Maximum depth of frozen ground during the winter. The term may refer to an individual winter, to an average over a number of years, or to the greatest depth since observations began. The frost line varies with the nature of soil and the protection afforded by vegetal ground cover and snow cover, as well as with the amount of seasonal cooling. Compare frost table, permafrost table.
The maximum depth to which the ground normally becomes frozen in a given geographic area and is an important consideration when installing pipes or other items that can be damaged or affected by freezing conditions.
In soil, the frost line or freezing depth is the level down to which the soil will normally freeze each winter in a given area. The depth this reaches depends on three factors, the length of the period below freezing (two months of −5 Â°C freezes deeper than a month of −5 Â°C), how much below freezing the temperature is (a month of −10 Â°C freezes deeper than a month of −5 Â°C), and the amount of snow cover (snow insulates the ground from the effect of the cold. Thus, drier areas with less snow are more prone to deeper soil freezing).
In astronomy or planetary physics, the frost line refers to 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. Depending on density, that temperature is estimated to be about 150K. The term is borrowed from the notion of "frost line" in soil science.
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".