Sometimes, you need to look for the simple answers not the "exotic" ones. This pile of rocks was created by ships, merchant ships to be specific. You see back in the day you needed a ship with a lot of buoyancy to carry a lot of cargo, more cargo, more money. But unlike today's ships which use computers to pump on or pump out water as needed, your typical merchant 4000 years ago would get a big rock on the 'empty' run (when they were just returning with profits to get more trade goods) and they would dump the rock overboard just before port so they could fill up on oils or skins or other trinkets.
So according to wikipedia, the Sea of Galilee is 13mi by 8mi. It's a lake. A big, but not very big one. Generally you wouldn't get ships on a lake that size, large boats sure, but not ships. Those boats generally don't need a lot of ballast, particularly because you are't going to get really large waves on a body of water that small. Even if you did, does it even make sense to move ballast stones down to the shore, then put them on a boat across this small of a distance, just to dump them, when in the same amount of time you could probably just load up a mule/horse/camel train and walk around the lake, and for better profit than pulling down the stones. (Note there is lots of historical evidence for trade by boat on the sea, I'm just not convinced of the need for ballast stones, and there is nothing on one side of the lake or the other that suggests an empty return voyage even makes sense).
Some other problems with this theory:
1) Ballast piles from wrecks are much much smaller than 50 meters by 50 meters, and not 5m high.
2) dumping ballast stones wouldn't occur in such a well confined way resembling a pile - there would be more outlying boulders, potentially increasing in density towards a central spot (the designated dump spot) rather than a pile with edges like this.
3) 4000 years ago, it is not clear to me that there were ships with the right properties to need balast stones anywhere. I'll be glad to be shown wrong, it's interesting. Similarly, trading in ancient times like this was usually far more circuit based than "there and back", so you get and drop items every stop.
Awesome discussion. The reasoning on my assertion is as follows:
The description of the pile of rocks, it matches the description of ballast piles outside of ports on the Mediterranean and larger inland seas.
Ship technology from the time [1] tended to flat bottomed and top heavy boats.
Ships in general, but merchant ships in particular, use ballast to adjust their buoyancy so that they sail per their design. In the case of merchant ships ballast is always something of low value and easily removed.
When adjusting ballast without pumps, solid ballast is easier to load on and off than either liquid ballast or sand ballast (which would require shovelling).
In terms of value to pound of ballast delivered, random basaltic rocks achieve excellent efficiencies.
It's certainly possible that this is something else entirely. I don't think we'll know until they do further research, until then it would be fun to hear other's reasoning on what they think this "structure" represents.
A 1 meter longest dimension boulder would probably weigh well over 500 pounds (conservatively). This size stone is not something you would use as ballast.
Hmm, that is a fair point. One cubic meter of basaltic rock is closer to 3 tons. There is a point where a rock is too big to be usefully used as ballast.
I've seen ballast bags as well (even on nominally "modern" sampan boats). If I were a sailor 4K years ago I'd probably optimize for cost first, speed second. But I don't have a good idea for how much effort it takes to fill ballast bags so I can be very confident in reasoning about where they would fall on that scale.
Not sure if that'd apply here - the Sea of Galilee is awfully tiny for the kind of merchant shipping you're talking about, just 33 miles in circumference, max depth of 141 feet, etc.
An empty boat has a higher center of gravity. Thus waves are more likely to capsize (tip it over) it. It is better (from a strictly economic sense) to have a slightly slower functional boat than one that is sunk.
Not very exciting I know. Sorry about that.
[1] ballast pile as result of wreck -- http://www.marinearcheology.org/Shooner.htm