Integral models of volcanic plumes in a cross wind

Mark Woodhouse1

with Andrew Hogg1, Jeremy Phillips2 & Steve Sparks2

1School of Mathematics2School of Earth ScienceUniversity of Bristol

Application to Eyjafjallajökull 2010

Application of the mass flux — rise height scaling relationships can lead to large and rapid variations in the estimated mass flux.

The integral model can used as an inversion tool, to determine source conditions from observations of the rise height with meteorology included.

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Model-derived mass flux estimate

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Beyond single point matching…

Matching to a single observation target height gives an estimate of the source mass flux, but the model prediction cannot be assessed.

By using additional observational data we can test the ability of the model to capture the detailed plume dynamics.

Additional observational data can be obtained from•Webcameras — test of the entrainment formulation?•Volcanic lightning — test of the moisture formulation?

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Webcamera at EyjafjallajökullDuring the 2010 eruption of Eyjafjallajökull, a webcamera installed by Mila telecommunications recorded images of the volcanic plume every 5 seconds.

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Matching plume model to webcam

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5 minute period – 60 imagesFrom plume edges, the centreline trajectory can be determined.

An optimization routine is used to adjust inputs to the integral plume model and match the predicted trajectory to the observation at a series of control points.

Matching plume model to webcam

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2160 snapshots are used to produce 36 averaged images for 0700 to 1000 on 11th May 2010, and model matching performed.

The model matches give estimates of the source mass flux of around 6.4×104 kg/s.

In comparison, Gudmundsson et al (2012) estimate a mass flux of 1×105 – 2×105 kg/s on 11th May.

Effect of entrainment coefficient

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Volcanic lightning

Lightning is often observed in volcanic plumes.It is thought that lightning occurs due to charging of ash particles that results from fracturing and collisions during transport.

Atmospheric conditions can also influence the occurrence of lightning.

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Volcanic lightning at Eyjafjallajökull (National Geographic)

Volcanic lightning at Eyjafjallajökull

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Lightning discharge data courtesy of Sonja Behnke

During the 2010 eruption of Eyjafjallajökull, there was an period of intense volcanic lighting during May.An array of VHF detectors captured the signal from the lightning.

The location of lightning flashes gives an indication of the plume trajectory in three-dimensions.

Charge structure

Sonja Behnke and colleagues at New Mexico Tech. are able to analyse the lightning signal and determine the charge structure of the volcanic plume.Behnke et al suggest the dipole occurs due to ice-formation in the plume and ice-contact charging.

(Behnke, S.A., R.J. Thomas, P.R. Krehbiel, W. Rison, and H.E. Edens (2012), Charge Structure and charging mechanisms in the plume of Eyjafjallajo kull, Eos Trans. Am. Geophy. Union, ̈�Abstract AE13A-0375; and JGR Atmospheres, in review)

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Monopole

Negative-over-positive dipole

17th M

ay

1200

—14

00

13th M

ay

2200

—00

00

Moisture transport in plumes• Volcanic plumes can transport large quantities of water vapour high into the

atmosphere.• On condensation, latent heat is released to the plume, increasing the energy

content.• For plumes that remain in the troposphere the additional energy can

significantly enhance the rise height of the plume.• Competition between moisture (enhancing rise height) and wind (reducing

rise height).

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Charge structure as a test of the moist plume model

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17th May 1200—1400

13th May 2200—0000

Charge structure as a test of the moist plume model

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11th May 1900—2100

12th May 2100—2300

12th May 0300—0500 Radar determined plume

height (5.1km) is too low—lightning detected up to 7.6km.

Undetermined points above 3.5km are likely to be from negative charge region.

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Charge structure as a test of the moist plume model

Radar determined plume height (7.9km) is too high—no lightning detected above 6.3km.

Switching between monopole and dipole. Suggests plume top is fluctuating near the level of condensation.

16th May 1400—1600

Conclusions

• Integral plumes models incorporating meteorology, in particular wind, can be used to determine estimates of the source mass flux from an observation of the plume height.

• Additional observational data can be incorporated allowing the model prediction to be assessed.

• Webcams can provide useful information on plume trajectories and test formulations of the entrainment process.

• The moisture formulation has been tested using volcanic lightning observations.

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Thanks

Funding from NERC VANAHEIM project and FUTUREVOLC.

Claire Witham (UK Met Office) for NWP data.

Halldor Bjornsson (Icelandic Meteorological Office) and Mila Telecommunications for webcam images.

Sonja Behnke (University of South Florida; previously Langmuir Laboratory, New Mexico Tech) for volcanic lightning data.

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