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. (HiRISE ESP_053594_2610 NASA/JPL/Univ. of Arizona)

Comments (2)

  1. Thank you for using ‘toward’. The urge to pluralize a word is a strong one. For me, this process is somniferous- which must be why I prefer to work on the cratering process and geomorphology.

    1. Honestly I think I use both words interchangeably. I’m more likely to write “toward” and more likely to say “towards”. English is a strange language.

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