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| Titel |
Izu-Oshima volcano, Japan: nine years of geochemical monitoring by means of
CO2 soil diffuse degassing |
| VerfasserIn |
Pedro A. Hernández, Toshiya Mori, Kenji Notsu, Masaaki Morita, Eleazar Padrón, Shin'ya Onizawa, Gladys Melián, Hirochicka Sumino, María Asensio-Ramos, Kenji Nogami, Nemesio M. Pérez |
| 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 |
250133267
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| Publikation (Nr.) |
 EGU/EGU2016-13857.pdf |
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| Zusammenfassung |
| Izu-Oshima is a 15×9 km active volcanic island located around 100 km SSW of Tokyo. The
centre of the island is occupied by a caldera complex with a diameter of 3 km. A large
post-caldera cone known as Mt. Mihara is located at the south-western quadrant of the
caldera. Izu-Oshima has erupted 74 times, consisting mainly in fissure eruptions, both inside
and outside of the caldera. The last eruption of Izu-Oshima occurred in 1986. Since 2007,
seven soil gas surveys have been carried out to investigate the spatial and temporal evolution
of diffuse CO2 emission from this volcanic system and to identify those structures controlling
the degassing process. Diffuse CO2 emission surveys were always carried out following the
accumulation chamber method. Spatial distribution maps were constructed following the
sequential Gaussian simulation (sGs) procedure. The location of the CO2 anomalies has
always shown a close relationship with the structural characteristics of the volcano, with
most of the gas discharged from the rim of the summit crater. Temporal evolution
of diffuse CO2 emission rate from Mt. Miharayama has shown a good temporal
correlation with the seismicity recorded in and around Izu Oshima island during
the period of study. The two peaks of seismic activity occur when highest CO2
diffuse emissions were computed, March 2007, August 2010 and July 2011, may
be associated with fluid pressure fluctuations in the volcanic system due to the
seismicity. In order to strength the contribution of deep seated gases to the diffuse
emission, we performed carbon isotopic analysis of soil gas samples at selected sites
during 2010, 2013 and 2015 surveys. At isotopic compositions lighter than ∼- 6‰
the soil CO2 effluxes were always low, while at heavier isotopic compositions an
increasing number of points are characterized by relatively high soil CO efflux as a
consequence of the addition of the hydrothermal CO2 source. Soil CO2 efflux peak
values (xBackground) showed also a good correlation with the observed seismicity,
with the largest value computed on June 2013. This parameter is a geochemical
expression of the magnitude of the anomalous degassing, and the observed change in the
trend may indicate an increase of the seismic-volcanic activity in the next future.
Therefore, performing regularly soil CO2 efflux surveys seems to be an effective
geochemical surveillance tool Izu-Oshima volcano in order to detect a change in the
tendency of the CO2 emission rate in case of future episodes of volcanic unrest. |
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