These formations are created when limestone or other carbonate rock is gradually dissolved by slightly acidic groundwater over an extended period. They typically contain tidally influenced water that can be fresh, marine, or a mix of both. These holes can be massive - some even bigger than entire cities! They tend to extend hundreds of meters below sea level and can connect to underwater cave systems.
The deep blue color of the hole is due to the deep, clear water and the white carbonate sand that reflects little light. The surrounding shallower water appears a lighter blue in comparison. The interior of a blue hole presents a fascinating paradox. The water column exhibits variations in salinity and temperature, creating a unique environment for marine life. While sunlight can penetrate the upper regions, deeper zones transition into a shadowy realm.
What is a Sinkhole?
A sinkhole can form due to natural processes or human activity, particularly in areas with “karst” terrains, where the underlying rock can be easily dissolved by groundwater. Karst terrain, created from the dissolution of soluble rocks like limestone and dolomite, features unique landforms such as caves, sinkholes, and springs. Human activities like broken land drains, water mains, sewerage pipes, or increased rainfall can also contribute to sinkhole formation.
Here are some of the most famous blue holes:
- The Great Blue Hole is a giant marine sinkhole off the coast of Belize. It is a popular destination for scuba divers.
- Dean's Blue Hole is located in the Bahamas and is another popular spot for divers. It is the deepest blue hole in the world that is accessible for free diving.
- Dragon Hole is in the South China Sea and is the deepest blue hole ever discovered. However, due to the depth and dangerous conditions, it is not explored very often.
- Taam Ja Blue hole: Recently, scientists have discovered a massive blue hole off the coast of the Yucatan Peninsula in Mexico.
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