江田島市東能美島における花崗岩の風化 <論文>

Weathering of granite at south end of the Higashi-Noumijima island was investigated by fi eld observations, measurements of rock hardness and observations under a microscope. The rock hardness is measured by the Schmidt rock hammer rebound to estimate the grade of weathering. The weathering features of this area are as follows:(1) fresh granite and slightly weathered granite are mainly distributed; (2)fresh granite gradually change to weathered one; (3) microsheeting joint is observed in the slightly weathered granite and is developed along sheeting joint; (4) weathered granite commonly referred as grus is observed only along a ridge. Higashi-Noumijima island is located in the Inland Sea of Japan and the characters of weathering as described above are typical in the islands in the Inland Sea. On the other hand, granite in the inland of the Chugoku district shows the thick grus and no microsheeting joint. These difference is possibly due to the difference of erosional and weathering processes.