ANALYSIS OF TRIGGERING FACTORS AT MT. SEMERU ERUPTION ON 4TH DECEMBER 2021 USING HIGH RESOLUTION OPTICAL AND RADAR IMAGES

• Main Author: Isanjarini, Vismaia
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/77744
• Institution: Institut Teknologi Bandung

Hundreds of eruptions have occurred since 1967, indicating Mount Semeru as one of the most active and hazardous volcanoes in the World. The eruption in 2021 caused 242 fatalities and 10,395 residents were evacuated from disaster-prone areas. The eruption seemed to happen suddenly as reported by CVGHM (Center for Volcanology and Geological Hazard Mitigation). Before the eruption on December 4th 2021, there was no evidence of deep volcanic earthquakes (VTA) or shallow volcanic earthquakes (VTB), reducing the possibility of a magmatic intrusion process from the deep part to the near surface. To observe the phenomena occurring on the surface prior to the eruption, Landsat-8 30 m, PlanetScope 3 m, and Sentinel-1 SAR 3 m images were used. The Gram-Schmidt pan-sharpening transformation was performed to increase the spatial resolution of the 30 m Landsat-8 image equivalent to the 3 m PlanetScope image. This method was applied to images before and after the eruption to detect changes on the surface that triggered the eruptions such as flank collapse. The pan-sharpening results showed that after the eruption there were incisions in the southeastern part of Mount Semeru which were interpreted as traces of an avalanche. These results were validated with statistical values of minimum, maximum, average, and standard deviation. Pearson correlation is close to 1. Based on an integrated analysis using pan-sharpening images and the InSAR (Interferometric Synthetic Aperture Radar) deformations, thirteen days prior to the eruption the volume and area of the summit had decreased about 9,682 m3 and 270,000 m2 respectively. Data from the period of August 2019 to August 2022 revealed two patterns: a reduction pattern before the eruption and an increase pattern after the eruption. This may indicate landslide precursors before the eruption, suggesting that before the eruption, the summit of Mount Semeru had lost load, triggering sporadic magma release from the shallow reservoir, resulting in explosive eruptions. This phenomenon is also indicated by detected deformation, including landslides at the summit, suggesting that the eruption was not directly related to the addition of magma in the shallow reservoir. The sudden load reduction is further supported by visual observations, high rainfall, and the morphology of landslides obtained through drone surveys.