Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Poster

S (Solid Earth Sciences) » S-VC Volcanology

[S-VC41] Active Volcanism

Wed. May 23, 2018 1:45 PM - 3:15 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Yuta Maeda(Nagoya University), Takahiro Miwa(National research institute for earth science and disaster prevention), Yosuke Aoki(東京大学地震研究所, 共同), Takeshi Nishimura(Department of Geophysics, Graduate School of Science, Tohoku University), Takahiro Ohkura(Aso Volcanological Laboratory, Institute for Geothermal Sciences, Graduate School of Science, Kyoto University), Satoshi Okumura(Division of Earth and Planetary Materials Science, Department of Earth Science, Graduate School of Science, Tohoku University), Tomofumi Kozono(Department of Geophysics, Graduate School of Science, Tohoku University)

[SVC41-P51] Estimation of viscosity of erupting magma from lava flow morphology analysis

*Taketo Okazaki1, Tsuneomi Kagiyama1 (1.Kyoto University)

Keywords:lava flow, magma, viscosity, aspect ratio

Eruption types of volcanoes and morphologies formed by lava depend on magma viscosity, so it is meaningful to investigate viscosity of extruding lava flow viscosity in studying volcanoes. Rock composition is one of the factors that determine lava flow viscosity, and Shaw (1972) suggested prototype of the method of calculating viscosity using it. However, some lava morphologies show quite different forms in spite of similar chemical compositions, and some studies indicate that crystallinity and water contain causes such disagreement (Sato et al., 2013). In this case, when difference of viscosities estimated by rock composition and lava morphology becomes clear, it may help studying factors that change viscosity before eruption by clearing the reason of its difference.

In this study, we focus on morphological features of lava flow formed by volcanic eruptions, and aim to establish the method of estimating erupting viscosities and restore them of various volcanoes.

Formulas of calculating viscosity from morphology are suggested in previous studies such as Stevenson et al. (1994). In this study, we used aspect ratio which indicates the ratio of height to square of area. We calculated aspect ratio from the results of lava flow simulation that Earthquake Research Institute, The University of Tokyo offers, and derived relationship between aspect ratio and erupting viscosity.

We applied this formula to several real lava flows. As a result, the error by effusion rate was no more than one digit, so this method was confirmed to be useful. When we compare viscosities estimated by aspect ratio and rock composition, we found that the ratio of them was bigger when magma viscosity was higher. It is thought that it is because high viscosity magma effuses in low temperature. According to the study of Sato (2005), the crystallinity of lava makes this ratio bigger. When we consider the effect of crystallization, we gain the result which previous studies show. However, we cannot explain individual lava flows enough, so we have to consider the effects of water content and foam forming.