"Desert Varnish" Top 5 Page for this destination Arches National Park Off The Beaten Path Tip by Trekki
Arches National Park Off The Beaten Path: 32 reviews and 44 photos
During my travels in Southwest US, I often came across these funny vertical stripes on the walls. Looked as if someone had poured down varnish from the walltop.
Later on, I learned that this indeed is called "desert varnish".
I checked the web, and found the following infos:
(for more details please check NPS.gov website, the Canyonlands' one):
Desert varnish only appears where water flows over rocks, and bacteria are present. It is composed of fine-grained clay minerals, which contain black manganese oxide and red iron oxide, or hydroxides.
The third picture shows a path of dried water, which obviously contained much of salt and manganese minerals - the greenish-whitish color shows it.
Now directly from NPS/Canyonlands Website:
Desert varnish consists of clays and other particles cemented to rock surfaces by manganese emplaced and oxidized by bacteria living there. It is produced by the physiological activities of microorganisms which are able to take manganese out of the environment, then oxidize and emplace it onto rock surfaces. These microorganisms live on most rock surfaces and may be able to use both organic and inorganic nutrition sources. These manganese-oxidizing microorganisms thrive in deserts and appear to fill an environmental niche unfit for faster growing organisms which feed only on organic materials.
The sources for desert varnish components come from outside the rock, most likely from atmospheric dust and surface runoff. Streaks of black varnish often occur where water cascades over cliffs. No major varnish characteristics are caused by wind.
Thousands of years are required to form a complete coat of manganese-rich desert varnish so it is rarely found on easily eroded surfaces. A change to more acidic conditions (such as acid rain) can erode rock varnish. In addition, lichens are involved in the chemical erosion of rock varnish.
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