## 5 Discussion
### Magma Chamber Dynamics from MODIS NLST Data  
The four geothermal anomaly zones in the study area show significant fluctuations in both multi-year monthly average LST (Figure 11) and annual average LST over the past 21 years (Figure 12). The LST variation trends in these anomaly zones are generally consistent but display a bimodal pattern in June and August, whereas the corresponding average air temperature (AT) shows no similar features, and its monthly trend differs markedly from that of LST (Figure 11). Typically, regions north of the Tropic of Cancer experience only one solar radiation peak [63], thus, the bimodal pattern in LST may be attributed to non-solar factors. Based on this observation, the study hypothesizes that the bimodal pattern is closely associated with subsurface magma activity, potentially reflecting the influence of the underground magma system on geothermal anomalies.  
Figure 11: Monthly Variations in Multi-Year Average Land Surface Temperature at the Inferred Heat Source Locations.  
Figure 12: Interannual Variations in Multi-Year Average Land Surface Temperature at the Inferred Heat Source Locations (2003–2023).  
This hypothesis is further supported by Figure 12. Interannual LST fluctuations significantly exceed those of AT over the same period, indicating that long-term average ground temperature in the anomaly zones is influenced not only by meteorological factors but also predominantly by subsurface magma activity [55]. Zones with greater LST variability may indicate more active and open underlying magma systems, accompanied by more pronounced variations in surface and groundwater recharge. Based on these observations, the study further proposes that geothermal anomalies in the region are primarily driven by magma activity, and infers the potential presence of magma chambers beneath the four anomaly zones.  
This hypothesis is strongly supported by previous studies. Since the 1980s, multiple research teams--including Sino-French and Sino-Japanese collaborations, Geotermica Italiana, and the INDEPTH project--have identified low-resistivity layers or partially molten bodies at depths of 10-20 km in the Yangbajing geothermal field, proposing these as primary heat sources or magma chambers [6; 42; 64; 65; 66]. More recent studies have revealed the presence of a heat source at depths of 6-14 km beneath the Yangbajing area, which aligns with the hypothesis proposed in this study [43]. Additionally, [PERSON] et al. [67] identified a low-resistivity, umbrella-shaped magma body at approximately 6 km depth beneath the Yangyi geothermal field using Audio-frequency Magnetotellurics (AMT), which serves as the primary heat source for the region's geothermal system, further supporting the reliability of this hypothesis.  
Although specific local survey data are lacking for the Yangjingxue and Regaguo areas, large-scale geophysical studies by [PERSON] et al. [68] and [PERSON] [69] indicate that these areas lie within low-resistivity bodies, which may host partial melt bodies or magma chambers. Therefore, the four potential heat source areas identified in this study using LST data not only align with existing research on Yangbajing and Yangyi but also receive support from low-resistivity features in the newly hypothesized areas, further confirming the role of subsurface magma activity in driving geothermal anomalies.