Bristol Wind-blown plume model

Mark Woodhouse, Andrew Hogg, Jeremy Phillips and Steve Sparks

To forecast the spreading of ash in the atmosphere, knowledge of the height at which material spreads laterally (the plume height, H) and the rate at which ash is delivered from the volcano (the source mass flux, Q) is needed.

Q and H are related through the dynamics of buoyant plume rise.

For volcanic eruptions, the relationship between Q and H has been calibrated using historical eruptions.

An observation of plume height can then be used to estimate the source mass flux. This is the approach currently used during volcanic eruptions.

However, this approach does not account for the meteorological effect on plume rise.

V = 0 m/sV = 10 m/sV = 20 m/sV = 30 m/sV = 40 m/s

EyjafjallajökullWeak plume

KatlaStrong plume

Wind has a very strong on weak effect on volcanic plumes, as demonstrated at Kirishima volcano, Japan (left) and at Eyjafjallajökull, Iceland (below).

Wind enhances the mixing of the volcanic material (gases and ash) with the air and so reduces the height of plume rise.

Simple mathematical models of volcanic plumes have been used extensively to understand the dynamics of plumes rising in calm environments.

We’ve extended these models to include the effects of wind.

Using our wind-blown plume model, we can estimate a source flux at Eyjafjallajökull using plume heights observed using a weather radar.

Wind speed measurement

Plume heightRadar observation (denoted by ●)

Source mass flux

Match plume height from model to observation by varying source mass flux at 1200 on 14th April.

This gives an estimate of the source mass flux.

Now fix the source mass flux, but allow meteorological input to vary.

Much of the variation in plume height (given measurement error) can be captured by wind-blown plume model with a constant source mass flux.

Our model estimates a source mass flux that is a factor of 10, or even 100, larger than the estimate from the simple curve fit.

Factor of 7

Factor of 35

Factor of 100

“safe” for flights Airspace closed

Source flux estimated from curve fit (no wind effect)

Estimate from our model with wind

Ash concentration (arbitrary units)

Our results could have very significant implications for airspace management.

Ash dispersion 25 hrs after start of eruption.

Try using our model yourself at www.plumerise.bris.ac.uk