Permafrost, mollisol, frost weathering and thufurs

The succession of freezing and thawing sometimes creates strange shapes. Rocks fractured by frost weathering hurtle down the slopes by the action of water, which, when freezing, makes fissured rocks explode. Deep down, the soil, when permanently frozen, is called permafrost. The top layer, called mollisol, thaws in the spring. The softened mollisol slides over the permafrost and forms visible ripples on the surface. Around lakes, bumpy areas called thufurs often appear.