4:15 PM - 4:30 PM
[SVC36-10] How does water enter the interior of pumice? -Example of Sakurajima Taisho eruption pumice-
Keywords:pumice, drift, pore, water
In a Plinian eruption of a terrestrial volcano adjacent to the sea, there are cases where the ejected pumice drifts away. Previous studies on the floating behavior of pumice have indicated that pumice with a larger volume tends to float in water for longer periods of time (Whitham and Sparks, 1986; Manville et al., 1998; Fauria et al., 2017). However, even when the volume of pumice is the same, there are often differences in the length of time that pumice can float, and there is room for research into the reasons for this and what size and shape of void is most likely to trap air or allow water to enter. This study aimed to elucidate these points.
Five samples of Sakurajima Taisho-eruption pumice with different volumes and porosities were floated on water, and the time they floated was recorded. In addition, the total porosity, connected porosity (pores open to the outside), transport porosity (pores connecting both ends of the sample), dead-end porosity (of the connected pores, those other than transport pores), and isolated porosity (pores closed to the outside) of each sample were determined (classification based on Yokoyama and Takeuchi, 2009). As a result, there was no correlation between the floating time and the sample size, but there was a strong correlation between the floating time and the total porosity or dead-end porosity. Furthermore, the size distribution of pore water was measured using the water extrusion method (Nishiyama et al., 2012) for each of the following conditions: immediately after the pumice was soaked in water, after 3 days, and when all the pores were filled with water. By comparing the results of each state, the order in which water enters the pores of each diameter was investigated. As a result, it was found that (1) in the process of water inflow at the beginning, water enters the larger diameter pores first, and (2) in the process of water inflow into the remaining pores afterwards, water enters the dead-end pores preferentially over the transport pores.
Five samples of Sakurajima Taisho-eruption pumice with different volumes and porosities were floated on water, and the time they floated was recorded. In addition, the total porosity, connected porosity (pores open to the outside), transport porosity (pores connecting both ends of the sample), dead-end porosity (of the connected pores, those other than transport pores), and isolated porosity (pores closed to the outside) of each sample were determined (classification based on Yokoyama and Takeuchi, 2009). As a result, there was no correlation between the floating time and the sample size, but there was a strong correlation between the floating time and the total porosity or dead-end porosity. Furthermore, the size distribution of pore water was measured using the water extrusion method (Nishiyama et al., 2012) for each of the following conditions: immediately after the pumice was soaked in water, after 3 days, and when all the pores were filled with water. By comparing the results of each state, the order in which water enters the pores of each diameter was investigated. As a result, it was found that (1) in the process of water inflow at the beginning, water enters the larger diameter pores first, and (2) in the process of water inflow into the remaining pores afterwards, water enters the dead-end pores preferentially over the transport pores.