Satellite Thermal imaging of the Milos volcano, Cyclades, Greece

Thermal imaging of the Milos volcano (Cyclades, Greece) is used to monitor its active hydrothermal system, specifically focusing on the Eastern part of Milos. Satellite data is essential for tracking Land Surface Temperature (LST) anomalies and radiative heat flux in this dormant but active volcanic field. Milos hosts a well-known shallow geothermal field mainly developed beneath the eastern part of the island. In this work we aim to establish the background surface temperature level for this volcano and observe possible fluctuations related to seasonal effects or changes in the shallow hydrothermal activity.

Thermal sensors Landsat 8 and Landsat 9 (8-day sampling interval) at 100-m resolution during the year 2025 were used for this study. The final dataset contained 65 satellite images, each with cloud and shadow coverage below 40%. Initially, a pixel-based geostatistical analysis was done, where 12 monthly mean LST maps and 12 monthly standard deviation maps were produced to investigate the surface thermal conditions of the island. To mitigate climate change's influence, a further investigation was followed by producing 3 more maps, to detect and locate the accurate annual spatial distribution of valid clear-sky Landsat LST observations, derived by each pixel’s counts over 40^oC and its relevance to the normalized annual frequency. The analysis was done completely on Google Earth Engine.

The results showed that the monthly analysis of land surface temperature imagery consistently detects temperatures inside the Zephyria depression (eastern Milos) that are 5–25 °C warmer than the surrounding terrain, which can reach up to 58^oC. Additionally, the final analysis succeeded in mitigating the external weather conditions and revealed that 34 observations (out of 65) present a land surface temperature over 40^oC inside the Zephyria depression, with a clear spatial correlation to the shallow geothermal field of the island. Another important outcome was that despite the limitations due to atmospheric interference, the limited land-coverage of the island and the small scale of fumaroles onshore Milos, Landsat 8 and Landsat 9 are both able to detect the thermal anomalous pixels by using one year as a referenced period.