fech fech

{{Short description|Very fine powder commonly found in deserts}}

Fech fech ({{langx|ar|فش فش}}) is a very fine powder caused by the erosion of clay-limestone terrain and it is most commonly found in deserts.{{Cite book|title=Desert geomorphology|last=U.|first=Cooke, Ronald|date=1993|publisher=UCL Press|others=Warren, Andrew., Goudie, Andrew., Cooke, Ronald U.|isbn=0203020596|location=London|oclc=71368681}} It consists of a surface horizon of pulverized soil with low particle cohesion{{Cite book|title=Encyclopedia of geomorphology|url=https://archive.org/details/encyclopediaofge0001unse|url-access=registration|date=2004|publisher=Routledge|others=Goudie, Andrew.|isbn=1134482760|location=London|pages=[https://archive.org/details/encyclopediaofge0001unse/page/364 364]|oclc=252833849}} protected under a thin crust. Fech fech is derived from ancient lake muds or on certain argillaceous rocks and is one of the desert surfaces that produces dust.{{Citation|chapter=Dust Entrainment, Transport and Deposition|date=2006|pages=13–31|editor-last=Goudie|editor-first=Andrew S.|publisher=Springer|language=en|doi=10.1007/3-540-32355-4_2|isbn=978-3-540-32355-6|editor2-last=Middleton|editor2-first=Nicholas J.|title=Desert Dust in the Global System}} It is not determinable from the surface and can therefore pose a significant transportation hazard acting as a surprise "trap" as the ground collapses beneath a vehicle, miring it in a quicksand-like substance.

Fech-fech is classified into two types:

• Fech-fech that developed during the Holocene, in lake mud or fluvio-lacustrine sediments.
• Fech-fech that developed from shale.

Fech fech is common in the Qattara Depression in Egypt, making that portion of the Sahara Desert impassable by most vehicles.