Probabilistic volcanic hazard assessment during quiescence: a scenario-based approach for Gede, West Java (Indonesia)

One of the first steps towards reducing volcanic risk is assessing the area likely to be affected by hazardous phenomena. This typically involves analysis of a volcano’s past eruptions to forecast the expected size and style of future eruptions and the spatial extent of the expected hazards. However, there are many active volcanoes worldwide that do not have extensive eruption records from which to forecast future behaviours; Gede volcano in Indonesia is one example. In this work, we conducted the first probabilistic volcanic multi-hazard assessment for five different hazards from six eruptive scenarios for Gede, the closest active volcano to Jakarta city. To supplement Gede’s eruption record, we used analogue volcanoes and global datasets to develop eruption scenarios and to parameterise hazard models. Our analysis suggests that the major explosive eruption scenario and the Plinian explosive eruption scenario, which have column heights of 10–20 km and 20–30 km respectively, can deposit sufficient tephra to disrupt airport operations and vital lifelines across Jakarta, while tephra fall from the continuously explosive or intermittently explosive eruption scenarios may obscure road markings and disrupt agricultural operations proximal to the volcano. Hazards from effusive scenarios primarily impact the volcano’s northeastern flank; lava flows are confined to ~ 3 km in this direction while block-and-ash flows are expected to extend up to ~ 11 km. Pyroclastic density currents from a collapsing column from the minor explosive eruption scenario (column height 1–10 km) can extend up to ~ 15 km but could reach up to ~ 20–25 km for major and Plinian eruption scenarios. Through this work, we provide a probabilistic hazard assessment for Gede and a framework for volcanic hazard assessment in data-limited contexts. This assessment serves as an essential tool for enhancing risk mitigation through planning and preparedness in one of the most exposed regions of the world.