TY - JOUR
T1 - Fragility and an extremely low shear modulus of high porosity silicic magma
AU - Namiki, Atsuko
AU - Tanaka, Yukie
AU - Okumura, Satoshi
AU - Sasaki, Osamu
AU - Sano, Kyohei
AU - Takeuchi, Shingo
N1 - Funding Information:
We thank Monodukuri Plaza at Hiroshima University for machine work of our apparatus. This work is supported by JSPS KAKENHI grants 16H04042 and 19H00721 . Appendix A
Publisher Copyright:
© 2019 Elsevier B.V.
PY - 2020/2/15
Y1 - 2020/2/15
N2 - The rheology and strength of bubbly magma govern eruption dynamics by determining the possibility of fragmentation of ascending magmas. They are also required parameters for understanding seismic monitoring. We measured the rheology and strength of high porosity rhyolitic magma at 500–950 °C. The measured shear modulus and strength are several orders of magnitude lower than bubble-free rhyolite melt, implying that high porosity magma cannot avoid fracturing during magma ascent. The occurrence of fractures is observed in the low-temperature magma (≤800 °C). In this temperature range, the measured attenuation is low. That is, the elastic energy originated by deformations avoids attenuation and is stored in the bubbly magma until released by fracturing (Q > 1). The newly found porosity-dependent strength based on our measurements comprehensively explains three different fragmentation criteria that have been previously proposed independently. Our measurements also show that the shear modulus becomes lower by increasing porosity, which can slow the shear wave velocity. These results suggest that knowing the attenuation of the seismic wave is useful to evaluate magma temperature and the possibility of a fragmentation event that may determine subsequent volcanic activities.
AB - The rheology and strength of bubbly magma govern eruption dynamics by determining the possibility of fragmentation of ascending magmas. They are also required parameters for understanding seismic monitoring. We measured the rheology and strength of high porosity rhyolitic magma at 500–950 °C. The measured shear modulus and strength are several orders of magnitude lower than bubble-free rhyolite melt, implying that high porosity magma cannot avoid fracturing during magma ascent. The occurrence of fractures is observed in the low-temperature magma (≤800 °C). In this temperature range, the measured attenuation is low. That is, the elastic energy originated by deformations avoids attenuation and is stored in the bubbly magma until released by fracturing (Q > 1). The newly found porosity-dependent strength based on our measurements comprehensively explains three different fragmentation criteria that have been previously proposed independently. Our measurements also show that the shear modulus becomes lower by increasing porosity, which can slow the shear wave velocity. These results suggest that knowing the attenuation of the seismic wave is useful to evaluate magma temperature and the possibility of a fragmentation event that may determine subsequent volcanic activities.
KW - Bubble
KW - Fracture
KW - Magma
KW - Rheology
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U2 - 10.1016/j.jvolgeores.2019.106760
DO - 10.1016/j.jvolgeores.2019.106760
M3 - Article
AN - SCOPUS:85077388935
VL - 392
JO - Journal of Volcanology and Geothermal Research
JF - Journal of Volcanology and Geothermal Research
SN - 0377-0273
M1 - 106760
ER -