The Dead Sea is famous for being one of the saltiest bodies of water on Earth. Its water is so dense and salty that most ordinary aquatic life cannot survive in it, and people can float unusually easily. But why did so much salt accumulate there?
The main reason is simple: the Dead Sea has water flowing into it, but no water flowing out. That’s why it is about 9.6 times saltier than the ocean.
It Has No Outlet
The Dead Sea is actually a salt lake, not a sea connected to the ocean. It lies in a closed basin between Jordan and Israel, and the Jordan River is its main natural source of surface water.
Rivers and streams carry dissolved minerals from rocks and soil as they travel toward the lake. This is a normal process that makes many bodies of water slightly salty. Rainwater and groundwater can also carry dissolved minerals into the basin.
The important difference is what happens afterward.
A normal river eventually carries its dissolved minerals into another river, lake, or the ocean. The Dead Sea has no natural outlet, so the minerals remain there.
Evaporation Leaves Salt Behind
The Dead Sea is located in a very hot and dry region. Large amounts of water leave the lake through evaporation. The U.S. Geological Survey estimates that around 1,300 to 1,600 millimeters of water can evaporate each year in the area.
When water evaporates, the dissolved minerals do not simply disappear with it. The water turns into vapor and leaves the lake, while the minerals remain behind.
Imagine pouring a glass of salty water onto a plate and leaving it in the sun. Eventually, the water disappears, but salt crystals remain on the plate.
The Dead Sea has essentially been undergoing this process for a very long time, although its chemistry is much more complicated than ordinary table salt. As water repeatedly enters and evaporates, dissolved minerals become increasingly concentrated.
It Contains More Than Table Salt
Calling the Dead Sea “salty” can be slightly misleading because its water contains much more than sodium chloride, the main component of ordinary table salt.
Its water contains high concentrations of minerals including magnesium, potassium, calcium, and bromide, along with chloride and other dissolved substances. The unusual mixture is one reason Dead Sea water has different properties from ordinary seawater.
In fact, the concentration of dissolved solids in Dead Sea water has been measured at roughly 322,000 milligrams per liter in USGS data, although the exact concentration changes as water levels and conditions change.
Why Isn’t the Ocean This Salty?
The oceans also receive minerals from rivers, weathering of rocks, and other geological processes. So why haven’t they become as salty as the Dead Sea?
The key difference is that the oceans are part of a huge, connected water system. Water circulates between the oceans, atmosphere, land, rivers, and underground systems. Some dissolved materials are also removed through biological and geological processes.
The Dead Sea is a closed drainage basin. Its water has essentially one major natural way out: evaporation. That makes it much easier for dissolved minerals to accumulate.
Why Can People Float So Easily?
The enormous amount of dissolved minerals makes Dead Sea water much denser than ordinary freshwater and seawater.
When you enter the water, your body is surrounded by this unusually dense liquid. The denser water provides greater buoyant force, making it easier for you to stay on the surface.
This is why visitors often find that they can float without much effort.
The same extreme salinity, however, makes the environment difficult for most aquatic organisms. The Dead Sea gets its name partly from this lack of ordinary aquatic life.
The Dead Sea Is Getting Smaller
There is another important part of the story today. The Dead Sea has been losing water and its level has fallen substantially over recent decades.
Reduced inflow from the Jordan River and other water sources, along with water use in the surrounding region and continued evaporation, have contributed to the decline. USGS research has linked recent falling water levels partly to water withdrawals in the Jordan River basin.
As the lake loses water, its remaining water becomes more concentrated, although the relationship is not always straightforward because different minerals can begin to crystallize and settle out when concentrations become very high.
So the Dead Sea’s extreme salinity comes down to a combination of mineral-rich water entering a closed basin and enormous amounts of water leaving through evaporation. Over a very long period, this process has concentrated minerals to extraordinary levels, creating one of the world’s most unusual lakes.
Reference
U.S. Geological Survey. (1978). Recent and projected changes in Dead Sea level and effects on mineral production from the sea. (Link)
U.S. Geological Survey. (2022). Dead Sea. (Link)
U.S. Geological Survey, EROS Center. (n.d.). Dead Sea, Palestine, Jordan, West Bank. (Link)
