struktuurse pinnase vorm; igikeltsaalal korduva külmumise ja sulamise tagajärjel laienenud külmalõhedesse kergitatud kivimmaterjal, mis moodustab erineva suurusega ringstruktuure, kohati ka erineva konfiguratsiooniga polügone ja labürinte, type of patterned ground in permafrost areas with fine sediments in the center of polygon surrounded by a circle of larger stones; range in size of circles from a few centimeters to several meters in diameter. In places other striking patterns can be formed like polygons, stripes, islands and labyrinths.