Access to the Fagradalsfjall 2021–2023 volcanic eruptions: a case-study of pedestrian routes mapping with least-cost-path analyses

This study illustrates the potential of least-cost-path analyses (LCPAs) in mapping pedestrian routes over dynamic volcanic terrain, using the Fagradalsfjall 2021–23 eruptions as a case study. Access of the public to the eruption site was permitted during the syn-eruptive phase, leading to significant foot traffic on a few authorised trails. The research model paths and hiking durations of approximately 1,000 potential hiking routes, from the road infrastructure up to the eruption site, using slope-dependent cost functions. Energetic costs of a selection of modelled routes are also estimated. Six scenarios are tested, that account for the evolution of lava flows, the hazard assessments provided to the authorities by the scientific community, and the impact of slope and terrain ruggedness on walking speeds. Computational times for key tasks are provided. The study highlights the potential of LCPAs to quickly identify optimal routes in crisis management contexts, accommodating evolving volcanic activity and enhancing safety and accessibility for visitors.