Study on Fissure Water in Mishima Lava Flow -Estimation of Flow Velocity Distribution of Groundwater, Porosity and Amount of Groundwater Flow in the Section of Lava Flow-

The Mishima lava flow is located within the length of 40 km in the valley between Mt. Ashitaka and Hakone which is at the southern east slope of Mt. Fuji. There are rich fissures and caves in the lava flow and they make a large-scall subterranean stream. There are many springs of with yield of about 1. 5 million m³ per day at the end of lava flow.
The groundwater in Mishima lava flow is not completely investigated. That is because there is no drop in the groundwater level even if the pumping test is carried out, so that the specific permeability is not obtained.
The actual velocity v of the groundwater in lava flow and the porosity P of lava were measured by using the isotope flow meter, which was designed by the author (Fig. 6) and γ-γ loggin in 6 measuring holes of 2 sections of lava flow are shown in Fig. 3.
Amount of groundwater flow Q was obtained by the following formula ;