Vulcano's Fumaroles
and
Geochemical Monitoring
of Volcanoes

Christoph Moder
2004-05-25

Contents

What are Fumaroles?

Emitted Gas

Gas Composition

Influences on Solubility

Geochemical Monitoring

Monitoring: Why?

Monitoring: How?

Measuring Methods

General Patterns for Activity

Examples for Monitoring

Fumaroles on Vulcano

References

1. What Are Fumaroles?

holes in the ground where hot gas comes out

gas comes out of the magma chamber (where differentiation occurs)

fumarole + groundwater
= geyser

2.1 Gas Composition

composition:

H2O (35%-90%)

CO2 (5%-50%)

SO2 (2%-30%)

HCl

H2S

the atmosphere and hydrosphere are of volcanic origin

2.2 Influences on Solubility

solubility in the magma depends on:

pressure

temperature

viscosity

chemical structure

saturated magma  gas is released

release order: CO2, S, Cl, H2O, F

3.1 Monitoring: Why?

to understand what happens in the magma chamber

eruption warnings

geophysical methods are more common

several methods are combined

volcanic gas itself can be a danger

Lake Nyos (Cameroun, 1986, CO2), 1700 fatalities (suffocation)

Dieng Plateau (Java, CO2)

Laki (Iceland, 1783, HF), >10000 fatalities (famine)

3.2 Monitoring: How?

Continuous Monitoring:

only few types of gas

shortage of energy (clouds!)

maintenance required

measuring interval must be short

Laboratory Analysis:

more exact

not realtime

not regularly

somewhat dangerous

3.3 Measuring Methods

gas chromatography, ion chromatography

mass spectrometer

chemically selective sensors

optical methods:

COSPEC (COrrelation SPECtroscopy): SO2 measurement by UV absorption

FTIR (Fourier Transform InfraRed spectroscopy): CO2 measurement with an interferometer

LIDAR (light detection and ranging): measurement of light scattering with different wavelengths (DIAL, DIfferential Absorption Lidar)

3.4 Patterns for Volcanic Activity

appearance of fumaroles in general

rising gas temperature

shift of the chemical equilibrium:

rise of the ratio F/Cl and NH4/B (= higher pressure)

decrease of Cl/S

more CO2

more HCl

other atypical things like oscillation of concentration

3.5 Examples for Monitoring

Colombia: Galeras

Indonesia: Merapi (Java)

France: Soufrière (Guadeloupe), Pelée (Martinique), Piton de la Fournaise (Réunion)

USA: Kilauea (Hawaii)

Japan: Mt Mihara

increase of F, Cl, S between 17th and 30th of July 1957, eruption on 5th and 6th of August

ditto in the beginning of October 1957, eruption on October 13th

4. Fumaroles on Vulcano

References

Hans-Ulrich Schmincke: “Vulkanismus”, Wissenschaftliche Buchgesellschaft, Darmstadt 2000

Jacques-Marie Bardintzeff: “Vulkanologie”, Ferdinand Enke Verlag, Stuttgart 1999

Ollier Cliff: “Volcanoes—An Introduction to Systematic Geomorphology”, MIT Press, Cambridge MA (USA) and London (UK) 1975

http://volcanoes.usgs.gov/About/What/Monitor/Gas/continuous.html + sample.html

http://www.volcanolive.com/gases.html

http://www.dgg.tu-berlin.de/tagungen/dgg2002/abstracts/VU/Faber_P.htm

http://www.seismo.com/msop/nmsop/13%20volcano/volcano5/volcano5.html#13.5.3

http://homepage.ntlworld.com/volcano/gas.htm

http://www-volcano.geog.cam.ac.uk/research/degassing.html

Gas temperature: ca. 150-800 °C, sometimes >1000 °C

Geyser: a lot of water => it does not evaporate completely in the underground

water vapour has condensed or been split up to oxygen and hydrogen

water: biggest part is ground water, but also from magma

water in magma = molecular and hydroxyl group (amphibole, mica)

water lowers the melting point of the mantle

high temperature/much oxygen: SO2 (sulfur dioxide) instead of H2S (hydrogen sulfide) and vice versa

atmosphere:

a lot of oxygen has been used to oxidise iron

carbon dioxide has been consumed by plants

sulfur oxide has been bound to metal ions as sulfate

Die Gase befördern verschiedene Metalle an die Erdoberfläche. Sie fallen i.d.R. an der Erdoberfläche aus. Beispiele sind Silizium, Natrium, Calcium, Magnesium, Zink, Arsen, Zinn und Silber. Die hohe Temperatur im Inneren des Erdkörpers bewirkt eine hohe Lösungsfähigkeit, vor allem für Kieselsäure (SiO2) und Schwermetalle. Das Vorhandensein von Säuren wie Salz- oder Schwefelsäure trägt zudem zur Lösung von Schwermetallen bei. An der Erdoberfläche kühlt sich das Wasser bzw. der Dampf ab, der Sättigungsindex wird überschritten und die geförderten Produkte werden ausgefällt. In den hochthermalen Gebieten, in denen Fumarolen die Landschaft bestimmen, werden Schwefel, Gips, Ammoniumchlorid, Sulfide, Sulfate, Alkali- und Erdalkali-Chloride akkumuliert. Auch Pyrit, Goethit und Limonit werden durch den Transport von Eisen ausgefällt. Dringt der heiße Dampf der Fumarolen durch die Gesteinsdecken der Lava, so finden Mineralumwandlungen statt. Es entstehen verschiedene Tonminerale, wie z.B. Kaolinit, Montmorillonit und Chlorit.

chemical structure: compatible elements (more SiO2 = more volatiles)

early crystallizing minerals like olivine, spinel, pyroxene, feldspar => gas accumulates in the residual melt

solubility: increases with pressure, decreases with temperature

exception CO2: better soluble at low pressures

low temperatures: CO2, H2S

areas around volcanoes are often densely populated

fertile soil in the endangered valleys

crater lakes in Cameroun 1984/1986

HF: hydrofluoric acid; transparent, burns skin and respiratory tract, can cause blindness, acid rain

Laki: soluble in water, adhesive to particles => sheep killed, people sick

400 W solar panel not sufficient for 15 W monitoring system

possible problems: sulfur plugs pipes

measurements on Stromboli showed rapid changes, e.g. CO2 from 0% to 45% or H2O from 0% to 45% in less than 3 min)

dangerous: because interesting, when the volcano is active

gas chromatography: corrosive gas, cold gas instead directly in the fumarole

ion chromatography: when dissolved

sensors: semiconductor sensors

FTIR: heated ceramic source, interferometer, fourier transformed

optical methods: LIDAR (over craters), Diodenlaser-Absorptionsspektroskopie (in fumaroles); correlation spectrometer COSPEC: UV-Absorption durch SO2; FTIR (Fourier transform infrared spectrometer system); LI-COR (infrared carbon dioxide, CO2)

in Munich there are no fumaroles and there will never be a volcano

CO2: example: Arenal/Costa Rica, limestone in the river

Christoph Moder

2004-05-13T11:55:31