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Wikenigma - an Encyclopedia of Unknowns Wikenigma - an Encyclopedia of the Unknown

Beach cusp formation

Beach Cusps are the very well-known shoreline formations which take the form of a repeating, curved 'sawtooth' pattern. They can be composed of various grades of sediment, i.e. sand, pebbles, mud etc..

They can form a large-scale arrays, sometimes stretching for kilometres along a beach. The cusps vary in spacing and size - with regular spacings of a few metres up to 60 or so.

They tend to be quasi-permanent - sometimes growing or retracting - but largely self sustaining. Although storm surges can remove the entire pattern, they usually re-emerge fairly quickly.

Possible ways in which they form and maintain themselves have been debated for many years.

There are two main theories :

• The standing edge wave theory : The idea that the patterns are formed by groups of circular 'edge waves' along the shoreline interacting with incoming waves from the ocean (see Wikipedia).

and the :

• Self-organization theory : The idea that feedback processes between currents and sediment can result in patterns which 'self-organize' (see Journal of Geophysical Research: Oceans, Volume 105, Issue C9, pp. 21,991-22,002)

The self-organization theory is currently the most accepted explanation.

Further reading and technical details :Geosciences 2021, 11(4), 148;

Also see : Yardangsplugin-autotooltip__plain plugin-autotooltip_bigYardangs

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).
and 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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