## 4 Discussion  
In this study, we aimed to determine the surface deformation occurring in the Tendurek volcano. A total of 150 Sentinel-1 images from descending and ascending orbits were used, and two different atmospheric correction approaches were applied to estimate the atmospheric phase contribution in the study area. Although both atmospheric correction approaches show a similar deformation pattern, the deformation rates obtained from the linear phase-based approach were used in the continuation of the study because the linear phase-based approach exhibited lower standard deviation values. In this context, the results obtained from both satellite geometries show that there was a maximum subsidence of \(-50\) mm over 5 years at the Tendurek volcano. The standard deviations of the deformation rates are \(\sim\)5 mm, which is approximately 10 times less than the deformation rate in both cases.  
Profile analyses of both geometries show a bowl-shaped pattern that continues from the summit of the volcano to the eastern flanks and demonstrates that the maximum subsidence rate decreases linearly with the distance from the summit of the volcano. In addition, when the deformation time series of four PS pixels selected from the ascending and descending orbits are examined, it is observed that the subsidence occurs in a linear structure and there is no increase or decrease in the deformation rate in any period. As a result, the subsidence occurred in a summit caldera-centered region of the Tendurek volcano. However, to investigate whether the horizontal movement affects the obtained deformation rates, the deformation components were calculated, and the horizontal deformation was small enough to be neglected. When the vertical deformation components were examined, a deformation of \(-15\) mm/yr was detected in the Tendurek volcano.  
Figure 8: Horizontal and vertical deformation derived from LOS direction results. (**a**) Vertical mean deformation velocity. Positive values (green) represent uplift and negative values (warm colors) represent subsidence. (**b**) Horizontal E-W mean deformation velocity. Positive values (green) represent movements toward the west direction and negative values (warm colors) toward the east.  
As mentioned above, ref. [40] used ERS satellite images and detected a 10-20 cm subsidence at the Tendurek volcano summit between 1993 and 2000, which is consistent with our study considering that 15-20 mm/yr corresponds to a deformation of 12-16 cm over 8 years. In the study performed by [41] using Envisat satellite images, a subsidence of 11 mm/yr was detected in an area of 10 \(\times\) 14 km on the Tendurek volcano between 2003 and 2010, and the cause of this subsidence was attributed to a magmatic threshold-like source located 4.5 km below the summit. Another study conducted in the region was carried out by [42] using Sentinel-1 satellite images of 10 volcanic systems in Turkey, including the Tendurek volcano, between 2015 and 2020, and no significant deformation rate was detected in the Tendurek volcano during this period. Their observation is not consistent with the results of our study. In the study conducted by [42], a reliable interpretation cannot be made because a detailed deformation map of the Tendurek volcano or time series of deformation were not given. In addition, the fact that the two studies cover different periods, using different methods and images, may explain this difference. Overall, we obtained similar results to those obtained by [40; 41], and we conclude that the deformation in the Tendurek volcano has been ongoing since 1993.