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Volcanic Intrusions Steve Sparks (Earth Sciences ). Structure of eruption columns. Volcanic plume dynamics. H = 8.1Q 0.25. Height of plume in km Q magma mass flux (thermal flux). Strong plume and weak wind. Weak plumes: strongly wind affected. High Intensity eruptions (stratosphere).

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Volcanic Intrusions

Steve Sparks (Earth Sciences)

slide3

Volcanic plume dynamics

H = 8.1Q0.25

Height of plume in km

Q magma mass flux (thermal flux)

Strong plume and weak wind

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High Intensity eruptions (stratosphere)

Mount St Helens 1980

16 km Wind ~ 33 m/s

Lascar 1993 23 km

wind 15 m/s

Umbrella cloud expansion

increasingly dominates as

intensity increases

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Ungarish and Huppert, JFM 458, 283-301, 2002

Holasek et al. JGR 101, 635-655, 1996

Pinatubo 1991

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Exponential thinning

(Thorarinsson & Pyle)

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Ash transport in umbrella cloud

Hazens law:

ash well mixed by internal turbulence

C = Coexp[-pV(r2- ro2)/Q]

V is terminal velocity,

Q is is volume flux into umbrella

r is radial distance from vent

ro is umbrella corner radius

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1815 Tambora distal ash fall

Combine ash falling out while the cloud advances and ash depositing once the eruption stops:

C1 = C0exp [-B(r2-r02)] vs C2= 2BrC0exp [-B(r2-r02)]

-> dependent on eruption duration and particle fall velocity

Thanks to JessyKandlbauer

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Giant co-ignimbrite clouds from very

large magnitude eruptions (M>6.5)

Coriolis gravity balance

Baines and Sparks, GRL, 2005

Oppenheimer Quat. Sci. Rev., 2002

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1315 Kaharoa eruption

Distal ash transport in the atmosphere

Advection-diffusion models

e.g. TEPHRA 2: deposit

NAME III: suspended ash

Particles fall out by settling and dispersed by atmosphere. No internal buoyancy and no plume dynamics

Bonadonna et al., JGR, 2005

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Buoyancy and thin ash Layers

Courtesy Peter Baines