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| Titel |
Identifying open and closed system behaviors at Tungurahua volcano (Ecuador) using SO2 and seismo-acoustic measurements |
| VerfasserIn |
Silvana Hidalgo, Jean Battaglia, Benjamin Bernard, Alexander Steele, Santiago Arellano, Bo Galle |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250099726
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| Publikation (Nr.) |
 EGU/EGU2014-15541.pdf |
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| Zusammenfassung |
| Tungurahua is one of the most active volcanoes in Ecuador. It is located in Central Ecuador,
160 km South of Quito and 8 km South of the touristic town of Baños. Tungurahua had one
eruption every century since 1500, with an activity characterized by ash fallouts and
pyroclastic and lava flows. The current eruptive period of Tungurahua began in 1999 with
multiple episodes of explosive activity that have threatened the local population.
The monitoring network is constituted by 5 short period and 5 broadband seismic
stations, 4 DOAS permanent instruments, 4 tiltmeters, 2 permanent high resolution
GPS, 4 digital cameras and 10 acoustic flow monitors. The correct interpretation of
the different data acquired by this network allows a better understanding of the
eruptive behavior of Tungurahua in order to provide early warning to the local
population.
Tungurahua changed its behavior from a continuously erupting volcano, as it was until
2008, to a sporadically erupting one, showing clear quiescence phases lasting from 40 to 184
days, and intense activity phases lasting from 15 to 70 days. Activity phases are characterized
by Strombolian and Vulcanian eruptive styles, producing ash fallouts and in a few occasions
pyroclastic flows. In terms of hazard to the local population, one of the goals of monitoring
Tungurahura is to forecast the onset and evolution of eruptive phases. In particular the
occurrence of large Vulcanian explosions which occur when the conduit is closed is a major
issue.
Since 2010 we focused our study on the relation between SO2 gas emissions, the seismic
and acoustic energies of explosions and the tremor amplitudes. The first observation of
comparing these different datasets is that the correlation between seismic and SO2 degassing
is not straightforward, and actually the relation reflects the conditions at the vent: open or
closed.
The onset of eruptive phases in open conduit conditions can be identified which leads to
an effective eruption forecasting. An example of this behavior is the eruptive phase between
December 2009 and March 2010 when SO2 measurements increased 4 days before the
amplitude of tremor and 9 days before the occurrence of the first explosions. Conversely, if
the vent is closed at the beginning of a phase and no evident seismic precursors are
observed forecasting is hardly possible. During an ongoing eruptive phase, the
relation between these parameters allows to identify periods when the conduit is
totally open as degassing may occur almost without generating any seismicity.
Therefore the forecasting of escalating open conduit activity or a partial closing
of the system is possible. Such a case was observed and forecasted on December
2011.
In this work, we present observational evidence of these mechanisms which are used to
identify possible patterns of evolution of the activity, contributing to a more effective volcanic
hazard assessment. |
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