Quantifying entrainment in pyroclastic density currents from the Tungurahua eruption, Ecuador: Integrating field proxies with numerical simulations

Quantifying entrainment in pyroclastic density currents from the Tungurahua eruption, Ecuador: Integrating field proxies with numerical simulations

The entrainment of air into pyroclastic density currents (PDCs) impacts the dynamics and thermal history of these highly mobile currents. However, direct measurement of entrainment in PDCs is hampered due to hazardous conditions and opaqueness of these flows. We combine three‐dimensional multiphase...

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Bibliographic Details
Published in:Geophysical research letters Vol. 43; no. 13; pp. 6932 - 6941
Main Authors: Benage, M. C., Dufek, J., Mothes, P. A.
Format: Journal Article
Language:English
Published: Washington John Wiley & Sons, Inc 16-07-2016
Subjects:
Air entrainment
Air flow
Bed load
cauliflower bombs
Coefficients
Computer simulation
Concentration gradient
Density
Density currents
Deposits
Dilution
Dynamics
Ecuador
Entrainment
History
Mathematical models
Measurement
Multiphase
multiphase models
Numerical simulations
Opacity
Particle concentration
Proxies
pyroclastic density currents
Sediment transport
Suspended load
temperature
Texture
Three dimensional flow
Volcanoes
Ecuador
ISE, Ecuador
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Summary:The entrainment of air into pyroclastic density currents (PDCs) impacts the dynamics and thermal history of these highly mobile currents. However, direct measurement of entrainment in PDCs is hampered due to hazardous conditions and opaqueness of these flows. We combine three‐dimensional multiphase Eulerian‐Eulerian‐Lagrangian calculations with proxies of thermal conditions preserved in deposits to quantify air entrainment in PDCs at Tungurahua volcano, Ecuador. We conclude that small‐volume PDCs develop a particle concentration gradient that results in disparate thermal characteristics for the concentrated bed load (>600 to ~800 K) and the overlying dilute suspended load (~300–600 K). The dilute suspended load has effective entrainment coefficients 2–3 times larger than the bed load. This investigation reveals a dichotomy in entrainment and thermal history between two regions in the current and provides a mechanism to interpret the depositional thermal characteristics of small‐volume but frequently occurring PDCs. Key Points Multiphase modeling and thermal proxies in pyroclastic density currents indicate that air entrainment varies both spatially and temporally Eruptive flows develop distinct particle concentration and thermal structures as a result of variable entrainment Thermal proxies and clast textures constrain the fluid dynamics of entrainment in otherwise inaccessible flows
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ISSN:0094-8276
1944-8007
DOI:10.1002/2016GL069527