Crystals formed prior to a volcanic event can provide evidence of processes leading to and timing of eruptions. Clinopyroxene is common in basaltic to intermediate volcanoes, however, its ability as a recorder of pre-eruptive histories has remained comparatively underexplored. Here we show that novel high-resolution trace element images of clinopyroxene track eruption triggers and timescales at Mount Etna (Sicily, Italy). Chromium (Cr) distribution in clinopyroxene from 1974 to 2014 eruptions reveals punctuated episodes of intrusion of primitive magma at depth. Magma mixing efficiently triggered volcanism (success rate up to 90%), within only 2 weeks of arrival of mafic intrusions. Clinopyroxene zonations distinguish between injections of mafic magma and regular recharges with more evolved magma, which often fail to tip the system to erupt. High Cr zonations can therefore be used to reconstruct past eruptions and inform responses to geophysical signals of volcano unrest, potentially offering an additional approach to volcano hazard monitoring.