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Pyroclastic flows are mixtures of volcanic gases and particles that can be very hazardous owing to their fluid‐like behavior. One possible mechanism to explain this behavior is the reduction of particles friction due to the internal gas pore pressure. To verify this hypothesis, we present a numerical model of a granular flow with high initial pore pressure that decreases with time as the gas‐particle mixture propagates. First, we validate the model by reproducing laboratory experiments. Then, the numerical code is applied to pyroclastic flows of Lascar volcano (1993 eruption, Chile). The simulation reproduces the runout and the morphological features of the deposits, with lateral levées, a central channel, and a lobate front. Our results support the hypothesis of the role of gas pore pressure in pyroclastic flows and explain both the fluid‐like behavior of the flows and the formation of lateral levees. The effect of pore pressure is considered to model pyroclastic flows with Coulomb rheologyThe numerical model is validated by comparing with experiments and is applied to simulate real pyroclastic flowsPore pressure diffusion provides a possible explanation for levée formation in pyroclastic flows