Talk:Natural arch

Vanity

The link to Castell de Castells is not for vanity as mentioned by someone who wishes to remain anonymous. — Preceding unsigned comment added by Casayvonne (talk • contribs) 23:07, 27 April 2007

Role of downward pressure in creating sandstone arches and pillars

The following statement is inaccurate? Arches and pillars form even where there is no harder capstone above it and the sandstone is uniform.

″The softer rock stratum erodes away creating rock shelters, or alcoves, on opposite sides of the formation beneath the relatively harder stratum, or caprock, above it. The alcoves erode further into the formation eventually meeting underneath the harder caprock layer, thus creating an arch. The erosional processes exploit weaknesses in the softer rock layers making cracks larger and removing material more quickly than the caprock″

A 2014 study shows that downward stress and gravity has much more to do with creating the arch or pillar shapes: Sandstone arches form under their own stress. Downward pressure and erosion combine to create celebrated rock formations.

In a block of uniform sandstone with a horizontal crack, downward pressure from the mass of sandstone propagates in an arching field which locks the grains together to form an arch, as the grains under less pressure erode away. With a vertical crack, it will form a pillar that, again, locks down under its own weight. Of course the erosion continues on until collapse, but it seems the main phenomenon creating the shape is the stress field, not just a presence of a harder capstone. Even in formations with a harder capstone on the top, it seems it is the weight of the capstone forming the stress field in the softer strata underneath creating the resulting shape (depending on initial shape of cracks).

Technicality nitpicker (talk) 17:45, 30 September 2020 (UTC)[reply]