I'm interested about this rock formation in Arabian desert. The rock looks like melting chocolate.

enter image description here

enter image description here Not sure where the exact Location, the source says it around Al-Ula, Saudi Arabia. Here the image source: https://www.instagram.com/p/CKAGbRcoa1r / https://www.instagram.com/p/CKAZR1yohtM

What this formation called? what is the cause and how was this rock formed?

I made a little research on google, some says this was fomed by water and/or wind. I know, there was water and rarely snowfall in Arabian desert (obviously wind too). My presumptuous opinion, it doesn't look like was formed by fast flowing water like river or flood or wind. Sorry for that, i'm not geologist.

If the rock was eroded by water, how was it? By flood, river Or by glacial snow?

I need more scientific detail from the people in geology field. Can somebody please explain to me and provide me some scientific literature about this rock formation. Thank you..


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    $\begingroup$ A specific location for the formation in Arabia & a common name would be helpful $\endgroup$ – Fred Feb 17 at 20:34
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    $\begingroup$ I've seen quite similar rock formations at Isalo (Madagascar); they are sandstones eroded by wind. $\endgroup$ – Jean-Marie Prival Feb 18 at 9:46

There are two water-related erosional process at work here:

  1. The exhumation of main sandstone blocks caused by heavy rainfall, incising channels and carrying away the loose debris for deposition elsewhere as "sand".

  2. Formation of weather resistant surfaces caused by dissolution and re-precipation of iron-rich minerals.

You often see this process at work in any desert environment bearing iron-rich sandstones. The morphology, however, will differ based on the internal structure of the rock. Where high winds can carry sand, these iron-rich surfaces can become highly polished into a varnish-like surface.


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