It snows with salt. The strange phenomenon occurring deep in the Dead Sea

The giants of salt and other striking formations in the Dead Sea reveal how the evaporation and the dynamics of fluids shape the geological past of the earth and the present.

The Dead Sea represents a unique convergence of the conditions: it is at the lowest point on the surface of the earth and contains one of the highest concentrations of salt on the planet. This extreme salinity makes water unusually dense, and its distinction as the deepest hypersaline lake produces remarkable processes, often focused on temperature, below the surface that scientists always work to understand.

Among the most intriguing characteristics are the so -called giants of salt – large accumulations of salt in the earth’s crust.

“These large deposits in the earth’s crust can be numerous, several kilometers horizontally, and they can have more than a kilometer in the vertical direction,” said UC Mechanical Engineering Professor Santa Barbara, Eckart Meiburg, principal author of an article published in the Annual examination of fluid mechanics. “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. ”

Although massive salt deposits are also present in places such as the Mediterranean and the Red Sea, the Dead Sea is the only place where they are actively formed. This makes it an unrivaled site to study the physical processes that govern their development, including the way in which their thickness varies to the other of space and time.

Evaporation, precipitation, saturation

In their study, Meburg and the co-author Nadav Lensky of the Israel geological investigation describe the dynamics of fluids and the transport processes of sediments currently shaping the Dead Sea. These processes are controlled by several factors, including the classification of the Dead Sea as a terminal salt lake – a body of water without natural flow. Evaporation is therefore the only means of water loss, a process that has narrowed the lake for thousands of years while leaving extensive salt deposits. In recent decades, the Jordan river dam jumping, its main influx, has intensified this drop, the water level now lowering at an estimated rate of about 1 meter (3 feet) per year.

The temperature differences within the water column also play a key role in the formation of salt giants and related characteristics such as salt domes and chimneys. During a large part of its history, the Dead Sea was “meocically” (stratified stable), with a warmer and less dense surface layer resting above a cooler, more salty and more dense layer in depth.

Meromidicic conditions

“Previously, even in winter, when things cool, the upper layer was even less dense than the lower layer,” said Meburg. “And therefore accordingly, there was a stratification in salt.”

This balance moved in the early 1980s when the partial diversion of the Jordan river reduced freshwater entries, allowing evaporation to dominate. At this stage, the surface salinity has reached levels comparable to deep waters, allowing the two layers to mix. This change has transformed the lake from meroticism to Holomicicia (a lake in which the column of water is overturned each year). Today, stratification still occurs, but it only persists for about eight months during the warmer part of the year.

In 2019, Meburg and his colleagues observed an unusual process in summer: the precipitation of halite crystals, or “salt snow”, generally associated with colder months. Halitis (commonly called rock salt) forms when salinity exceeds the quantity that water can dissolve, which makes the layers deeper and colder and more dense the usual precipitation site in winter. However, during the summer, the researchers discovered that, even if the evaporation increased the salinity of the upper layer, the heat of the water allowed the salts to continue to dissolve. This has produced a condition called “double diffusion”, where hot and more salty water plates near the surface cool and flow, while parts of the deeper and colder water warmed up and increased. While the dense top layer was cooling more, salt started to rush, creating the unexpected phenomenon of “snow of salt”.

Salt snow and giant training

The combination of evaporation, temperature fluctuations and density changes throughout the water column, in addition to other factors, in particular internal currents and surface waves, conspire to create salt deposits of different shapes and sizes, tell the authors. Unlike the less deep hypersalins in which precipitation and deposits occur during the dry season, in the dead sea, these processes were the most intense during the winter months. This season of “snow” all year round at depth explains the emergence of salt giants, found in other saline bodies such as the Mediterranean Sea, which once dried during the Messinian salinity crisis, around 5.96 to 5.33 million years.

“There was always an influx of the North Atlantic to the Mediterranean through the Strait of Gibraltar,” said Mebururg. “But when the tectonic movement closed the Strait of Gibraltar, there could not be a water entrance from the North Atlantic.” The sea level has dropped 3 to 5 km (2-3 miles) due to evaporation, creating the same conditions currently found in the dead sea and leaving behind the thickest of this salt crust which can still be found buried under the deep sections of the Mediterranean, he explained. “But then, a few million years later, the Strait of Gibraltar opened again, and you therefore had entries from the North Atlantic and the Mediterranean again filled.”

Meanwhile, the flow of salinity and the presence of springs on the seabed contribute to the formation of other interesting salt structures, such as salt domes and salt chimneys, according to researchers.

In addition to acquiring a fundamental understanding of some of the idiosyncratic processes that can occur in evaporating hypersaline lakes, research on the transportation processes of associated sediments occurring on emerging beaches can also give an overview of the stability and erosion of the arid coasts under the change of sea level, as well as the potential for the extraction of resources, according to the authors.

Reference: “Dead Sea Fluid Mechanics” by Eckart Meburg and Nadav G. Lensky, September 11, 2024, Annual examination of fluid mechanics.
DOI: 10.1146 / Annurev-Flui-031424-10119

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