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Why don’t you sink when you swim in the Dead Sea?

The Dead Sea is an inland lake 50km long by 15km wide in the Middle East between the West Bank and Jordan. The Jordan River is the main source of the Dead Sea water.

It is about 430m below sea level, the lowest point on the surface of the Earth. The water level has been dropping even lower for the past 60 or so years, mostly because river water is being used elsewhere rather than flowing into the Dead Sea. It drops about 1m each year.

It’s a popular place for people to have a holiday, partly because it’s in the desert, which means lots of hot, sunny days.

Hotels and resorts line the shores, except that as the water level drops, the shoreline moves further away from the buildings. Some hotels that were on the shore are now more than a kilometre from the water.

IS IT DEAD?

It’s called the Dead Sea because it is full of mineral* compounds* (called salts). Dead Sea water is perhaps 10 times as salty as open ocean seawater and nothing much can survive in it.

Exactly how salty it is varies through the depth of the lake and with how much water is flowing in from the Jordan River and how much water is evaporating* (leaving salt behind).

It is so salty that bacteria is the only living thing that can survive. Fish that come in with river water quickly die.

Plants called halophytes that are adapted to extreme salt grow here and there along the shoreline.

Fish, birds and even ibex and leopards gather around several oases* fed by fresh spring water. About 500 million birds visit on their biannual* migration between Africa and Europe, but as the water level drops, the oases are drying up.

WHERE DOES THE SALT COME FROM?

When it rains, salt washes from rocks on land into the water.

In regular sea or ocean water the type of salt is mostly sodium chloride (the salt we eat with our meals). In the water of the Dead Sea, there’s less sodium chloride and more of other kinds of salts.

WHY CAN’T YOU SINK IN THE DEAD SEA?

The Dead Sea is landlocked and in the lowest valley on earth. All the minerals of the surrounding countryside get washed into one pool, which in turn gets baked by the sun. This concentrates the salts so much so that the Dead Sea becomes times as salty as the ocean, which defines why people don’t drown in the dead sea.

The more salt is dissolved in water, the denser it becomes.

Objects which drop in water stop sinking when they displace a mass of water equal to their body mass.

In dense, salty water, a little body displaces a lot of mass, and most of the body stays out of the water so, it’s hard to drown a person when most of their body is floating on top of the water.

The Dead Sea water has a density of 1.24 kg/litre, which makes swimming similar to floating.

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