Rising magma, dike intrusions, and flank collapse are observed at many volcanoes worldwide, but how they interact is still poorly documented. Extensive synthetic aperture radar interferometry and continuous global positioning system observations captured a sharp dike intrusion at Mount Etna, Italy, during the 2018 paroxysm that triggered a vigorous seaward sliding of the eastern flank connected with brittle failure and deep magmatic resourcing. We propose a feedback process between flank acceleration and magma intrusion that derives from the interaction between the long- and short-term deformation of the volcano. The flank sliding acts as a valve that modulates the emplacement and eruption of magma within the shallow system. Rapid flank acceleration could potentially evolve into sudden collapses and seismic release at shallow depth. In turn, flank slip events could act as a sentinel for changes in magma depth and paroxysmal eruptions at Mount Etna.