It’s the last Ice Age. Huge limestone caves collapse and flood with ocean water as sea levels rise. The caves transform into blue holes. Fast forward to today. At the very bottom of these undersea sapphire caverns lie layers of sand that show a record of hurricane activity. Like rings of a tree can be counted to calculate a tree’s age, strata of silt can be numbered to identify storms.
It wasn’t easy to discover these ocean floor archives. Take a boat to the largest marine sinkhole, the Great Blue Hole off Belize. It’s about 1,000 feet wide. You can scuba dive easily until about 290 feet; you’ll see the usual sharks, corals, and turtles. But below that, it’s safest to explore in a submarine if you want to survive.
There’s no oxygen beneath that point. A thick, toxic layer of hydrogen sulfide lies like a blanket over the width of the hole. It’s the most dangerous kind of dead zone; animals and plants that have fallen into the hole have used up all the oxygen decomposing. Almost nothing can survive. But this means that no creatures disturb the sandy storm record.
While natural currents fling small grains of sand into blue holes, raging hurricanes throw larger grains. A discerning eye can spot different textures and layers. These natural records show that violent storms used to be a lot more common than they are now.
How do we know blue holes were once dry caves? At the bottom of the Great Blue Hole are stalactites, which are fingerlike projections that form when water drips down stone. Mineral deposits build up over time. Some stalactites in the Great Blue Hole are 40 feet long and two feet in diameter.
Most of the world’s blue holes are in the Bahamas. Hines Hole is halfway between Cuba and the Florida Keys. Far from land, this blue hole preserves evidence of storms that have blown in from multiple directions. It has almost 200 feet of accumulated silt and can tell the stories of more than 2,000 years of hurricane history.
Low levels of light and oxygen at the base of blue holes also mean less decay to fossils. Shells of long-extinct land tortoises, the remains of freshwater crocodiles thought to live only in Cuba, and bones of the ancient Lucayan people have been discovered.
Nancy Albury, project coordinator for the Bahamas’ national museum, says, “It’s not buried gold but it’s really a treasure. It’s telling us an amazing story.”
Why? God uses blue holes to provide us with a history of caves, storms, weather patterns, and animal life.