Why does salt 'snow' down, in opposition to laws of physics?

Geologists float an answer to the mystery of salt flurries beneath Dead Sea

New computer simulation and research helps scientists understand how salt makes its way down rather than up, providing a glimpse into formation of massive deposits around the world

A salt flat on the shores of the Dead Sea on January 11, 2017. (Melanie Lidman/Times of Israel)
A salt flat on the shores of the Dead Sea on January 11, 2017. (Melanie Lidman/Times of Israel)

Underneath the surface of the Dead Sea, it looks like it’s snowing. Geologists poking their heads beneath its surface have wondered for years about salt crystals that dreamily float to the bottom of the lake bed like flurries. The salt “snows” down in complete opposition to the laws of physics that would expect to see the crystals float upwards, like all other objects in the Dead Sea.

Scientists first noticed the phenomenon in 1979. The salt layer on the seabed is rising about 10 centimeters (4 inches) per year from these salt deposits floating downwards, even though most things in the Dead Sea float upwards to the surface.

For the first time, a new study published in the American Geophysical Union’s Water Resources Research proposes an explanation for this phenomenon. As the Dead Sea shrinks, the remaining water becomes even saltier. During the summer, the sun’s heat divides the Dead Sea into two distinct layers: a warmer layer on top, heated by the sun, and a cooler layer below.

The two layers do not mix, because the top layer is warmer and less dense. Water evaporating from the Dead Sea evaporates from this top layer, making the top layer even saltier and less likely to mix with the cooler layer below. Researchers knew that the “snow salt” originated in the top layer, but they couldn’t figure out how it got mixed into the lower, cooler level.


Nadav Lensky, a geologist with the Geological Survey of Israel and co-author of the new study, first proposed the existence of “salt fingers” that slowly funneled salt from the top layer to the bottom layer in 2016. But new research and computer simulations published recently support the existence of these salt fingers that slowly push salt from the top layer to the cooler bottom.

“Initially you form these tiny fingers that are too small to observe… but quickly they interact with each other as they move down, and form larger and larger structures,” said Raphael Ouillon, a mechanical engineer at the University of California Santa Barbara and lead author of the new study.

In this undated photo, salt crystals form on instruments researchers used to measure the disruptions in the water and understand how salt floats downwards in the Dead Sea. (Nadav Lensky/Geological Survey of Israel)

The researchers propose that when the top layer of the lake is disturbed by waves or other motion, like wind or a splashing swimmer, tiny pockets of warm water enter the cooler pool of water below. As soon as it enters the lower level, it rapidly cools. As it cools, it holds less salt, so the salt precipitates out and forms crystals that fall like snow, sinking to the bottom of the lake bed. The researchers call these initial disturbances that begin the process “salt fingers,” like dipping your fingers into a bowl of water, creating tiny disruptions.

“The initial fingers might only be a few millimeters or a couple of centimeters thick, but they’re everywhere across the entire surface of the lake,” said Eckart Meiburg, also a mechanical engineer at UC Santa Barbara and co-author of the new study. “Together these small fingers generate a tremendous amount of salt flux.”

These findings are significant not only to understand the mechanics of the Dead Sea, but also to help geologists around the world understand how giant salt deposits formed within the Earth’s crust.

“We know that many places around the world have thick salt deposits in the Earth’s crust, and these deposits can be up to a kilometer thick,” Meiburg said. “But we’re uncertain how these salt deposits were generated throughout geological history.”

Salt crystals in the Malcham Cave, the longest salt cave in the world, on March 22, 2019 near the Dead Sea. (Courtesy Anton Chikishev/Hebrew Unviersity)

The Dead Sea is the only place on Earth where this salt fingering is happening in real time that geologists can observe, although the same process is likely responsible for other massive salt deposits around the world.

“Altogether this makes the Dead Sea a unique system,” Lensky said. “Basically, we have here a new finding that we think is very relevant to the understanding of the arrangement of these basins that were so common in Earth’s history.”

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