The Hokkaido Eastern Iburi Earthquake caused over 3300 landslides in volcanic deposits of Atsuma and Abira including Spfa and En-a, influenced by substantial rain from three weeks prior to the earthquake. A series of one-dimensional particle crushing tests were performed to investigate the effect of soaking time on the reduction of peak shear stress. Intra-particle saturation ratio of En-a and Spfa pumice has a good correlation with the Logarithmic value of soaking time. Intra intraparticle saturation ratio of the En-a particle is higher than the Spfa. The median crushing strength (σf)50 of Spfa and En-a reduced consecutively by 56%, and 57% when the soaking time increased from 0 to 504 hours.