Abstract
So-called Shirasu (volcanic ash and sand) which is considered to have been derived from Aira Volcano has a pecuriality different from common fine-grained sediments. The authors examined physicodynamic features and mineral arrangement in the Shirasu in order to know its pecuriality.
From such viewpoint, after, the Primary Shirasu was cemented in the natural state and their thin sections were made.
As the result of examination of physical and dynamical properties such as water permeability, entraped air volume, penetrating and shearing resistances of the Primary Shirasu, the obvious differences were recognized between in vertical and horizontal direction
On the other hand, thin sections under the microscope, show that the manner of mineral arrangement is quite different from one another in each direction.
Consequently, it was possibly assumed that physico-dynamic properties of the Primary Shirasu has a close relation with the manner of pores and mineral arrangement.
