Deepest Sinkhole: Xiaozhai Tiankeng (China)
China’s double-nested Xiaozhai Tiankeng was discovered in 1994 during the search for a new exploration site for British cavers in the China Caves Project. It measures 535 meters wide, has a maximum depth of 662 meters and a total land area of 274, 000 square meters. “Tiankeng” is a Chinese term which means “heavenly pit.” The term was coined in 2001 and is used in collapse dolines that are more than 100 m wide and deep.
Deepest Water-filled Sinkhole: Cenote Poza El Zacatón (Mexico)
According to studies made by Marcus Gary, a hydrogeology graduate student, Zacaton began to form during the Pleistocene as a result of volcanic activity from below.
Deepest Blue Hole: Dean's Blue Hole (Bahamas)
At 202 m (663 ft) deep, Dean’s Blue Hole in Long Island, Bahamas is the deepest blue hole in the world. It has a diameter of 25 to 35 m (82-110 ft) which widens into a cavern measuring 100 m across (330 ft) after descending 20 m (66 ft). Dean’s Blue Hole is also the second largest water-filled cavern body and world’s eighth largest cave body of any type.
The largest blue hole is the beautiful Great Blue Hole of Belize.
Deepest Man-made Hole: Kola Superdeep Borehole (Russia)
In May 24, 1970, the former USSR started an ambitious drilling project whose goal was to penetrate the Mohorovičić discontinuity or “Moho”, the part where the Earth’s crust and mantle intermingle. The project is known as the Kola Superdeep Borehole (KSDB-3) located in Kola Peninsula, Russia. Several boreholes were drilled by branching from the central hole but the deepest, SG-3, a hole about nine inches wide reached a final depth of 12,261 m (40,230 ft) in 1989, and still remains the deepest hole ever drilled until today. The drill was halted due to the higher than expected temperatures at this depth and location, 180 °C (356 °F) instead of the expected 100 °C (212 °F) and drilling deeper was deemed unfeasible the reason the drilling was finally stopped in 1994, about 2.7 kilometers (1.7 miles) short of its 15,000-meter goal. The site was able to share many surprising information about what lies beneath the Earth’s surface and is still scientifically useful until today as research still continues.