Effects of particle mixtures and nozzle geometry on entrainment into volcanic jets

• Published in: Geophysical research letters Vol. 41; no. 11; pp. 3858 - 3863
• Main Authors: Jessop, D. E., Jellinek, A. M.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 16-06-2014; John Wiley & Sons, Inc; American Geophysical Union
• Subjects: Aerodynamics; Atmosphere; Atmospheric models; Buoyancy; Clouds; Composition; Computational fluid dynamics; Earth Sciences; Eddies; Entrainment; Erosion; Fluid Dynamics; Geophysics; Height; Inertia; Inflow; Jets; Marine; Nozzle geometry; Particle inertia; particle-laden flow; Physics; Plumes; Properties; Sciences of the Universe; Sedimentation; Shape; source geometry; Turbulence; Turbulent entrainment; Velocity; Vents; volcanic jets; Volcanology; Vortices
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2014GL060059

Efficient turbulent entrainment causes otherwise dense volcanic jets to rise high into the atmosphere as buoyant plumes. Classical models suggest that the inflow of air is 10–15% of the axial velocity, giving predictions for the height of the plume and, in turn, the composition and structure of the resulting umbrella clouds. Crucially, entrainment is assumed independent of source geometry and mechanically unaffected by the pyroclastic mixture properties. We show that particle inertia and vent geometry act to modify the shape of the largest eddies defining the jet's edge and thus entrainment of the ambient. Whereas particle‐free flows are essentially unaffected by vent shape, entrainment into particle‐laden flows is enhanced for flared vents and reduced for cylindrical vents. Our results predict that vent erosion during an explosive eruption reduces the height of volcanic jets, alters the structure and sedimentation regime of the umbrella cloud, and the resulting deposit.
Key Points
Source geometry plays an important role in entrainment
Certain sizes of particles combine with source effects to modify entrainment
Cloud structure and deposits change during an eruption for same conditions