Comparative Study of the Effect of Volcanic Activity and the El Niño Phenomenon on Surface Thermal Changes in the Arjuno-Welirang Crater Area Using GEE Cloud Computing

Abstract

The increasing seismic activity of Arjuno Welirang on February 7, 2018, warned about the dangers of volcanic eruptions that must be watched out for, so that activity needs to be monitored continuously. There is little information available about seismic activity at the Arjuno Welirang complex. Most studies have investigated geothermal potential and subsurface structures. Due to the limitations of this data, land surface temperature (LST) analysis was carried out in this research to monitor the development of Arjuno-Welirang volcanic activity. Several volcano studies have used LST criteria in remote sensing applications to detect volcanic activity. However, the performance of LST has not been tested in the case of normal volcanic activity, which is influenced by external thermal disturbances. This study aims to show the performance of LST detection on changes in the normal volcanic activity of Arjuno Welirang, which is disturbed by temperature noise caused by the El Niño phenomenon. The LST calculations are carried out by including surface emissivity corrections obtained based on Normalized Difference Vegetation Index (NDVI) values. The LST calculation algorithm is implemented with the Google Earth Engine (GEE) platform. LST analysis was carried out on Landsat 8 images for the May-August 2023 time period obtained from the United States Geological Survey (USGS) database via GEE cloud computing. The reason for determining this time period is because the release of the daily Arjuno Welirang volcanic activity report by Magma Indonesia coincided with the Meteorology Climatology and Geophysical Agency (BMKG) notification regarding the occurrence of El Niño phenomenon. The output is an LST curve against time, which shows a tendency for the surface temperature of the Arjuno-Welirang crater to increase in July. This is similar to the trend of increasing seismic activity reported on the Magma Indonesia website and conversely is not similar to the increase in temperature due to the El Niño effect predicted by BMKG. The highest temperature increase occurred on July 24 2023, reaching 31.78 ⁰C, and then the temperature decreased. The method used in this research has proven that LST analysis is able to detect changes in normal volcanic activity in the Arjuno-Welirang crater even though there is thermal noise due to the influence of the impact of El Niño. LST values are more dominantly influenced by volcanic activity than by extreme El Niño weather.