Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Evening Poster

S (Solid Earth Sciences) » S-VC Volcanology

[S-VC43] Volcanic and igneous activities, and these long-term forecasting

Sun. May 20, 2018 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Teruki Oikawa(GSJ, National Institute of Advanced Industrial Science and Technology), Takeshi Hasegawa(Department of Earth Sciences, College of Science, Ibaraki University), Daisuke MIURA(一般財団法人 電力中央研究所 地球工学研究所 地圏科学領域, 共同), Nobuo Geshi(Geological Survey of Japan, The National Institute of Advanced Industrial Science and Technology)

[SVC43-P01] Heating experiments on the obsidian from Shirataki, Hokkaido, Japan -Relations between foaming texture (perlite) and lava structure-

*Kyohei Sano1, Keiji Wada2 (1.Shirataki-Geopark, 2.Hokkaido University of Education at Asahikawa)

Keywords:obsidian, heating experiment, perlite

The recent observation on Cordon Caulle (Chile, 2011–12) reported the explosive-effusive hybrid activity (Schipper et al., 2013), and we can consider that this eruption reflects heterogeneous processes such as vesiculation and outgassing in volcanic conduit. Obsidian can be observed as pyroclastic and effusive-lava products of such a silicic and viscous magma eruption, and we can consider that obsidian contains the heterogeneities in rock textures such as crystallinity, water concentration oxidation state, and structure of glass networks.

The effusive obsidian contains the small amount of water (-0.5 [wt.%]) and can be foamed by the heating experiment. The foamed obsidian is known as a perlite. Recent experimental study to form the perlite revealed that (1) the foaming-start temperatures (Tf) of perlite have a positive correlation with water concentration in obsidian from different lava eruptions and (2) perlite texture shows the differences in bubble number density and size (Wada et al., 2016 JpGU), and we could use these characteristics as the indicator of heterogeneity in viscous lava flow. Thus in this study, we conducted the obsidian heating experiment with focusing on the heterogeneity of lava structure in the single lava flow.

We conducted the heating experiments by using the obsidian samples from Horoka-Yubetsu lava from Shirataki, Hokkaido, Japan. We collected the samples of the obsidian layer from the bottom-up within the Horoka-Yubetsu lava. We made the obsidian cube with 10 [mm] on each side and use this cube for heating experiment. The experimental condition was he heating temperature (T) between 900 and 1150 [deg.C] and duration of 30 [min].
On the basis of the experiment we newly identified the heterogeneity of Tf in the obsidian layer of single obsidian lava. The Tf of the sample from the bottom of the obsidian region is 1000 [deg.C], on the other hand, the Tf of the sample from the upper part of the lava is 1100 [deg.C]. Furthermore, the bubble textures in 1150 [deg.C] experiments apparently show that samples from the bottom of the lava show the low bubble number density and large size of bubbles, on the other hands the upper samples show high bubble number density and small size of bubbles. In this study, we discuss the heterogeneity of obsidian lava based on experimental results, rock texture and bubble textures of perlite.