Universal law always works perfectly well.
Wherever there is sand and an atmosphere, prevailing winds may whip the grains into undulating shapes, pleasing to the eye with their calming repetition.
Certain sand waves, with wavelengths between 30 centimeters (almost 12 inches) and several meters (around 30 feet), are known as megaripples: they’re between ordinary beach ripples and full dunes in size, and we’ve seen them not just on Earth, but even on other planets such as Mars, well known for its all-encompassing dust storms.
Aside from their size, a key characteristic of these middle-ground ripples is the grain size involved – a surface of coarse grains over an interior of much finer material. Yet this mix of grains is never the same, and nor are the winds that blow across the sand to create the ripples in the first place.
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