Why do I keep finding more new rocks in my garden year after year?

[sepcurio]

I can completely clear out all large rocks from my garden so it's just soil and pebbles down to about a foot. Then come next spring I find new large rocks again. Happens each year. This is a common problem for farmers and gardeners.

Causes I've considered include:
-- Ice heaves that push up rocks to the surface: But frost only goes down to the frost level in the ground (~4-8 ft) so it would have cleared out all the rocks to that depth long ago.
-- Buoyancy; the rocks "float" to the top of the soil: But the rocks are very dense. Sometimes more dense than the particles of soil.
-- Particle sorting: I'm not sure what this is called - when smaller particles fall to the bottom and larger particles move to the top of a container of mixed-sized, equally dense particles. This is my best guess so far, but wouldn't the Earth just be covered only with large rocks and no sand and dirt if this was a dominant geologic process?

 

[mitochan]

Hello. I have got another cause to add on the list.
--Rain water streams flow sand and small pebbles grain out of the garden every year. Large pebbles and rocks in soil remain and appear on the ground surface.

 

[DrClaude]

Particle sorting

That's the "Brazil nut effect," or granular convection. See in particular
https://en.wikipedia.org/wiki/Granular_convection#Geology

 

[sepcurio]

That's it! Granular convection. When I read the article, apparently granular convection is a process that happens over geologic time periods as well as in the short term assisted by frost cycles.

The answer to my sub-question: The Earth isn't covered only by large rocks because erosion and deposition continually deposit smaller sediment over the rocks. (An interesting side note from the article: rubble pile asteroids that are effected by granular convection can be covered only by large rocks -- large rocks on the outside and small ones on the inside -- because there is no significant erosion on them.)

 

[Nik_2213]

Earthworms ??

 

[DEvens]

Is it possible that rocks come in male and female?

https://en.wikipedia.org/wiki/Or_All_the_Seas_with_Oysters
Or, being much older, maybe they predate the invention of sex.

Also, have you correlated the number of rocks in your garden with the number in your neighbor's garden?

 

[Nik_2213]

"...have you correlated the number of rocks in your garden with the number in your neighbor's garden?"
ROFL !
My father's grumpy neighbour kept complaining that my father was throwing 'used' plant markers over the wall. That they were some-how arriving in a neat heap in the middle of wide lawn didn't strike him as odd...

Then, one day, he glanced out at a movement on the lawn, found one of our young Siamese cats placing a freshly plucked plant-marker in the usual place...

That was Bluepoint 'Oliver', call-sign 'Mawrrr', who grew up to steal pencils, biros & screwdrivers and, once, leopard-drag my good cable-strippers...

 

[Baluncore]

-- Particle sorting: I'm not sure what this is called - when smaller particles fall to the bottom and larger particles move to the top of a container of mixed-sized, equally dense particles. This is my best guess so far, but wouldn't the Earth just be covered only with large rocks and no sand and dirt if this was a dominant geologic process?

It is not a dominant process, except in a very few places. In some dry places the wind blows soil from around rocks making dust storms. The dust settles elsewhere.

In wetter regions rocks provide shelter for weeds like thistles to grow. Following in the shelter of weeds come small shrubs and trees that lock soil movement with their roots. So the rising rock problem occurs in ploughed or fallow ground where the temperature swings are accentuated by the lack of vegetation, or in periglacial regions.

I have been on top of a plateau where glaciation cut into the walls but did not sweep the flat top bare, as happened with ice sheets in the northern hemisphere. There the surface was covered in rocks that made crossing in a strong wind hazardous, because the rocks were all the size of cars and houses. There was no soil or smaller rock visible in the deep crevices.

 

[sepcurio]

Developing a mathematical model for the process has been non-trivial. Current geometric functional analyses don't use traditional Euclidean space, but instead use filbert space.

 

[Baluncore]

I think that should read "Hilbert Space".

 

[Anachronist]

I can completely clear out all large rocks from my garden so it's just soil and pebbles down to about a foot. Then come next spring I find new large rocks again. Happens each year. This is a common problem for farmers and gardeners.

If you ever visit Croatia, particularly the island of Brač, you'll be struck by the sheer amount of stone the locals have to deal with. To get any sort of useful land, you pick up a rock and move it to the border of your property. Then repeat until your land has enough dirt with few enough rocks to grow something on it.

Over the years, huge stone walls get built up around all the properties. The stones generally have a cubic structure so they need no mortar, they just stack up. See this image for example.

If you did this in your yard, how long would it take to build a wall?

 

[jim mcnamara]

Is your garden physically close to a neighbors yard/garden? If the new rocks are mostly on the surface then the source may be outside your property.

 

[256bits]

Then come next spring I find new large rocks again

Maybe you are destined to grow a rock garden.

 

[HankDorsett]

you never heard of the rock fairies?

 

[sepcurio]

I think that should read "Hilbert Space".

Too dry? Maybe I should have tacked a smiley on the end of it.

Hint: What's a filbert?

 

[jim mcnamara]

filbert=hazelnut, which fits the kind of odd but interesting topic of this thread.

Did you carefully dismiss obvious rock sources before we delved into modeling?
To paraphrase Carl Sagan
'Exceptional explanations require exceptional proof'

In other words how did you exclude simpler explanations? Ex: Do your neighbors with gardens have the same experience? They should, otherwise you are "barking up the wrong tree".

You have, IMO, yet to demonstrate this current deep dive into Physics is at all necessary. I don't buy it.

 

[Baluncore]

Hint: What's a filbert?

I'm sorry but I missed it as it is not a term used in Australia. Here the seasons are inverted, so Hazel nut gathering is not connected with St Philibert's day.

 

[Steelwolf]

Then there was the hiker came across an old man plowing his farm way up in the hills, a high valley, and he had to stop and move rocks out of his way every so often. The hiker watches this for a while and then finally, his curiosity bursting, asks the old man why he does not just move the stones from his field, build a fence with them or something. The old man mutters something about it not mattering because the Glacier having brought them. The hiker is incredulous, and says yes, but the Glacier is all gone now. "Yes" said the farmer, "But that is only because it went back for another load of rocks!"

 

[sepcurio]

I'm sorry but I missed it as it is not a term used in Australia. Here the seasons are inverted, so Hazel nut gathering is not connected with St Philibert's day.

Oh. I guess comedians need to know their audience. My provincialism is more magnified on the internet...

I wasn't aware of that etymology. Thanks for that tidbit.

 

[Baluncore]

Developing a mathematical model for the process has been non-trivial. Current geometric functional analyses don't use traditional Euclidean space, but instead use filbert space.

For those who missed the relevance of Hilbert space.
https://en.wikipedia.org/wiki/Packing_problems#Spheres_into_a_Euclidean_ball

The problem of finding the smallest ball such that k disjoint open unit balls may be packed inside it has a simple and complete answer in n-dimensional Euclidean space if k ≤ n+1, and in an infinite dimensional Hilbert space with no restrictions.

 

[Nik_2213]

"To get any sort of useful land, you pick up a rock and move it to the border of your property."

Could that be the origin of the Medieval 'strip fields', being a reasonable width for each 'yet-another' fist-sized lump to be hurled to border and, later, collected or stacked ??

IIRC, that trad '22 yds = 1 chain' measurement shows up in 'strip fields', cricket and 'American Football'...

 

[Baluncore]

Could that be the origin of the Medieval 'strip fields', being a reasonable width for each 'yet-another' fist-sized lump to be hurled to border and, later, collected or stacked ??

I think you are conflating too many concepts. The world is not that simple.

If the ground was rocky, you would not be farming there. On a rocky island, the size of the vegetable gardens in a fishing village will be decided by how far you can efficiently move a rock. The wall will form a windbreak. Windbreaks cannot be far apart or they do not break the wind. The thickness of the walls will be determined by the amount of rock that must be removed to expose the soil.

If 22 yards was the distance a rock could be thrown, or a ball bowled, then the width of a strip would be 44 yards. Throwing rocks onto a neighbour's strip would be actively discouraged by social pressure, and the Manor court. Any available rocks would be used to strengthen the outer wall.

Open-field strip farming involved a commonly used open-field, subdivided for use by different families. The field boundary was fenced or walled to keep out pigs or grazing animals, by the serfs, for the Manor. Inside the field, the individual strips were marked by fixed corner stones. The movement of a corner marker was an offence. Interference with a survey marker is still an offence today.

Strip farming predates Gunter's 22 yard chain.
Before Gunter's chain was standardised in 1620, open-field strip farming had been used for 1000 years. Gunter's chain facilitated accurate surveying, and so the buying and selling of land. That lead to the end of open-field strip farming, an end to serfdom, and the rise of the industrial revolution.

One reason Gunter's 22 yard chain with 100 links became the standard was because it used the very recently developed decimal number system that could be conveniently used by land surveyors.

There have been many different chains in use.
https://en.wikipedia.org/wiki/Chain_(unit)#Measuring_instruments

 

[chemisttree]

Oh. I guess comedians need to know their audience.

...and I was going to say the rocks keep showing up because it’s a rock garden. Probably only funny in my neighborhood.

 

[Keith_McClary]

The guy who built my fence ("Zorro Fencing") made the post holes taper wider towards the bottom before pouring the concrete. He said if they were tapered the other way, Mother Nature would just spit them out.

 

[WWGD]

Or maybe you can make some money by setting up a confusingly-named "Rock Festival" in your land. Hard Rock(s), Soft Rock(s), all types in your festival.

 

[cobalt124]

It's the neighbours!

 

[jim mcnamara]

The OP lives on top of a huge deposit of glacial alluvium. LOTS of rocks > 2cm. Soil maps, free from the County Agent, will tell you exactly what is going on. @jrmichler probably can give you more information.

And sometimes lazy neighbors can make things worse...

 

[bhusebye]

Rocks float around like shuffleboard pieces on flat ground during frost but it is a mixture of all the ways a rock can surface. It's Rock and Roll. Your tractor creates furrows so you can plant, you find rocks, you pick rocks out and next year you find more rocks in the same place. As you compact the earth, driving over it and creating more furrows the next year you find more rocks because you are inches deeper into the ground then last year. Plant a stake in the field and do a measurement using lasers. Do the same measurement years later, it should be lower.