## 4 Results and Analysis
### Long-Term Deformation and Time Series Deformation in the Northern QTP
To illuminate the freeze-thaw cycle of permafrost, we used the ALOS, ALOS-2 and Sentinel-1 datasets to map the ground deformation of permafrost around the braided stream plain from 2007 to 2021. The results are shown in Figure 4g-i. To further study the time series deformation of permafrost around Salt Lake, we selected four points (Figure 4c). The details for these points are provided in Table 4. A  
Figure 4: Permafrost evolution in two typical areas, Salt Lake and braided stream plain. (**a**) Average deformation rate during 2017–2021. (**b**) Salt Lake in December 2008 from Google Earth. (**c**) Average deformation rate during 2007–2009. (**d**) Salt Lake in December 2018 from Google Earth. (**e**) Average deformation rate during 2017–2021. (**f**) Braided stream plain from Google Earth image. (**g**) Average deformation rate during 2007–2009. (**h**) Average deformation rate during 2015–2020. (**i**) Average deformation rate during 2017–2021. 25 km profile (Figure 4g) was selected to reveal the relationship between the permafrost deformation and the elevation. Figure 5a,b shows the long-term deformation trend deformation of selected points around Salt Lake. From March 2007 to April 2008, the four points could balance the freeze-thaw process. However, from July 2009 to March 2010, point A breaks the cycle, and the ability to have is stronger than the ability to freeze, which may increase the thickness of the active layer. From Figure 5b and Table 3, at point C, the average uplift deformation from 2007 to 2008 changed into the average subsidence deformation from 2017 to 2021. At point D, the results reveal that the subsidence of the ground increased 10 times from 2007 to 2021. From Figure 5c, we find that there is a negative correlation between the subsidence and the elevation. This may be due to the melting of glaciers around the braided stream plain, resulting in a large amount of water, accumulating on the slope. Finally, the thickness of the permafrost active layer is increased, which causes permafrost degradation. In the freezing and thawing process of permafrost, the moisture in permafrost can move and change, which may cause rock damage, ground deformation and thawing disasters. The sudden thawing of permafrost may lead to environmental disasters, such as ground collapse and rapid erosion. The thawing mud flow of the permafrost occurs on the slope of the permafrost. In summer, the thawing of the active layer could not flow downslope due to the existence of permafrost, resulting in abundant water in the active layer. Under the condition of excessive moisture, the permafrost creeps downward along the slope, resulting in the thermal melting collapse. We combined optical data (GF-1, GF-2) [64] to reveal the thermal melting collapse of permafrost. In Figure 6a, the red color indicates the positions of thermal melting collapse, which were generated from 2019-2020 GF-1/2 data. In Figure 6b, the red color indicates the subsidence in the LOS direction. In Figure 6b, we used the ALOS-2 dataset to reveal the \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Point** & **Position** & \begin{tabular}{c} **Long-Term Deformation** \\ **Velocity during 2007–2009** \\ \end{tabular} & \begin{tabular}{c} **Long-Term Deformation** \\ **Velocity during 2017–2021** \\ \end{tabular} \\ \hline Point A & \begin{tabular}{c} 93.467\({}^{\circ}\)E, \\ 35.547\({}^{\circ}\)N \\ 93.473\({}^{\circ}\)E, \\ 35.485\({}^{\circ}\)N \\ 93.363\({}^{\circ}\)E, \\ 35.476\({}^{\circ}\)N \\ 93.312\({}^{\circ}\)E, \\ 35.532\({}^{\circ}\)N \\ \end{tabular} & \
\begin{tabular}{c} \(-\)12.5 mm/year \\ \(-\)4.3 mm/year \\ \(-\)4.3 mm/year \\ 8.7 mm/year \\ \(-\)2.3 mm/year \\ \(-\)2.3 mm/year \\ \end{tabular} &
\begin{tabular}{c} -\)20.3 mm/year \\ \(-\)20.3 mm/year \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The details of the four selection points around Salt Lake. Figure 5: The time series deformation of the study points and the deformation of the selected profile.