Cracked Soil Stock Image

Some soils have a high content of clay minerals known as smectites. When smectite clays get wet, water moves into a space between the structural units that make up the clay mineral. The presence of the water molecules pushes the structural units apart, causing the clay mineral to expand, or swell. When these clays dry out, the water molecules are removed from the inter-structural spaces and the clays shrink. When this shrinking takes place in millions of clay structural units in a volume of soil, the shrinking can be enough to create large cracks in the soil. Soils with a high shrink-swell clay content are known as Vertisols.