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| Titel |
Can bromine/sulphur ratios be used to forcast volcanic eruptions? An example study at Mt Etna. |
| VerfasserIn |
Nicole Bobrowski, Giovanni Bruno Giuffrida |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053291
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| Zusammenfassung |
| During three years, 2006-2009, scattered sky light DOAS measurements have frequently
taken place at Mt. Etna about six kilometres downwind from the summit craters. At the same
time frame volcanic observation were carried out by visiting various parts of Mt Etna
regularly.
Results from theses measurements are presented and discussed. The investigations are
focussed on the bromine monoxide/sulphur dioxide (BrO/SO2) ratios which varied an order
of magnitude over the investigated time frame.
That halogen/sulphur ratio can serve as precursor or indicator for the development of
eruptive activity was supposed already by earlier investigations (e.g. Noguchi and Kamiya
1963, Menyailov 1975, Pennisi and Cloarec, 1998, Aiuppa 2002). Nevertheless still today
there is only a limited understanding because of the complexity with which halogen gases are
released under various magma compositions and degassing conditions, e.g. the rate and
mechanisms of bubble nucleation, growth and ascent in silicate melts (Carroll and Holloway,
1994), the halogen vapour-melt partitioning and the volatile diffusivity in the melt (Aiuppa et
al., 2009).
With this study we aim to add one more piece to the puzzle what halogen/sulphur ratios
might tell about volcanic activities. The BrO/SO2 ratios in our data set show an increase
several weeks’ prior eruptions (up to 3.9 -
10-4) followed by a decreasing trend before and in
the beginning of eruptive activities (down to 0.4 -
10-4) BrO/SO2 increases to medium
values (about 1-2 -
10-4) with an ending phase of activity and stays with medium values
during generally quite phases. A first empirical model to explain the observed changes in the
BrO/SO2 ratio is proposed and suggests that bromine is, in contrast to chlorine and
fluorine, less soluble in the magmatic melt than sulphur. This approach is motivated
by general consideration about solubility’s in melt and in the context with visible
observations.
We are aware that by using the DOAS method we measure the main part of the emitted
sulphur at Mt Etna by determining SO2, but might measure only a smaller or even a variable
part of the bromine by measuring the radical bromine monoxide (BrO). We will show first
investigations that cause the assumption that despite of the above mentioned disadvantages
BrO could serve nevertheless as a new parameter giving indication of the state of a volcano
simply by taking the measurements under certain, but still relatively broad conditions. |
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