Wind Entrainment in Jets with Reversing Buoyancy: Implications for Volcanic Plumes. Issue 10 (26th September 2020)

• Record Type: Journal Article
• Authors: Michaud‐Dubuy, A.; Carazzo, G.; Kaminski, E.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 10(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-09-26
• Subjects: Plinian eruption -- eruptive dynamics -- atmospheric crosswind -- turbulent entrainment -- laboratory experiments -- column collapse; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2020JB020136
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Explosive volcanic eruptions commonly undergo a transition from stable plume to collapsing fountain with associated destructive pyroclastic density currents. A major goal in physical volcanology is to predict quantitatively the limit between the flow regimes as a function of the source and environmental conditions. Atmospheric winds influence the dynamics and stability of the column causing bending and enhancing turbulent air entrainment. However, the predictions made with 1‐D models of volcanic plumes accounting for the presence of wind strongly depend on the wind entrainment coefficient β, a parameter whose value varies in the literature. Here we present a new theoretical model to identify an analytical criterion for column collapse in windy conditions. We then present new laboratory experiments on turbulent jets with reversing buoyancy rising in a crossflow in order to better constrain β . Our results show that a single value of β = 0 . 5 can be used to describe the behavior of laboratory jets with arbitrary buoyancy. The results allow us to parameterize our 1‐D model of volcanic plumes PPM and to show the crucial importance of wind gradient and profile on volcanic column dynamics through the use of the 1991 Mt. Hudson eruption as a case study. Finally, we propose a new transition diagram between the stable plume and collapsing fountain regimes, as a function of wind speed and mass discharge rate only, which can be used for the rapid assessment of major hazards during an explosive eruption. Key Points: We quantify the wind entrainment coefficient using laboratory experiments of jets with a reversing buoyancy We show the crucial importance of wind gradient and profile on volcanic column dynamics We use the Mt. Hudson eruption in 1991 to test our 1‐D model and show that strong winds prevented the volcanic plume to collapse