Written by the Treasureguide for the exclusive use if the Treasure Beaches Report.
Yesterday, I think it was, I mentioned that modern coins were being found southeast of the scattered small cuts, and I mentioned that I might follow up on that post with additional explanation. I'll try to do that today.
(ADDITIONAL CLARIFICATION ADDED LATER: This illustration assumes a shoreline that runs north to south, however most of our beaches are not precisely north to south and the shoreline is curved rather than straight. It is necessary to take into account the actual angle of the shoreline as well as the direction of the swells.)
The above illustration shows a cut beach caused by northeast swells. The swells are hitting the beach at an angle. When the water creates cut, sand and other objects are moved down the slope. The blue line shows the direction of the water as it comes up onto the beach and returns, and the big black arrow shows the general direction of the sand and other materials washed out as the beach erodes.
When the water comes from a good angle, and slices along the beach, the water maintains a more continuous flow, unlike when the water comes directly up the beach and then washes back down, colliding with the incoming waves.
A lot of sand is processed when a cut occurs. For example, a three-foot-high cut that runs for fifty yards and the erosion extends towards the water twenty yards, would sift something close to 500 cubic yards of sand and spread it out over the slope and perhaps drag it down into the water. When you get a six-foot cut, something near twice the amount of beach sand would be spread and sifted.
The magic occurs because sand is moved at a different rate than the coins and other objects. As a result, there is sifting or classification. As the sand is being dragged down the slope and into the water or being spread out on the beach, the coins move much more slowly and are deposited where the force of water decreases enough to drop them. The coins move a distance with each wave or flow of sufficient force.
I've done the experiment quite a few times myself. When a beach is being cut, I would stand in front of the cut, and throw a coin into the rushing water and track it with my metal detector. That is how I know. A coin will move in the direction of the outflowing water in a step-by-step fashion, pausing between waves. That is what I am attempted to show with the big black arrow in the illustration.
Of course the tide will go down, and the water will quit hitting the top of the dune. The longer the water is moving with enough force the coins will be moved, finally reaching a resting point.
When there are strong northeast swells, the coins will be deposited southeast of where they came out of the dunes. That is what was going on yesterday. There were scattered small cuts and the coins were found near the water line to the southeast of the cuts.
When there are strong southeast swells that cut the beach, they will end up northeast of where they came out of the dunes.
When the water is hitting the cut straight on, and causing the face of the cut to collapse, the coins will fall down not far from the cut until the wind and swells change. The incoming and outgoing waves will hit and cancel each other on the slope, so there will not be the same type of flow on the beach as when there is a northeaster.
Coins that were washed out earlier will have a greater chance of being washed farther down the slope.
Here is a related post with another illustration.
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Hurricane Roslyn is a major hurricane hitting the west coast of Mexico.
The surf is supposed to be 3 - 5 feet tomorrow. That is some increase.
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| Source: MagicSeaweed.com |
Good hunting,
TreasureGuide@comcast.net