十万个为什么·科学阅读30篇（4）

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为什么盐滩在旱季会形成六边形裂纹？

When shallow saline lakes evaporate completely, thin salt crusts shrink unevenly due to differential moisture loss across the surface.
Cracks begin at stress points and propagate outward until they meet neighboring fractures at nearly 120-degree angles.
This geometry minimizes total energy required to relieve tension—similar to soap bubbles or basalt columns.
Satellite images confirm hexagonal patterns appear consistently across dry lake beds from Bolivia to Iran.
The size of each polygon depends on crust thickness, salinity concentration, and drying rate—not random chance.
Microscopic analysis shows crystal lattice alignment guides crack direction along preferred cleavage planes.
Wind and minor thermal shifts accelerate crack widening but don’t determine initial symmetry.
These patterns help scientists estimate past evaporation rates and reconstruct paleoclimate hydrological cycles.
Robotic rovers on Mars use similar crack geometries to infer ancient water presence in dried basins.
Hexagons emerge spontaneously whenever contraction forces distribute uniformly across brittle, flat surfaces.