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Composition and size characterisation of volcanic ash

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Presentation on theme: "Composition and size characterisation of volcanic ash"— Presentation transcript:

1 Composition and size characterisation of volcanic ash
Gemma Prata Supervisors: Tamsin Mather and David Pyle

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4 Clarisse et al

5 Refractive index influence on retrievals
Francis et al. ran some sensitivity experiments and showed that retrieved quantities are strongly dependent on the choice of ash refractive index data used in the radiative transfer model Plot shows scaled mass extinction coefficient at three wavelengths used by the retrieval scheme as a function of ash effective radius, as well as the ratio of 10.8/12.0 µm (black) Francis et al. 2012, JGR

6 Eyjafjallajökull, 13th May 2010
Andesite Pollack et al. 1973 Obsidian Pollack et al. 1973 1.5% Hematite dust Balkanski et al. 2007 Volcanic dust (basalt?) Volz 1973 Francis et al. 2012, JGR

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8 Particle size measurement
Malvern Mastersizer 2000 Size range: 0.02 – 2000 µm Uses Mie and Fraunhofer scattering Mie: requires sample refractive index Fraunhofer: refractive index not required Need about a teaspoon of sample

9 Particle size distributions

10 Effect of size distribution
Volume percentage

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12 Bulk composition – XRF

13 Individual component composition – Microprobe

14 Size-resolved and internal composition – QEMSCAN

15 Individual component composition Size-resolved composition
Bulk composition Individual component composition Size-resolved composition

16 X-Ray Fluorescence (XRF)
Melt whole sample quick and easy bulk composition assumes no size dependence of composition Quench to glass

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18 Electron Probe Microanalysis (EPMA)
gives composition at specific points user selects points beam diameter 10 µm

19 Glass vs. bulk composition
Denser crystals are not normally found in ultra-distal deposits, however Smith et al – used biotite crystals to fingerprint ultra-distal deposits from the YTT eruption

20 QEMSCAN Example from Etna 2006 Colour key: Sulphates (purple)
Silicates (green, blue, pink) Sulphur/sulphides (yellow, claret) Martin et al. 2008, JGR

21 Complex index of refraction:
n*  =  n + i · k n – real part k – imaginary part Literature values compiled from Narcisi & Vezzoli, Global and Planetary Change, 1999 P < 0.05

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23 Questions?

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