09:30 〜 09:45
[SCG49-09] マグマレオロジーにおけるエイジング -1986年伊豆大島割れ目噴火溶岩を例に-
キーワード：マグマ、レオロジー
Magma rheology is a key to understand widespread volcanic phenomena related to the flow of magma and lava. The rheological behavior is controlled not only by temperature, pressure, and chemical composition, but also by the presence of crystals (e.g. Sehlke et al., 2014; Vona et al., 2017). In various other solid-liquid two phase systems, aging, the slow evolvement over time with increasing viscosity of a sample left at rest, strongly affects the rheological behavior, so that it has been under intense study (e.g. Cloitre et al., 2000; Hexner et al., 2020). Many of the systems show aging through coarsening dynamics, or through glassy rearrangement of domains, or both (Fielding et al., 2000). Although melt-crystal textures of magma can rearrange with time in the same manner, there is no study that has examined the appearance of aging in magma until now. Therefore, whether magma ages must be examined to characterize widespread volcanic phenomena related to the flow.
To achieve this, we performed rheological measurements together with microstructural observations using SEM and micro-CT on the basaltic andesite lava produced by the 1986 Izu-Oshima eruption. The rheology shows an overshoot of the shear stress in the start-up flow after sufficient pre-rest time with either no or weak shear, indicating that the yield stress increases with aging. The 2D and 3D microstructures of quenched samples under different conditions for pre-rest show the growth of clustering with aging without changing the crystal volume fraction. By comparison between the rheology and the microstructure, we discuss the relationship in terms of aging. We also refer to how the aging in magma rheology may practically affect the dynamic flow at a volcano.
To achieve this, we performed rheological measurements together with microstructural observations using SEM and micro-CT on the basaltic andesite lava produced by the 1986 Izu-Oshima eruption. The rheology shows an overshoot of the shear stress in the start-up flow after sufficient pre-rest time with either no or weak shear, indicating that the yield stress increases with aging. The 2D and 3D microstructures of quenched samples under different conditions for pre-rest show the growth of clustering with aging without changing the crystal volume fraction. By comparison between the rheology and the microstructure, we discuss the relationship in terms of aging. We also refer to how the aging in magma rheology may practically affect the dynamic flow at a volcano.