Volcanic eruptions often generate fast-moving clouds of gas and particles, such as ash and rocks. How these particles move—whether rising, falling, or remaining suspended in the air can influence the distance and danger of volcanic flows. One important factor that affects this behavior is clustering, where particles group together during motion. In this study, we recreated similar conditions in the lab by blowing air upward through a vertical pipe containing both small and large particles. As more particles were added, falling clusters moved faster, while rising clusters slowed down—especially when more large particles were present. Interestingly, some large particles were carried higher than expected, showing that they are influenced significantly by collisions and interactions with small particles and turbulence. These findings suggest that mixtures of different-sized particles behave differently from single-size ones in gas–particle flow. Understanding how particles and clusters interact and move helps scientists improve models that predict how ash and pyroclastic material settle during eruptions, which is crucial for forecasting hazards and protecting communities.