The geological history of underwater caves and sinkholes

Rising sea levels at the end of the last Ice Age, about 10,000 years ago, submerged land-based sinkholes and caves formed during lower sea levels, creating underwater features like blue holes in the Bahamas.

Limestone, a carbonate rock, is highly soluble in slightly acidic water, making it the primary rock type for karst formations like underwater caves and sinkholes worldwide, such as in Florida and the Yucatan.

Hranice Abyss in the Moravia region of the Czech Republic is the deepest known underwater cave, with a confirmed depth of 473 meters as of 2016, formed in limestone through karst processes.

Fluctuations in water levels, caused by rainfall, drought, or human activities like groundwater pumping, reduce soil cohesion and destabilize cavities in limestone, speeding up sinkhole collapse in karst terrains.

The Great Blue Hole, a 124-meter-deep, nearly circular sinkhole off Belize, formed during the Quaternary glaciation. Its unique geology and marine life make it a UNESCO World Heritage Site, attracting divers worldwide.

Stalactites, formed by dripping water depositing minerals in dry caves, are found in underwater caves like the Great Blue Hole. Their presence shows these caves were above sea level during lower sea levels in the Ice Age.

The Yucatan Peninsula in Mexico is riddled with cenotes, formed when limestone cave roofs collapsed, exposing groundwater. The Maya used them as water sources and for rituals, believing they were gateways to the underworld.

The deep blue color of blue holes results from light absorption and scattering at depth, where clear water absorbs red wavelengths, leaving blue light to dominate. This optical effect is enhanced by the sinkhole’s depth and clarity.

During the Quaternary glaciation, sea levels were lower due to ice-locked water, exposing limestone caves that later flooded when sea levels rose about 10,000 years ago, forming underwater sinkholes like the Great Blue Hole in Belize.

Karst processes involve the chemical dissolution of soluble rocks like limestone by slightly acidic groundwater or rainwater, creating cavities and caves over thousands of years. When these collapse or become submerged, they form sinkholes or underwater caves, such as blue holes.