Written by the TreasureGuide for the exclusive use of treasurebeachesreport.blogspot.com.
|Small Silver Pendant With Chalky White Stone.|
Shown on penny.
Yesterday I showed some new erosion on a couple of South Hutchinson Island beaches. I went back after the next high tide to see what happened. At the end of the day, it was worse instead of better. Some of the erosion had disappeared.
The erosion that I found in the morning was created by a small surf and as a result was close to the front of the beach. .
On the beach where the erosion was, the waves had been breaking right at the foot of the beach. At another beach which had no erosion, the waves were breaking farther out and there was a lot of sand far out into the water.
We know that the waves break where the water becomes too shallow for the swells to continue without breaking. That means that the water right in front of the beach was deeper on the beach where the waves weren't breaking until they hit shore.
The beach without erosion was a beach which eroded during the high tides back a week or so ago. The eroded sand was now in front of the beach and provided protection.
The area between the low tide mark and the breakers is very important. It is also the area that is most turbulent and difficult to observe, especially during rough water. Coins that wash up onto rather than out of the beach come from that zone.
When there is a lot of sand in front of the beach, not only is the beach protected from the waves, but coins and things can remain buried and protected. For coins to wash up onto the beach, they have to be uncovered, or at least moved to surface layers of sand that will be moved. You can get a lot of erosion without coins washing up.
As far as I can figure out, there are two ways that coins in front of the beach can be uncovered. One is when the sand in front of the beach is dragged out into deeper water thus exposing the coins. After the coins are exposed, or at least brought close enough to the surface that they are in layers of material that can be moved, they can then be washed up onto the beach.
You'll recall that sand can be moved while other materials are left behind (the process of classification).
The best shallow water hunting that I've ever encountered has been in dips right in front of the beach after the sand had been removed from the dip, leaving coins and jewelry on a bed of packed rocks.
The other way coins and things can be uncovered in the shallow water is by strong long shore currents moving sand roughly parallel to the beach.
In both cases, for coins to be washed up onto the beach after being uncovered, the force of the water then has to be strong enough to wash them up. For those coins to remain on the beach, the backwash can not wash them back into the water.
When the backwash is not interrupted or does not slacken enough, both the sand and coins can be washed back into the water.
I've talked before about the importance of the long shore currents and the importance of the north/northeast winds, which push the long shore currents. The long shore currents move sand away from in front of newly eroded areas.
Waves approaching from the east will tend to build beaches. Sand can come in from farther out and fill any dips.
Unusually big swells can move items up onto the beach, but from my experience items moved by swells hitting from the east are generally the easier to move items such as half reales rather than eight-reales or gold. Big swells of course can hit the cliff at the back of the beach and release harder to move items and if the backwash is sufficient also uncover items that were buried under the beach.
Bill F. sent me this related email back a few weeks ago.
Was reading the current one about cuts and backwash. An important
aspect is that coarse material forms a steep beach. 2 reasons.
First, the higher the velocity of the water, the larger the material
which can be transported (pushed) by water movement. Strong waves
move coarse material up the slope.
Then, a second feature comes into play. As the water velocity slows
and stops, much of the volume of water soaks into the coarse material.
Thus, the returning water is much lower in volume and velocity, and
moves less material back to the ocean. At low tide, you see this
water running back out of the beach, often at the top of the hardpan
layer. Beach is kinda like a big sponge!
If you know what the chalky white material in the pendant is, please let me know. I can think of it right now.
The Treasure Coast surf is only supposed to be 1 - 2 feet through Sunday. I don't expect the beach conditions to improve this weekend, however they are still predicting up to a seven foot surf on Monday and northeast winds. That might work. So far the are also predicting something like a 4 - 6 foot surf through out the coming week. That could definitely create some erosion. We'll have to wait and see.