10 Geological Oddities That'll Blow Your Mind (and Maybe Your Geography Teacher's Too!)

5. The Great Blue Hole: Belize's Underwater Marvel

One of the most amazing geological formations on Earth is off the coast of Belize in the glistening clean Caribbean Sea. Visible from satellite, this enormous undersea sinkhole is a perfect circular abyss of deep blue among the less blue tones of the nearby shallow seas. The Great Blue Hole, which measures over 300 metres (984 feet) broad and 124 metres (407 feet) deep, is evidence of the extraordinary geological processes over millennia that have sculpted our earth. Comprising the second-largest coral reef system worldwide following Australia's Great Barrier Reef, the Great Blue Hole is a component of the larger Belize Barrier Reef Reserve System, a UNESCO World Heritage site. Its beginnings lie in the last Ice Age, about 14,000 years ago, when sea levels were far lower than they are now. The hole started out as a sequence of dry land limestone caverns. The circular pit we know now results from caves flooding and finally collapsing when the ice sheets melted and sea levels increased. Renowned oceanographer Jacques Cousteau declared this unusual creation one of the top five scuba diving destinations worldwide, bringing it under international notice in 1971. Using sonar technology to chart its form and submersibles to plumb its depths, Cousteau and his colleagues investigated the Blue Hole aboard his well-known ship, the Calypso Their trip exposed the nearly perfect circular form of the hole and its pure walls, which added to its appeal to both divers and researchers. The Great Blue Hole is a treasure trove of geological and climatic data as much as a breathtaking visual display. Stalactites and other cave formations created when the cavern was above sea level find expression in the limestone walls of the sinkhole. These formations offer important information on last Ice Age sea levels and temperature conditions. By means of their composition analysis, researchers have been able to remove cores from these stalactites, therefore reconstructing previous climate patterns and clarifying the changes in the ecology of the area over thousands of years. Anotherworldly experience is plunging into the Great Blue Hole. Diving through layers of glistening clean water, each depth reveals fresh beauty. Diversity of marine life including various types of fish, sharks, and sea turtles calls the higher levels home. But the surroundings drastically shift as divers descend. Lack of oxygen and light causes the water to becoming considerably darker and barren of most life forms below roughly 40 metres (130 feet). Divers can see the ancient stalactites and stalagmites developed when the cave was dry at these depths; some of them have unusual angles because of past geological occurrences. Massive limestone shelves and overhangs cover the walls of the pit, producing a spooky, nearly lunar scene under the waters. The Great Blue Hole is still a difficult and maybe dangerous place to visit even if it is somewhat well-liked for diving. Its depth and unusual form generate particular hazards, including nitrogen narcosis and decompression sickness, which calls for divers to be quite experienced and ready. Many divers decide to see the wonders of the hole from the relative security of submarines or glass-bottom boats, which provide amazing vistas free from the dangers of deep diving.