Sand “bores”?

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I’ve got a question that I’m hoping you might be able to help with, and the internet so far has been less-than-helpful. I notice in the Explorer charts and many other guides the use of the term “sand bore.” Explorer defines this on several charts as a “fluid, shifting, live sand bar.”

Can anyone shed some light on the origins of the term, or perhaps point me towards some reference materials? How exactly is a bore different than a “shifting sand bar,” a term often used on the same chart near the same feature? I know there are several geographic places where the term is used, but my question is mostly academic. What exactly is a sand bore?

Thanks in advance! Matt Claiborne s/v Dulcinea