Effect of geomorphologocal setting on the erosion rates of sandstone in the coastal spray zone

弥生桥连接日本九州主岛和青岛岛，由四个桥墩支撑，桥墩由砂岩砌块砌筑而成，呈金字塔形截锥体，高3米，墙角70角。桥墩的四个侧壁大约分别面向东、南、西、北。由于风化和侵蚀作用，每个砂岩块都有一个盘状凹陷。在1992年和1994年分别测量了四个桥墩的所有块体的凹陷深度，分别对应于桥梁建成后的41年和43年。我们的研究结果总结如下：1。平均侵蚀深度南墙最大，西墙和东墙依次递减。这种侵蚀深度的差异主要是由于日晒造成的。侵蚀深度与日照量之间的关系用线性函数表示。四个桥墩的回归线在方格纸上平行。最上面的线是第4码头的线，最下面的线是第1码头的线。提出并建立了一种无损原位岩石表面水分监测新技术。该方法和仪器对阐明盐类风化的实际条件和机理具有重要意义。岩石-地表水分变化的测量表明，岩石-地表水分大波动的分布与深坳陷的分布一致。利用热示踪仪对桥墩进行热红外成像。从这些图像中，我们可以获得有关盐风化的有用信息。

Yayoi Bridge, connecting Aoshima Island with Kyushu main island in Japan, is supported by four piers, which are masoned with sandstone blocks and are frustum of pyramid in shape, 3 m in height and 70ﾟ in wall angle. Four side walls of the piers face approximately east, south, west, and north, respectively. Each sandstone block has a dish-like depression due to weathering and erosion. The depth of the depression was measured for all blocks of the four piers in 1992 and 1994 corresponding to 41 and 43 years after the completion of the bridge respectively.The results of our research are summarized as follows.1. The average erosion depth is the largest on the south-facing wall, becomes gradually smaller on the west- and east-facing walls in this order. This difference in erosion depth acording to wall aspect mainly due to insolation. The relationship between erosion depth and insolation is expressed by linear function. The regression lines of four piers are parallel on graph paper. The uppermost line is a line of 4th pier and the lowest is of 1st pier.2. A new technique for nondestructive in situ rock-surface moisture monitoring was developed and established. This method and instruments are very useful to clarify the actual conditions and the mechanism of salt weathering.3. The measurement of rock-surface moisture change indicates that the distribution of large fluctuation in rock-surface moisture is coincident with the distribution of deep depression.4. Thermal infrared images of the piers were taken by themo-tracer. From the images, we can obtain useful informations on salt weathering.