Ground that is permanently frozen.
Layer of permanently frozen subsoil in polar regions.
Condition in which a deep layer of soil does not thaw out during the summer. Permafrost occurs under periglacial conditions. It is claimed that 26% of the world's land surface is permafrost.
Permafrost gives rise to a poorly drained form of grassland typical of N Canada, Siberia, and Alaska known as tundra.