Some Observations about Rock Weathering at Fugoppe Cave Wall, Hokkaido

Abstract

On the wall of interior cave Fugoppe, many carvings consisting of reliefs were inscripted. Recently intensive crumbling of the cave wall were observed. In order to preserve the wall carvings, the investigations on basal rock of cave were carried out.
The entire cave consists of Tertiary tuff and tuff breccia. Weathering of the exposed rock potion is severe and crumbling in the form of sand granules has occurred. There are a number of joints in the bed rock and at some parts blocks of rock have fallen out along the lines of joints.
For the purpose of obtaining a concept of the state of weathering and crumbling of the cave walls, on-the-spot investigations and experimental works consisting of microscopic examinations of rocks, measurements of void rations and monoaxial compressive strengths, measurements of elastic wave velocities (Vp) by Ultrasonic methods, freezing and thawing tests, vibration experiments and measuring of crumbling of outcrops were carried out in the present study.
As a result, the peculiar weathered condition of the bed rock, especially the increase and enlargement of voids accompanying weathering process was pointed out. However, when the cave has been closed off for a long period, the cave walls were preserved with relatively little weathering, and attention should be paid to this feature.