Frozen ground worddefinitions

active layer

the soil above permafrost, that melts each year in the summer sun. The active layer is where plant roots and burrowing insects are found.

ice wedge

a buildup of ice in frozen soil, that is wedge-shaped in cross-section.

permafrost

permanently frozen ground.

pingo

a hill created when water pools and freezes under the root mat. When the water freezes, it expands, pushing up the soil.

polygon

a pattern on the surface of frozen ground formed above ice wedges. Polygons can have low or high centers. Low-center polygons are shown and described in this web site.

thermokarst lake

an arctic lake formed when water holds heat that thaws the permafrost below.