Written by the TreasureGuide for the exclusive use of the Treasure Beaches Report.
Beautiful photo, but also informative.
I've done some posts talking about the movement of sand and objects on a beach. I talked a lot about force. ]I was talking primarily about horizontal movement or flow rather than vertical. In the photo above you see that as well as horizonal flow, there is a lot of upward and downward force and flow. te chart that I've posted a number of times (below), shows how the amount of water force relates to the movement of objects, The chart shows the threshold levels of force required to move loose and cohesive materials. It makes sense that some cohesive substances, such as clay, because of the cohesioin require more force to dislodge than if it was not so cohesive, but once those fine particles are suspended, they will remain suspended longer and be moved more than loose materials of similar size.
In the above photo at the top of the post, you will see sand being picked up, or sucked up, into the wave. That is upward movement that, as the wave proceeds, will become downward movement. Of course, the sand will be moved ahead, and the wave will crash, dislodging more sand, which makes it move more fluidly.
On a very rough-water day, with high tides and waves, this high intensity area where the waves are crashing will move high up onto the beach as the tides increase. As the tide comes in, the maximum mpact area will move up the beach, dislodging sand and moving it. That would cause huge erosion if it were not for the subsequent incoming waves that interacts with the outflowing water of the previous wave. You can have very high water, but little erosion at some locations. The high water can cause a lot of turbulence and pick up a lot of sand, but the net movement is relatively small.
In the second photo, you see brown water churning around the photographer. Right in front of his camera, you see a brown fountain where sand has been picked up high into the wave. You can see that the sand therre is being picked up several feet before being thrown ahead.
A lot of sand will be moved, but will it be moved onto or off the beach? As the tide comes in and the impact zone moves up the slope, the net movement can be onto the beach and more than off, even though the water will flow back down the beach. If in the shallow water there is a good supply of sand to be picked up, it will be moved onto the beach.
The outflow of water will be at a high rate if the water hits a cliff or obstacle and bounces back down the slope. That outflow, however, will be impeded as more incoming waves meet and reduce the outflow, so there is movement in multiple directions. The net movement will be the result of those interactions, with sand and other objects dropping out of suspension accordingly.
Objects that require more force to move, such as coins, will be moved in the area of crashing waves where there is a lot of turbulence and a relatively fluid beach surface. Where they are depositied, will, like sand, be determined by the interaction of forces, which will determine where those items drop out of suspension. As the waves decrease in size and the force of water movement decreases, objects like coins, will be deposited before sand gains, which will then cover those objects that require more force to move.
It may be easier to visualize how objects will be moved when the water force runs somewhat parallel to the shore and dunes and there is a more continous flow in one direction, such as when you have a strong north wind that pushes water onto the beach, but keeps it moving primarily in a north to south direction, slicing along the beach and moving the sand, and when the flow is great enough, other objects along with it. The northeasters can can also have a lot of flow and sand movement at the base of the beach, so sand washed down will be carried away to the south, perhaps along with other materials that are a little more difficult to move.
You might be able to look at the movement of water and see the movement of sand, and visualize the changing amount of force so you can approximate where coins and things will be deposited. Since sand is more easily moved, it will not be dropped so soon, which is why you normally find the coins covered by sand.
I believe I've previously described the movement of sand and objects relatively well for conditions involving a more steady flow along the beach such as what you might see during a strong north wind with north swells, but this is an attempt to describe what happens in the highest impact areas, such as those shown in today's photos. That is more the type of thing could result in coins being washed up onto the beach. The photos of Clark Little show the a lot of big sand-moving force, and I think you can see how coins and things like that could easily be moved with that kind of impact. Of course, coins will not be moved onto the beach unless they are in the shallow water at that location or on the beach front to begin with, and any protective covering of sand is moved first.
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| A Piece of Black Glass From a Bottom Rim. |
I went back ot the area where I saw the big planks uncovered and not too far away found this piece of black glass. That is the second piece of black glass from that location. When held up to bright light, this one shows a little dark green color.
I'm going to try to get a better look at those planks. I doubt if I can move them. Maybe if the tide gets really low sometime, I'll get a better look.
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The most true and significant thing Obiden ever said, is that it matters who counts the votes and how they count them.
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There is still nothing of interest on the NHC map today.
The tides are moderate, but the surf will run around three fee this week, with swells from east and south.
Good hunting,
TreasureGuide@comcast.net
