frost line

Noun

frost line (plural frost lines)

1. The depth to which the water present in the soil is expected to freeze in winter.
   • The uninsulated water pipes must be installed below the frost line to prevent them from freezing.

   Synonyms:

   frost depth, freezing depth

2. The depth to which the water present in the soil is actually frozen in a given place at a given point in time.
   • Due to the thin layer of snow on the ground the frost line has penetrated unusually deep this year.

   Synonyms:

   frost front

3. In a solar system, the distance from the protosun beyond which hydrogen-containing gas compounds freeze.
   • In our Solar System the frost line lies between Mars and Jupiter at about five astronomical units from the Sun.

   Synonyms:

   snow line, ice line