Earth’s Ten Depressions with the Lowest Dry Land:
- Dead Sea Depression (Israel, Jordan, Syria)
- Lake Assal (Djibouti)
- Turfan Depression (China)
- Qattara Depression (Egypt)
- Karagiye Depression (Kazakhstan)
- Denakil Depression (Ethiopia)
- San Julían’s Great Depression (Argentina)
- Death Valley (USA)
- Akdzhakaya Depression (Turkmenistan)
- Salton Trough (USA, Mexico)
What Causes Below-Sea-Level Depressions?
Most major depressions are associated with tectonic plate boundaries. They form when converging plates deform or when spreading centers open. A few are volcanic in origin.
Most of these depressions are in the northern hemisphere for a good reason: this is where most of the land is and where most of the plate boundaries occur. Many are found in the vicinity of where the African, Arabian and Eurasian plates meet. Most are found in hot desert regions of the planet where high evaporation rates prevent them from filling with water. A few are found in high temperature climates.
Many well-populated places in the world are below sea level. About a third of the Netherlands including Schiphol Airport is below sea level. So too are the Jordan River and parts of many coastal cities including New Orleans and Bangkok, Thailand.
Other regions below sea level are the Enriquillo-Cul de Sac Depression (Haiti and Dominican Republic), Chott Melrhir Depression (Algeria), Sebkhet Shunayn and Sabkhat Ghuzayyil (Libya), Shatt al Gharsah (Tunisia), Lammefjord (Denmark), Sebkha Tah (Morocco), Hachiro-gata (Japan), Sariqarnish Kuli (Uzbekistan), The Fens (UK) and Lake Eyre, Australia. Of the two hundred and fifty five recognized countries or protectorates in the world, 33 have land below sea level. Most of these are only a few meters down.
Some below-sea-level depressions are dry, most others have salt lakes. The lakes are undrained, which means water flows in but does not flow out. Since water cannot flow up hill, the lakes cannot empty into the sea like most do and so they accumulate salt (halite) as their waters evaporate.
Where does the salt originate? Some of it comes from ancient sea floor salt deposits that have been uplifted then weather and release the salt which reaches the depressions via rivers. Many other rocks weather to yield sodium and chlorine ions that are carried to the lake by rivers. The Sea of Galilee (Israel) is below sea level but is a freshwater lake because it drains into the Dead Sea through the Jordan River.
Owing to variations in rainfall, evaporation rates, and human water use, most of the lake levels fluctuate from year to year. Some have come and gone in historic times. The present Salton Sea (California, USA) was produced by a canal construction accident in 1905, though the lake has come and gone naturally many times in the last thousand years.