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| Titel |
Post-eruptive gravity changes at Unzen volcano (Japan): a window into hydrologic dynamics |
| VerfasserIn |
Hakim Saibi, Joachim Gottsmann, Sachio Ehara, Jun Nishijima, Yasuhiro Fujimitsu |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250037097
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| Zusammenfassung |
| We report on results from post-eruptive time-lapse gravity investigations performed between 1999 and 2004 at
Unzen volcanic complex, Shimabara Peninsula, Kyushu Island, southwest Japan. One of the most active volcanoes
in Japan, Unzen saw its most recent eruption between 1990 and 1995.
We demonstrate that annual residual gravity variations reflect subsurface mass changes most likely coupled to
changes in shallow aquifer levels on the order of several meters. We find a positive correlation between rainfall
and gravity data with a 3 to 4 month lag time. We interpret this link as a delayed aquifer response to local rainfall
and show that high permeability rocks of the Unzen complex are indicative for low aquifer storativity, which in
turn results in substantial water table fluctuations upon deviation from average rainfall budgets. While aquifer
dynamics may represent a first order explanation to the observed gravity data, hydrothermal fluid circulation in
the feeder system of the recent eruptive episode are also likely to contribute to the gravity signals by deteriorating
the signal-to noise ratio compared to hydrothermally quieter volcanoes. This study shows that shallow hydrologic
processes may dominate temporal changes in the gravity field after dome-building eruptions identifying a clear
need for a better understanding of the interaction between magmatic and aquifer systems at volcanoes. Future
investigations of this link may provide valuable insights on coupling between these reservoirs with implications
for hazard assessment during pre-, syn- and post-eruptive stages. |
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