The physics of items sinking in the ground

[Rich jaws]

Have been doing a lot of detecting the past couple of months and have found a lot of clad and some silver and gold jewelry. Have found two large cent pieces and a number of wheats but no pre 1964 silver coins. Of course it depends on the type of soil, conditions, rainfall, temperature, etc. but does anyone else wonder what the sink rate of items would be in the soils they normally search. Just trying to understand the physics a little. It is a fascinating hobby metal detecting.

 

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[Rich jaws]

Thanks for the research and information. Very interesting. I just had time for a quick read right now but I am not sure it provides any definitive statement regarding the question of coins sinking. Perhaps some answers can be extrapolated from the text. The Mindlab article was interesting also.

 

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[Nugs Bunny]

Thanks for the research and information. Very interesting. I just had time for a quick read right now but I am not sure it provides any definitive statement regarding the question of coins sinking. Perhaps some answers can be extrapolated from the text. The Mindlab article was interesting also.

You're welcome! There is a lot more information at the links I provided, I tried to keep my previous post to the basics.

The answer is the coin really does not move much at all, the entire layer it's resting in does.

Soil formation occurs downward, this explains how blades of grass can be between two buried coins while a sidewalk or tree stump has remained at the surface. Basically as new parent material accumulates at the surface older decomposing layers sink.

 

[HenryWaltonJonesJr]

I have heard that the average is that items get earth on top of them and/or sink at 1in per decade. That seems to be correct in my area. Since my AT Pro only finds coins at about 4 to 4 1/2 in max this is why I never find silver!


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[Jason in Enid]

Now.... here is another kick in the teeth for all of us turf hunters....

I used to believe in the theory that "almost everything is in the top 6 inches" which is thrown around a lot. I believed it until I had the chance to hunt a local construction site. Now, before construction began I hunted this site (1890 use and onward). I dug the typical mix of clad and some deep older coins with a few shallow old. Fits the theory, right? Then the scraper came in to begin work for a parking lot. They took off 6 inches in one area and I began cleaning up! wheaties, indians, barbers, seated, v-nickels, buffalos were everywhere. They were from the new surface down to another 6+ inches deep. Then they continued the work and took is down over a foot in one part. I WAS STILL DIGGING TARGETS. I estimate the original depth of these coins was about 18 inches from the original surface. I never would have imagined coins from no later than 1890 could be so deep. Now I know what you are thinking, but there has been zero construction or dirt work other than a sidewalk in this ground. I have pics of the land back to the beginning, it has always been flat, open, public land. This land is nowhere near any waterway or anything else that would "liquefy" the soil or deposit huge amounts over time. This is was simply the depths the coins migrated down into the soil in 120 years.

So next time you think you are cleaning out a site, remember there is probably 90% more that you just can't reach.

 

[TerryC]

A very "deep" (get it?) subject. Since I saw no PROS in the thread that can confirm or deny coin sinking, we all must back off and try to formulate a project that works for our "theories". I believe they sink AND rise! I believe it is the rain and moisture that dominates the movement. Ice and frost make them rise. (check out farmer's that take out rocks from the field every spring due to ice and frost) and then rain will make them sink.Not much, but they do sink. Overburden also is involved but only by a small amount. My 2 cents (clad) TTC

 

[DDancer]

Hehh, Lot of fun ideas. Thing is there is a lot of positive and negative ideas to the physics behind coin depth. I does depend on area and soil conditions as they relate to moisture, temperatures and the local flora/fauna. Just to put it simply~ you find it where you find it. Ones area dictates where one may reasonably find a target. Use your observations and make reasonable predictions for what ya expect to find... and don't be surprised when a road scrape shows you the oldies are much deeper than expected... or that the desert winds reveal things you never expected..
Fun thread

 

[RustyGold]

Great posts! Whatever method the coins use to migrate deeper into the soil, I'm just happy they're there or I wouldn't have a hobby!

 

[NWMP]

the ground builds up over them.

I see it out here on the prairies. You see/taste dirt clouds blowing in off of farm fields being worked. Then there is the build up of cuttings/flora die off.

 

[infotraker]

Last summer I was detecting a hydralic mining area. I found a 2005 penny 4 inches down in hard dirt. I have heard that some detector it's put a coin in the hole were they found something else.

 

[ConceptualizedNetherlandr]

There are small tree stumps in my yard from trees I cut down at least 20 years ago. I cut them about 3 inches from ground level, but guess what? They're still sticking up 3 inches from the ground and I still hit them every year with my lawnmower! I don't use a bagger on my mower and most years I don't even rake my leaves! Why aren't all those grass clippings and endless oak leaves covering up those pesky stumps by now?

Sorry, but your theory is just as flawed as all the other theories posted here.

Wood floats.

 

[ConceptualizedNetherlandr]

A very "deep" (get it?) subject. Since I saw no PROS in the thread that can confirm or deny coin sinking, we all must back off and try to formulate a project that works for our "theories". I believe they sink AND rise! I believe it is the rain and moisture that dominates the movement. Ice and frost make them rise. (check out farmer's that take out rocks from the field every spring due to ice and frost) and then rain will make them sink.Not much, but they do sink. Overburden also is involved but only by a small amount. My 2 cents (clad) TTC

Plated, not clad?

 

[Nugs Bunny]

Coins "migrate" to different depths, at different rates according to the soil composition, soil density, amount of rainfall and overall mass of the coin.

Soil forms in layers, rain moves particles from the surface layers to the lower layers, rain also leeches salts and clays to the lower layers. This process causes things to move downward, a rock laying on the surface will move down through each layer of soil until it reaches the point where it's density matches that of the surrounding soil.

Soil formation starts on the surface, the rest happens underground.

The theory that soil builds on top of the coins is correct, the theory that they sink is also correct. As each successive layer of soil builds on top of the coin the layers below it are moving downward. Take a stack of paper place a coin on top, now remove the bottom sheet and place it on the top of the stack, continue this process and eventually the coin will be at the bottom, soil moves the same way.

There is more info on the process here Plant and Soil Sciences eLibrary

Four Soil Forming Processes

•Additions: Materials added to the soil, such as decomposing vegetation and organisms (organic matter--OM), or new mineral materials deposited by wind or water.
•Losses: Through the movement of wind or water, or uptake by plants, soil particles (sand, silt, clay, and OM) or chemical compounds can be eroded, leached, or harvested from the soil, altering the chemical and physical makeup of the soil.
•Transformations: The chemical weathering of sand and formation of clay minerals, transformation of coarse OM into decay resistant organic compounds (humus).
•Translocations: Movement of soil constituents (organic or mineral) within the profile and/or between horizons. Over time, this process is one of the more visibly noticeable as alterations in color, texture, and structure become apparent.

Soil Profiles and Horizons

Through the interactions of these four soil processes, the soil constituents are reorganized into visibly, chemically, and/or physically distinct layers, referred to as horizons. There are five soil horizons: O, A, E, B, and C. (R is used to denote bedrock.)

There is no set order for these horizons within a soil. Some soil profiles have an A-C combination, some have an O-E-B, an O-A-B, or just an O. Some profiles may have all the horizons, O-A-E-B-C-R. And some profiles may have multiple varieties of one horizon, such as an A-B-E-B.

 

[outdoorfunblonde]

Sorry guys, in general coins do NOT sink in the ground. The ground builds up over them. I have been hunting in lower NY state for forty five years, and on sites that have never been landscaped I and friends have found many colonial coins at 4-6"" deep. If you find coins at 10" deep it means the soil has been added to by landscaping, or in some areas by river flooding or dirt sliding down hill. I have found a lot of coins on school yards that were probably buried by kids, being 8" deep while all other coins and jewelry found in the same area have been 4-6" deep. Many parks, school fields, and a huge amount of homes have had landscaping work done over the last 60 years, usually adding soil to reduce water ponding, or to fill in natural low spots for a more "perfect" lawn. Soil builds up by decaying grass cuttings, and wind born dust and dirt and water born dirt. Not to mention the deposits of bird and animal doo. Most experienced detector folks I know also believe the coins don't sink, the ground builds up over them. I have done a lot of hunting in the sandy soil of the Cape Cod area and also have found most colonial coins at less than 7" in undisturbed sites even in the very sandy soil there. Look at all the ancient sites in the world, cities found under 15' of overburden. These places didn't sink, over thousands of years the blowing sands and dirt of dust storms has buried them.

This is true...my yard alone, I have seen the changes in levels of dirt/ rock change dramatically just in the 12 yrs I've lived here. Lots of flooding, fast water running down hill. Also, lots of tree leaves etc. I live on the side of a hill. Probably wouldn't have noticed the changes except I'm the one who did/ does my landscaping. And yes, most everything beeps at 6-8" deep. Kinda sucks, cuz I dig that deep to find modern coins in my yard. Many hills here too, so It's not just my yard either.
I also think coins CAN sink, but mostly covered.

 

[hikerdude]

Most of the silver coins I find are around 4 to 5 inches deep. I have found some 3 inches, and one quarter 8 inches deep. If I had to guess, I'de say 4 inches for most of my silver coins. I don't believe they sink that fast. Most of my silver is found in parkways, and front yards of homes built in the 30's 40's or 50's.
HH everyone

 

[FreeBirdTim]

Wood floats.

Not sure what your point is, since a dead stump has roots and is still attached to the ground. Maybe the stumps in your yard float, but mine are still firmly rooted to the ground!

 

[Nugs Bunny]

I believe it is the rain and moisture that dominates the movement. Ice and frost make them rise. (check out farmer's that take out rocks from the field every spring due to ice and frost) and then rain will make them sink.Not much, but they do sink. Overburden also is involved but only by a small amount. My 2 cents (clad) TTC

Frost heave is what the phenomenon is called. This is why in colder climates they recommend fence posts and the like be a minimum of three feet deep, objects below the frostline are unaffected.

I found a great research video on the subject, the objects in the test move several inches and it's a good example of how soil moves in layers along with objects suspended in them.

I estimate the original depth of these coins was about 18 inches from the original surface. This land is nowhere near any waterway or anything else that would "liquefy" the soil or deposit huge amounts over time. This is was simply the depths the coins migrated down into the soil in 120 years.

The composition of the soil along with the horizon profile is probably slightly different in that area, dense compacted soil cannot transfer material from one horizon to the next as efficiently. Liquefaction can occur when frozen ground thaws, water cannot drain through the frozen ground below it. Scroll to 1:00 in the video they explain it much better.

Frost Action In Soils



Here is an older production of the same video in case anybody is feeling nostalgic or retro lol!

 

[Jason in Enid]

Awesome video! It was really interesting to watch the soil heave and how it moved items. I would have liked to see the back end with the thawing too, but that wasn't part of their experiment.

I can see how coins at different depths would be affected by varying freeze/thaw cycles to different depths as cold temps move in and out.

 

[Rich jaws]

It really is amazing to watch. Mother Nature is constantly at work below our feet and yet while we don't see or feel it, we do see the results in the coins and relics we dig.