## 4 Discussion
### Temporal Coupling between Crater/Vent Activity and Deep Seismicity  
Over the years, seismic data have been largely used to predict eruptive cycles, eruption sizes, and other changes during eruptions [12; 56; 58], as well as the coupling between deep, shallow or distal processes. Similar coupling of the deep and shallow storage regions was also inferred during the 2021 La Palma eruption [59], propagating from 10 km depth to the Tajogaite eruption site in less than one week. We compared our remote sensing data and the emergence of venting activity and crater formation to seismic activity. We noted a period of approximately 14 days with a higher number of seismic events, during which the highest seismicity peak (24 to 26 October) concurred with the transition from Phase 1 to Phase 2. This happened again toward 28 November, which marks a pronounced seismicity peak, and the transition from Phase 2 to Phase 3. In addition, other short and distinct peaks of seismic activity occurred almost simultaneously with newly emerging craters toward the SE flank as well as high lava fountain activity, which we see in the kymographs, as well as newly emerging craters toward the SE flank. For a number of these changes, we can infer that seismicity increased prior to changes observed at the surface, although we noted that the SAR satellite data barely have the temporal resolution to further substantiate such a causal relationship. By closer examining the seismicity, it may be possible to distinguish more than three phases, albeit these did not have a clear impact on the eruption processes on the surface, which we observe with SAR and camera data. Of particular interest is the timing of significant changes other than seismicity. During Phase 1, we could identify a strong fluctuation of lava fountain activity occurring toward the NW of the crater alignments. Within Phase 1, a number of spectacular gravitational collapses occurred, involving parts of the Tajogaite cone and the NW crater walls on 25 September [60], as well as on 4, 9, 11 and 26 October. These collapses were excavating a deep open crater on the NW flank also visible in our SAR data from 11 October (Figure 4f). A closer look at both our SAR intensity peak profiles and the kymographs reveals that after every collapse, the lava fountain activity changed. Specifically, we found fountain activity that apparently alternated between closer vents on the NW craters. This suggests that the crater wall collapses influenced the dynamics and location of lava fountain activity at those vents located close by. However, looking at the seismic data of these dates, it is evident that the latest crater wall collapse is coincident with a peak in seismic activity and with the transition from Phase 1 to Phase 2 that we identified from the crater analysis. This may lead to speculations about possible joint-driving mechanisms. We conjecture that seismicity changes may be related to pressure changes at depth. As there is only a small delay between these observations, we believe that pressure surges in the underground may be responsible for the observed conjoint changes at the eruption site. Similar concepts were applied for explaining the communication between eruption sites and the caldera at Kilauea [14; 61], between the Holuhraun eruption and the Bardabunga earthquakes [62], and between neighboring volcanoes in Kamchatka [63; 64]. Such a pressure surge may have initiated the collapse of a crater wall, which then changed the venting activity in the craters, which marked the transition from Phase 1 to Phase 2. Similarly, the oblique dike intrusion that dissects the previously aligned crater row and the development of new and clustered craters may have been initiated by a pressure surge, marking the transition from Phase 2 to Phase 3. On some occasions, we identified simultaneous activity at more than one crater. On 17 November 2021, a rapid increase in the number of shallow seismic events occurred, escorted by a rapid jump of activity to the SE crater visible in the kymographs (Figure 5b).