Why Is the Dead Sea So Salty? Evaporation, a Falling Lake and the Lowest Land on Earth
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A person who wades into the Dead Sea and leans back will float like a cork, with feet and shoulders above the surface, because the water is about a third dissolved salt and denser than a human body; the same water stings a cut, tastes bitter rather than salty, and kills anything but a few microbes, which is what the name means. The lake lies 430 metres below sea level, the lowest exposed land on Earth, and it is falling by more than a metre a year, leaving a shore of salt crust and sinkholes where the beaches used to be. Both the salt and the fall have the same cause, which is that the water only leaves by going up.
A lake with no outlet
The Dead Sea is a terminal lake: the Jordan river and a few streams and springs flow into it, and nothing flows out, because it sits at the bottom of the Jordan Rift Valley, a trench where the African and Arabian plates are pulling apart, and there is nowhere lower for the water to go. In a hot, dry climate the only exit is evaporation, and evaporation takes the water and leaves the salt behind. Every river carries dissolved minerals from the rocks it crosses, a trace in any glass of it, and a lake that has been receiving rivers and losing only vapour for tens of thousands of years accumulates the trace into a brine. The ocean is salty for the same reason and is much larger and less concentrated; the Dead Sea is about 34 percent dissolved solids, against 3.5 for seawater, and its salt is unusual, richer in magnesium, calcium and bromide than in sodium, which is why it tastes bitter and feels oily.
Why it is so low
The rift that holds the lake is part of the same fault system that runs from East Africa through the Red Sea, and along this stretch the two sides are sliding past each other with a pull-apart between them, so that the floor of the valley has dropped several kilometres over millions of years and filled with sediment and salt. The lake's surface is 430 metres below the Mediterranean, its deepest point 300 metres below that, and beneath the floor lie layers of salt hundreds of metres thick from earlier lakes that dried completely. The whole depression was, in the last ice age, a much larger lake, Lake Lisan, whose shorelines are visible as terraces on the valley sides a hundred metres and more above the present water.
Living with it
The lake has been used for its salt and its bitumen since antiquity, and its shores hold some of the oldest human sites in the region:
- •Jericho, at the northern end, with a settlement dating to about 9000 BC, among the oldest towns known
- •Masada, the fortress on the western shore where the last Jewish rebels against Rome held out until 73 AD
- •The Qumran caves, where the Dead Sea Scrolls lay in jars for two thousand years in air dry enough to keep parchment
- •The potash works at the southern end, on both the Israeli and Jordanian sides, which evaporate the brine in vast ponds for fertiliser and bromine, and which are now the main body of water in the southern basin
- •The resorts, where the dense water, the mineral mud and the thick air, which filters ultraviolet at that altitude, draw people with skin conditions and everyone else
Why it is shrinking
The lake has fallen about 40 metres since the 1960s and is losing more than a metre a year. The Jordan, which once delivered over a billion cubic metres a year, delivers a tenth of that, since Israel, Jordan and Syria divert most of it for farms and cities, and the potash works pump brine from the northern basin to their evaporation ponds. With less coming in and evaporation unchanged, the lake retreats, and as it retreats the fresh groundwater that follows it down dissolves the salt layers beneath the old shore, so that the ground collapses into sinkholes, thousands of them, which have swallowed roads, a campsite and a section of the main highway. The southern basin dried out in the 1970s and exists now only as the industry's ponds.
What could be done
The remedies all involve bringing water from somewhere else. A canal from the Mediterranean was studied in the 1980s and a pipeline from the Red Sea, agreed by Israel and Jordan in 2013, would have desalinated water for both countries and pumped the brine 200 kilometres into the Dead Sea to stabilise it; the project was cancelled in 2021 amid the politics of the region and doubts about what mixing seawater into the brine would do, since the two waters differ in chemistry and the mixture might turn the lake white with gypsum or red with algae. Restoring the Jordan's flow is the alternative that hydrologists prefer and that the countries that drink from it have not found a way to afford. The lake will not disappear, since as it shrinks its surface falls and its concentration rises until evaporation slows, and models suggest it will stabilise a hundred metres or so lower, smaller and saltier still, the sinkholes marking where the shore used to be.
The takeaway
The Dead Sea is ten times saltier than the ocean because it is a terminal lake at the bottom of a rift valley 430 metres below sea level, from which water leaves only by evaporation while the Jordan and its springs bring in dissolved minerals that stay behind, a brine rich in magnesium and bromide dense enough to float a person. It has fallen 40 metres since the 1960s because the Jordan is diverted and the potash works pump its water, the retreat opens sinkholes along the old shore, and a Red Sea pipeline meant to refill it was abandoned in 2021.