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Why do stones in a garden rise to the surface?

I haven't done my own research on the subject, but experienced gardeners seem to suggest that, even if the garden is cleaned from stones, they reappear after some time. Brief internet search confirms this assertion (e.g., this link pops up among the first), however the explanations seem to differ, including:

  • the ice formation under stones, which pushes them upward (then presumably the phenomenon is less pronounced in warm climates)
  • soil particles flow, where light particles more easily find path downwards when shaken up or washed by waterflow (but this should be then accompanied with noticeable lowering of the soil surface level)
  • effects of plants and animals (should then depend on the concentration of these latter - but apparently taken quite seriously)

Perhaps experts in soft matter, sands, or physical chemistry could provide a solid answer? (Preferably with references.)

Related: How can I prevent stones from rising to the soil surface each year?

Remark
As the comments have pointed out, the second bullet above refers to granular convection/Brazil nut effect/muesli effect

Roger V.
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    Related: https://physics.stackexchange.com/q/646153/2451 – Qmechanic Mar 12 '24 at 11:11
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    I would guess this is granular convection, though soil is probably more complex that simple granular materials. – John Rennie Mar 12 '24 at 11:28
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    I am curious if this phenomenon happens where large lawns are kept for playing fields, in the regions it appears. I have not noticed it in our fields (Greece) – anna v Mar 12 '24 at 11:54
  • @annav seems to be common knowledge in Normandy, even applied to small gardens. The winters are not terribly cold here, so I don't believe in the ice hypothesis. But it rains a lot. – Roger V. Mar 12 '24 at 12:05

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If the soil is made less compact by any mechanism, the smaller grains can fall down easier than the coarse ones. It is like a region of a street with slow traffic, where the motorcycles passes through the spaces between cars.

The soil can be made less compact due to the movement of plant roots, worms or dilation due to water freezing for example.

Claudio Saspinski
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  • Granular convection has been already mentioned in the Q, and named correctly in the comments. I think the last paragraph does add a somewhat different perspective, but it really should have been a comment, unless you plan to expand it with a deeper discussion and references. – Roger V. Mar 13 '24 at 07:09