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A-Z listing (archived)plugin-autotooltip__plain plugin-autotooltip_bigA-Z listing (archived)

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Wikenigma - an Encyclopaedia of Unknowns Wikenigma - an Encyclopaedia of the Unknown Science

Yardangs

Yardangs are enigmatic wind-parallel ridges found in arid environments. They often form downwind of rocks in sandy environments. They can be unusually stable structures, given their sandy / dusty composition, and the fact that the wind which forms them can also erode them.

“Yardangs come in a large range of sizes, and are divided into three different categories: mega-yardangs, meso-yardangs, and micro-yardangs. Mega-yardangs can be several kilometers long and hundreds of meters high and are found in arid regions with strong winds; meso-yardangs are generally a few meters high and 10 to 15 meters long and are commonly found carved in semiconsolidated playa sediments and other soft granular materials; and micro-yardangs are only a few centimeters high.”
Source: Wikipedia

Despite their prevalence, the physics behind their semi-permanence is unclear :

“No general theory exists to explain the long-term evolution of yardangs, curtailing modeling of landscape evolution and dynamics of suspended sediment release.”
“[…] major unanswered questions remain. What boundary conditions are responsible for yardangs? Can yardangs erode in perpetuity (or do they have a life span)? And are constant erosion (or sediment release) rates reasonable through yardang evolution?”

See: 'Yardang evolution from maturity to demise' in Geophysical Research Letters, 2015. [with illustrations]

Also see :Sand dune formationplugin-autotooltip__plain plugin-autotooltip_bigSand dune formation

"Large swaths of Earth’s surface are covered in loose sediment. The grains that make up this sediment form fascinating bedforms from meandering riverbeds to wavy dunes, whose shapes are constantly changing as water or air currents move the grains.…


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