Suffice it to say this is a bit specific for google. Erosion likely still builds up huge sandfields but I wonder if, given the force of the wind, they'd be moved from being spread out as an actual erg or if they would build up in a corner, such as into a valley (as an unrelated example).

  • $\begingroup$ you do realize sand migrates across dunes constantly, eventually it ends up in the ocean. the only reason those done fields exist is because new sand is constantly being generated. $\endgroup$
    – John
    Dec 20, 2023 at 21:46
  • 1
    $\begingroup$ If winds blew 500 mph regularly for millions of years, what corner would exist for the ergs to be blown into? You would have solid structures below the surface of the constantly shifting sands just as you do below the surface of a water ocean, but you might not have any structures above "sand level." $\endgroup$
    – JBH
    Dec 21, 2023 at 1:07
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    $\begingroup$ Is it a generic water less world with atmosphere? Or are there oceans? Plate tectonics? $\endgroup$ Dec 21, 2023 at 1:50
  • $\begingroup$ the process you are looking for is called saltation and the suitable site should be earth science.se 😉 $\endgroup$
    – user6760
    Dec 21, 2023 at 3:24
  • $\begingroup$ @user6760 Do you know about magic links? They're convenient ways of quickly linking useful pages in comments. For example, [earthscience.se] gets you Earth Science. $\endgroup$
    – JBH
    Dec 21, 2023 at 4:07

1 Answer 1


Yes, and it would be the one place where the wind is calm.

Even from a theoretical standpoint, it’s impossible to have wind blowing on every point on a spherical surface. This comes from the impossibility of mapping differentiable tangent vector spaces to the sphere, but that’s an issue for math.se. Point is, there is always (always always, not just sometimes always) a point on a planet’s surface where the wind is calm. That point can move, change, disappear and reappear, or be multiple places simultaneously, but there must always be a point where the wind is still.

So, there’s always one spot where the wind is calm. That’s the spot where sand drops from the wind and doesn’t move again, and logically where your ergs will eventually be piled up. That one spot will be your “corner”.

Of course, as the spot where wind is calm changes, the ergs will move with it. Sand might circulate all over the planet before it eventually ends up back at the corner, but it will end up there eventually.

  • $\begingroup$ There is always at least one point where the wind is calm. There is nothing which says that there is only one such point, and there is nothing which says that the set of points where the wind is calm has to be the same now at is was one second ago or as it will be one second from now. $\endgroup$
    – AlexP
    Jan 12 at 17:50
  • $\begingroup$ This is true, but given the 500 mph winds imply a huge amount of energy going into the planet to keep them from stopping due to friction with the ground, I find it very hard to believe that there would be any more than one point at a time, or that the winds (already moving very fast) could simply shift directions to move that one point around quickly. $\endgroup$ Jan 12 at 17:53

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