Real time monitoring of gas-geochemical parameters in Nisyros

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Real time monitoring of gas-geochemical parameters in
Nisyros fumaroles
M. Teschner1,∗, G.E. Vougioukalakis2, E. Faber1, J. Poggenburg1 and G.
Hatziyannis2
1
Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany.
2
Institute for Geology and Mineral Exploration (IGME), Athens, Greece
ABSTRACT
In this paper the installation and operation of a system for continuous monitoring of
fumarolic gases are described. Several physicochemical and gas parameters such as the
concentration of CO2, H2S and Rn in the fumarolic emissions, as well as the temperature
of the fumarolic gas and its pressure are measured in intervals of seconds and
transferred to a remote station by digital telemetry. Variations in the monitored
parameters which were observed during a short flurry of seismic activity in close
vicinity to Nisyros are also reported.
Keywords: Nisyros, fumaroles, volcanic gas composition, real-time monitoring,
geochemistry
1. INTRODUCTION
Many of the phenomena observed by effusive, explosive and eruptive behaviour of
volcanoes are initiated, influenced and controlled by different complex processes. They
are related to the transport of fluids in the magmatic and in the near-surface
hydrothermal systems. These processes generate a broad variety of chemical and
physical signals on different time scales which may be used as input for monitoring and
quantifying changes in the volcano’s activity or for modelling the dynamic processes
which produce them (Martinelli, 1997).
Whereas geophysical methods are widely introduced as surveillance tools,
geochemical monitoring is used only infrequently and lacks some general acceptance by
the community of volcanologists. In the past sampling and analysing of volcanic gases
from fumaroles have been performed mostly discontinuously with time intervals of
weeks or even months between measurements. Any short term variation in geochemical
∗
Corresponding author: email: [email protected]
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parameters will be missed. Undoubtedly these sampling frequencies are too low to
allow efficiently comparing gas data and e.g. seismic information. Therefore,
continuous monitoring systems, when successfully developed and correctly applied, will
improve the understanding of processes in volcanic systems.
Optical techniques for gas analysis at remote locations have been introduced since
long. Using a correlation spectrometer (COSPEC) technique SO2 flux has routinely
been measured at various volcanoes (e.g. at Kilauea (Hawaii) since 1979 (Sutton et al.,
2001), at Mt. Etna (Italy) since 1987 (Caltabiano et al., 1994) or at Soufrière Hills
(Montserrat) since 1995 (Young et al., 1998)). The application of various optical
techniques to monitor fumarolic gases has recently been reviewed by De Natale et al.
(2001). However, with these techniques SO2 concentration can only be measured within
plumes. Thus, fumaroles are difficult to monitor individually by optical techniques.
Few instrumental systems for continuous gas monitoring have been discussed in the
literature. Investigation of gases from a well located at the foot of the active cone on
Vulcano Island, Italy, have been presented by Toutain et al. (1992) with data for CO2,
He and 222Rn. Japanese scientists report on a monitoring system for volcanic gases
extracted from an observation well in the vicinity of Izu-Oshima volcano (Shimoike and
Notsu, 2000). They also review other papers on gas-monitoring systems.
Because of the presence of hot water vapour and the variable contents of corrosive
components like CO2, SO2, H2S or HCl in the volcanic fluids, analytical equipment may
be damaged in short time. Only limited technical information is available in the
literature and from manufacturers on suitable monitoring equipment which can be
directly installed to active fumaroles. Zimmer and Erzinger (1998, 2003) and Zimmer et
al. (2000) applied a gas chromatographic system which has been operated continuously
at the summit of Merapi volcano. A system which analysed fumarolic gases pumped
through a pipe to a station composed of a gas chromatograph, a mass spectrometer and
several other physical instruments was described by Faber et al. (1998).
For direct, on-site monitoring of gases like CO2, H2S, Rn and of physical parameters
like fumarolic pressure lightweight and corrosion-resistant instruments with low power
consumption have not been available. Here we present information on a system which
was briefly described by Faber et al. (2000) and – after installation and operation for a
long period at Galeras volcano, Colombia – in more detail by Faber et al. (2003). The
basic components of this monitoring system have been developed in BGR laboratories,
commercialization is not excluded.
2. GEOLOGICAL SETTING AND LOCATION OF FUMAROLES
Nisyros volcanic island, built up during the last 150 ka, lies at the eastern end of the
south Aegean active volcanic arc (Francalanci et al., 1995). The last magmatic activity
of Nisyros is of unknown age (>15ka). However, hydrothermal eruptions were frequent
in historical times. They affected the southern part of the Lakki plain, presently the site
of widespread fumarolic activity. The last hydrothermal eruptions were recorded for the
M. Teschner et al. / Real time monitoring of gas-geochemical parameters in Nisyros fumaroles
249
Fig. 1. View of recent hydrothermal craters and place of installation of monitoring station.
19th century and they formed the craters of Polyvotis and Phlegethon (1871–1873) and
Polyvotis Mikros (1887) (Fig. 1).
It seems likely that seismic shocks played a fundamental role in triggering at least
the last hydrothermal eruptions in the 19th century. Again a strong seismic crisis was
observed on Nisyros island in 1996 –1997 and, fortunately, this crisis was not followed
by any hydrothermal eruption. Chiodini et al. (2002) noted increasing H2S/CO2 ratios
and decreasing CH4/CO2 ratios for several of the active fumaroles and interpreted these
chemical changes as an increasing contribution of sulphur-rich, oxidizing magmatic
fluids into the hydrothermal system below Nisyros island. Considering the historical
information about hydrothermal eruptions, the recent changes in the fumarolic gas
composition and the physical phenomena affecting Nisyros may be interpreted as longterm precursors of a new period of volcanic unrest possibly culminating in a magmatic
eruptive phase.
3. MONITORING SYSTEM
We decided to connect the gas extraction device directly to a fumarole, as the hot
vapour and gases escaping the fumaroles seem to be linked in a short way to regions
influenced by the magmatic body of the volcano and/or to its overlaying hydrothermal
systems. In the fumarole gases we believe to sense changes in temperature and gas
composition at depth more rapidly than by analysing diffusive emanating soil gases.
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Fig. 2. Sketch of the instrumental set up of the gas monitoring system.
No real time monitoring system for any volcanologically important parameter has
been installed up to now on Nisyros island. Our multi-parameter station has been
installed close to one of the active fumaroles of the youngest hydrothermal intra-caldera
crater (Polyvotis Mikros, 1887; Fig. 1). The installation of the equipment was started
during April 2003 and was supplemented during August and November 2003. The
operation of the monitoring system is performed in the frame of a BGR-IGME research
project, in straight collaboration with the municipality of Nisyros.
The Nisyros monitoring station includes the following main components (Fig. 2):
physical sensors to measure temperature of fumarolic gases and of surrounding
soil
physical sensors to measure fumarolic and atmospheric pressure
a system to remove water vapour
gas-geochemical sensors for the measurement of CO2, H2S and 220Rn/222Rn (Rn
sensor temporarily disconnected). Electrical signals from all gas-geochemical
sensors have to be considered as proxies for the variation of concentration over
time, exact calibration will be performed later.
an electronic system including A/D-converters, interconnected by a digital bus
power supply using solar panels and back-up batteries
digital telemetry (868 MHz) to a remote station in Emborios (a small village on the
caldera rim). From here connection to BGR or IGME offices by standard
telephone line or GSM is used.
software to control all components of the monitoring system and to store measured
data (software developed by BGR)
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251
4. DISCUSSION AND CONCLUSIONS
Fluctuations of instrumental records may have various reasons. Instabilities due to
technical reasons have to be detected first and afterwards to be corrected which may be
a difficult task. But this is a prerequisite to detect and interpret fluctuations which are
caused by geological, volcanological, meteorological or other “natural” events. Fig. 3
shows a data set recorded between 4 – 25 August 2003. The temperature of the
fumarolic gas shows some pronounced scattering during short time periods, usually
with durations of several hours (which are not due to instrumental problems). The
bottom graph of Fig. 3 indicates some earthquakes recorded on 5, 10, 11 and 15 August
2003, together with their magnitude and a weighted distance to Nisyros monitoring
station, but a correlation to fumarole temperature scattering is not obvious. It may be
speculated whether the temperature fluctuation in the morning of the 4. August 2003 is
linked to an earthquake which occurred about 63.9 km away from the monitoring site at
midnight. A fluctuation with a similar magnitude was found around noon of 8. August
2003, but the next seismic events in close vicinity have been recorded about 2 and 3
days later. There are other, smaller fluctuations in the temperature record where the time
off-set to a seismic event is only one day. A strong earthquake with a magnitude over 6
on the Richter scale was recorded on 14. August 2003. The distance to the hypocenter
Fig. 3. Part of a data set from August 2003. CO2 data are not completely calibrated.
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Fig. 4. Part of a data set from November 2003. Data for 222Rn/220Rn measurements show an integration time
of 60 minutes. CO2 and H2S data are not yet exactly calibrated.
was over 600 km, so it is not surprising that we do not find a good proxy in the
fumarole temperature record.
The pressure of the fumarolic gas is very low and does not exceed a few hectoPascal. It seems to fluctuate without a clear correlation to the seismic events in the
vicinity of the monitoring station or to changes in the fumarole temperature record.
During August 2003 these fluctuations of the fumarole pressure were independent of the
atmospheric pressure.
The concentration of CO2 in the total gas mixture shows a slight modulation over
some weeks. Until exact calibration on site the data of this sensor have to be taken as
proxy only. The CO2 concentration in the fumarolic gas mixture seems to be somewhat
higher during periods of seismic unrest. However, a direct correlation to an earthquake
in the vicinity of the monitoring station was not yet established.
Fig. 4 shows a one day record of CO2, H2S, Rn and temperature signals obtained
after the installation of a more sensitive CO2 sensor and additional equipment in mid
November. Although the on-site calibration of the total flow system has not yet been
completed the concentrations estimated are in good agreement with gas geochemical
data for Nisyros fumaroles given by Brombach et al. (2003) (e.g. 7867 ppm CO2 in the
total fumarolic gas mixture for a sample taken during February 2001). The same applies
M. Teschner et al. / Real time monitoring of gas-geochemical parameters in Nisyros fumaroles
253
to the H2S concentration. For the sample mentioned above Brombach et al. (2003)
report a value of 1819 ppm H2S.
Radon and Thoron concentrations are very low in the fumarolic gas of Polyvotis
Mikros. These data were recorded with an integration time of one hour (Fig. 4).
Fluctuations observed are small and do not correlated with changes in other gas
components, temperature or atmospheric pressure. These first results point to the
necessity that we have to collect time series for longer periods to judge on a possible
correlation of seismic events occurring in the South Aegean region and gas geochemical
or physical parameters.
Acknowledgements
We kindly acknowledge the continuous support and encouragement of IGME and
BGR staff for this monitoring project. Severe thanks go to the municipality of Nisyros
in Mandraki which supported the project by providing manpower during the phase of
installation of the monitoring station and by balancing some running expenses. We are
thankful that part of the equipment installed as well as travel expenses could be financed
by a BGR project with the German Ministry of Economics and Labour, grant number
BMWi VI A 2-27/01. Financial support of the IGME team was supplied by the 3rd
Framework EU IGME project “Continuous monitoring of the Hellenic geothermal
fields”.
REFERENCES
Brombach, T., Caliro, St., Chiodini, G., Fiebig, J., Hunziker, J.C. and Raco, B., 2003.
Geochemical evidence for mixing of magmatic fluids with seawater, Nisyros
hydrothermal system, Greece. Bulletin of Volcanology, 65: 505-516.
Caltabiano, T., Romano, R. and Budetta, G., 1994. SO2 flux measurements at Mount
Etna (Sicily). Journal of Geophysical Research, 99: 12809-12819.
Chiodini, G., Brombach, T., Caliro, St., Cardellini, C., Marini, L. and Dietrich, V.,
2002. Geochemical indicators of possible ongoing volcanic unrest at Nisyros
Island (Greece). Geophysical Research Letters, 29(16): 1759-1762,
doi:10.1029/2001GL014355.
De Natale, P., Gianfrani, L. and De Natale, G., 2001. Optical methods for monitoring of
volcanoes: techniques and new perspectives. Journal of Volcanology and
Geothermal Research, 109: 235-245.
Faber, E., Inguaggiato, S., Garzón-Valencia, G. and Seidl, D., 1998. Continuous gas
measurements at volcanic fumaroles. Mitteilungen Deutsche Geophysikalische
Gesellschaft e.V. DGG Special Volume III/1998, ISSN-Nr. 0947-1944: 83-87.
Faber, E., Poggenburg, J., Garzón, G., Morán, C. and Inguaggiato, S., 2000. Gas
monitoring at volcanoes. Mitteilungen Deutsche Geophysikalische Gesellschaft
e.V., DGG Special Volume IV/2000, ISSN-Nr. 0947-1944: 77-80.
254
M. Teschner et al. / Real time monitoring of gas-geochemical parameters in Nisyros fumaroles
Faber, E., Morán, C., Poggenburg, J., Garzón, G. and Teschner, M., 2003. Continuous
gas monitoring at Galeras volcano, Colombia; first evidence. Journal of
Volcanology and Geothermal Research, 125(1-2): 13-23.
Francalanci, L., Varecamp, J.C., Vougioukalakis, G., Defant, M.J., Innocenti, F. and
Manetti, P., 1995. Crystal retention, fractionation and crustal assimilation in a
convecting magma chamber, Nisyros Volcano, Greece. Bulletin of
Volcanology, 56: 601-620
Martinelli, B., 1997. Volcanic tremor and short-term prediction of eruptions. Journal of
Volcanology and Geothermal Research, 77: 159-171.
Shimoike, Y. and Notsu, K., 2000. Continuous chemical monitoring of volcanic gases
in Izu-Oshima volcano, Japan. Journal of Volcanology and Geothermal
Research, 101: 211-221.
Sutton, A.J., Elias, T., Gerlach, T.M., Stokes, J.B., 2001. Implications for eruptive
processes as indicated by sulfur dioxide emissions from Kilauea Volcano,
Hawaii, 1979-1997. Journal of Volcanology and Geothermal Research, 108:
283-302.
Toutain, J.P., Baubron, J.-C., Le Bronec, J., Allard, P., Briole, P., Marty, B., Miele, G.,
Tedesco, D. and Luongo, G., 1992. Continuous monitoring of distal gas
emanations at Vulcano, southern Italy. Bulletin of Volcanology, 54: 147-155.
Young, S., Francis, P.W., Barclay, J., Casadevall, T.J., Gardner, C.A., Darroux, B.,
Davies, M.A., Delmelle, P., Norton, G.E., Maciejewski, A.J.H., Oppenheimer,
C., Stix, J., Watson, I.M., 1998. Monitoring SO2 emission at the Soufrière Hills
volcano: implications from changes in eruptive conditions. Geophysical
Research Letters, 25: 3681.
Zimmer, M. and Erzinger, J., 1998. Geochemical monitoring on Merapi volcano,
Indonesia. Mitteilungen Deutsche Geophysikalische Gesellschaft e.V., DGG
Special Issue III/1998, ISSN-Nr. 0947-1944: 89-92.
Zimmer, M. and Erzinger, J., 2003. Continuous H2O, CO2, 222Rn and temperature
measurements on Merapi Volcano, Indonesia. Journal of Volcanology and
Geothermal Research, 125(1-2): 25-38.
Zimmer, M., Erzinger, J. and Sulistiyo, Y., 2000. Continuous chromatographic gas
measurements on Merapi volcano, Indonesia. Mitteilungen Deutsche
Geophysikalische Gesellschaft e.V., DGG Special Volume IV/2000, ISSN-Nr.
0947-1944: 87-91.