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| Titel |
CO2 driven weathering vs plume driven weathering as inferred from the groundwater of a persistently degassing basaltic volcano: Mt. Etna |
| VerfasserIn |
Marcello Liotta, Walter D'Alessandro |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250126899
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| Publikation (Nr.) |
 EGU/EGU2016-6693.pdf |
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| Zusammenfassung |
| At Mt. Etna the presence of a persistent volcanic plume provides large amounts of
volcanogenic elements to the bulk deposition along its flanks. The volcanic plume consists of
solid particles, acidic droplets and gaseous species. After H2O and CO2, S, Cl and F
represent the most abundant volatile elements emitted as gaseous species from the craters.
During rain events acidic gases interact rapidly with droplets lowering the pH of
rain. This process favors the dissolution and dissociation of the most acidic gases.
Under these conditions, the chemical weathering of volcanic rocks and ashes is
promoted by the acid rain during its infiltration. Subsequently during groundwater
circulation, chemical weathering of volcanic rocks is also driven by the huge amount of
deep magmatic carbon dioxide (CO2) coming up through the volcanic edifice and
dissolving in the water. These two different weathering steps occur under very
different conditions. The former occurs in a highly acidic environment (pH < 4)
and the reaction rates depend strongly on the pH, while the latter usually occurs
under slightly acidic conditions since the pH has been already neutralized by the
interaction with volcanics rocks. The high content of chlorine is mainly derived from
interactions between the plume and rainwater, while the total alkalinity can be completely
ascribed to the dissociation of carbonic acid (H2CO3) after the hydration of CO2.
The relative contributions of plume-derived elements/weathering and CO2-driven
weathering has been computed for each element. In addition, the comparison between the
chemical compositions of the bulk deposition and of groundwater provides a new
understanding about the mobility of volatile elements. Other processes such as ion
exchange, iddingsite formation, and carbonate precipitation can also play roles,
but only to minor extents. The proposed approach has revealed that the persistent
plume strongly affects the chemical composition of groundwater at Mt. Etna and
probably also at other volcanoes characterized by huge open-conduit degassing activity. |
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