A landscape built from rust
The distinctive red earth of Nakhon Ratchasima Province is the product of an intense, prolonged weathering process called laterization. Occurring over millions of years in hot, wet tropical climates, this geological transformation leaches soluble minerals from parent rock. The alternating wet and dry seasons accelerate the chemical breakdown. Heavy rainfall dissolves and washes away elements like silica, sodium, potassium, and magnesium. This leaves behind high concentrations of less-soluble elements, primarily iron and aluminum. The rusty red color comes from iron(III) oxides, specifically the minerals goethite (α-FeO(OH)) and hematite (α-Fe2O3), which become dominant in the resulting soil.
The parent rocks for laterite can be igneous, metamorphic, or sedimentary. In the Khorat Plateau, the surface geology largely consists of Mesozoic sedimentary rocks like sandstone and siltstone. The laterization process transforms this bedrock into a thick, clay-rich soil profile that can be up to 30 meters deep. This soil, technically an oxisol, is often porous and contains iron oxides that can make up between 30% and 60% of its mass by weight. The main iron-bearing mineral formed is goethite, a common component of rust. The entire Khorat Plateau, a saucer-shaped region covering 155,000 square kilometers, shows evidence of this geological process.