Metodi di camionamento ed analisi di gas vulcanici e geotermici

Tecniche di campionamento gas di ambiente vulcanico Prima (e unica) legge universale: L’intepretazione dei dati anaitici dipende in prima istanza dalla loro qualità, che dipende dal metodo di raccolta ed analisi, che dipende dal tipo di emissione, dal tipo di analisi che si intende svolgere e dalla composizione stessa del gas

…a brief preliminary remark Why , where and when fluid geochemistry ? Is a sampling-analytical protocol already existing ? What does it remain to improve ? Everything?

Are we ready to start the sampling experience? …some considerations To be a direct or a remote sampler ? ..or not to be

Two opposite (?) views direct approach. Remote sensing

Advantages …. sampling Disadvantages Indirect measurements are easy to be done, allow to abtain a high number of data, imply low hazard Direct measurements have a long tradition, permit a complete analysis. Disadvantages Indirect measurements depend on parameters that cannot be exactly evaluated, complicate models calculations and assumptions. Direct measurements imply a high hazard and tedious operations at the lab.

fumaroles AND plume volcan Lascar flanco sur-oeste

outline To sample, to analyze volcanic (and geothermal) gases A possible way for data interpretation magmatic vs. hydrothermal gases from Andean systems Key studies to look for problems and solutions

sampling The collection of a naturally discharged gas phase depends on the type of emission : Atmospheric contamination Gas-gas chemical reactions Reactions with the sampling devices Type of analysis Safety conditions

sampling Looking for a good place to take a gas sample in a steaming area…. The place was found …or not ?

Which is the “best” fumarole ? some parameter to decide sampling Which is the “best” fumarole ? some parameter to decide Flux Temperature Type of emission Sampling point access Hazard

Thermal spring with bubbling gas sampling A dirty guy A giant Deep temptation Etna volcano (Sicily, Italy) Black Smokers (middle ocean ridges) mud volcano (Azerbaijan) Muddy and burning Black monster Thermal spring with bubbling gas (Yellowstone Park, U.S.) Lava lake (Erta Ale, Ethiopia)

Fumaroles, the best way to discharge collectable gas sampling Fumaroles, the best way to discharge collectable gas …a fumarolic field is even better

Discussing about the “correct “sampling way Discussing about the “correct “sampling way. More questions than answers…but at the end all of us are Giggenbach’s followers

Muestreo de una fumarola a baja temperatura (78 °C)-Volcan Masaya - Nicaragua

Muestreo de una fumarola a alta temperatura (829 °C) -Volcan Satsuma Iwojima - Japan

Gas diffusi dal suolo– campionamento con camera di accumulo

Manifestacioni gassose Un classico domo vulcanico (150- 450 °C). Anche con fumarole ad alto flusso è molto difficile evitare contaminazione di gas atmosferici in quanto è il domo stesso permeabile a tali gas.

Volcano Momotombo Località: 12.4N; 86.5W Altitud max: 1258 m Ultima eruzione: 1905 15 eruzioni dal 1524; nel 1605-1606 fu distrutta la ciuttà di Leon. Tipo de vigilanza: geofisica (INETER); visuale (Web cam).

Manifestacioni gassose Il vulcano presenta un esteso campo fumarolico all’interno del cratere sommitale. Presenti numerosi punti di emissione a bassa (100°C), media (200-500°C) e alta temperatura (hasta 740°C). La scelta è caduta su due fumarole (614 y 741°C), Aprile 2002.

Vulcano Poas Località: 10.2N; 84.2W Altitud max: 2704 m Ultima eruzione: 1992 (freatica) 39 eruzioni dal 1828 Tipo de vigilanza: geofisica (OVSICORI); geochimica (OVSICORI-Univ. Florencia - CNR Pisa); visuale

Once upon a time…the Dragër tubes

SAMPLING THE METHOD HAS TO ANSWER TO SPECIFIC REQUIREMENTS Avoid atmospheric contamination Avoid reactions between gaseous species after the sampling Avoid reactions with sampling materials Simplicity, hardiness, lightness and cheapness of materials Safeguard the operator health DEPENDS ON THE TYPE OF EMISSION FUMAROLES BOILING/BUBBLING POOLS SOIL

Separation of soluble (liquid) and insoluble (headspace) compounds sampling Separation of soluble (liquid) and insoluble (headspace) compounds

Why not a simple glass vial ? chemical solutions are a problem at the duty and the sampling time seems neverending… BUT Insoluble gases are to be “concentrated” Gas-gas reactions must be prevented Use of wet chemistry

NaOH dissolve the acidic gases + H2O + Cd(OH)2 to catch H2S as CdS A modified Giggenbach flask Non condesable gases NaOH dissolve the acidic gases + H2O + Cd(OH)2 to catch H2S as CdS Solid residue (sulfur) Gas and ionic chromatography (mass spectrometry)

Gas Acidi

Water isotopic data can strongly improve our knowledge, thus… sampling Water isotopic data can strongly improve our knowledge, thus…

“the glass sampling lines”

sampling inlet Cooling water circulation Dry gas condensate

BOILING/BUBBLING POOLS SOIL GASES

…or underwater vents

vacuum vial filled with NaOH solution and Cd(OH)2 plastic funnel

Chemicals analyzed in a basic lab (titrator, IC, GC) analysis Chemicals analyzed in a basic lab (titrator, IC, GC) CO2, acidimetric titration HF, HCl, SO2, H2S HBr ionic chromatography H2O by weight difference H2, O2+Ar, N2, CH4, CO (TCD, He carrier) H2, He, Ne (TCD, Ar carrier) O2, Ar (TCD, He carrier, 0°C) CH4, C2-C15 (FID, He carrier) CO (FID, H2 carrier)

Useful parameters analyzed by…less basic lab (GC-MS, polyMS, ICP-MS) VOCs 3He/4He 40Ar/36Ar 13dC-CO2 13dC-CH4 dD-CH4 dD-H2O d18O-H2O 34S/32S-SO2 34S/32S-H2S Metals …

analysis The final aim Different sources produce different compositions …and various sampling and analytical problems

Gas-cromatografo

volcano monitoring Why do we need these data ? Geothermal prospection Low cost information of geothermal potential evolution of the geothermal reservoir changes of the volcanic status (precursory) hot fluid characterization (geothermal application ?)

interpretation

interpretation Evaluation of deep (magmatic) and shallow (hydrothermal) fluid contribution is the aim of volcano geochemical monitoring Geothermal and volcanological investigations involve the same geochemical tools