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Larger sand grains rise to the surface in soil (smaller substance)?

 
 
Reply Wed 8 May, 2019 04:14 pm
When I was working in my garden last summer I noticed a phenomenon that surprised me. I picked away larger sand grains from the soil (grains big enough to pick away by hand) but every day new sand grains had risen to the surface in the soil My question is what causes this phenomenon - what is it called? I would like to know the word, so I can research it further...
Is it a chemical reaction, physical phenomenon, that causes this seemingly illogical phenomenon to happen? (My first guess would have been that bigger particles, like the bigger sand grains, would sink down because they are heavier, but the opposite happens - the smaller bits "push" the bigger bits up).
I hope you take this question as a honest question, and allow me to maybe have expressed the question wrong.
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Type: Question • Score: 3 • Views: 551 • Replies: 13
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izzythepush
 
  1  
Reply Thu 9 May, 2019 12:35 am
You can do this with a jam jar full of different balls/grains whatever. You can even do it with a bowl of muesli. Tap it on the table and the small grains drop to the bottom while the big ones go to the top.

It's because the small grains can fit in the tiny spaces below the larger ones.
Marblerevealer
 
  1  
Reply Thu 9 May, 2019 02:28 am
@izzythepush,
I understand that, and thank you for answering. I can reveal that the underlying question I have is if this phenomenon, principle, possibly also applies to deeper crust and mantle of Earth. Usually one assumes and reads that "heavier matter sinks down", but here we have a physical phenomenon where the heavier/bigger particles stays on top while lighter/smaller particles sinks down.
The answer you gave is a geometric explanation (=in perfect spherical spaces, in a collection of 1-radius spheres - let´s say in a bowl with 1-radius spheres - then a sphere that has the radius of 0,1547... exactly 1/(3+squareroot(12))... can move freely/can´t be blocked by the bigger spheres) and I am wondering if the same effect happens deeper in the Earth?
I realize a lot of other effects come into play in the depth of Earth, chemistry, surface tension, temperature, phase shifts - when atoms e g become gaseous before other atoms etc, but this geometric relation also possibly plays a role - or does it?
As you see the question becomes complicated and I asked the original question to see if I quickly could find keys to where to look.
Marblerevealer
 
  1  
Reply Thu 9 May, 2019 02:44 am
@Marblerevealer,
And I should mention that it seemed like a neverending task to pick sand-grains from my garden - every new day new sand-grains had been "pushed up" to the surface. So it is clearly an ongoing process - at least on the top few meters of our surface, the sand grains I picked up after three months obviously had started much deeper in the soil.
And I started to wonder how deep this phenomenon goes - if it possibly applies even to deep crust and mantle of Earth?
izzythepush
 
  1  
Reply Thu 9 May, 2019 02:51 am
@Marblerevealer,
At some point there will be hard rock.
izzythepush
 
  1  
Reply Thu 9 May, 2019 02:57 am
@Marblerevealer,
Marblerevealer wrote:

And I should mention that it seemed like a neverending task to pick sand-grains from my garden


That's gardening for you. How old is the property? At some point it should settle down.
Marblerevealer
 
  1  
Reply Thu 9 May, 2019 03:10 am
@izzythepush,
Yes... but I was wondering if the principle still would apply. And besides... if one applies "geologic time" - millions of years, to hard rock then the rock could be seen, visualized, as molten - even the most solid rock moves around in geologic time.
And in the case of slow moving rock the principle possibly could still be valid - with rock layers of different composition acting as a "block" relative to another layer made of different matter.
I am not declaring facts here, since I am still in search of the answer to the underlying question. I am sure there´s a field of study about these things and I am trying to find it. But I have not been able to find the right key words where to look.


izzythepush
 
  1  
Reply Thu 9 May, 2019 03:14 am
@Marblerevealer,
I'm not the person to ask. Farmerman is our resident geologist maybe he can help.
0 Replies
 
Marblerevealer
 
  1  
Reply Thu 9 May, 2019 03:18 am
@izzythepush,
Last year was my first on this lot - an allotment garden, and it was in one particular spot where there was more sand than elsewhere, and things also had difficulty to grow right there. I have dug up and added a lot more organic material now, so I hope the problem of this spot has been solved. But I expect to spend time picking sand for years to come... I guess it qualifies as a hobby...
izzythepush
 
  1  
Reply Thu 9 May, 2019 04:04 am
@Marblerevealer,
Sounds like you might have a bit of builder's rubble from way back.
0 Replies
 
rosborne979
 
  1  
Reply Thu 9 May, 2019 07:16 am
@Marblerevealer,
The phenomenon by which large grains move up and small ones move down during shaking (or agitation) is called granular size separation. This is a general process in physics and as such, applies in many areas, not just soil or sand.

It is primarily a physical phenomena, not chemical.

See the following article for more info: https://www.scientificamerican.com/article/why-does-shaking-a-can-of
Marblerevealer
 
  1  
Reply Thu 9 May, 2019 08:47 am
@rosborne979,
Thank you very much. Looks like exactly the thing I was looking for. Will start reading now.
0 Replies
 
mark noble
 
  -1  
Reply Fri 10 May, 2019 07:39 am
@Marblerevealer,
Heavier Non-solubles are less magnetically-orientated than lighter ones.
Tauroidal QED

Go find
mark noble
 
  0  
Reply Fri 10 May, 2019 07:41 am
@mark noble,
Please excuse last post's 'go find' directive.

You ain't 'there' yet.
mea culpa .... or Not...Smile
0 Replies
 
 

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