- 応用地質 (ISSN:02867737)
- vol.36, no.5, pp.349-358, 1995-12-10
Downward infiltration of rainwater within the Quaternary pyroclastic plateau have been studied by using continuous and automatical survey of electric prospecting and chemical analysis of seepage water from the foot of the plateau. Reduction of apparent resistivity and its downward extension are recognized within the plateau just after the heavy rain. This means the existence of downward infiltration of rainwater. However, the style of infiltration is various, and it seems to be strongly influenced by rainfall condition and surface humus soils. Downward velocity of the infiltration is estimated to be 60 meters/12 hours, and this value is too rapid compared with the well-known value of 1〜3 mm/day. Probably, two types of downward infiltration may co-exist because of cooling joints or pipe structures within the pyroclastic flow deposits. On the other hand, chemical analysis of seepage water shows that the concentration of ions may change depending on that of rainfall. This may support the result mentioned above of the rapid velocity.