Volcanic islands worldwide are characterized by diverse environments such as marine-coastal, terrestrial, agricultural, climatic, and touristic (Geist and Harpp 2018a), which generate productive activities to the towns (López-Saavedra and Martí 2023). Most of these islands are considered fragile systems(Selva et al. 2019) due to their geographic location, anthropogenic and natural hazards that affect the ecosystem services of the Socio-Ecological System (SES) (Talubo, Morse and Saroj 2022).
During decades, the population growth (Lakshmi and Kumar 2015; Del Puerto and Martínez 2021) has led to a pollution and overexploitation of the limited resources and ecosystems available on volcanic islands (Del Puerto and Martínez 2021), resulting in anthropogenic hazards (Gill and Malamud 2017). Meanwhile, the natural hazards that develop on these islands are often unpredictable, making them more likely to have negative impacts on society, the economy, infrastructure, and the environment (Zou et al. 2023; Ma and Mei 2021). These natural hazards can be hydrometeorological and geological, such as volcanic eruptions, tsunamis, earthquakes, and storms (López-Saavedra et al. 2021).
The union of anthropogenic and natural events are called "multi-hazards", which are sequential chain reactions that can lead to a disaster precursor event (Zhang et al. 2023), thereby affecting the SES. Generally, multi-hazards cause a high impact on the population and their ecosystems and as a consequence many years may be taken to develop the resilience capacity (Tilloy et al. 2019; Zuccaro et al. 2018). As an example, in 2022 the eruption of the Hunga Tonga-Hunga Haapai volcano (southeast of Tonga) triggered the primary cascading hazards, which are eruptive column with ash and gases that extended over 30 km high (Zhao et al. 2022). Then, secondary events such as tsunamis, significantly affected the local and parts of the Pacific coasts, causing flooding in populated areas (Freeshah et al. 2024). According to the World Bank (Partnership et al. 2022), the economic damages reached approximately 90 million dollars.
Previous studies analyze the hazard as a single event, but not as a chain reaction with consequences (Mead et al. 2022; Vandrie et al. 2023; Abu Bakar and Mohamad 2023). Previous researches on volcanic islands, such as the Canary Islands study case (López-Saavedra et al. 2021; López-Saavedra and Martí 2023), relates direct and indirect hazards through the creation of an event tree or cascade effect diagram.
In 2011, a 9.0 Mw earthquake was generated on the eastern coasts of Japan due to the subduction processes of oceanic tectonic plates (Pazmiño and Michaud 2009). This event triggered a tsunami effect observed around the entire Pacific Ocean (Dunbar et al. 2011), affecting countries such as New Zealand, Australia, Russia, Northern Mariana Islands, United States, Central America, Colombia, Peru, Chile, Ecuador, among others (U.S. Department of the Interior 2011). As an effect, according to the INOCAR report (INOCAR 2011), the Galápagos Islands was affected by the Japanese tsunami with run-up heights of 1.70 meters that covered 400 meters inland, causing the evacuation of 240,000 residents.
Since 2021, the "Tsunami Ready" project has been implemented in the Galápagos Islands. This program is oriented to reach a standard level of tsunami preparedness; and aiming to delimitate and map risk zones based on the population and identification of economic, infrastructure, and social resources. It is developed in collaboration with various entities, including the National Risk Management System (SNGRE), the Oceanographic Institute of the Navy (INOCAR), the Geophysical Institute of the National Polytechnic School (IG-EPN), the Galápagos Governing Council, and the Decentralized Autonomous Municipal Governments of Isabela, San Cristóbal, and Santa Cruz.
The collaborative approach of the project has strengthened tsunami-specific preparedness in the Galápagos Islands. This collaboration among various entities has enabled greater awareness and capacity to address this particular risk. However, it is important to note that while progress has been made in tsunami preparedness, other natural risks are not receiving the same comprehensive attention. For example, individual hazards such as earthquakes, volcanic eruptions, or other natural disasters are not being studied in terms of their potential triggers and combined scenarios. This lack of comprehensive analysis can compromise the overall effectiveness of preparation and response to multiple threats.
In this context, the present study focuses on considering all the multi-hazards that can affect the Galápagos Islands through an event tree diagram. This will allow for planning existing preventive measures against possible threats and minimizing response time to events during their development, with the aim of reducing impacts on the SES. This tool is designed for government entities such as the Red Cross and ECU911.