Written by the Treasure Guide for the exclusive use of the Treasure Beaches Report.
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| Beach Profile Illustration. |
Yesterday I posted an illustration of a hypothetical beach profile. It is shown above with one addition - a red arrow showing the general direction of dense objects over time.
Items can be washed up onto the beach, but the net direction of dense objects over time will be as shown. Such objects will tend to move down and out towards the water. Each time an erosion event occurs, the objects can move in that direction. If the erosion event is a large one, the objects will move farther. Smaller erosion events can combine over time to move objects long distances over time even though each event might move those objects a short distance.
Last October or November we had unusually high water due to high tides combined with unusually a high surf.
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| TBR2020.blogspot.com. |
The high water and waves hit the face of the back dunes in some places, as shown by the illustration above. The waves cut into the dune face, resulting in items in the back dunes falling to the flat beach.
That is one of two ways that old dense objects end up being found on top of or near the surface of the top layers of sand. They come from higher layers of sand that was removed.
When the water level cuts into the dune face, as would happen in the situation shown above, the dune face is undercut and the items fall down, where they continue to be moved around by the water. Both dense and less dense objects are washed out of the dunes, as items from different layers fall to the lower beach surface. The face of the back dunes will recede, but the sand and other items are sifted and sorted as long as there is sufficient water force at those high levels of the beach. Of course the tide will recede after that, and if the tides and surf remain high, the same thing can happen for additional tide cycles. Sometimes the water hits the same high level of the beach multiple times and sometimes only during one high tide.
Depending upon how the water is hitting the beach, both sand and other items will be dragged down and towards the front of the beach, perhaps eventually resting on rock in the water in front of the beach. There dense items will eventually get covered by sand.
Items will not always be dragged that far. During a single erosion even they will very often remain on the beach, only to be covered again when the sand returns. The depth of the items after the event will depend upon how much of the sand was removed during erosion. As multiple erosion events occur over time, the items will tend to go deeper. The areas of target concentrations will move as additional erosion events occur. Sand will return and dense targets that were left at deeper layers will remain undisturbed until erosion events uncover those areas once again. That happen soon, or it can be a very long time.
Back in October or November or whenever it was, not only did items fall out of the dunes, but the front beach was moved back too. At one beach, something that doesn't happen very often occurred - old targets were found from the bottom of the dune face all the way down the slope and to the low tide water level after the erosion was over. Rocks, which are not often seen at the water's edge, were exposed.
Look at the illustration again. Notice how much additional water is over the beach when the surf and tides were high. That is a lot of water and a lot of weight. That is a factor that I believe is not appreciated. All that weight must have a great affect on the surface of the beach. Add to that the turbulence caused by waves and water passing over the beach, and also the changing water line as the tides come and go.
I did not discuss all of the factors and the continuing changes that occur, but as you know, eventually the sand will begin to build again. I think that is a good place to stop today.
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The tides are still small. The surf is too. The wind is coming from the south/southwest.
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| Source: MagicSeaWeed.com. |
The predictions are still showing a 4 -6 foot surf for Sunday, but only for a brief time. The wind will be out of the north Saturday.
Happy hunting,
TreasureGuide@comcast.net
