Snapshot from a numerical simulation of a falling, supersonic gas-particle mixture impacting the ground and then moving outward along the ground. Contours represent Mach numbers (ratio of flow speed to mixture sound speed), with the black contour representing Mach number of one. The transition of a falling flow to a lateral flow plays a key role in determining the dynamics of devastating pyroclastic flows during large explosive volcanic eruptions. Computations carried out at the UB Center for Computational Research. See Valentine & Sweeney (2018, Journal of Geophysical Research) for details.