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Where dune fields begin

12 Feb 2018, 17:54 UTC
Where dune fields begin NASA/JPL/Univ. of Arizona

This is the upwind edge of a dune field (825×625 m, 0.51×0.39 mi). Winds blow down a cliff (offscreen) from the lower right, blowing sand toward the upper left. Elongated dunes have formed parallel to the resultant wind direction, only avalanching into slip faces once enough sand has piled up (there are two slip faces at the upper left). The tan/black mottling shows where tan dust has settled or been removed from the dark sand by recent winds. Large grains are heavier and harder for the wind to move, so they form into ripples (with a 10 m or 33 ft spacing) that trail behind the dunes – ripples like these are common on the upwind edge of dune fields on both Earth and Mars.

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