After the heavy rain the landslide occurred at the beside of local road near Kuroda village, Manba-cho, Tano-Gun, Gunma Prefecture in J apan on the middle of June, 1974.
By the boring for geological survey and prospect working of this place, we recognized the nature of the test pieces of rocks and clay minerals.
This area mainly consists of schalstein of paleozoic system as we called Chichibu formation including thin layers of slate and chert.
Not only the test boring but also the observations on local tohography, it was considered that many landslides has been occurred from early times.
We can fined the two kinds of clay minerals in the cracks and joints of altered strata. One of them (sample No.1002 and 1003) has the elements of fine minerals derived from country rocks and also ammounts of clay minerals (micaceous clay minerals and chlorite) and occured from the horizontal thin cracks and joints in the country rocks, not so long continued.
The other (sample No.1001) comes from the more thick clayey beds of altered zone of schalestein strata, consists of chlorite, micaceous clay and little ammount of montmollironite.
Especially we can recognized the random mixed-layers of mica-montmollironite minerals.
The landslide of this place is considered by such clay minerals as random mixed-layer mica-montmollironite, montmollironite, mica clay minerals and chlorite filling up the pore of rock bed.