A retrospective study of the pre-eruptive unrest on El Hierro (Canary Islands): implications of seismicity and deformation in the short-term volcanic hazard assessment

Stefania Bartolini,Laura Becerril,Rosa Sobradelo,Joan Martí,Carmen López

doi:10.5194/nhess-18-1759-2018

Abstract

Abstract. The correct identification and interpretation of unrest indicators is useful for forecasting volcanic eruptions, delivering early warnings, and understanding the changes occurring in a volcanic system prior to an eruption. Such indicators play an important role in upgrading previous long-term volcanic hazard assessments and help explain the complexities of the preceding period of eruptive activity. In this work, we present a retrospective analysis of the 2011 unrest episode on the island of El Hierro, Canary Islands, that preceded a submarine eruption. We use seismic and surface deformation monitoring data to compute the susceptibility analysis (QVAST tool) and to study the evolution over time of the unrest (ST-HASSET tool). Additionally, we show the advantages to be gained by using continuous monitoring data and hazard assessment e-tools to upgrade spatiotemporal analyses and thus visualize more simply the development of the volcanic activity.

Highlights

The most challenging aspect of forecasting volcanic eruptions is the correct identification and interpretation of precursors during the episodes of unrest that normally precede eruptive activity
In the case of the rift volcanism and the submarine layers, we applied the least square cross-validation method (LSCV) (Cappello et al, 2012; Bartolini et al, 2013) to obtain the bandwidth parameter, as it better represents the geometry of the vents distribution, NE–SW elongated
Short-term hazard assessment should always be conducted based on a previous long-term hazard assessment, as a systematic study of past eruptive activity conducted well before a new volcanic crisis starts can help forecast the most probable scenarios and avoid confusion regarding the potential outcome of the forthcoming eruption

Summary

Introduction

The most challenging aspect of forecasting volcanic eruptions is the correct identification and interpretation of precursors during the episodes of unrest that normally precede eruptive activity. During this phase, the short-term volcanic hazard assessment can be computed by combining a longterm hazard analysis with real-time monitoring data, updating continuously the status of the volcanic hazard (Blong, 2000; Sobradelo and Martí, 2015; Tonini et al, 2016). The parameters associated with the volcanic process are the geophysical and geochemical signals that provide information on magma movement within the volcanic system and on how the magma is preparing to reach the surface (Chouet, 1996; McNutt, 1996). Changes may be detected on the surface that reflect variations in the geophysical (e.g., seismicity, surface deformation, and changes in potential fields) and/or geochemical (e.g., gas flow rate and gas composition) parameters sensed by the network that is monitoring the activity of the volcano (Scarpa and Tilling, 1996; Sparks, 2003; Vallianatos et al, 2013; Telesca et al, 2015)

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