Control of Vent Geometry on the Fluid Dynamics of Volcanic Plumes: Insights From Numerical Simulations

Abstract

We present three-dimensional numerical simulations of eruption clouds from circular to linear fissure vents to investigate the control of vent shape on the height and stability of volcanic plumes during large explosive eruptions. Our results show that clouds ejected from circular or low-aspect-ratio (nearly square-like) fissure vents can be associated with radially suspended flow (RSF) at the top of the jet region, whereas those emitted from narrow-fissure vents are not. Non-RSF plumes are more stable than those associated with RSF because the highly concentrated parts of the ejected mixture are easily dissipated and mixed with air near the vent. Plume height in the RSF regime decreases while that in the non-RSF regime increases with increasing aspect ratio, even for a fixed magma flow rate. These observations suggest that the efficiency of air entrainment is influenced by the vent shape, which in turn controls the dynamics of eruption plumes.