Identification of lava presence on Anak Krakatau volcano using normalized hotspot index before a flank collapse in 2018

Abstract On December 22, 2018, a catastrophic tsunami struck Anyer Beach in Banten, Indonesia, resulting in numerous casualties and extensive damage to the region. A flank collapse in the southwest sector of Anak Krakatau primarily triggered this tsunami. Intense eruptions and subsequent lava discharges precipitated this collapse. Indonesia’s Vulcanology Geological Hazard Mitigation Center has reported heightened activity at this location since June 2018. Comprehensive field studies, bolstered by remote sensing data, have been pivotal in enhancing our understanding of the behavior of Anak Krakatau over recent years. This research strives to pinpoint lava’s presence in Anak Krakatau during its eruptions. The methodologies employed include the Normalized Hotspot Index (NHI) transformation index combined with the SWIR-1 and SWIR-2 channels of the Landsat 8 OLI imagery. The goal is to elucidate the intense lava flow patterns associated with the flank collapse. Our findings indicate that the NHI can detect elevated lava flow activity in Anak Krakatau. Within the 13 datasets from 2018, lava flow was discerned on seven occasions between July 29 and December 20, predominantly directed towards the southwest sector of the volcano.