9/4/14 Report - How Coins and Rings Sink In Beach Sand. Targets Only Sink As Far As The Disturbed Layer.

Written by the TreasureGuide for the exclusive use of treasurebeachesreport.BlogSpot.com.

Same Cup of Water and Sand
Shown Yesterday.

Just in:  I have some great new pictures of treasure ship finds sent by Captain Jonah!   Probably tomorrow.


I accidentally did an ingenious experiment.  I should probably call it an observation rather than an experiment.  I'll get back to that in just a minute. 

I always enjoy receiving emails from this blog's readers.  They are an educated and intelligent bunch.

Yesterday I talked about how objects of interest sink in sand.  I received an email from Bill F., who has a degree in physical oceanography and did his undergrad thesis on beach erosion at Ponce Inlet.  

Here is some of what Bill said.

1)  The finer the sand particle, the flatter the beach
2)  The faster the current, the bigger the particles which are moved
3)  As you show, without wave/water energy, objects don't settle on their own.
4)  The heavier/denser an object, the less likely it is to move horizontally.
5)  Shape makes a difference.

Thanks Bill!   Those are some good points to remember.


Above is a picture of the same cup that I showed yesterday.  The ring and coin in this cup never sank so much as a micro inch while it sat undisturbed.   That clearly demonstrates one thing Bill said -  without wave/water energy, objects don't settle on their own. 

I decided to see what it actually takes for objects to sink in the sand.  I put my hand over the cup and moved the cup in a semi-circular motion so that the water moved.  When the water moved the very top layer of sand lifted and the suspended sand moved with the water while the objects pretty much stayed in place.  When I stopped, a little sand covered the objects, but very little.  With gentle only the sand above the green line moved.  This is important, and I'll get back to it.

When the objects got covered there were a couple of ways I could tell how deeply they got covered.  You'll notice that the surface of the sand in the cup (below the yellow line) is not exactly horizontal. 
A perfectly circular even motion moved the water so that the sand remained level across the cup, but by moving in a more jerky  manner resulted in the sand moving from one side to the other of the cup to the other. 

I could see how deeply the objects got buried either by sticking my finger in and finding the objects or I tilting the cup and moving it so that the sand then uncovered one side and one object.   I could then see where the previously covered object had stopped sinking.  

Here is an important point.  The amount of sand that moved when I moved the cup was directly related to how fast I moved the cup and therefore how fast the water moved. 

I had no idea how important it was going to be for me to be able to see through the container when I started this experiment. 

When moving the cup gently, a small amount of sand moved - only a thin layer.  Approximately the amount of sand above the green line which I drew on the picture of the cup moved when I moved the cup gently.  The top of that layer moved the most, decreasing as the moving layer got deeper until there was no suspension and movement of sand at all.

The fastest moving sand was clearly suspended, and the grains appeared farther apart than the grains that were lower in the moving layer, which moved more slowly and less overall.

 How deep do you think the objects sank in the sand when the cup was moved gently?   Now this is an important principle.  The objects sank to the surface of the layer of stable sand, and then stayed there.

I recalled how many times in the past few years that I dug an object and found it on the surface of a lower layer of sand.  If you go back through this blog I'm sure you can find that.  Often the lower layer was a different color or texture.  Often it was a layer composed of course shells.

That might not be surprising finding, but it sure was interesting to see.  I could keep the water moving at a relatively slow rate and no more sand would be suspended or moved.  No matter how long I kept the water moving at the same speed, the objects sank no deeper than to the surface of the layer of stable sand.

I know this is not a highly controlled experiment and what happens on a beach will be somewhat different, but in I think this principle will hold.  Just like in the previous report, the objects did not sink into the undisturbed sand no matter how long they sat there in the cup.  In this demonstration the objects did not sink into undisturbed sand even though they did sink through the suspended moving sand.

Here are a few observations that held up all through these demonstrations with the moving cup.

 (1) Only a relatively thin layer of sand was disturbed by the moving water. 
(2)  When the cup and water was moved more forcefully, a larger layer of sand was moved.
(3)  The speed of the sand decreased in the moving layer of sand from top to bottom until there was no movement at the bottom of the layer.

At first I moved the cup gently and only the layer above he green line moved, but when I moved the cup more forcefully, then the sand moved as deep as the light blue line, and that is where the objects ended up, and when I moved it even more forcefully, the sand moved as deeply as the dark blue line, and that is about where the objects ended up.

On the beach, different storms will disturb deeper layers of sand allowing targets to sink deeper.  They will then often be covered again by incoming sand. 

In this demonstration I'm only addressing sinking targets, which occurs primarily when the trigger point for sand is reached but not the trigger point for targets. 

This simple experiment has many limitations, but it reveals some important principles that I've observed in operation on the beach.  I reasoned that objects in deeper layers of undisturbed sand would remain in place, but with this demonstration I observed it and am much more certain of it.

Another thing I observed with this little experiment is how it is only suspended sand that moves.  I could see this on the beach just yesterday.  The waves were crashing on a sand bar.  In front of the sand bar was what I might call a flat topped creeping sand bar.  You could see a clear edge of a layer of sand that was moving from the crash zone towards shore.  The crash would suspend sand, and then that suspended sand would be washed ahead in the surge.

Where the sand was suspended, you couldn't see through the water.  That makes sense.  But closer to shore, where there was a dip beyond the creeping sand bar, and the water there was clear.  That is where I found a couple of relatively new coins that had not yet been covered by the incoming tide and creeping sand bar. 

As the tide comes in, the area where the waves crash and most sand is suspended closer to shore.  Obviously that means that a greater area of sand is affected.  The crash zone changes and the area of surge comes in and then goes out again.

If you've spent much time down in the Fort Lauderdale and Miami area, you know that they have much more calm water than we do.  Many days the shallow water sits still almost like you are in a bath tub, especially before the sun starts to heat things up.   The shallow water on the Treasure Coast seldom has that kind of flat water even when the surf is down to one foot.  That small difference in roughness appears to make a big difference in the average sink rate of targets.  They'll stay in detector range down there a lot longer than on the Treasure Coast.  Couple that with the absolute number of people and what they wear and there is an even bigger difference between South Florida and the Treasure Coast.  Bottom conditions are very different.

Well, I'll quit there for today.  This is getting long.  The principles demonstrated are important and help explain how things settle and therefore how and where things will be found.  I know that I did not address all of the relevant factors and situations. 

I'll do some more experiments someday to help answer some of the remaining questions.

I'm sure some of you will find this post tedious although several of you used the +1 button to indicate that you particularly liked the previous post.  For my own purposes and understanding, I'm glad I did the demonstration.


There are no storms to watch in the Atlantic right now.

On the Treasure Coast we still have a one foot surf and will continue to have a calm surf for at least a few more days.

Happy hunting,
Treasureguide@Comcast.net

9/2/20 Report - How Objects Sink in Beach Sand, Density of Common Metals. Movement of Sand. Tropical Storm Dolly

Written by the TreasureGuide for the exclusive use of treasurebeachesreport.BlogSpot.com.



Gold Ring and Quarter In Cup of Sand and Water.

I always read  about how "heavy" objects sink in beach sand.  I understand why people say that, but it is not correct.

To the left you see a cup of genuine Treasure Coast beach sand and tap water.  I poured about half a cup of water into the cup and then about a half a cup of sand.  The sand filled the cup up over three fourths of the way with about a half inch of water on top of the surface of the sand.  I then put a quarter and thin gold ring on the sand.

How much do you think the quarter and ring sank in the last week?

Here is the answer.  Not at all!  

The way some people talk, or write, it sounds like gravity pulls objects like these right down through sand.  That didn't happen in this cup. 

You might say that this is a poor experiment, and it is nothing like a beach where the water and sand move.  Precisely!  It is not like a beach.  Everything is stable, and gravity alone will not pull coins or a rings like these down through this sand.  Other forces are at work when an object settles down to lower layers of sand on the beach.

On a beach the water and sand moves, and the moving sand covers  objects like these that do not move as much as sand.  But that is just part of it.

The objects will move some too, but much more often it is the sand that does MOST of the moving.

Before I go on I want to address another part of this.  People say that "heavy" objects sink, but it is not the weight of the object alone that determines if an object will find its way to lower levels of sand.  As I've explained in the past, a one-ton block of Styrofoam weighs one ton but will float in water and will not sink into the sand.  It is not the weight, but the density that has more to do with it.  But it isn't just the density of the object either that determines how an object will sink in the sand.  The shape of the object will have something to do with it too.

Lets focus on density for a bit.  The site linked through the following link presents a list of common metals along with their density.

http://www.engineeringtoolbox.com/metal-alloys-densities-d_50.html

Here are some of the most relevant metals listed on that web site.  (Density is given in Kg. per cubic meter.)

Aluminum  2712
Brass  8400 - 8700
Copper  8940
Gold  19320
Iron 7850
Lead 11340
Platinum 21400
Silver 10490
Steel  7850
Titanium 4500
Tungsten 19600
Zinc 7135

This correlates somewhat with how things will be distributed on a beach - but not perfectly

Aluminum is the least dense of the above group followed by titanium.  You'll see those often during poor beach conditions.

Copper and zine are sort of in the middle, with zinc being slightly less dense than copper.  Zinc cents will be found more towards the outer boundaries of coin holes, and copper cents just a bit closer to the center.

Lead is slightly more dense than silver.

The most dense of those listed above are platinum followed by tungsten, followed by gold.

(You might remember the tungsten ring that I found not long ago.  I caught it in the right light yesterday and saw on the inside of the ring that it was marked as tungsten.  On a detector the target ID came up as nickel.  I could tell when I picked it up that it was heavy for its mass, although without really thinking, I called it titanium at first before being corrected.)

If you look at that list, you'll have some indication of how those objects will sink into sand.  But as I showed above using the cup, they won't sink by themselves unless there are other forces at work.

The water moving the sand is a very big part of it.  I've explained before about trigger points.  Different objects require different amounts of water force to move them.  Grains of sand move relatively easily.  They have lower trigger points.  It takes less water force to move sand.  Objects like the coin and ring require more force to get them moving.  They have a higher trigger point.

When the water isn't moving much, the sand will be moved while the object remains relatively stationary.  Sand will be washed over the object, out from around the object, and if the shape is right, even from under the object.  This movement of sand is one of the biggest factors in determining how a object will sink into the sand.  With stationary sand, there is little to no sinking.

The shape of the object is also important in determining how an object will be moved on a beach.

I once showed an experiment in which lead sinkers having different shapes but the same weight were moved by crashing water - a disk shaped sinker was moved less by the same water than a egg shaped sinker, which was moved more than one of those fish shaped sinkers.  That is exactly what I predicted before the experiment.

The disc shaped sinker provided less surface for horizontally moving water to push against.  It hugged the surface of the sand something like a coin would.

Flat thin sheets are moved more by water - much more so than most other shapes.  As a result, even though copper is about three times as dense as aluminum, you will find thin copper sheets being deposited on a beach very much like aluminum.

Again, shape has a lot to do with how an object will sink in beach sand or be moved around and deposited.

For a more complete discussion of trigger points and the lead sinker experiment see my 3/10/14 post.
http://treasurebeachesreport.blogspot.com/2014/03/31014-report-experiments-on-movement-of.html

I also once showed an experiment that showed how an object "stepped" down a sand slope when the water current was rushing up the slope.  What happened is that the current moved the sand from around the object and from in front of the object as the object sat on the slope, and when enough sand was removed from the lower side of the object, the object slipped down the slope into the void, where it came to rest until the current moved enough sand for it to slip down another step.  Again, it was more about the sand being moved than the object sinking through the sand.

Of course loosely packed sand will move more easily and permit objects to "sink" lower more quickly than would packed sand.  That affects how much the sand moves too.  I can't get into all of the factors here, but wanted to make it perfectly clear that objects do not sink into sand simply by the force of gravity pulling the object down through the sand.

This might not seem important, but to me it is very important to me because it helps me understand how different types of objects will move on a beach, and therefore, where they are most likely to be found.  Sometimes when an object seems to be sinking, it is actually being covered rather than sinking.   And, of course, there are times when the water force is enough that more dense objects are moved forcefully by the water.  Coins have been observed to flip up and over a sand berm, for example.

That's all of that for today.


On the Treasure Coast we're supposed to have a one to two foot surf for a week or so.

There is a new tropical storm Dolly, but she will be hitting Texas.

Happy hunting,
TreasureGuide@comcast.net
jewelrymarks.html#art