Composition and size characterisation of volcanic ash

Gemma PrataSupervisors: Tamsin Mather and David Pyle

Clarisse et al. 2010

Refractive index influence on retrievals

Francis et al. 2012, JGR

Francis et al. 2012, JGR

AndesitePollack et al. 1973

ObsidianPollack et al. 1973

1.5% Hematite dustBalkanski et al. 2007

Volcanic dust (basalt?)Volz 1973

Eyjafjallajökull, 13th May 2010

Particle size measurement

Malvern Mastersizer 2000

Size range: 0.02 – 2000 µmUses Mie and Fraunhofer scattering

Mie: requires sample refractive indexFraunhofer: refractive index not required

Need about a teaspoon of sample

Particle size distributions

0.25 2.5 25 250 25000

2

4

6

8

10

12

14VA10ETNA2001 1

VA10ETNA2001 2

VA10ETNA2001 3

VA11CHAI2008 1

VA11CHAI2008 2

VA11CHAI2008 3

VA15CHAI2008 1

VA15CHAI2008 2

VA15CHAI2008 3

VA1ASO1993 2

VA1ASO1993 4

VA1ASO1993 6

VA8EYJA2010 1

VA8EYJA2010 2

VA8EYJA2010 3Diameter (µm)

Vo

lum

e p

erc

en

tag

e (

%)

Effect of size distributionV

olu

me

per

cen

tag

e

Bulk composition – XRF

Individual component composition – Microprobe

Size-resolved and internal composition – QEMSCAN

Bulk composition Individual component composition

Size-resolved composition

X-Ray Fluorescence(XRF)

Melt whole sample

Quench to glass

• quick and easy• bulk composition• assumes no size dependence of

composition

35 40 45 50 55 60 65 70 75 800

2

4

6

8

10

12

14

16

Total Alkalis vs. Silica DiagramIUGS classification

VA1ASO1993 VA2EYJA2010 VA3EYJA2010 VA7EYJA2010VA8EYJA2010 VA9EYJA2010 VA15-2EYJA2010 EZJEYJA2010VA4GRIM2011 VA5GRIM2011 VA6ETNA2002 VA10ETNA2001VA14ETNA2002 VA11CHAI2008 VA15CHAI2008 VA12BOINA2005VA13BOINA2005 VA16MONT1997 VA16-2TONG2012 VA17ASKJ

SiO2 (Wt%)

Na2

O +

K2O

(w

t%) Foidite

Phono-tephrite

TephriteBasanite

Tephri-phonolite

Trachy-andesite

BasalticTrachy-andesiteTrachy-

basalt

Picro-basalt

Basalt BasalticAndesite

Andesite

Trachyte

Dacite

RhyoliteTrachydacite

Phonolite

Electron Probe Microanalysis(EPMA)

• gives composition at specific points• user selects points• beam diameter 10 µm

35 40 45 50 55 60 65 70 75 800

2

4

6

8

10

12

14

16

Total Alkalis vs. Silica DiagramIUGS classification

Aso 1993 glassAso 1993 bulkEyja 2010 glassEyja 2010 bulkEtna 2001 glassEtna 2001 bulkChaiten 2008 glass (VA11)Chaiten 2008 bulk (VA11)Chaiten 2008 glass (VA15)Chaiten 2008 bulk (VA15)

SiO2 (Wt%)

Na2

O +

K2O

(w

t%)

Foidite

Phono-tephrite

TephriteBasanite

Tephri-phonolite

Phonolite

Trachy-andesite

BasalticTrachy-andesiteTrachy-

basalt

Picro-basalt

Basalt BasalticAndesite

Andesite

Trachyte

Dacite

RhyoliteTrachydacite

Glass vs. bulk composition

Colour key:Sulphates (purple)Silicates (green, blue, pink)Sulphur/sulphides (yellow, claret) Martin et al. 2008, JGR

QEMSCAN

Example from Etna 2006

Literature values compiled from Narcisi & Vezzoli, Global and Planetary Change, 1999

Complex index of refraction:n* = n + i · k

n – real partk – imaginary part

P < 0.05

Questions?