Why Do Salt Flats Form Hexagons? The Hidden Flow Below

The mystery of repeating desert shapes

Across dry lakebeds, the ground sometimes forms a mosaic of raised white borders surrounding flatter centers. The shapes are often described as hexagons, although real polygons vary in size and number of sides. Their regularity looks almost engineered, but researchers have shown that fluid motion beneath the crust can organize the pattern.

A 2023 study in Physical Review X combined field observations, experiments, and numerical simulations to investigate the phenomenon. The researchers found that buoyancy-driven convection in porous soil provides a consistent explanation for polygonal salt crusts.

What happens beneath the surface?

Step 1: Evaporation concentrates salt

Water near the ground surface evaporates into dry air, but dissolved salt is left behind. The remaining brine becomes more concentrated. Saltier water is generally denser than less salty water, so a layer of concentrated brine near the top can become gravitationally unstable.

Step 2: Dense brine begins to sink

If conditions allow, the denser brine sinks through the pore spaces in the soil. Less salty groundwater moves upward elsewhere to replace it. This creates slow convection cells. Unlike boiling water in a pot, the flow occurs through porous ground and can be extremely gradual.

Step 3: Salt transport reinforces a surface pattern

The circulating groundwater redistributes dissolved salt. Where salt is delivered and deposited more strongly, ridges can grow. As neighboring convection cells interact, the surface develops a network of polygonal boundaries. The precise geometry depends on the physical conditions, and the polygons are not all perfect hexagons.

Why are hexagons so common in nature?

Hexagons efficiently tile a flat surface, but that observation alone does not explain salt flats. It is tempting to compare them with honeycombs or cooling lava columns; those patterns can arise from very different mechanisms. The salt-flat explanation involves fluid instability, salt transport, and crust growth rather than bees, cracking alone, or a hidden blueprint.

The best scientific explanation is one that predicts more than the shape. Researchers also ask whether a model can account for the typical spacing of polygons and how that spacing changes with evaporation and the properties of the ground.

Are salt-flat polygons made entirely by cracking?

Cracking may occur in salty crusts and can modify their appearance. However, the convection model explains why raised ridges can organize into repeated patterns across broad surfaces. Calling every polygon a simple 'drying crack' ignores the role of moving groundwater described in the research.

Where can you see these patterns?

Polygonal salt crusts occur in dry, saline basins in several parts of the world. Famous photographs often show broad desert floors from a low viewpoint, where raised boundaries cast shadows. A photograph alone cannot tell you the groundwater flow rate or salt chemistry beneath a particular location; those require measurements.

Related FactLomia topics include why deserts get cold at night and why the ocean is salty. Both connect the behavior of water to the landscapes it helps create.

Frequently asked questions

Are salt-flat polygons always perfect hexagons?

No. Many are irregular polygons. Hexagonal patterns are common enough to stand out, but the geometry varies.

Is salt-flat patterning caused only by surface cracks?

Not necessarily. Research supports a major role for convection and salt transport in groundwater beneath the crust.

Do the patterns form overnight?

No single timescale applies to every salt flat. Their development depends on evaporation, water movement, and local conditions.

The takeaway

The geometry of a salt flat can reveal motion hidden underground. Evaporation-driven differences in brine density set up circulation that redistributes salt and helps create the striking polygonal ridges visible at the surface.