In the Riukiu Islands aquifers consist of Riukiu limestone, sandstone-tuff beds of Shimajiri formation and Paleozoic limestone.
Among the above, Riukiu limestone will be the best aquifer for developing ground water in future. Riukiu limestone is either porous limestone or calcareous sandstone in Plio-Pleistocene age, forming terraces and hills of islands.
The ground water is counted as fissure ground water, also having a character of bedding ground water. Therefore, as far as the development of ground water in Riukiu limestone is concerned, it is suggested to make a scientific ground water inquiry such as adopting to drill wells after investigation of the depression of bed rocks by using either electrical resistivity method or seismic refraction method.

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For the purpose of disaster prevention caused by excavation of Building stone, many fundamental investigations were carried out.
1) The Oya stones have been excavated as building stones since olden time and as a result many enlarged caves have been remained under ground.
2) Oya stones are divided into three stratum, hard-coarse (Koshitu-arame), soft-coarse (Nanshitu-arame) and fine (Saime) textures, in ascending order. Especially, in the portion of the fine texture stones, rock-falls and depressions were occurred remarkably.
3) Characteristic fracture systems are of NW and NE directions filled by fissure clay, that is, clinoptirolite. The distribution chart of the fracture systems in the fine texture rock are illustrated in Figs.

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This study has been done with the view of clarifying some characters of collapse occurred in the granite mountains by heavy rain fall, in relation to the topographical and geological features.
From the genetic point of view, these collapse are classified into the following six types.
(1) Landslide closely related to the rock joints.
The character of this type are that occur mainly at foot of slope composed of weathered granodiorite.
(2) Landslide of upper most layer on the vegetation slope.
It arise from difference of physical properties to the water between upper most layer and its basement rock. This landslide occur mainly on the slope composed of weathered biotite granite.
(3) Landslide possessed both characters, (1) and (2), together.
(4) Landslide closely related to the dykes intruded to granite.
(5) Landslide or landcreep occurred in the fault brecciated zone.
(6) Landslide or landcreep occurred in the talus deposits. The great part of collapse occurred in the granite mountains are the type (1), (2) and (3).

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