Multitemporal satellite images for monitoring the volcanic activities and geothermal potential of Ternate Island's Gamalama Volcano, Indonesia's densest active volcanic island

Throughout history, Ternate, a diminutive volcanic island located in the North Maluku Province of Indonesia, has functioned as a significant center of the nation's social and economic activity. The Gamalama Volcano constituted a significant element of Ternate Island's topography, and its eruption resulted in substantial disruption. The aims of this current contribution are: to monitor the historical activities of the Gamalama volcano and understanding the geothermal potential to support the energy needs in Ternate Island. The multi-temporal analysis was conducted to monitor the activity of Gamalama Volcano, utilizing satellite imagery spanning a period of 50 years. The imagery sources included Landsat 1, Landsat 4, Landsat 5, Landsat 7, ASTER, and Landsat 8. The present study employed the single-channel algorithm to derive the land surface temperature (LST). The band combination and ratio were utilized to infer the geological context and geothermal capacity of the Gamalama Volcano. The analysis of normalized differential vegetation index (NDVI) utilized in the calculation of LST has revealed that vegetation growth has occurred subsequent to certain volcanic eruptions. As per the LST data, the average temperature of the surface within the crater escalated to 38.472 °C during the eruption of 1997, thereby establishing it as the maximum temperature recorded in the past half-century. The volcanic activity of Gamalama Volcano was elucidated through the utilization of the LST technique, which has the capacity to cover various temporal intervals. The congruence between the LST data derived from Landsat and ASTER data substantiates the dependability of the LST methodology. The geothermal potential of approximately 16 °C has been observed in the crater and sand region of the volcano, along with the identification of supplementary hot spots in the north-eastern and western regions of the volcano's primary structure. The utilization of Landsat 8 band combinations and band ratios has substantiated the presence of an area exhibiting elevated geothermal potential within the andesite and basaltic andesite geological formations. The practicality of utilizing multi-source optical satellites for monitoring volcanic activity has been exemplified by the multiple eruptions that have occurred at Gamalama Volcano. Furthermore, this technology could potentially be employed for conducting exploratory research into the geothermal potential of the region.