A vocabulary of landscape — a landscape of words
1469 entries
ice lens
An ice lens is a flat body of pure ice that grows inside freezing soil, fed by water drawn up from below through the fine pores of the ground rather than by water that was already there. Because the ice takes up more room than the water did and keeps being resupplied, the lens grows and lifts everything above it. This is frost heave, and it is the reason a road cracks, a fencepost rises out of the ground over a winter, and stones work their way to the surface of a field.
Etymology
The name is a plain description of the shape, which is flat and lens-like in cross-section, and the term came out of soil mechanics and cold-regions engineering in the twentieth century. The process itself has an older name in ordinary English: frost heave, which farmers and road builders were describing long before anyone worked out that liquid water was migrating through frozen ground to feed the growth.
Notes
The lifting force is considerable. Ice lenses generate enough pressure to raise a building, and cold-regions foundation design is largely about keeping them from forming under one. On a larger scale they sort ground into patterns: the stone circles, polygons, and stripes of patterned ground in the Arctic and on high mountains are made by repeated lens growth pushing coarse material aside over centuries.