Analysis of the 4 December 2021 lahar on Mount Semeru using optical and SAR remote sensing

This study characterizes the amplitude changes associated with the 4 December 2021 eruption of Mount Semeru and maps the resulting deposits using Sentinel-1 SAR backscatter and PlanetScope optical imagery. Results show that lahar deposits caused surface smoothening which reduced SAR backscatter, whereas pyroclastic density currents (PDCs) increased backscatter due to higher moisture content. We have also shown the potential of differential polarimetric responses between surface cover types to identify areas of channel widening and vegetation destruction, providing a rapid means of identifying impacted areas in the context of volcanic crisis management. The supervised classification of SAR and high-resolution optical images enabled the production of an accurate geomorphological map able to separate different pyroclastic flow and lahar flow deposits both sedimentologically and spatially. Classified channelized lahar deposits were also used to quantify channel widening associated with the eruption, which significantly impacted the Supiturang Village. • We characterize amplitude changes associated with the 4 December 2021 Mount Semeru eruption using Sentinel-1 SAR data. • RGB amplitude change images to map wet pyroclastic density currents and lahar deposits. • Classification of PlanetScope images and SAR data to map volcanic deposits and quantify channel retreat. • SAR for volcanic hazard monitoring in tropical environments.