Rheology of Crystal-bearing Magmas

The rheology of magma is one of the most crucial physical properties in volcanic eruptions. Eruptions are phenomena where magma reaches the Earth's surface, so how magma can move easily before solidification directly influences the occurrence of eruptions and their eruption styles. If magma close to the surface fragments into small pieces, explosive eruptions occur, affecting a wide area. Brittle fragmentation may be required to generate small fragments of magma, and this process also depends on the rheology of magma. Magma is a suspension in which crystalline particles and gas bubbles float in a silicate melt composed of molten rock. The silicate melt is generally regarded as a Maxwell fluid; however, the presence of crystals complicates the rheology of magma. In densely packed suspensions, solid particles interact with each other, and repeated transitions between solid-like and liquid-like states appear, depending on strain and strain rate. Recently, similar measurements have been reported for actual molten magma. Such measurements are based on oscillatory rheology measurements. In oscillatory rheology measurements, a sinusoidal strain is applied to a sample, and the ratio of the elastic component to the viscous component of the sample can be calculated from the phase difference between strain and stress. Oscillatory rheology measurements of crystal-bearing magma are introduced in this paper.