The Great Blue Hole is a former Karst-eroded sinkhole. Jurassic reefs originally created the limestone formation 195-190 million years ago. Water seeped through the limestone and formed a large chambered cave where stalactites and stalagmites formed many times over thousands of years before the roof fell in and eventually created a 984ft wide hole 407ft deep. The hole flooded as sea levels rose, which put a halt to all further stalactite and stalagmite formation. Some stalactites are over 20ft long and they are not exactly as straight as stalactites grown where past earthquake movements and substrate shifts have not so obviously occurred periodically. It can take a stalactite 100 years just to grow an inch, but it takes a diver just a brief second to be impressed by these slightly skewed cone shaped geological structures.
During the last 18,000 years when the area surrounding Chicago was 2 miles under glacial ice, the sea level of Belize was down some 394ft. There were at least four distinct times when seas rose and left ledges where waves slapped against walls and shorelines, before reaching the current sea level. Some 10,000 years ago the ocean was still 148ft lower than it is today, but as the ocean water and fresh water both rose close to their