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Transient seismicity at active volcanoes poses a significant risk in addition to eruptive activity.This risk is powered by the common belief that volcanic seismicity cannot be forecast, even on a longterm. Here we investigate the nature of volcanic seismicity to try to improve our forecasting capacity. To thisaim, we consider Ischia volcano (Italy), which suffered similar earthquakes along its uplifted resurgentblock. We show that this seismicity marks an acceleration of decades‐long subsidence of the resurgent block,driven by degassing of magma that previously produced the uplift, a process not observed at othervolcanoes. Degassing will continue for hundreds to thousands of years, causing protracted seismicity andwill likely be accompanied by moderate and damaging earthquakes. The possibility to constrain the futureduration of seismicity at Ischia indicates that our capacity to forecast earthquakes might be enhanced whenseismic activity results from long‐term magmatic processes, such as degassing.