The Earth’s crust is shaped by forces both seen and unseen, and few geological phenomena capture the imagination quite like the sinkhole. These sudden, often immense depressions represent a dramatic collapse where the surface gives way to a hidden subterranean void. The search for the “biggest” among these geological marvels reveals a competition based not just on depth or width, but on overall volume and the scale of the landscape they transform.
What Defines a Sinkhole
Sinkholes primarily form in karst terrain, where the underlying bedrock is soluble, such as limestone, dolomite, or gypsum. Water, slightly acidified by carbon dioxide, slowly dissolves this bedrock, creating intricate networks of underground caves and passageways. This continuous subterranean erosion weakens the structural integrity of the ground above.
The process typically results in two main types of large-scale sinkholes. Dissolution sinkholes occur gradually, forming a bowl-shaped depression as the surface rock wears away. Cover-collapse sinkholes are the most dramatic, forming where a layer of cohesive material, like clay, bridges a growing underground cavity. When this natural arch weakens, the surface suddenly drops into the void below.
Identifying the World’s Largest Terrestrial Sinkhole
The title for the world’s largest sinkhole by combined dimensions and volume belongs to the Xiaozhai Tiankeng, located in Fengjie County, Chongqing Municipality, China. The name translates to “Heavenly Pit,” and it is the most significant example of a tiankeng, a Chinese term for massive sinkholes that are both deep and wide.
The Xiaozhai Tiankeng has a depth of 2,172 feet (662 meters), a length of 2,054 feet (626 meters), and a width of 1,762 feet (537 meters), encompassing a volume of nearly 119 million cubic meters. This immense pit was carved out by an underground river that still flows beneath it, which initially hollowed out the Difeng cave system. The sinkhole features a distinct two-tiered structure, with the upper bowl descending about 1,050 feet before reaching a sloping ledge that drops into the lower bowl. This layered formation results from different rock strengths within the Triassic-age limestone.
Comparing the Contenders: Deepest and Marine Sinkholes
The designation of “biggest” becomes complex when considering different metrics like depth or environment. While the Xiaozhai Tiankeng is the largest by volume, other sites are notable for their vertical drop. For instance, Mexico’s Sótano de las Golondrinas, or the Cave of Swallows, is a massive vertical shaft plunging over 1,600 feet, making it one of the world’s deepest open-air pit caves.
In the marine environment, the largest sinkholes are known as “blue holes,” vast underwater vertical caves that formed during past ice ages when sea levels were lower. The Great Blue Hole off the coast of Belize is the most famous, known for its near-perfect circular shape, measuring about 984 feet across and 410 feet deep.
The deepest known marine sinkhole is the Taam Ja’ Blue Hole, located in Chetumal Bay, Mexico. Recent research using advanced profiling instruments revealed its depth to be at least 1,380 feet (420 meters), surpassing the previous record holder, the Dragon Hole in the South China Sea. This immense underwater pit remains largely unexplored, demonstrating that the measurement of the world’s largest features continues to evolve.