The Puebla–Morelos earthquake (19 September 2017) was the most damaging event in central Mexico since 1985. The seismic shaking produced hundreds of shallow landslides on the slopes of Popocatépetl Volcano. The larger landslides transformed into large debris flows that travelled for kilometers. We describe this exceptional mass wasting cascade and its predisposing factors, which have important implications for both the evolution of the volcanic edifice and hazard assessment.