Japan Geoscience Union Meeting 2015

Presentation information


Symbol S (Solid Earth Sciences) » S-VC Volcanology

[S-VC48] Mitigation of Volcanic disaster - Basic and applied research

Sun. May 24, 2015 11:00 AM - 11:45 AM A05 (APA HOTEL&RESORT TOKYO BAY MAKUHARI)

Convener:*Kazutaka Mannen(Hot Springs Research Institute of Kanagawa Prefecture), Shinji Takarada(Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Eisuke Fujita(National research Instituite for Earth science and Disaster prevention, Volcanic research department), Hisashi Sasaki(Asia Air Survey Co., Ltd.), Chair:Kazutaka Mannen(Hot Springs Research Institute of Kanagawa Prefecture)

11:30 AM - 11:33 AM

[SVC48-P01] Augmentation of Magma Database by using a simple method to estimate groundmass SiO2 content

3-min talk in an oral session

*Shingo TAKEUCHI1, Kiyoshi TOSHIDA1, Daisuke MIURA1 (1.Central Research Institute of Electric Power Industry)

Keywords:magma, petrological analysis, eruption magnitude, database

We developed a simple method to estimate groundmass SiO2 contents (preeruptive melt SiO2 contents) by using masabalance calculation between bulk rock, bulk phenocryst and melt compositions. This method helps us to augment the Magma Database, which has been constructed to examine relationship between magma properties and eruption behavior for volcanic eruptions in Japan during the last one hundred thousand years.

The simple method is based on uniformity in total phenocryst SiO2 content. We examined total phenocryst SiO2 contents of 44 magmas, ranging from basaltic to rhyolitic bulk composition, in the Magma Database. The total phenocryst SiO2 contents were calculated from modal data and representative phenocyrst compositions. We found that the magmas have uniform total phenocryst SiO2 contents of 47.4 wt% (S.D.=1.5 wt%) if their phenocyst assemblages are quartz-free. If quartz phenocyrst are contained, the total phenocryst SiO2 contents increase with fractions of quartz phenocyrst and have 64 wt% at the maximum. This evidence validates an assumption of uniform total phenocryst SiO2 contents (47.4 wt%) in massbalance calculation for the quartz-free magmas.

We compiled ca.40 literature data of bulk SiO2 and phenocryst content for mainly lava eruptions, which are minor in the Magma Database. Melt SiO2 contents of the compiled examples were estimated by the simple method, and their relationship between melt SiO2 content and eruption magnitude (M) were compared with those of the Magma Database. This compilation augmented examples of small to intermediate magmatic eruptions (M=3-5) with basaltic to rhyolitic melt compositions. This data augmentation has little effect on the already known maximum magnitude of M=5 for basaltic to dacitic melt eruptions.