Keynote Talk: An Overview on Should-be-Challenged Issues Relevant to Fluidization in Nature

A variety of fluidization phenomena taking place in nature are briefly reviewed to evaluate sufficiency/insufficiency of our knowledge on fluidization by covering avalanche of earth and snow, volcanic eruptions and plateau formation, potential fluidization on the Moon, hailstorm from cumulonimbus clouds and crowd dynamics. It is suggested that since our present datasets are insufficient to deal with the large-scale fluidization phenomena in nature, new challenges are needed to provide comprehensive fluidization phase diagrams for a wide range of particles and fluidizing conditions.