During the summer 2001 eruption of Mt. Etna, Italy, we developed a method for monitoring explosive activity through the study of airborne ash. The method is based on two routine and fast techniques for ash characterization: i) component analysis, that quantifies the proportion of juvenile particles, crystals, and non-juvenile lithics in the ash; ii) Scanning Electron Microscope semi-quantitative description of the morphology of ash particles. With these techniques we daily analyzed airborne ash from the eruption plume. Temporal evolution of particle shape and vesicularity, and of component proportion in the ash, documented initial crater excavation by hydromagmatic explosions, strong magmatic activity due to volatile exsolution, and final fragmentation of a cooling top of magma column. Favorable conditions of the studied eruption allowed validation of these results by comparison with other monitoring techniques. We also evaluate the applicability of the method to other cases, as well as its limits.