Determination of potential secondary lahar hazard areas based on pre-and post-eruption UAV DEMs: Automatic identification of initial lahar starting points and supplied lahar volume

Secondary lahars, generated after volcanic eruptions, may pose significant threats to life and infrastructure. Secondary lahars typically develop from ash deposits and other volcanic debris that remobilize downstream via intense rainfall. The lahar inundation zone after eruptions must be predicted to minimize the impact. This prediction can be modeled based on digital elevation models (DEMs) and two parameters associated with lahar simulations: the lahar starting point (LSP), which indicates the potential locations at which a lahar flow may initiate, and supplied lahar volume (SLV), which is the lahar volume corresponding to each LSP. These parameters are typically determined by assumptions based on past lahar events, which may be unrealistic and often misinterpreted in the inundation prediction. To address this problem, this paper proposes an automated method to estimate the LSP and SLV based on pre-and post-eruption DEMs generated by unmanned aerial vehicle (UAV) images and simulate the inundation zone using the LAHARZ model. The study site is located in the southeast region of Mount Agung (Indonesia), and the objective is to mitigate the potential secondary lahar hazard after the 2017–2019 eruption crisis. Results show that the parameter estimations using the high-resolution UAV DEM and LAHARZ produce a realistic lahar simulation, with a satisfactory similarity of 82%, as verified against the lahar footprint. Moreover, we compare the results with those obtained using TerraSAR-X DEM and demonstrate the importance of using a detailed UAV DEM to avoid underestimating the lahar runout and ensure that the simulated inundation zones mimic real lahars.