Monitoring the surface deformation of an active volcano during a new unrest phase (Askja caldera, central Iceland)

In the summer of 2021, Askja caldera entered a renewed period of unrest, which was marked by a significant uplift of the caldera floor (over 70 cm in 2.5 y) and a slight increase in background seismicity. These indicators suggest the presence of magma rising from depth, potentially heralding an eruption in the months or years ahead. The renewed activity has increased the risk of landslides, particularly along the already unstable slopes of the eastern Öskjuvatn caldera. A major landslide in 2014 triggered a tsunami in the adjacent lake that inundated the lakeshore, reaching several tens of meters above its pre-event surface. To gain a deeper understanding of the unresting phase and its associated hazards that may lead to an eruption, the installation of a comprehensive monitoring system is key. In the summer of 2023, a dense monitoring network was established to address these shortcomings. Three time-lapse cameras were installed to track ground movement along the unstable eastern caldera rim. Three corner reflectors were deployed to capture InSAR data, even during the snow-covered winters. A continuous GNSS instrument was also installed to monitor ground displacement continuously. We also covered the entire Öskjuvatn caldera rim with several drone surveys, in 2020, 2021 and 2023, obtaining high-resolution DEMs and orthomosaics to study ground deformation in the past few years. However, arctic conditions prevail during winter months at Askja caldera. Extensive wind-sculpted ice structures have formed on the stations and prevent using the corner reflectors and time-lapse cameras at their full capacity. Storm- to hurricane-force winds have damaged highly exposed stations on the shoulders of the caldera ring faults. We propose technical improvements for extreme conditions and show preliminary results of our monitoring system. In particular, we show a detailed structural map based on our drone data and extensive field observations, thousands of fractures and other geological features providing a kinematic analysis for different parts of the caldera ring faults cliffs. This collaborative effort between Swiss and Icelandic institutions has established an unprecedented monitoring system for an unresting volcano susceptible to eruptions and landslides. The multi-tools approach offers valuable insights into the behaviour of such calderas and could serve as a model for similar monitoring efforts worldwide.