The Dead Sea is one of the most unique bodies of water on the planet. Sitting at the lowest point on Earth’s land surface, it’s known for its extreme salinity and incredible density. But there’s more happening beneath its surface than meets the eye.
Among the many unusual things scientists are learning about this hypersaline lake is the ongoing formation of what they call “salt giants” – massive underground salt deposits.
“These large deposits in Earth’s crust can be many, many kilometers horizontally, and they can be more than a kilometer thick in the vertical direction,” noted Eckart Meiburg, a professor of mechanical engineering at UC Santa Barbara..
“How were they generated? The Dead Sea is really the only place in the world where we can study the mechanism of these things today.”
Salt formation in the Dead Sea
While salt formations have been found under other seas – including the Red Sea and the Mediterranean – only the Dead Sea lets scientists observe them forming right now.
This gives researchers a rare chance to understand the actual physical processes behind these deposits, especially how their thickness changes across space and time.
A recent paper published by researchers at UC Santa Barbara and the Geological Survey of Israel explains how evaporation, water temperature, and salt saturation all combine to build these structures.
Because the Dead Sea is a terminal lake – one with no outlet – water can only leave by evaporation. As that water vanishes, salt stays behind, accumulating layer by layer.
This process has been going on for millennia, shrinking the lake and increasing salinity. The damming of the Jordan River, the lake’s main water source, has sped up this decline, with the lake now dropping by about one meter (three feet) per year.
Layers of salt and shifting temperatures
Temperature also plays a crucial role. The Dead Sea used to be what scientists call “meromictic,” with a stable layering of warm, less salty water on top and cooler, saltier water at the bottom.
“It used to be such that even in the winter when things cooled off, the top layer was still less dense than the bottom layer,” Meiburg explained. “And so as a result, there was a stratification in the salt.”
That changed in the early 1980s when water levels fell and surface salinity caught up to deeper levels.
Mixing between the layers began, turning the lake from meromictic to holomictic – meaning it now undergoes full mixing in the water column each year. Today, the Dead Sea stays stratified only during the warmer eight months of the year.
Salt snow in the summer
In 2019, scientists made a surprising discovery: halite crystals – or “salt snow” – were forming in the lake during the summer, not just in winter as expected.
Halite, or rock salt, forms when water can no longer dissolve salt due to high concentrations. Normally, this happens in the colder, deeper parts of the lake. But in summer, something unusual was happening.
The top layer of the lake grew even saltier due to evaporation. At the same time, its warm temperature allowed it to keep dissolving salt. This led to a special process known as “double diffusion.”
In this process, salty warm water from the top cools and sinks, while slightly less salty cool water below warms and rises. When the upper layer cools, the salt falls out, like underwater snowfall.
The constant shift in density and temperature, along with other factors like waves and currents, creates salt deposits in all kinds of shapes and sizes.
Unlike other shallow salt lakes where this happens mostly in dry seasons, the Dead Sea sees the most salt formation in winter. This year-round activity helps explain the birth of the salt giants.
A lesson from the distant past
The process happening in the Dead Sea today may also explain salt formations from long ago. Around 5.96 to 5.33 million years ago, the Mediterranean Sea dried up during what’s known as the Messinian Salinity Crisis.
“There was always some inflow from the North Atlantic into the Mediterranean through the Strait of Gibraltar,” Meiburg said. “But when tectonic motion closed off the Strait of Gibraltar, there couldn’t be any water inflow from the North Atlantic.”
The sea level dropped dramatically – up to 5 kilometers (about 3 miles) – due to evaporation, leaving behind thick salt crusts. These can still be found beneath parts of the Mediterranean. Later, the Strait of Gibraltar reopened, and the sea filled again.
Salt features of the Dead Sea
The Dead Sea continues to be full of surprises. Springs on its floor and varying salt flows create even more formations – including salt domes and chimneys.
Beyond learning how these features form, the study of the Dead Sea could have broader implications.
Watching how sediment moves on the newly exposed beaches may help scientists understand how coastlines in dry regions respond to sea level changes. It could also point to new ways to manage resources from such salty environments.
With its strange physics and active processes, the Dead Sea gives researchers a rare look at how massive salt deposits grow – one underwater snowflake at a time.
The full study was published in the journal Annual Review of Fluid Mechanics.
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