Blue holes, which form in oceans around the world, usually open up in soft rock like limestone. Over centuries, the rock dissolves, creating caves underneath the sea floor, reports Stephanie Pappas at LiveScience. Chemical reactions between freshwater and saltwater can cause chemical reactions that produce weak acids that may eat away the rock and cause blue holes to open in certain areas, Lisa Park Boush, a geoscientist at the University of Connecticut who studies blue holes in the Bahamas, tells Pappas. Microbes may also hasten erosion and the opening of a hole in the earth’s crust. The resulting hole, when seen from above
— Read on www.smithsonianmag.com/smart-news/explore-worlds-deepest-blue-holes-180959977/