2:15 PM - 2:30 PM
[SCG74-15] Rheological variety of mixtures of water and ash collected at Ontake and Sakurajima volcanoes
Based on the background, we have performed rheological measurements of mixtures of volcanic ash and water, which are major compositions of lahar. The volcanic ash used in this study was collected at Sakurajima and Ontake volcanoes in Japan. The reason why the two volcanoes are focused is that lahar had flowed there after recent eruptions although the two types of volcanic ash are apparently different. In order to reveal key features in rheology and to compare rheological characteristics, the viscosity was measured changing the particle concentration and the shear rate. An important point of our findings is that the two types of mixtures show non-linear characteristics differently. For instance, Sakurajima samples show strong shear-thinning regardless of the particle concentration whereas the viscosity fluctuates in a longer time scale than rotational period of rheometer within a certain definite range of shear rate in the case of Ontake samples. Interestingly, the range of shear rate corresponds to that at which the relation between the viscosity and the shear rate shows positive slope or shear-thickening deviating from shear-thinning. Since these non-linear characteristics are considered to be induced by variations in particles such as size and shape [C. Chang and R. Powell, 1994; D. Genovese, 2012; S. Mueller et al., 2014], we mainly discuss the rheological changes of mixtures of volcanic ash and water with consideration for the particle size distribution.