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In Colombia, many grassy hillsides are terraced, like in the photo below. This terracing also occurs on hillsides that never had these palm trees on them. I assume that it also occurs outside of Colombia. How does this terracing happen?

Just from my first-hand observations, I think the answer is: The terracing was formed by grazing livestock. Grazing livestock is common in these areas, and the barbed wire fence hints that it is occurring here. On flat ground, the livestock wander in random directions. On steep ground, the livestock prefer to follow the hill's contour lines, as that is the easiest path to walk, as opposed to more directly uphill or downhill. When a livestock initiates a contour path on a not-yet-terraced hillside, that path is repeatedly trod by subsequent livestock, as it is a little flatter and easier to walk than other contour paths, eventually leading to significant terracing. The terracing is uneven (not level) because the livestock have to go up or down a bit to graze elsewhere on the hill.

Can anybody confirm my answer, or provide another answer that is objectively correct, preferably with citations? I asked the same question in the form of an SE puzzle, which is currently on hold because "This question may invite speculative answers, as the question is not fully defined. The validity of some answers may be based upon opinion. Good questions for this site [puzzling.stackexchange.com] have a limited number of objectively correct answers." I may be able to save the puzzle with a definitive answer here.

Angela Calle and Daniel Di Palma [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Click for high-resolution photo

Photo credit: Angela Calle and Daniel Di Palma [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)] https://commons.wikimedia.org/wiki/File:Valle_del_cocora_-_wax_palm_02.jpg

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  • $\begingroup$ Look at the Wickipaedia pictures by clicking "ancient chalk figures on English hillsides". Everyone seems afraid to look at them. They won't bite you, honest! The most reliable evidence is the evidence of your own eyes. $\endgroup$ – Michael Walsby Oct 11 at 17:35
  • $\begingroup$ I found the Wikipedia photos by typing "ancient chalk figures on English hillsides" into my Bing search engine. There were about a dozen of them, with high definition.. Other search engines like Chrome or Google should produce a similar result. The key question which nobody seems keen to answer, is why these 'natural earth movements' only occur on hillsides which are grazed by livestock. The very best examples I have seen look almost exactly like contour lines on a map. $\endgroup$ – Michael Walsby Oct 13 at 13:09
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These are terracettes
https://en.wikipedia.org/wiki/Terracette#targetText=In%20geomorphology%2C%20a%20terracette%20is,them%20to%20move%20slowly%20downhill
These are caused by natural earth movements as the slope angle is beyond the natural resting angle of the soil. These slopes are a result of rapid erosion e.g. by rivers and glaciers. Solifluction https://en.wikipedia.org/wiki/Solifluction is a similar process.

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  • $\begingroup$ Have you ever asked yourself why these 'natural earth movements' only occur where there are grazing animals? $\endgroup$ – Michael Walsby Oct 10 at 17:27
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    $\begingroup$ Since there's a disagreement between two answers here, perhaps it would be helpful if one or both of them were to give a peer-reviewed reference or two. $\endgroup$ – Semidiurnal Simon Oct 10 at 17:43
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    $\begingroup$ @MichaelWalsby a picture on Wikipedia is not "better than" a peer reviewed reference. I just did go to the Hill Figures page on Wiki, as you asked, and from a quick skim I couldn't see either terracettes or livestock in any of the pictures. But I admittedly didn't spend very long looking, because I don't see that this would prove anything. Seeing livestock there does not mean that they caused the structures. $\endgroup$ – Semidiurnal Simon Oct 11 at 18:06
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    $\begingroup$ (wiki links are, similarly, not good evidence for the soil creep answer either. Maybe both of these theories are true in some cases. Maybe neither is. I don't think any firm evidence has been linked by anybody here) $\endgroup$ – Semidiurnal Simon Oct 11 at 18:09
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    $\begingroup$ You're probably right that the hills are grazed (although I'm not sure whether grass might naturally stay short on chalk hillsides - it's terrible soil). But that does not prove that the animals created the terracettes. Maybe they do - I don't know. We have two competing explanations here, and no authoritative sources for either of them. We should, therefore, be rather cautious about declaring one of them to be correct. $\endgroup$ – Semidiurnal Simon Oct 13 at 17:27
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When I looked at your photograph it immediately occurred to me what the explanation was, but when I read your text I could see you already knew the answer. I can confirm that you are right. These contour lines appear all over the world where grazing animals are kept and there are hills to negotiate, so there is nothing unusual about them.

If you click 'ancient chalk figures on English hillsides' on Wickipaedia, you will find that almost all the chalk figures have these contour lines around them,and by some amazing coincidence all these hillsides are frequented by grazing animals! One of the best photos showing what I mean is the Long Man Of Wilmington, which not only shows clear contour lines, but shows the sheep as well.

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    $\begingroup$ According to the Wikipedia article linked by MiguelH, this is an old belief that is now thought to be incorrect. (Not my field, I have no knowledge of my own to bring to bear here) $\endgroup$ – Semidiurnal Simon Oct 10 at 17:01
  • $\begingroup$ I read somewhere that, like crop circles, they are made by aliens. I don't believe it, but if you'd rather believe that, I can't stop you. $\endgroup$ – Michael Walsby Oct 10 at 17:16
  • $\begingroup$ I am not suggesting that they are made by aliens. What does that have to do with anything? $\endgroup$ – Semidiurnal Simon Oct 10 at 17:23
  • $\begingroup$ These markings have the same association with grazing animals that crop circles have with mischievous nocturnal humans. No grazing animals - no 'natural earth movements', no mischievous humans - no crop circles. $\endgroup$ – Michael Walsby Oct 10 at 17:38
  • $\begingroup$ shrug I don't claim expertise in this area. I won't argue. But please only answer things that you actually know about. (maybe this is one of those things) $\endgroup$ – Semidiurnal Simon Oct 10 at 17:43

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