Geochemical Monitoring of the Hydrothermal System of Nisyros

Geochemical Monitoring of the Hydrothermal System of Nisyros
Systematic periodic measurements of thermal waters from Nisyros, Kos and Yali

Geochemical Monitoring of the Hydrothermal System of Nisyros

The geochemical surveillance of active volcanoes is based on the measurement of both intensive variables (chemical and isotopic composition of the fluids circulating in the volcanic system, Fig. 28 and 29) and extensive variables (flux of fluids and energy).

Possible variations of such monitored parameters can only be profitably interpreted if a reliable geochemical model of the hydrothermal-volcanic circulation is available.

The compositional data of hydrothermal fluids released by volcanoes (i.e. fumaroles and thermal springs) were used to define suitable 'conceptual' models of the system, which formed the basis for the interpretation of chemical and isotopic changes observed during the periods of monitoring.

Typical questions which geochemical techniques attempted to address were:

1) What are the sources of the hydrothermal fluids (magmatic, meteoric, seawater, metamorphic reactions)?

2) What are the relative proportions of the sources in the fluids?

3) Do the sources change over time (e.g. is the proportion of the magmatic component increasing)?

4) What are the temperature-pressure and redox conditions of the hydrothermal systems?

5) Are the hydrothermal systems in a steady state or in a transient state (increasing temperatures and pressures)?

The analyses necessary to address these questions include analyses of the major and minor components (H₂O, CO₂, H₂S, CH₄, H₂, CO, N₂, O₂, Ar, He), isotope ratios of H, C, N, O (Fig. 29) and S, as well as noble gas analysis ³He/⁴He, ²⁰Ne/²²Ne and ⁴⁰Ar/³⁶Ar).

Fig. 28 Geochemical surveillance of the Nisyros and Solfatara hydrothermal systems. The apparatus was specifically designed to collect gases from fumaroles. Osservatorio Vesuviano Napoli
(OVNI) (Click on image to enlarge).

Fig. 29 Variation in D and ¹⁸O of fumarolic gases, thermal waters, and seawater (SW) collected from Nisyros. Osservatorio Vesuviano Napoli (OVNI) and University of Lausanne (UNIL)
(Click on image to enlarge).

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