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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[Phantasman]

Sink isn't the word. Coins and jewelry, etc. "settle" into the ground. The conditions all around a target can change "slightly most of the time" as a target finds a resting place and the surrounding conditions have reached a stable state where they no longer fluctuate. Many natural and unnatural events can cause target movement. The most being water and vibration. The movement of vegetation growth over time can have effect. Grass roots expand and contract over the Seasons. Though slow, the ground moves as well.

Years ago I read a great article on this by a treasure hunter group that studied the effects that created target depths throughout time. I remember a statement by them that said 90% of "all" dropped lost coins, jewelry sized targets by humans are estimated to be no deeper than 4-6" below the ground.

 

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[cudamark]

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

It doesn't get stepped on or had a tractor/lawnmower run over it either. I agree that after the coin gets 3-4 inches deep (by whatever means) it doesn't "sink" further, but, rather gets buried deeper.

 

[BigWaveDave]

Anyone who hunts in the sandy soils of Florida, which is subjected to heavy annual rainy seasons, will have a hard time being convinced that coins do not sink.

 

[finderskeepers]

Sink isn't the word. Coins and jewelry, etc. "settle" into the ground. The conditions all around a target can change "slightly most of the time" as a target finds a resting place and the surrounding conditions have reached a stable state where they no longer fluctuate. Many natural and unnatural events can cause target movement. The most being water and vibration. The movement of vegetation growth over time can have effect. Grass roots expand and contract over the Seasons. Though slow, the ground moves as well.

Years ago I read a great article on this by a treasure hunter group that studied the effects that created target depths throughout time. I remember a statement by them that said 90% of "all" dropped lost coins, jewelry sized targets by humans are estimated to be no deeper than 4-6" below the ground.

...and earthworm, insect, mouse activity and decaying tree roots.

 

[Phantasman]

Anyone who hunts in the sandy soils of Florida, which is subjected to heavy annual rainy seasons, will have a hard time being convinced that coins do not sink.

Growing up in Ft Lauderdale from 1957 to 1982, Florida is sinking. Since my early years, a lot of the beaches have "eroded". A fight the Army Corp of Engineers have been fighting since the days of Flagler. There are old stories of Seminole graves coming up from the ground due to this process. When I buried my mother in 1981, a special vault was required by the city for the casket to go into. Completely sealed air tight as to not let remains seep into Florida's wet underground cavity, or the water to enter the internments.

The movement of ground.

 

[sjvalleyhunter]

I have to respectfully disagree with those of you who believe that coins don't sink. Coins and other objects absolutely do sink into the ground, and I will explain how.

If someone were to drop a penny into a glass of water what happens? It drops through the water and to the bottom of the glass. The reason this occurs is because the penny has mass, and gravity takes an effect on it. In a simplified explanation, as gravity pulls down on the coin, the molecules of water under it move out of the way, or displace, allowing the penny to sink to the bottom. This is a fairly simple concept.

Now drop a penny onto the ground. Of course it doesn't disappear into the ground right away because the dirt doesn't move out of its way. However, over time it does. Some folks theorize that rather than sinking, the coin gets buried as dirt and organic matter is deposited on top of it. Although this contributes to the coin disappearing into the ground, the more influential factor is that the ground beneath the coin does actually move, allowing the coin to sink.

So taking the same principles as the water example, in order for a coin to sink the molecules beneath it (in this case the particles of dirt), have to move out of the way. This does occur by a variety of means.

First of all, and the most powerful, is water. Put a coin on a patch of dry dirt. Now wait for it to rain. After the rain stops, pick up the coin. Obviously the dirt will be wet underneath it. This is because the water flowed under the coin. What happens when water flows? It erodes the ground and moves the particles of dirt. Whether it be rain or sprinklers, we have now begun the slow process of moving the dirt particles out from under the coin. The sinking process has begun.

Now enter grass. When grass or other plants grow, they produce roots. Roots extend into the ground and under the coin. The roots move (displace) the dirt so they can take up the space they need as they grow. Any mildly experienced detectorist has dug up a coin that had been encased in grass roots. Well eventually those roots under the coin die. Because plant material is mostly made of water, when that organic material dies it decomposes and reduces in volume. What is left is a void, or space under the coin, where this small root once was. So what happens? This minuscule hole collapses, allowing the coin to ever so slightly fall (aka sink).

Let's add some earth worms into the mix. Worms essentially eat dirt. They take in dirt, digest the organic material in it, and discard the rest. So when a worm burrows under a coin, it leaves yet another void (hole) in the ground. Eventually the mass on top of this void, be it the coin or otherwise, is pulled down by gravity and the hole collapses and fills in the void. Well the coin has now sunk just a bit more.

Now let's add rain and snow melt into the equation. The water seeps into the ground and by simple physics, it will flow into areas of lesser concentrations of dirt. Basically it will fill in those voids left by dead roots, worms, etc. And when water flows, it causes erosion. Dirt is moved which allows the coins to sink further into the ground.

This is why most coins, even the oldest of colonial ones, are typically found no more than ten inches deep. This first few inches is where there is the most activity in the ground occurs. The roots of grass and other foliage only grow so deep. When it rains, water only soaks so far into the ground. Worms and bugs eat organic material so they burrow only as far down as they need to find food. For these reasons, coins don't sink farther and farther into the ground over time. They do reach a limit because at some point there is very little occurring under the coin to cause the dirt to move. But they absolutely DO sink some over the years.

I mean no disrespect, but the jar example that Jason In Enid gave is flawed. Of course a coin dropped into a jar of wet dirt won't sink. But that jar and its contents aren't exposed to any environmental factors, such as weather, plant growth, etc.. A closed jar is a static environment. The real world is not.

If you still think that coins don't sink and instead are covered up over time, think about this. My family owns a house that was built around the turn of the century. I have hunted the property and have found many old coins along the cement walkway that leads to the house, as well as along the cement sidewalk in front of the house. These coins are routinely five or six inches deep, below the level of the sidewalk and walkway. So if you subscribe to the theory that coins don't sink, then it would have to be concluded that the sidewalk and walkway have raised up five or six inches over the years. And since the walkway to the house still meets the foundation of the house at the same place it did 100 years ago, then it would have to be concluded that the whole house has also raised up five or six inches over the years. And this was all occurring while the coin was staying in the same spot on the ground and just being covered up. Obviously this isn't what happened.

Water, plants and worms aren't the only factors that contribute to coins and other objects being able to sink into the ground. The freezing and thawing of the ground during the seasons can have an effect, as well as other things. But the bottom line is this: over periods of time and with the right conditions, coins do sink into the ground. The rate by which they do and the depth that they get is determined by a number of factors.

 

[Keppy]

I have to respectfully disagree with those of you who believe that coins don't sink. Coins and other objects absolutely do sink into the ground, and I will explain how.

If someone were to drop a penny into a glass of water what happens? It drops through the water and to the bottom of the glass. The reason this occurs is because the penny has mass, and gravity takes an effect on it. In a simplified explanation, as gravity pulls down on the coin, the molecules of water under it move out of the way, or displace, allowing the penny to sink to the bottom. This is a fairly simple concept.

Now drop a penny onto the ground. Of course it doesn't disappear into the ground right away because the dirt doesn't move out of its way. However, over time it does. Some folks theorize that rather than sinking, the coin gets buried as dirt and organic matter is deposited on top of it. Although this contributes to the coin disappearing into the ground, the more influential factor is that the ground beneath the coin does actually move, allowing the coin to sink.

So taking the same principles as the water example, in order for a coin to sink the molecules beneath it (in this case the particles of dirt), have to move out of the way. This does occur by a variety of means.

First of all, and the most powerful, is water. Put a coin on a patch of dry dirt. Now wait for it to rain. After the rain stops, pick up the coin. Obviously the dirt will be wet underneath it. This is because the water flowed under the coin. What happens when water flows? It erodes the ground and moves the particles of dirt. Whether it be rain or sprinklers, we have now begun the slow process of moving the dirt particles out from under the coin. The sinking process has begun.

Now enter grass. When grass or other plants grow, they produce roots. Roots extend into the ground and under the coin. The roots move (displace) the dirt so they can take up the space they need as they grow. Any mildly experienced detectorist has dug up a coin that had been encased in grass roots. Well eventually those roots under the coin die. Because plant material is mostly made of water, when that organic material dies it decomposes and reduces in volume. What is left is a void, or space under the coin, where this small root once was. So what happens? This minuscule hole collapses, allowing the coin to ever so slightly fall (aka sink).

Let's add some earth worms into the mix. Worms essentially eat dirt. They take in dirt, digest the organic material in it, and discard the rest. So when a worm burrows under a coin, it leaves yet another void (hole) in the ground. Eventually the mass on top of this void, be it the coin or otherwise, is pulled down by gravity and the hole collapses and fills in the void. Well the coin has now sunk just a bit more.

Now let's add rain and snow melt into the equation. The water seeps into the ground and by simple physics, it will flow into areas of lesser concentrations of dirt. Basically it will fill in those voids left by dead roots, worms, etc. And when water flows, it causes erosion. Dirt is moved which allows the coins to sink further into the ground.

This is why most coins, even the oldest of colonial ones, are typically found no more than ten inches deep. This first few inches is where there is the most activity in the ground occurs. The roots of grass and other foliage only grow so deep. When it rains, water only soaks so far into the ground. Worms and bugs eat organic material so they burrow only as far down as they need to find food. For these reasons, coins don't sink farther and farther into the ground over time. They do reach a limit because at some point there is very little occurring under the coin to cause the dirt to move. But they absolutely DO sink some over the years.

I mean no disrespect, but the jar example that Jason In Enid gave is flawed. Of course a coin dropped into a jar of wet dirt won't sink. But that jar and its contents aren't exposed to any environmental factors, such as weather, plant growth, etc.. A closed jar is a static environment. The real world is not.

If you still think that coins don't sink and instead are covered up over time, think about this. My family owns a house that was built around the turn of the century. I have hunted the property and have found many old coins along the cement walkway that leads to the house, as well as along the cement sidewalk in front of the house. These coins are routinely five or six inches deep, below the level of the sidewalk and walkway. So if you subscribe to the theory that coins don't sink, then it would have to be concluded that the sidewalk and walkway have raised up five or six inches over the years. And since the walkway to the house still meets the foundation of the house at the same place it did 100 years ago, then it would have to be concluded that the whole house has also raised up five or six inches over the years. And this was all occurring while the coin was staying in the same spot on the ground and just being covered up. Obviously this isn't what happened.

Water, plants and worms aren't the only factors that contribute to coins and other objects being able to sink into the ground. The freezing and thawing of the ground during the seasons can have an effect, as well as other things. But the bottom line is this: over periods of time and with the right conditions, coins do sink into the ground. The rate by which they do and the depth that they get is determined by a number of factors.

OH i said before i do not read long post's and i can not make it all the way through yours it is like a book .. to much to read to much to make a point...

 

[sjvalleyhunter]

OH i said before i do not read long post's and i can not make it all the way through yours it is like a book .. to much to read to much to make a point...

Yeah, I didn't realize how long winded I got until it was posted. I'll summarize it. Coins do sink.

 

[Rich jaws]

Wow, that is a great outline and it makes perfect sense. It didn't make sense that coins don't sink and you articulated the sink theory extremely well. Thanks so much. Your time and effort in writing the post are greatly appreciated.

 

[worldtalker]

Yeah, I didn't realize how long winded I got until it was posted. I'll summarize it. Coins do sink.

How else does a stinkin lincoln get to 6 inches. I just don't like plugging those things!!

 

[Phantasman]

Yeah, I didn't realize how long winded I got until it was posted. I'll summarize it. Coins do sink.

To a point. They "settle" at a point when the packed dirt (over time) matches the density of the coin. The top layer of dirt is kept less dense by rain and temperature. In this (6") range, some water may continue seeping, while the top layer also gives up moisture through evaporation as well as root absorbing. The ever so slow movement of soils causes the denser coin (metal) to "sink down" until it finds a spot where this effect is no longer at play. It's not like gravity pulling the coin through the dirt. It's more like shaking the dirt, and the coin settling into air pockets left in the process.

Not much root, bug, water activity at the 6" level. Or even the 3" level at some places. Throw a coin on the Salt Flats in Utah, come back in 100 years and there's a good chance it could still be on top of the soil, or an inch down at best.

 

[Jesse James]

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.

Not to mention the aluminum can that has been mutilated by the mower, sending fragments all over a 5ft x 5ft area. I find that a lot.

 

[Keppy]

Yeah, I didn't realize how long winded I got until it was posted. I'll summarize it. Coins do sink.

That's better .. But you can make it a little longer if you want...

 

[556baller]

objects sink

 

[finderskeepers]

Sjvalleyhunter...nothing wrong with your post. It's thoughtful discussion by a person who seems to care more about sharing and learning, than being so pleased with the sound of their own voice. After seeing a few of the responses, I actually feel a little silly having allowed any doubt in my mind...of course they move/sink/settle.

 

[finderskeepers]

Awwww thank you Kippy! Now run along and play somewhere else, you've gotten your share of attention out of this thread.

 

[Higgy]

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.

Good Answer! That deserves a,

 

[sjvalleyhunter]

To a point. They "settle" at a point when the packed dirt (over time) matches the density of the coin. The top layer of dirt is kept less dense by rain and temperature. In this (6") range, some water may continue seeping, while the top layer also gives up moisture through evaporation as well as root absorbing. The ever so slow movement of soils causes the denser coin (metal) to "sink down" until it finds a spot where this effect is no longer at play. It's not like gravity pulling the coin through the dirt. It's more like shaking the dirt, and the coin settling into air pockets left in the process.

Not much root, bug, water activity at the 6" level. Or even the 3" level at some places. Throw a coin on the Salt Flats in Utah, come back in 100 years and there's a good chance it could still be on top of the soil, or an inch down at best.

I agree with what you are saying. I think your "settle" and my "sink" can be used synonymously in this case. The point that I was trying to make is that over periods of time coins do, in fact, drop below the surface of the ground as a result of sinkage, rather than only being covered from the top by dirt and debris.

 

[Jesse James]

Gravity...

 

[worldtalker]

Gravity...

Is it a push or a pull?