial, a la definición de los planes de emergencia o la gestión de crisis volcánicas.

La presente Tesis doctoral está enfocada al desarrollo y aplicación de diferentes herramientas informáticas para los análisis espacial y temporal del peligro volcánico en campos volcánicos monogenéticos. En primer lugar, hemos desarrollado una nueva herramienta, QVAST, diseñada para llevar a cabo el análisis espacial, que permite calcular la susceptibilidad volcánica de la zona de estudio, utilizando datos estructurales directos e indirectos. En segundo lugar, hemos desarrollado una nueva herramienta, HASSET, para llevar a cabo el análisis temporal. La combinación de ambos instrumentos y una herramienta anterior, VORIS 2.0.1, que utiliza modelos de simulación para predecir los escenarios eruptivos más probables y aquellas áreas que podrían verse afectadas por un futuro evento eruptivo, nos permite evaluar de forma probabilística el peligro a largo plazo, representado por un mapa cualitativo que nos permite identificar los diferentes niveles de peligro en el área de estudio. En esta tesis se presentan diferentes casos de estudio en campos volcánicos monogenéticos: la isla de El Hierro (Islas Canarias), la isla Decepción (archipiélago de las Shetland del Sur, Antártida), el campo volcánico de La Garrotxa (NE de España).

Por último, teniendo en cuenta la importancia de la cantidad y la calidad de los datos volcánologicos disponibles y un mecanismo de almacenamiento óptimo, se describe el diseño de una nueva estructura de base de datos espaciales, VERDI, que permite manipular, organizar y gestionar diferentes tipos de datos. Las metodologías descritas en esta tesis establecen líneas guía generales de un procedimiento que facilita la realización de la evaluación del peligro volcánico de forma sistemática, los cuales se pueden aplicar a cualquier zona volcánica o sistema, y en particular, a cualquier campo volcánico monogenético.