TY - JOUR
T1 - Post-eruptive gravity changes from 1999 to 2004 at Unzen volcano (Japan)
T2 - A window into shallow aquifer and hydrothermal dynamics
AU - Saibi, Hakim
AU - Gottsmann, Joachim
AU - Ehara, Sachio
N1 - Funding Information:
The authors would like to thank Dr. Jun Nishijima, Dr. Yasuhiro Fujimitsu and the students of the Laboratory of Geothermics, Department of Earth Resources Engineering, Kyushu University for support with field work and collection of gravity data. Thanks to Mr. Yamauchi (Fukuoka District Meteorological Observatories) for providing GPS data. We also thank Dr. Nathalie Vigouroux (Simon Fraser University, Canada) and Dr. Maurizio Battaglia (University of Rome, Italy) for their comments on an earlier draft of the paper. We wish to thank Dr. Nico Fournier and an anonymous referee for their careful reading of our manuscript and numerous constructive suggestions that helped improve this paper. The authors would also like to thank Professor Jürgen W. Neuberg (Editor of Journal of Volcanology and Geothermal Research) for his kind cooperation. HS acknowledges the financial support of the Japan Society for the Promotion of Science (JSPS) for research activities in Japan. JG's research was supported by grants from the Royal Society ( UF051396 ) and NERC ( NE/E007961/1 ).
PY - 2010/3/10
Y1 - 2010/3/10
N2 - 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. Here 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 is 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 hydrological 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 hydrological systems at arc volcanoes.
AB - 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. Here 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 is 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 hydrological 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 hydrological systems at arc volcanoes.
KW - Japan
KW - Unzen volcano
KW - aquifer
KW - gravity changes
KW - hydrothermal system
KW - magma
UR - http://www.scopus.com/inward/record.url?scp=77349096396&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=77349096396&partnerID=8YFLogxK
U2 - 10.1016/j.jvolgeores.2010.01.007
DO - 10.1016/j.jvolgeores.2010.01.007
M3 - Article
AN - SCOPUS:77349096396
SN - 0377-0273
VL - 191
SP - 137
EP - 147
JO - Journal of Volcanology and Geothermal Research
JF - Journal of Volcanology and Geothermal Research
IS - 1-2
ER -