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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/204643
Multi-hazard assessment and risk management in volcanic islands
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[eng] Our planet is impacted by diverse natural and human-induced events, including weather-related events (floods, droughts, forest fires, etc.) and geological events (landslides, earthquakes, volcanic eruptions, etc.). These events disrupt the geosphere and the biosphere. Understanding these hazards is crucial to anticipate and provide warnings to exposed populations. Interconnections between phenomena are being discovered, such as volcanic eruptions impacting the ocean, atmosphere, and climate. These events can lead to economic losses, fatalities, infrastructure destruction, and mental health burdens. The frequency and magnitude of these events, especially weather-related hazards, are increasing due to climate change. Preparation, information, and decision support systems are needed to mitigate their impact. Volcanic islands are highly vulnerable due to their isolation, fragile economies, and multi- hazard nature, being often the source of complex successions of disastrous events. Moreover, climate change exacerbates vulnerability by increasing the magnitude and frequency of these events, as well as contributing to rising sea levels. Anticipating and preparing for such events are crucial to ensuring safe and sustainable lifestyles.
The island of Tenerife in the Canary Archipelago is an excellent example of where both cascading non-extreme and extreme hazards have occurred along its history and could occur again in the future. Both phonolitic and basaltic volcanic eruptions on Tenerife have occurred frequently during the Holocene. These eruptions cause ash falls, lava flows, and explosive projections of pyroclasts. They also generate seismic activity, risking damage to buildings and infrastructure, which adds to the tectonic seismicity experienced by the region, with a lower magnitude and intensity. Therefore, the probability of a volcanic eruption on the island in the next few years is not negligible. This is higher for basaltic eruptions along the rift zones, as they have been all the historical eruptions, which today could have a significant affectation on the surrounding areas, as most of them are now highly populated. However, the probability of an eruption from Teide is also high, assuming the level of current activity and the fact that its last eruption occurred 1,000 years ago. In this case, volcanic and associated hazards would be of much higher intensity and could affect mostly the northern side of the island, in particular the Icod and La Orotava valleys. In addition, annual floods and torrential episodes, triggered by storms, produce severe human and economic losses and affect cities like Santa Cruz de Tenerife and San Cristóbal de La Laguna. Sediment transport, debris flows, and rock falls occur during these events. The island also experiences phenomena such as Sahara haze, forest fires, and the possibility of tsunamis in the surrounding Atlantic Ocean. On the other hand, a cascading sequence involving a caldera-forming eruption, high-magnitude seismicity, mega-landslides and
tsunamis occurred at least twice during the construction of this island and could occur again in the future. Its population growth and consequent urban expansion, especially focused on the construction of tourist infrastructure on the coast, lead to the population encroaching on areas with higher risk of these events. However, scientific knowledge and protocols mainly focus on individual hazards and risks. Predicting the outcomes of multi-hazard scenarios remains challenging. The multi-hazard concept emerged in the 1990s to address this issue. However, conflicting perspectives hinder its implementation in disaster reduction policies.
This contribution presents a methodological development based on scientific knowledge for decision-making in vulnerable regions facing natural hazards, using Tenerife as a case study. To accomplish this, we first explored and clarified the issues surrounding the implementation of a multi-hazard perspective in disaster risk reduction strategies to understand the main challenges of this approach. Following this, a comprehensive long-term multi-hazard assessment was conducted for the island of Tenerife, covering both non-extreme and extreme events. For the former, a Bayesian-inferred Event Tree framework was applied to calculate the probabilities of natural hazards in Tenerife based on its historical event records from 1496 to 2020. On the other hand, to address the existing gap in risk management protocols regarding cascade effects for extreme events, we simulated the extent and potential impact of a multiple, extreme geohazard episode similar to the last recorded one that took place on the island of Tenerife around 180 ka. According to these analyses, the island is facing a high probability of future floods, which have caused the most significant human and economic losses to date in the island. Furthermore, a potential caldera-forming eruption in Teide could generate Pyroclastic Density Currents that would cover almost the entire island, along with high-magnitude seismic activity that could trigger large-scale landslides in the north resulting in tsunami waves reaching up to 200 meters in height.
Land management based on long-term assessments of multiple hazards, as carried out here, is crucial to strengthen Tenerife's current risk mitigation plans. This will enable the sustainable development of the island through the sustainable use of currently exploited energy and material resources, as well as through a two-way relationship between sustainable tourism exploitation and the education of its population, both focused on the conservation of its geological heritage. All of this will contribute to increasing society's resilience to multiple hazards in the context of climate change, without having to forego the opportunities offered by volcanic regions like Tenerife. For this reason, this doctoral thesis emphasizes the importance of establishing a cross- cutting, climate change-oriented, socially inclusive, and scientifically based multi-hazard risk management system. This system should be aligned with the critical needs and solutions of society.
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LÓPEZ SAAVEDRA, Marta. Multi-hazard assessment and risk management in volcanic islands. [consulta: 30 de novembre de 2025]. [Disponible a: https://hdl.handle.net/2445/204643]