Abstract:The difference between the fluidization mechanisms of the Tsukidate flowslide triggered by earthquake and the Yamashina flowslides induced by rainfall was examined through field investigations,soil tests and numerical simulations. In the case of the Tsukidate flowslide,after a liquefaction of sliding mass,the combination effect of grain crushing and rapid shearing rate of the pyroclastic material on the excess pore pressure generation was concluded as the main reason. While,in the case of the Yamashina flowslides,the low shear strength mobilized in the fully saturated weathered mudstone debris with a very low permeability was attributed to the high mobility of the flowslides.