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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)


Volcanic plume dynamics

H = 8.1Q0.25

Height of plume in km

Q magma mass flux (thermal flux)

Strong plume and weak wind


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


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

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

Pinatubo 1991


Exponential thinning

(Thorarinsson & Pyle)


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


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


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


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


Buoyancy and thin ash Layers

Courtesy Peter Baines