polygonal ground[pə′lig·ən·əl ′grau̇nd]
a form of microrelief and mesorelief in regions with seasonally and permanently frozen rocks. Polygonal ground is produced by frost and desiccation cracks that form a network of rectangles or polygons with five or six sides. Frost-crack polygons with convex or concave surfaces—the latter are surrounded by ridges—may reach several hundred m in diameter and are separated from one another by cracks, which are frequently filled with ice wedges. Stone polygons and other smaller polygons are surrounded by elevated walls made of large gravel fragments. Desiccation-crack polygons range in diameter from a few cm to 3 m.