Written by the TreasureGuide for the exclusive use of treasurebeachesreport.blogspot.com.
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| Sand Being Aerated and Fluidized. Source: See Nerdist.com link below. |
I started my study of beach movement many years ago by just observing how old coins and objects show up on a beach after a storm. Everybody knows that happens, but I wanted to understand more than that. I wanted to know how that happens so I could predict where and when different kinds of things would be found.
I observed how items were uncovered by erosion, and I pretty much understood how that happened, but I didn't understand the processes involved in how things washed up onto the beach so well. I couldn't observe that because it was always hidden by big waves and turbulent water. Although I had many times observed erosion and objects being uncovered and washed down the beach, I was never able to observe them as they were being washed up onto the beach so I looked for anything I could find that would explain how that happens.
Eventually I learned about liquefaction that is cause by vibrations during earthquakes. I also studied how sand is compacted and cponsidered friction between grains and the pressure in the pores between grains. Then there was Clark Little's photographs that showed sand appearing to flow with the water in a very fluid form. And now I found another great illustration that shows that sand can be fluidized by pumping air into it.
When sand is infused with air so that the friction between grains is reduced, it will act very much like a fluid even without water. Light objects will float to the surface and heavy objects will sink in it. Here is a video that illustrates that process very well.
It is amazing. Take a look.
There are two videos. You might want to watch both.
I''ve now read of three things that can cause sand to liquefy. They include vibrations, and both water and air injected into sand. All three of those probably happen when we have big waves, and considering the Scott Little photographs along with those other principles, I now feel pretty confident that some significant amount of liquefaction of the sand occurs when the waves are big and the surf is rough. While you normally can't see it while it is happening, you can get a look at it in Little's photos.
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I just went out and did a little experiment, although not a very good one. It was more a matter of exploring how I could conduct experiments.
I got a three-sided length of PVC drain that I added as an extension to my down spout. I filled the bottom of the PVC drain with a couple inches of sand and placed a quarter and a ring on the surface of lightly packed sand. I put a hose in the top of the gutter so a pretty even stream of water flowed down the gutter and over the coins and through the chute.
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| Quarter and Silver Ring on Couple Inches of Lightly Packed Sand Inside Water Shoot. |
I placed the ring and coin beside each other in the drain. When the water was running, it covered the items. It was maybe about an inch deep over the surface of the sand and objects and flowed swiftly.
What would you expect to see? Do you think the quarter or ring will get covered by sand? Do you think either will be moved by the flowing water.
Here is what it looked like after a couple minutes of water flowed swiftly over the sand for a couple minutes.
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| Same Quarter and Ring After Exposure To a Couple Minutes of Flowing Water. |
Neither object got covered with sand at all, and neither moved very much although the ring moved a little. That is just water on the quarter - no sand.
The quarter is low profile and was not moved. But the water pushed on the raised edge of the ring, moving it slightly with the current. In this experiment the amount of movement was slight. In future experiments I could vary the amount and velocity of water and measure the movement. There are a couple of tweaks I can make to the apparatus.
A small amount of sand was washed out of the chute.
The experiment was far from perfect. It was just a hurried attempt to see if the water chute could possibly be of some experimental value, and I think it can. I was generally pleased with how it worked, but the experiment, if you can call it that, could have been much better.
I would not have been surprised if sand began to cover the quarter. In this case it didn't.
This is a very different situation than would exist on a beach during big waves and rough water. The water in the experiment only had horizontal velocity. On a beach during rough surf, not only would there be more water, there would also be a drastic difference in the movement of the water. Instead of the flowing in a steady horizontal stream, it would be lifting and crashing, pumping air and water into the sand, suspending grains and moving it in waves. I could go into that in more detail, but will stop there for now.
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Terry T. said the pointed object I showed yesterday was a horseshoe crab tail. That is right. I think someone else told me that years ago, but I forgot by the time my wife found it yesterday.
Here is a good link to some information on horseshoe crabs. Some people call them living fossils, and they are used to test vaccines.
And DJ sent a link to a picture of a Spanish Mackerel skull, and the jaw seems to match the one I showed yesterday very well.
Here is that link.
Thanks guys!
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A couple days ago the counter quickly blew through 2.5 million page views.
I'm going to have to make some changes. I'm going to have to separate new posts on a new blogger page. It won't cause too much inconvenience.
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Nothing of interested on the NHC maps now.
And the surf remains small and the weather hot.
Happy hunting,
TreasureGuide@comcast.net
