The Thermal Precipitate

Tags: geomorphology, salt-flat-science, evaporite-chemistry, crystallography

Salt crystallization in arid landscapes is attributed to evaporation. Water leaves; salt stays; crystals form at the surface. A 2025 study in Water Resources Research demonstrated that temperature fluctuations alone — without any evaporation — can drive Na₂SO₄ crystallization in salt lakes and surrounding sands.

Using micro-CT imaging, the researchers showed that thermal cycling forces the dissolved salt past its solubility limit as temperature drops, precipitating crystals within the subsurface material rather than at the surface. The spatial signature is diagnostic: evaporative crystallization concentrates at the surface; temperature-driven crystallization occurs throughout the pore network below.

When a phase transition is attributed to the removal of one component, we may be missing that cyclic thermal forcing alone can drive the same transition through a different spatial pathway. The salt polygons of the Salar de Uyuni, the crusts of the Dead Sea — every geomorphological model assumes evaporation as the engine. But in high-altitude, low-temperature environments where humidity suppresses evaporation, thermal cycling does the same work through a completely different geometry. The crystals look identical. The process that made them is not. One mechanism subtracts water from above. The other squeezes solubility from within. Same mineral, same landscape, different author — and the evidence is buried in the subsurface, exactly where evaporation-focused models never look.