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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[relicmeister]

Don't know about sink rate,-an item dropped in the southwestern desert if now covered by blown sand could remain on the surface for centuries. I think the more dominant cause of items being buried is the accumulation of decomposing leaves and
such, as well as the effects of weather and the action of earthworms as well as other factors -

 

[Rich jaws]

Some good points relicmeister. The areas I have been searching are generally open grass fields so leave deposits are generally not an issue. I will bet that the earthworm activity does have an important effect though. I see lots and lots of them I the areas I dig.

 

[jeepGold]

It is pretty interesting. Lately all I do is MD at local grass parks. Almost a constant 4"-6" cuts are where I find all of my clad. Those coins are typically 1985 to 2000 or so. Anything newer is about an inch or two under. The rings I have found tend to be about 3" down. What I HATE is finding coins that are cut in 1/2 and mutilated by mowers. They do more harm than ANY metal detector enthusiast. I also hate when a penny screams like a quarter.... I wish I could find old areas like in the south. Everything I hunt is pretty much from the 1950's fwd.

 

[atx]

The density of an object will sink over time until the density of the earth matches that of the object. This is why gold is usually found deeper as it is denser.

 

[Johnnoh]

Do you ever notice the grass pattern in the dirt under the coin? I have seen that up to 7" - pretty cool.

 

[worldtalker]

Do you ever notice the grass pattern in the dirt under the coin? I have seen that up to 7" - pretty cool.

Get a signal at that depth......stinkin Lincoln,coulda been an IH!! I see that grass pattern quite often..pretty strange to say the least.

 

[gunsil]

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.

 

[Jason in Enid]

COINS DON'T SINK! They get pushed down, they get buried, they get grown over, but they don't sink.

 

[Jason in Enid]

Get a signal at that depth......stinkin Lincoln,coulda been an IH!! I see that grass pattern quite often..pretty strange to say the least.

The coolest thing is digging stacked coins and still having 50+ year old blades of grass sandwiched between them!

 

[finderskeepers]

Another opinion to add to the pile...maybe they do?? Here in New England, our soil layer is constantly being added to with the breakdown of organic litter. (certainly more so in the forest, where it's not treated as debris and removed). But, the freeze/ thaw activity here, has effects also. While it seems generally accepted that this freeze/ thaw( frost heave) can "push" stones to the surface, could it, at times have the opposite effect?

From the book "Stone by Stone" by Robert M. Thorson (professor of Geology @ University of Connecticut) page 111 [Fantastic book by the way!!]...

"A separate frost-heave process, called frost-push, is effective at shallow depth, perhaps ten inches or less. In this case, the cold is conducted into the ground more efficiently through the stone than through the more porous and organic adjacent soil. Hence the base of a stone, reaches the freezing temperature before the adjacent soil, nucleating the growth of ice that can push the stone upward."

OK...so can we interpret from this, this possible effect from the thaw part of freeze/ thaw cycle Is it possible that a coin (in that top 10") could conduct heat more rapidly to the frozen soil directly underneath it, allowing it to "settle" before the adjacent soil warms enough to collapse and fill any void beneath the coin??

 

[Maka]

I agree w gunsil. Things dont "sink" in the ground like we think of things sinking in liquids. Over time they get covered over for a myriad of reasons, and conversely over time can get closer to the surface or exposed for a myriad of other reasons.
Often for reasons that defy logic. After years in the waterproofing industry I can testify that water can run uphill. Usually from wicking, but not always. It is common knowledge that moisture in the ground rises to the surface where it is evaporated off. To keep our lawns hydrated we need to water down to 4" - 5" inches and keep the soils at that depth moist.
The point is, it can be difficult if not impossible to determine why objects are found at the depths we find them.
Having said that ... keep wondering, keep questioning, keep hunting.

 

[Rich jaws]

I just got back from detecting and after seeing the soggy/soft soil conditions from the 3 inches of rain we had this past week, I thought I now understood the process of the items sinking in the soil. The ground was soggy down to at least 6 inches deep. Now I am more confused than ever. Not sure I am convinced though that the items don't sink.

 

[Jason in Enid]

I just got back from detecting and after seeing the soggy/soft soil conditions from the 3 inches of rain we had this past week, I thought I now understood the process of the items sinking in the soil. The ground was soggy down to at least 6 inches deep. Now I am more confused than ever. Not sure I am convinced though that the items don't sink.

Not convinced? Go take a big scoop of that wet ground and put it in a jar. place a coin on top and put the lid on it so the soil stays just a soggy as it is right now. put that jar in your closet and go check on it in 10 years. do you REALLY think it's going to be anywhere other than right on top when you open it back up?

 

[Rich jaws]

The jar in the closet would not have a worm or frost/freeze/thaw action so I decline to conduct that experiment but thanks anyway. Lol

 

[worldtalker]

I agree w gunsil. Things dont "sink" in the ground like we think of things sinking in liquids. Over time they get covered over for a myriad of reasons, and conversely over time can get closer to the surface or exposed for a myriad of other reasons.
Often for reasons that defy logic. After years in the waterproofing industry I can testify that water can run uphill. Usually from wicking, but not always. It is common knowledge that moisture in the ground rises to the surface where it is evaporated off. To keep our lawns hydrated we need to water down to 4" - 5" inches and keep the soils at that depth moist.
The point is, it can be difficult if not impossible to determine why objects are found at the depths we find them.
Having said that ... keep wondering, keep questioning, keep hunting.

Back when the Romans built the Aqueducts water did run uphill...check it out!

 

[maxpower]

well it was pushed uphill -- after the winter the frost tends to push up stones and glass in my garden

 

[Keppy]

COINS DON'T SINK! They get pushed down, they get buried, they get grown over, but they don't sink.

Jason…Is right on here they do not sink… Dead grass loose dirt things like that blow over and cover them up ….. Pick a spot in your yard block it off place a coin there on top of the ground… Go back one year or 10 years later it will still be there

 

[Rich jaws]

Jason…Is right on here they do not sink… Dead grass loose dirt things like that blow over and cover them up ….. Pick a spot in your yard block it off place a coin there on top of the ground… Go back one year or 10 years later it will still be there

Keppy, whether it will be there or not might depend on the neighborhood you live in lol

 

[Keppy]

Keppy, whether it will be there or not might depend on the neighborhood you live in lol

OH Wow you are right there …I never thought about that..