In this paper, some of the processes involved in the generation and propagation of hazardous volcanic flows are described. The paper focuses on the high-speed dilute suspension flows that develop following (i) the explosive collapse and decompression of a lava dome; and (ii) the collapse of an ash-laden fountain erupting from a volcanic vent. Using the model, we calculate the approximate vertical distribution of pressure in the flow, and show how this and the flow force evolve as the flow advances from the vent. The effects of topography and sedimentation on the intensity and run-out of such flows are described. Where possible, we draw on field examples of the different phenomena, and we review some analogue laboratory experiments that provide support for the modelling approach.