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In geology, the frost line is the level down to which the soil will normally freeze each winter. By an analogy, the term is introduced in other areas.
The frost line—also known as frost depth or freezing depth—is most commonly the depth to which the groundwater in soil is expected to freeze. The frost depth depends on the climatic conditions of an area, the heat transfer properties of the soil and adjacent materials, and on nearby heat sources. For example, snow cover and asphalt insulate the ground and homes can heat the ground. The line varies by latitude, it is deeper closer to the poles. Per Federal Highway Administration Publication Number FHWA-HRT-08-057, the maximum frost depth observed in the contiguous United States ranges from zero to about eight feet (2.4m). Below that depth, the temperature varies, but is always above 0 °C (32 °F).
- Frost line (astrophysics), a particular distance in the solar nebula from the central protosun where it is cool enough for hydrogen compounds such as water, ammonia, and methane to condense into solid ice grains.
- Frost line (polymers) in polymer film manufacturing, a notion related to physical changes from melt into solid film during extrusion.
In astronomy or planetary science, the frost line, also known as the snow line or ice line, is the particular distance in the solar nebula from the central protostar where it is cold enough for volatile compounds such as water, ammonia, methane, carbon dioxide, carbon monoxide to condense into solid ice grains. This condensation temperature depends on the volatile substance and the partial pressure of vapor in the protostar nebula. The actual temperature and distance for the snow line of water ice depend on the physical model used to calculate it and on the theoretical solar nebula model:
The frost line is a term used in plastic film manufacturing by extrusion. It refers to the point beyond the die where the temperature of the molten plastic falls below the softening point and the diameter of the extruded plastic bubble stabilizes. The term was borrowed from the notion of "frost line" in soil science and refers to the frosted appearance of the plastic film above the "frost line".
