The NR-1 Sinkhole is a giant underwater sinkhole located in the Straits of Florida southwest of

Key West Key West ( es, Cayo Hueso) is an island in the Straits of Florida, within the U.S. state of Florida. Together with all or parts of the separate islands of Dredgers Key, Fleming Key, Sunset Key, and the northern part of Stock Island, it cons ...

, Florida. It is found at an approximate depth of of water at the foot of the Pourtales Escarpment, an area of

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

sediment. It was discovered in October 1994 during a survey conducted by the American submarine NR-1, a U.S. Navy nuclear research submarine, and is named for the submarine. It was first identified via side-scan sonar and near-bottom echo sounder data, prompting a second survey in May 1995 to confirm the finding. Discovery of the NR-1 Sinkhole prompted scientific interest, as sinkholes are generally believed to form only in environments which are

subaerial In natural science, subaerial (literally "under the air"), has been used since 1833,Subaerial
in the Merriam ...

, or exposed to the air. In contrast, the NR-1 Sinkhole is believed to be too deep underwater for the area to have been exposed to the air during formation in the

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...

. It was the first documented evidence suggesting that it is possible for

karst Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant ro ...

sinkholes to form entirely underwater.

References

{{reflist Sinkholes of Florida Florida Keys 1995 in science Karst formations