THEY may look like low dunes, but the cresting ridges pictured above are the world's largest "megaripples", a phenomenon that had been thought impossible on our planet.
Wind-formed ripples are not the same as dunes because they are shaped by the airflow less than 2 metres above the ground. The key factor for dunes is air fluctuations as high as 4 kilometres up.
Most such ripples are no bigger than those created by waves on a beach. Given high winds, light grains and geologic timescales, however, they can grow. Juan Pablo Milana of the National University of San Juan, Argentina, has found monster ripples of lightweight pumice on the country's Puna plateau, where winds may exceed 400 kilometres per hour. The ripples are up to 2.3 metres high and 43 metres between crests - triple the height and double the wavelength of the largest previously known on Earth (Geology, ...
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