Sandstone Stands Up Under Pressure


There are a lot of things in nature that are under a lot of pressure, but sandstone is one thing that stands up under tremendous pressure.  Scientists have long wondered how the sandstone arches came to be.  The amazing sandstone arches that are seen in many places around the world have been thought as being result of rain and sand. But this is not the case, according to researchers. Recently it was found that these amazing shapes are due to the sandstone itself.

According to Charles University hydrogeologist, Jiri Bruthans, erosion removes the excess material but does not create the shape.  Leading the research, Jiri discovered that erosion was just one tool which works along with the fundamental factors which are inside the rock.

The factors are the stress fields that the overlying rock’s weight creates.  Under low amounts of stress, according to Bruthans, there is an easy erosion of sandstone. As the stress mounts, such as when sections of a pillar or cliff erode, the remaining rock’s surface sand grains become locked together. This causes them to become much more resistant to erosion.

Bruthans discovered this insight on a trip to the Czech Republic and Stralec Quarry, where rock sand, sandstone that is loosely packed, is mined.

Although there is not any natural cement that binds these grains of sand into a rock form, when it is mined it needs to be blasted at the face of the sandstone so that the sand can be broken loose.  According to Alan Mayo, who is a Brigham Young University hydrogeologist and the study’s co-author, after the rock has been disrupted, it simply disintegrates.

Bruthans also added that following blasting, the quarry’s sandstone stood up under the immense pressure to quickly create arches along with other structures such as the ones seen in Arches National Park in Utah.

To figure out the way that soft material is able to do this, scientists took some samples into a laboratory, cut the samples into little cubes, and then utilized pressure places in order to simulate overlying material weight.  Then they subjected their cubes to forces that would cause erosion, such as simulated rain.

Their finding, as was reported today in the scientific journal Nature Geoscience, was that when they subjected the cubes to this kind of pressure, they eroded quickly into pillars, alcoves, and arches.  These structures were then very resistant to eroding further.  Further experiments using sandstones that were more consolidated had the exact same result.

According to Mayo, as the erosion is undercutting the sandstone in ways which normally would cause a collapse, the pressure is mounting along the rock that is remaining where the most material was removed.  Eventually, there is a critical amount of pressure and the grains of sand become locked and incredibly stable.

Numerical modelling showed that the shapes that resulted followed the stone’s stress fields. This finding is also applied to the natural landforms like the Delicate Arch in Utah, which is a structure that stands on its own and that is a staggering 65.62 feet tall.

Further supporting this theory, says Mayo, was the team’s expedition to a section of the iconic Arches National Park. There were some rock falls recently.  The team examined the blocks which had fallen.  The blocks had disintegrated completely due to the fact that the required critical stress was no longer present.

Other scientists, who include Chris Paola, a University of Minnesota sedimentologist, remark that the work gives science an answer that has been asked for years – how did these amazing landscapes form? According to research hydrologist Gordon Grant, the explanation is elegant, plausible, and simple.

This does not in any way mean all of the sandstone alcoves, arches, and other similar features need to be identical. The fact that the structures have been made because of the sandstone being under a lot of pressure and standing up to it is amazing. It also goes along with Bruthans’ statement that nature is very complex.

By Sharon Hendricks


Scientific American

Huffington Post


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