Written by the TreasureGuide for the exclusive use of treasurebeachesreport.BlogSpot.com.
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Everybody knows that treasure is often found on the Treasure Coast after a good Nor'easter. That has been observed and repeated for decades. It is nothing new. Just like everybody knows to look for erosion. That is nothing new about that either. But do you know why a Nor'easter is good for treasure hunting? And why doesn't it work the same when the waves come from some other direction?
I'll put it together for you today. I've never seen it explained like this before.
I've given you bits and pieces, but today I'll put together some of the most important key elements.
Why is it important? Because it will help you know how it works and that will help you know when and where to look.
I've mentioned many times how the angle of waves are important. Waves that hit the beach straight on do not generally create much if any erosion.
First of all waves hitting a beach directly at a ninety degree angle, wash up onto the beach and then back down the same path. The backwash from one wave will be hit by another incoming wave. At the place where they collide, much of the energy is lost.
If enough water is returning, just off the beach an undertow will be created as shown in the illustration below that I showed a few days ago.
On the East coast of Florida we have a north to south running long shore current as shown in the illustration below. You can tell that if you watch how the sand has accumulated at places such as Cape Canaveral and on the north side of the inlets.
The illustration on the left shows how when the waves hit the beach straight on, the water goes up onto the beach, and then retreats back down the same path.
To the right is an illustration of the same beach with the same long shore currents running north to south, but in this illustration the waves are shown hitting at an angle coming from the Northeast. The waves come up onto the beach at an angle and then the water washes back down towards the water.
In this example, when the next wave hits the retreating water, instead of hitting it head on, it hits the retreating water an angle and pushes the retreating water southward. A flow of water develops moving southward over part of the beach.
The net effect is that sand is moved southward along the beach and back into the off long shore current that keeps pushing it south.
I'm sure you've noticed when you have a Nor'easter and are seeing erosion as it happens, there is a north to south flow of water along the beach that moves the sand as well as other items north to south. That flow will erode the sand and create a cut as the sand is washed away.
During times when the sand is eroding like that, I've thrown coins into the swiftly moving water on the beach and tracked the coins as they move southward with the water.
As that happens, water from the dunes is sliced away and washed south and down into the water.
So why don't the coins get washed into the water?
Sometimes they do. When the velocity of the water is sufficient to keep them moving, they will be washed down and out. But when the force of the water decreases to the "drop point," they'll be deposited where that occurs.
You might want to refer to my previous discussions on trigger and drop points. That is terminology that I introduced.
So why don't waves hitting from the southeast do the same thing?
Waves hitting from the south or southeast can also at certain times create erosion, but that is less likely and usually not as much. That is because when the back swash runs down the slope of the beach, it runs into the long shore current which is normally going the opposite direction
While I've seen littoral drift frequently talked about and illustrated in the literature recent years, I have never seen anything in the literature about how the movement of sand along a beach is different when the waves and off shore currents are going in opposite directions. You are getting that here today.
It would seem natural to me that when the northward moving water from the swells and waves reenter southward moving long shore current, you would get turbulence. The south to north moving waves start out going against the natural flow of the off shore current, and then again when the water flows off he beach it again hits the south flowing current, so you don't get the synergism you would typically get with a Nor'easter.
That should advance your understanding of how a beach works and how and why Nor'easters more often produce good treasure hunting.
Here is a book on theory of maritime archaeology. You can get a good bit of it through the free preview. Click here for the preview.
We have at least a few more days of one foot surf along the Treasure Coast.