Sandstone Arches Were Not Sculpted by the Wind [VIDEO]
Graceful and awe-inspiring sandstone arches seen all over the globe have long been thought to be the products of wind and rain erosion. However, researchers are now suggesting that these factors are simply a means to an end, with gravity and the stone itself being the true sculptors.
According to a study recently published in the journal Nature Geoscience, "weight-induced stress lines" formed by packed sand and gravitational forces actually slow erosion along certain patterns, forming the backbone of the arch-like shapes we see today.
"Erosion gets [excess] material out, but doesn't make the shape," lead author Jiri Bruthans told Nature.
"The stress field is the master sculptor - it tells the weather where to pick," he added when speaking with BBC News.
While having long been theoretically suspected, this is the first study that conclusively puts the concept into practice.
Exposing 10-centimeter blocks of loose-sand sandstone from a Czech quarry to water, the researchers first exposed the blocks to accelerated erosion without any additional forces. The result was predictable, with the water forces crumbling the loosely set grain of the stone until the structure was no more.
However, when the researchers applied additional weight to the top of the blocks, sand particles locked up along certain stress lines, stiffening arc-like structures. When accelerated water erosion was again used on the block, the last part to go was a graceful sandstone arch - a structure that took significantly longer to erode.
According to the study, this naturally occurs in nature when wind and water erosion rates are more intense along the bottom of a heavy sandstone structure. With the base whittling down faster than the rest of a structure, it becomes increasingly top heavy, creating an equivalent of the additional weight seen in the experiments.
Writing in an accompanying editorial, Chris Paola of the University of Minnesota said this new research finally reveals the full details of how these awe-inspiring arches form.
"These natural sculptures have delighted countless visitors, some of whom must have paused to wonder where they come from," Paola wrote. "Here is an answer."
The study was published in Nature Geoscience on July 20.
[Vid Credit: Nature/Marek Janac]