Effects of Geomorphological Settings on Salt Weathering of Sandstone in the Coastal Spray Zone

从1999年开始，研究了波浪对海岸浪花区砖石桥墩用砂岩块体盐风化的影响。连接日本青岛岛和九州岛的弥生大桥的四个桥墩是一个金字塔形的平截头体。桥墩分别称为P1、P2、P3和P4。大多数砂岩块覆盖了桥墩的所有侧壁，其表面上有一个tafoni状的凹陷。各壁的平均凹陷深度在P4处最大，依次在P3和P2处逐渐减小，然后在P1处最小。因此，为了阐明海水喷射在上述趋势形成中的作用，我们测量了波浪对砂岩块体的海水补给量。在北向的岩壁上，海水对砂岩块体的补给量在P1时最大，然后向P4逐渐减小。这表明平均洼地深度与海水补给量成反比.在南面的墙壁上，P2的海水补给量最大。这与P2.3上喷雾区的凹陷深度最小有关。由于在正常海况下，波浪从北面接近，因此南北向墙的海水补给量有明显差异。此外，这种海水供应量的差异在P1.4上最大。P2各盘海水补给量以北向盘最大，南向盘次之，东、西向盘最小，说明海水对砂体的补给在凹陷形成中起着重要作用。

The effects of waves on salt weathering of sandstone blocks used for a masonry bridge piers in the coastal spray zone has been studied since 1999. Four piers of Yayoi Bridge, connecting Aoshima island with Kyusyu island in Japan, are the frustum of a pyramid in shape. The piers are called as P1, P2, P3 and P4 respectively. Most of the sandstone blocks, which cover all side walls of the piers, have a tafoni-like depression on their surface. The average depression depth of each wall is the largest on P4 and gradually becomes smaller on P3 and P2 in due order, then the smallest on P1. Therefore, the amount of sea water supply to sandstone blocks by waves has been measured in order to elucidate the role of sea spray in the formation of the tendency mentioned above.Results obtained are summarized as follows;1. On the north-facing walls, the amount of sea water supply to sandstone blocks shows the largest on P1, then gradually decreases toward P4. This indicates that the average depression depth are inversely proportional to the amount of sea water supply.2. On the south-facing walls, the amount of sea water supply shows the largest on P2. This is related to the fact that the depression depth in the spray zone is the smallest on P2.3. Because waves approach from the north under normal sea conditions, the amount of sea water supply shows notable difference between north and south-facing walls. Also this difference in the amount of sea water supply is the largest on P1.4. The amount of sea water supply on each wall of P2 is the largest on the north-facing wall and decreases on the south-facing wall, then becomes the smallest on the east and west-facing walls.These results suggest that the sea water supply to sandstone blocks plays an important role in the formation of depressions.