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  • DIVING THE LABYRINTH

BLUE HOLES

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<mce:style><!  st1\:*{behavior:url(#ieooui) } --> ·    Blue holes are named for the contrast between the dark   blue water of their depths and the shallow, lighter waters around them, both of which are reflections of the sky.
·    Blue holes can exist on land or in the sea.
·    300,000 years ago, rain began carving holes in the limestone base of the Bahamas. As sediment thickened the limestone, these holes became caves.
·    Limestone is porous and let in salt water, flooding the caves as the sea level rose.
·    Fresh water on top meets salt water below at a line called the Halocine.
·    The chemical reaction at the Halocine with limestone creates horizontal shafts.
·    The Halocine is below sea level.
·    Flooding a blue hole as sea levels rise could change the chemistry that allows blue holes to be time capsules.


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