Unique sandstone landforms, such as arches and pillars, are shaped by a feedback between erosion and the load carried by the sandstone under gravity, according to a study published online this week in Nature Geoscience.
Jiri Bruthans and colleagues conducted experiments and numerical models of the erosion of load-bearing cubes of sandstone. They observed that as the sides of the sandstone cubes eroded away, the weight of the stone above was carried by fewer and fewer sand grains, increasing the vertical stress on the grains. Once a critical level of stress was reached, the weight-bearing grains became tightly locked together and were more resistant to erosion. In contrast, the parts of the sandstone bearing less weight were left susceptible to further erosion. Their model showed that the interlocking of sand grains in areas of high stress leads to the emergence of a stable pillar-like landform. The researchers further demonstrate that weaknesses in the structure of the sandstone, such as fractures, modify the stress field and lead to the diversity of stable shapes observed in nature, such as at Arches National Park in the USA and Churi Tepui in Venezuela.
In an accompanying News and Views article, Chris Paola writes that “these natural sculptures have delighted countless visitors, some of whom must have paused to wonder where they come from. Here is an answer.”