A new method for determining weathering rate in weathering pits

Abstract: Determining the rates of rock weathering is difficult because, firstly, the weathering rate of rocks is usually so slow that it is difficult to measure; secondly, it is also difficult to determine the start time and duration of weathering. The Shanxi Riverbed in Fujian, China, dried up after a reservoir was built upstream in 1959, and became a stone quarry site. Quarrying ceased in 1977, so a large amount of quarry wastes with artificially excavated surfaces were left in the valley. The concave-upward curved rocky surface, broken by manual excavation, easily contains rain water in its central part, which was easily weathered into a more concave surface. Plaster mold casting was performed in situ on such a concave surface of an excavated stone rock in the valley and scanned with a high-precision 3D scanner to obtain 3D data of the concave-upward rock surface and its more concave middle part, which was considered as an initial weathering pit. The 3D model provided an in-depth understanding of the initial formation process of weathering pits, indicating that: (1) the average weathering rate of a weathering pit is 10.8±0.49 cm/ka; (2) weathering pits are generally formed by standing water in depressions on a flat near-horizontal rock surface due to weathering actions involving water; (3) the deepening rate of a weathering pit is about 4 times greater than that of the surrounding area; (4) the growth of a weathering pit can begin in some small concavities on the flat rock surface without pre-existing depressions and gradually expands; (5) a weathering pit is generally wider than deep or with a flat bottom due to expansion with a lateral weathering rate that is greater than that of the vertical, and the lamination of the host rock is not necessary for the formation of flat floored weathering pits.

摘要：确定岩石风化速率是困难的，因为首先，岩石的风化速率通常很慢，难以测量；其次，也很难确定风化的起始时间和持续时间。中国福建的山溪河床在1959年上游修建水库后干涸，变成了一个采石场。1977年采石活动停止，因此山谷中留下了大量带有人工挖掘面的采石废弃物。人工挖掘造成的向上凹的岩石表面中部容易积水，很容易风化成更凹的表面。在山谷中一块挖掘出的岩石的这种凹面上进行了石膏铸模，并使用高精度3D扫描仪进行扫描，以获得向上凹的岩石表面及其更凹的中部的3D数据，该中部被视为一个初始风化坑。3D模型深入了解了风化坑的初始形成过程，表明：（1）一个风化坑的平均风化速率为10.8±0.49厘米/千年；（2）风化坑通常是由近乎水平的平坦岩石表面上的洼地积水因涉及水的风化作用而形成的；（3）一个风化坑的加深速率大约是周围区域的4倍；（4）一个风化坑的生长可以在平坦岩石表面上一些没有预先存在洼地的小凹陷处开始，并逐渐扩大；（5）由于横向风化速率大于垂直风化速率的扩展，一个风化坑通常宽大于深或底部平坦，而且母岩的层理对于平底风化坑的形成不是必需的。